June 29, 2025 • 20 mins
In our last episode, we established the foundations of anal cancer therapy, proving that definitive chemoradiation with 5-FU and Mitomycin-C is the organ-preserving standard of care. But while this approach is highly effective, it is also notoriously toxic. The older 3D radiation techniques often led to severe side effects and treatment breaks that compromised outcomes.Today, we focus on the modern "how." We'll explore how IMRT has revolutionized our ability to treat this disease. We'll walk through a detailed, dose-painted IMRT planning workshop. And finally, we'll use a case to discuss the management of special populations you will frequently encounter: HIV-positive patients, those with high-risk disease, and those with recurrence.
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Episode Transcript
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(00:00):
Welcome to the Radonk Smart Review GI Cancer series.
Today we're not just discussing,we're taking a practical, really
in depth workshop on how we safely and effectively deliver
radiation therapy for anal cancer.
You know, in our previous sessions, we've really explored
the clinical cases, delved into the intricate anatomy, dissected
(00:21):
the detailed staging, and of course, thoroughly reviewed
those landmark trials that fundamentally guide our
treatment regimens. Right, the foundations.
Exactly. Now the time has truly come to
bridge the gap from theory to practice, to focus on the how,
the intricate hands on details of treatment planning.
This is where the rubber meets the road, so to speak.
(00:42):
That's exactly for residents at all levels.
Whether you're just starting outor, you know, prepping for your
boards, mastering the art of IMRT planning for anal cancer
isn't just a desirable skill, it's absolutely crucial.
It's not simply about knowing what dose to prescribe based on
a guideline. It's about understanding the
precise methodology, the meticulous steps required to
(01:03):
ensure that prescription is delivered with well sub
millimeter precision, all while minimizing side effects to the
healthy surrounding tissues. Today, we're essentially
stepping into a virtual treatment planning suite
together, using a really complexpatient case as our guide to
truly walk you through the entire process, from simulation
(01:24):
to final dose evaluation. OK, let's unpack this.
When we talk about modern radiation for anal cancer, IMRT
is almost synonymous with it now.
It's pretty much the default. It is, but for those who maybe
weren't practicing during that shift, or perhaps are studying
for their exams, why exactly hasthis particular technique become
the unwavering standard of care?What was the compelling evidence
(01:46):
that truly made IMRT indispensable?
That's a vital question because understanding the why often
solidifies the how, doesn't it? It does.
The pivotal evidence which genuinely redefined the
landscape for anal cancer radiotherapy comes most notably
from the RTOG trial O 529. Yes, O 529.
Exactly. This phase two trial was without
(02:08):
a doubt a game changer for our field.
Before this we were often using older 3D conformal techniques
and while they were effective, they came with a significant
cost to the patient in terms of acute toxicity.
Right, the side effects were rough.
Very rough. RTOGO 529 clearly demonstrated
that IMRT significantly reduces acute gastrointestinal or GI and
(02:30):
skin toxicity when compared to those older 3D approaches.
And critically, this reduction in toxicity achieved without
compromising any oncologic outcomes, meaning we got the
same great cancer control with adramatically improved patient
experience during treatment. So same curates, fewer side
effects. Precisely.
This trial wasn't just about reducing a few side effects, it
(02:53):
fundamentally redefined our standard of care.
It proved we could achieve the same life saving outcomes with a
dramatically improved quality oflife for patients during
treatment. It was the moment we truly
understood that precision wasn'tjust about targeting the tumor,
but also about protecting the patient's immediate well-being
that really paved the way for IMRT to become, well,
(03:15):
indispensable. That's an incredible insight.
It's not just about immediate patient comfort during treatment
then, is it? It sounds like there are
broader, more systemic implications to this toxicity
reduction. Can you elaborate on that a bit?
Absolutely. While the the upfront cost of
implementing and delivering IMRTmay appear higher initially, you
(03:36):
know the technology, the planning expertise required, the
downstream benefits are actuallyquite substantial both for the
patient and the healthcare system.
Think about it, severe acute toxicity, particularly GI and
dermatologic issues. They often lead to unscheduled
clinic visits, urgent hospitalizations, those critical
emergency department. Visits.
Yeah, those add up quickly. They really do.
(03:56):
Numerous studies have shown thatby significantly reducing these
severe toxicities, IMRT directlyreduces these associated
downstream costs. So in that sense, it truly makes
IMRT A valuable long term investment in comprehensive
patient care and from a broader perspective, a wise health
(04:17):
economic strategy. So a bit more investment upfront
saves money and hassle later. Exactly.
It's a classic example of spending a little more upfront
to save a lot more later, while also giving the patient a much,
much better experience through treatment.
That puts it into perspective. OK, before we jump into our
patient case, which I'm really looking forward to applying
these concepts to, let's establish the general principles
(04:37):
of modern anal cancer planning, specifically based on the new
American Society for Radiation Oncology or Astro guidelines.
The Astro guidelines. Right.
We'll start as always with target volume delineation or
contouring. When we're sitting down to
contour a patient's plan, what are the core components we
absolutely need to define OK? The two 2025 Astro guideline and
(04:58):
consensus atlases provide a veryclear and robust road map for
this, almost like a definitive playbook you could say.
First and foremost, we meticulously define the gross
tumor volume or GTV. This volume includes all visible
primary tumor, which we designate as GTV Dash P.
So if you see a palpable mass, an ulcer, or a lesion on
(05:20):
imaging, that's your GTV Dash P.What you can see or feel.
Exactly, Yeah. And then we also include any
involved regional nodes which welabel as GTV dash N.
Now it's important to be very specific here.
A node is generally considered gross disease if it is greater
than or equal to 1.5 centimeterson CT, or if it's PET positive
(05:40):
on the diagnostic imaging, or ofcourse if it's biopsy proven.
Clear criteria. Those are our unequivocal
criteria for gross nodal involvement.
Pretty standard stuff there. And then once we have that GTV
precisely defined, how do we build from that foundation to
create our clinical target volume or CTV?
That's where the margins come in, right?
Because we're not just treating what we see, but what might be
(06:01):
microscopically present nearby. That's absolutely right.
The CTV is designed to cover theGTV with an appropriate margin,
specifically accounting for thatmicroscopic extension we can't
see with our eyes or on routine imaging.
But it also includes all the necessary elective nodal regions
where there's a significant riskof subclinical disease even if
(06:22):
we don't see gross involvement there.
Got it. So the primary plus potential
spread. Exactly to be specific, the GTV
dash P, the primary tumor typically receives a generous
1.5 to 2.5 centimeter margin to encompass that potential
microscopic spread. 1.5 to 2.5 centimeters.
The GTV Dash N on the other hand, the involve nodes gets a
(06:43):
slightly tighter 1 to 1.5cm margin.
OK, one to 1.5 centimeters for nodes.
Right. This difference in margin
reflects the different patterns of microscopic spread from a
primary tumor versus a regional lymph node.
It's tailored. Makes sense.
And what about the comprehensiveelective CTV?
I know the Astro guideline has incredibly strong
(07:04):
recommendations here, making it a truly critical component for
anal cancer planning. This is where we ensure
recovering all those at risk regions, even if they're not
overtly involved because of those lymphatic drainage
patterns. This feels like a non negotiable
safety net. Indeed, this is truly a critical
concept and the Astro guideline makes a very strong explicit
recommendation. This comprehensive elective
(07:27):
volume must include the primary tumor with its appropriate
margin, the entire anal canal itself, the adjacent rectum
because of the direct extension and lymphatic pathways there,
and then a very specific non negotiable set of nodal basins.
This is where you know the detail really matters because
when we talk about comprehensivecoverage, we're not just
guessing. The Astra guideline lays out a
(07:48):
truly non negotiable checklist of nodal basins we must include,
almost like a safety net for microscopic disease.
OK, let's hear the list. So let's walk through those
critical regions. These include the mesorectal,
the presacral, the bilateral internal iliac, up the size, the
bilateral external iliac. Both sides again.
The bilateral obturator and the bilateral inguinot Lymphson
(08:10):
notes this extensive coverage isabsolutely non negotiable for
anal canal cancer as we know thelymphatic drainage can be quite
widespread and unpredictable, particularly down to those
inguinal regions. So you really have to cover the
pelvis, Andy the groins electively.
You absolutely do. If you miss one of these, you're
leaving a potential area for recurrence on the table.
(08:32):
It's that critical. There's a lot of nodal basins to
remember, especially under pressure.
For those of you studying or just wanting a quick recall
trick, here's a mnemonic that might help you keep track of
that comprehensive elective CTV nodal basins.
Oh, a mnemonic good idea. Yeah, think my perineum is
extremely obliging in going. So my other mazerectal perineum
(08:57):
for presacral is for internal iliac, extremely for external
iliac obliging for obturator andin going for inguinal.
My perineum is extremely obliging in going.
I like it. That's actually quite helpful.
Hopefully that sticks with you and helps you remember this
critical list. That's a fantastic mnemonic,
very helpful for remembering that extensive list and when I
(09:17):
know many residents will appreciate.
OK, shifting gears slightly, let's talk about dose and
fractionation. The Astro guideline endorses a
very precise risk adapted dosingstrategy that is based directly
on both the T stage and the end stage of the disease.
Right. It's not one-size-fits-all.
Not at all. How does this critical breakdown
of dosing look for the primary tumor depending on its size it's
(09:39):
T stage? OK.
For the dose of the primary tumor, we have a clear
stratification based on that T stage.
For clinical T1 to T2 tumors, which are generally smaller,
less bulky, the recommended doseis 45 to 50.4 Gray. 45 to 50.4
Kari. Right.
Typically delivered in 25 to 28 fractions.
This is usually sufficient for those smaller primary lesions.
(10:01):
However, for those larger, more advanced clinical T3 to T4
tumors where we have a higher tumor burden and potentially
more microscopic extension, a higher dose is recommended to
ensure adequate control 53.2 to 59.4 Gray. 53.2 to 59.4 Gray, so
a definite step up. A definite step up, yeah,
(10:21):
Usually delivered over 28 to 33 fractions.
The higher dose and slightly more fractions reflect the
increased challenge of eradicating a larger tumor.
Makes sense. More tumor needs more dose.
And what about the lymph nodes? This is a crucial distinction.
How do we approach dosing for both the clinically involved
nodes where we see gross diseaseand then those elective volumes
where we're aiming for prophylaxis, trying to prevent
(10:43):
subclinical disease from emerging and at risk areas?
It's not the same dose for both,is it?
No, it certainly isn't for clinically involved nodes or N
positive disease, the ones we identified as GTVN.
These should receive a definitive curative dose of 50.4
to 54 grey. 50.4 to 54 grey, similar to the higher T stage
primary dose range. Exactly.
Usually delivered in 28 to 30 fractions.
(11:06):
This is to ensure we eradicate the gross disease in the lymph
nodes, treating them with the same intensity as the primary
tumor, essentially. And then for those elective
nodal volumes where our goal is prophylaxis to cover those at
risk areas that don't have grossdisease but are known pathways
to spread, what dose do they get?
Those at risk nodal regions where we're targeting
microscopic or subclinical disease should receive a
(11:29):
prophylactic dose. That range is 36 to 45 Gray. 36
to 45 Gray lower dose. Right, a lower dose typically
delivered in 20 to 30 fractions.This lower dose is sufficient
for microscopic disease while sparing healthy tissues from
unnecessary high dose radiation,which really helps reduce long
term toxicity. OK, that stratification is key.
(11:50):
Now with these Astro guidelines in mind and the elegance of
IMRT, we often utilize the simultaneous integrated Boost or
SIB approach. This is a very elegant technique
that allows for incredible efficiency by treating multiple
dose levels at once. Can you explain how these
different dose levels, the elective and the involved noodle
(12:10):
doses for instance, are delivered simultaneously within
a single plan using this SIB approach?
How does it work in practice? Right, the Seb for a node
positive patient utilizing an SIB approach, the guideline
recommends a dose of typically 40 to 42 Gray and 28 fractions
or alternatively 45 Gray and 30 fractions to the elective
volume. OK.
(12:31):
The prophylactic dose level. Exactly what's crucial here is
that this is delivered simultaneously with 50.4 to 54
Gray, also in 28 to 30 fractionsto the clinically positive lymph
nodes and the primary tumor. So delivering both doses every
single day. Every single day.
So in one treatment session, you're hitting multiple targets
with different precise dose levels.
(12:53):
This simultaneous delivery allows for incredible efficiency
in the treatment schedule, collapsing what might have been
two separate phases into one continuous course.
Much more convenient for the patient too.
Absolutely. It also ensures we deliver that
precise risk adapted dosing to each target volume within the
same overall treatment time frame.
It's a very smart way to achieveour dose goals, maximizing
(13:15):
therapeutic effect while maintaining a reasonable overall
treatment time. It requires sophisticated
planning, definitely, but offerssignificant clinical benefits.
Very elegant. Now let's take all these
foundational principles, the rationale for IMRT, the Astra
guidelines on contouring and dose and apply them to a real
world, highly complex scenario. We have Missus Lee, a 58 year
(13:37):
old woman. Can you walk us through her
story and her presentation really set the stage for the
planning challenge she presents.Certainly Missus Lee presents
with a quite large 7 centimeter ulcerated anal mass. 7
centimeters. Wow.
Yeah, quite bulky. What makes her case particularly
challenging and relevant to our discussion today is that this
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mass extends directly into the lower vagina, indicating local
advancement. OK, so T3 at least.
Right biopsy confirmed that thisis human papilloma virus, or HPV
positive squamous cell carcinoma, a common type but
with a significant local extent that demands A robust approach.
And what did her comprehensive staging workup reveal?
(14:18):
Was there any distant spread or,more relevant to our discussion
today, extensive nodal involvement that would
complicate our planning? Her comprehensive staging
workup, which included APETCT, revealed concerning findings
beyond just the primary tumor. Specifically, she has a right
external iliac lymph node that is involved.
OK, pelvic node. Along with bilateral inguital
(14:39):
lymph nodes that are also clearly involved.
Both groins too. Yeah.
So this multi station nodal disease combined with her
already bulky primary tumor result in a clinical stage of
clinical T3N1CT3. N1C.
Correct. This is indeed a complex case
with a bulky primary and multi level nodal involvement, and it
will truly challenge our treatment planning approach,
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requiring very careful consideration of precision at
every step. This isn't your straightforward
T1N0 case. This is where thoughtful
planning truly shines. Absolutely.
So, given Missus Lee's complex presentation with that bulky
primary and multi station nodal involvement, let's walk through
the plan for her step by step, starting with simulation best
(15:21):
practices. What are the key considerations
we need to keep in mind for her setup to ensure not only
reproducibility but also the most accurate dose delivery
possible for such an extensive target?
OK, simulation for Missus Lee. We'll simulate her supine with
her arms positioned comfortably on her chest, and she'll be
immobilized securely in a vac lock bag.
Standard supine setup. Exactly.
(15:42):
Supine positioning is standard for IMRT and anal cancer, and
for good reason. It offers the highest level of
reproducibility, which is absolutely essential for precise
daily treatments day after day for many weeks.
It's also specifically necessaryfor adequately treating her
involved inguinal nodes, which can be particularly challenging
to target accurately in other positions due to potential
(16:03):
positional shifts or patient discomfort.
So supine is the go to. Any special positioning
requirements for the lower body?I can imagine with a tumor
extending into the vagina and inguinal nodes, you'd want to
manage skin folds and ensure consistent geometry down there.
Yes, definitely. This is a subtle but critical
detail. Will utilize A specialized knee
(16:24):
and ankle fixation device to maintain a comfortable frog leg
position for her lower extremities.
OK, the frog leg position, why is that important?
This particular position is critical because it helps to
pull the upper thighs slightly away from the perineum, which
minimizes skin folds in that sensitive.
Area. Oh right, skin dose.
Exactly. If not addressed, these folds
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can significantly impact dose distribution to the target
volumes, creating areas of overall underdosing and
dramatically increased skin toxicity, which is already a
significant concern in this area.
It's about creating the cleanest, most predictable
anatomy for treatment delivery. Makes sense.
And what about those standard bladder and rectum protocols?
We know those are often key for managing pelvic treatments and
(17:07):
protecting critical organs at risk.
Right, we will adhere to a full bladder, empty rectum protocol.
This is crucial. A full bladder helps displace
the small bowel superiorly and anteriorly out of the high dose
treatment field which is vital for reducing GI toxicity later
on. Get the bowel out of the way.
Precisely. An empty rectum, conversely,
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helps minimize rectal wall dose,especially as the primary tumor
is often directly adjacent to it.
We'll also place a radiopaque marker at the anal verge.
The BB marker. Yep, the BB marker.
This is a very simple but incredibly effective trick for
accurate daily setup and for clearly outlining the inferior
border of our target volumes, ensuring we don't miss any of
the primary down low. And given her vaginal
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involvement, anything specific there?
Yes, absolutely right. Given her vaginal involvement, a
crucial step for Missus Lee willbe to use a vaginal dilator
during both simulation and everysingle treatment fraction.
A dilator during treatment. Yes, this physically displaces
the uninvolved vaginal tissue away from the high dose region,
helping disparate from unnecessary radiation and
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significantly reducing the risk of late toxicities like vaginal
stenosis, which can severely impact a patient's quality of
life. Super important.
Wow. OK, that's a key intervention.
And for imaging, what will we acquire to ensure we have the
most precise anatomical information for contouring,
especially with her complex neural involvement?
We will acquire ACT scan with intravenous contrast.
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The contract helps us clearly delineate vessels, bladder and
importantly identify and confirmpotentially involved lymph nodes
with better precision. And then we will meticulously
fuse her diagnostic PTCT scan with this simulation CT.
TT, fusion critical. Absolutely critical for precise
contouring, especially for identifying and defining her
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metabolically active gross disease in both the primary
tumor and the involved lymph nodes.
It gives us that physiological correlate to our anatomical CT,
ensuring we are hitting the trueextent of the tumor.
You really need both. OK, great setup.
Moving on to contouring Missus Lee's plan itself, how do we
approach defining her GTV's and CTV's?
Given her complex presentation with both a bulky primary tumor
(19:17):
and multistation nodal involvement, this seems like
where the planning really gets intricate.
It does. This is where the art meets the
science. For her GTV's, we'll precisely
contour her 7 centimeter primarytumor, which we designate as GTV
dash P. This is our starting point for
the highest dose. GTVP the primary.
Right. Additionally, we'll contour her
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involved right external iliac lymph node and her bilateral
inguinal lymph nodes, all designated as GTV dash N.
GTVN the positive nodes. Exactly.
These are the areas of gross visible metabolically active
disease that absolutely need definitive doses Now For her CT
DS, given her extensive nodal involvement and the need for
(19:57):
comprehensive coverage of microscopic disease will define
three distinct CT VS to manage the different dose levels we
plan to deliver. Three CT VS OK break that down
for us. This multi tiered approach
allows for tailored dosing to different risk levels.
So CTV 1 is what we call the upper elective pelvis.
CTV 1 upper pelvis. This volume covers the upper
(20:19):
pelvic nodes at risk, extending cranially from L5S1 down to the
bottom bottom of the SI joint. This comprehensive volume
includes the presacral space anda 7mm margin around the internal
and external iliac vessels. OK.
It's designed to scoop up any potential microscopic disease in
those higher pelvic noble chainsthat are still at risk, even if
(20:39):
not grossly involved. And how about CTU 2?
Where does that pick up and whatdoes it encompass for Misses
Lee, especially concerning the primary tumor in those lower
nodes? Right.
CTV 2 is the lower pelvis and inguinal nodes volume.
This volume starts precisely at the bottom of the SI joint and
extends inferiorly, encompassingeverything below that point that
needs to be treated to an elective dose.
(20:59):
So from the SI joint down. Correct.
It's designed to encompass the entire mesorectum, a critical
emphatic drainage area, the remaining pelvic nodes that are
at risk and crucially, the bilateral inguinal nodal basins,
as well as the entire primary tumor volume and its associated
GTV dash P margin. Wow, so CTV 2 covers the
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primary, the lower pelvis and the groins.
Exactly This ensures A comprehensive coverage of the
primary site and the lower regional drainage, recognizing
the dual lymphatic pathways of the anal canal.
It's a big volume. And then CTV three, I imagine
this is where we concentrate thehighest dose, the boost volume
targeting her known gross disease.
(21:40):
How is that specifically definedfor Mrs. Lee, considering both
her primary tumor and her involved lymph nodes?
Exactly right. CTV 3 is indeed the high risk
boost volume. This is where we focus our
highest dose to the known gross disease.
We create it by taking her GTVP,that 7 centimeter primary tumor
and adding a 1.5cm margin aroundit.
GTVP plus 1.5 centimeters. Correct.
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This is our target for definitive local control.
We also include her GTVN, her involved lymph nodes with a 1cm
margin. GTB N + 1 centimeter.
Right. This volume, derived from CTV 3
and expanded to a PTV will be the target for our highest
definitive dose. It's the bullseye for maximum
tumor killing. OK. 3 distinct C2 VS driving 3PT
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VS. Now for the critical part,
prescribing misses Lee's dose. Given our clinical T3N1C
disease, which is quite advancedand complex, what specific dose
approach are we taking for her and how does it integrate those
different PT VS derived from theCT VS we just defined to deliver
tailored doses to different risklevels?
Good question for Missus Lee, given her bulky and extensive
(22:48):
disease, we'll use a specific combination of a simultaneous
integrated boost or SIB followedby a sequential boost.
OK, a hybrid approach, SC plus sequential boost.
Exactly. It's a hybrid approach,
meticulously tailored for these more complex and larger cases,
allowing for both efficient initial treatment and adaptive
dose escalation. It's about being smart with how
we deliver the radiation, especially with large tumors.
(23:10):
How does that breakdown phase byphase?
So in phase one, which is the SIB phase over 25 fractions. 25
fractions for phase one. Right.
We will simultaneously deliver 40 Grays in 1.6 Gray fractions
to PTV, one which covers her upper elective pelvic notes.
OK 40 dray in 1.6 dray fractionsto PTV 1.
(23:30):
Concurrently, within the very same daily treatment, we will
deliver 45 Gray in 1.8 Gray fractions to PTV 2 her lower
pelvis and elective inguinal nodes, which also includes the
primary tumor area. Got it. 45 GI in 1.8 Gray
fractions to PTV 2, so slightly higher dose per fraction to the
(23:51):
lower volume. Correct.
This sets the stage by covering all at risk and lower risk gross
disease areas upfront, and it treats the majority of the
field, including the primary, toa substantial dose.
OK. That's phase one.
Then after that initial phase, you mentioned a sequential
boost. How does phase two work and what
is its specific target, especially considering the
tumor's likely response to the initial treatment?
(24:12):
Right, for Phase 2, the sequential boost after
completing the 1st 25 fractions of the SIB phase, we will
deliver a sequential boost only to PTV 3 only.
PTV 3 the high risk volume. Exactly that highest risk volume
covering her gross primary tumorand involved nodes.
Based on the initial GT VS plus margins, she will receive an
additional 10.8 Gray delivered in six fractions of 1.8 Gray.
(24:36):
10.8 G and six fractions to PTV 3.
Correct. This means the highest
definitive dose is concentrated on the gross disease after an
initial phase of treatment, allowing for tumor shrinkage and
precise retargeting if needed. Though often planned upfront
this way, it's an adaptive strategy built in in a sense.
So we add those doses up, what does that bring her total
cumulative dose to her gross disease, both the primary tumor
(24:58):
and the involved nodes covered by PTV 3 by the very end of her
treatment course? OK, so PTV 3 was part of PTV 2
initially, right? So it received 45-D in 25
fractions during phase one. Then it gets the additional 10.8
Gigi boost in phase two, right? So 45 + 10.8 that brings the
total cumulative dose to a grossdisease to 55.8 Gray. 55.8 G
(25:19):
total. Exactly.
And this dose falls perfectly within the Astro recommended
range of 53.2 to 59.4 Gray for her T3 primary tumor and her
involved nodes. So we're delivering a highly
effective and guideline concordant definitive dose with
this approach. Excellent.
A common and very good question often arises, especially when
(25:40):
talking about these multi phase plans.
Why not just use a single SIB for the entire treatment course,
hitting all targets with their final doses from day one?
You know, just plan 40 to PTV 145 to PTV 2 and 55.8 to PTV 3
all simultaneously for say 31 fractions.
Why do we opt for this hybrid sib plus sequential boost
(26:02):
approach, especially for complexand bulky presentations like
Mrs. Lees? There has to be a compelling
clinical rationale behind this added complexity.
That's an excellent question, and one that often comes up in
practice. There are indeed three very
compelling clinical reasons why this hybrid approach is often
superior, particularly for complex and bulky presentations
like misses. Lee's is not just about
complexity for complexity's sake.
(26:24):
It's deeply rooted in patient safety and treatment efficacy.
OK, what are those three reasons?
1st and perhaps most importantly, is for toxicity
management. OK.
Imagine starting with the absolute highest dose per
fraction on a large ulcerated tumor like the seven centimeter
mass misses Lee has from day one.
This can cause a truly severe acute reaction in the patient.
(26:45):
Think intense skin breakdown, painful GI issues.
Yeah, a big flare up early. On exactly this dramatically
increases the risk of a treatment break, which we
absolutely want to avoid as breaks can compromise overall
oncologic outcomes. The initial SIB phase with
slightly lower daily fractions to the highest dose volume 1.8
grand instead of otentially higher if boosting from day one,
(27:08):
acts as a more tolerable induction period, right?
This allows the timber to start shrinking significantly, often
reducing its size and the associated inflammation.
This means that when we deliver the final highest boost dose
sequentially, it's going to a smaller, more manageable volume,
which in turn significantly reduces the likelihood and
severity of acute toxicity. It's about building tolerance
(27:29):
and letting things cool down a bit first.
So it's almost like you're training for a marathon by
starting with shorter runs before building up to the full
distance. You wouldn't just throw someone
into a marathon without preparation.
Exactly. And similarly you wouldn't blast
a large sensitive tumor with theabsolute maximum dose per
fraction from day one. It's a phased approach to allow
the body to adapt and the tumor to respond, making the entire
(27:52):
journey more tolerable for the patient.
That analogy really makes sense.Exactly.
That analogy perfectly captures the essence of it.
It's about a measured adaptive response, a strategic approach
to ensure a stronger finish withless acute pain along the way.
OK, reason 1, Toxicity management.
What's the second reason? Second, there's the aspect of
(28:13):
DOS symmetric feasibility. Can the computer even do it?
Pretty much creating a plan withthree or even more simultaneous
dose levels, all needing to meetspecific target coverage and
organ at risk or OAR constraintscan be extremely challenging, if
not downright impossible for thetreatment planning system to
optimize. Sometimes the complex dose
(28:35):
gradients and overlapping volumes required to deliver say
40 grey, 45 grey and 55.8 grey all simultaneously while sparing
critical organs like the bowel, bladder, femoral heads, it can
make it incredibly difficult to achieve all objective
simultaneously without compromise.
You might have to sacrifice OAR sparing or target coverage
(28:58):
somewhere. Exactly.
The hybrid approach, by separating the highest boost
into a sequential phase, simplifies the planning problem
considerably for the dosimetrists and physicists.
It makes it much more achievabledose symmetrically and often
leads to a higher quality plan overall, meeting all constraints
more reliably. OK, so it's just easier to plan.
Well, reason 3. And 3rd, and this is perhaps the
(29:19):
most elegant and clinically powerful reason, is for adaptive
radiotherapy. An adaptive OK.
The sequential boost is a powerful intrinsic form of
adaptive radiotherapy. Think about it.
After the first five weeks of treatment, misses Lee's tumor
will have likely shrunk significantly.
The initial radiation and concurrent chemotherapy will
have done their work. The final boost, that critical
(29:40):
highest dose, is then planned onthis smaller residual tumor
volume. Ideally we'd rescan and replan
the boost based on the new anatomy.
True adaptive planning. Right, that's the ideal form.
But even if planned upfront as asequential boost to the original
PTV 3, you're still delivering that highest dose after the bulk
of the tumor has responded. This adaptive strategy,
(30:03):
especially if replanned, spares a significant amount of normal
healthy tissue from the highest cumulative dose, which is
absolutely crucial for reducing the risk of late toxicity,
things like chronic bowel issues, bladder dysfunction or
long term sexual dysfunction. So concentrating the final punch
on a smaller target. Exactly.
By adapting to the tumors response, either implicitly or
(30:25):
explicitly, we improve her long term quality of life and make
the entire treatment more precise and personalized.
It's a truly patient centric approach.
Toxicity management. Does symmetric feasibility and
adaptive radiotherapy. Three very strong reasons for
the hybrid approach in complex cases.
Got it now, once the plan is designed and the doses are
(30:45):
rescribed, we absolutely must ensure it's safe.
This is where quality assurance and meticulous checking of oar
constraints come in. What are the critical organ at
risk or OAR constraints we're meticulously checking for in
anal cancer planning to minimizethose acute and late toxicities
you just mentioned. These are the numbers we live
by, right? Absolutely.
(31:06):
Patient safety is paramount and radiation oncology and in anal
cancer planning we have very specific non negotiable
constraints to meet for various OA Rs.
These aren't just suggestions, they're critical thresholds we
must respect. OK, let's run through the key
ones bowel. For the stomach, bowel and
duodenum, collectively the sensitive upper GI tract that
could dip into the field, we strictly limit the volume of
(31:27):
bowel receiving 20 Gray or V20 to be less than 150 cubic
centimeters. These two of me less than 150CC.
OK, right. And additionally, the dose
maximum, the hottest spot anywhere in the bowel, should be
less than 54 Gray. D Max less than 54 Gray.
Got it. This helps to prevent severe
acute GI reactions and avoid long term strictures or
(31:48):
ulceration. Very important constraint.
OK. What about the bladder?
It's right there in the pelvis. For the bladder, our constraint
is that the volume receiving 35 Gray or V-35 should be less than
50%. V-35 less than 50%, correct.
This helps preserve bladder function and minimizes the risk
of radiation cystitis, which canbe a persistent and irritating
(32:10):
side effect down the road. Makes sense.
The femoral heads are also oftenpartially in the field for these
treatments, especially with inbital node coverage, and we
need to protect bone integrity to prevent long term mobility
issues. Absolutely.
For the femoral heads, we aim for the volume receiving 44 Gray
or V44 to be less than 5%. V 44 less than 5%, that's a
(32:31):
tight constraint. It is, and it's crucial for
minimizing the risk of a vascular necrosis or significant
long term hip issues that could impact ambulation and quality of
life. We really want to avoid that if
at all possible. Definitely.
And finally, what about the external genitalia and perineum?
Very sensitive area, lots of potential for skin reaction and
(32:51):
late effects. Right.
For the external genitalia and perineum, which are very
sensitive to acute skin reactions and potential long
term fibrosis or sexual dysfunction, we constrain the
volume receiving 30 Gray or V30 to be less than 50%.
V30 Less than 50% for genitalia and perineum, correct.
Meeting all these constraints istruly vital for minimizing both
(33:12):
acute and late toxicities and maintaining the patient's
quality of life far beyond the completion of treatment.
It's about treating the cancer effectively and safely.
All right, having walked throughthat intricate plan for Mrs. Lee
and a critical safety checks, what are the absolute undeniable
must knows that our listeners, especially those cramming for
boards, should lock into memory?Let's distill this into some
(33:35):
high yield clinical pearls that are practically guaranteed to
show up on an exam or be crucialin clinic.
OK, clinical pearls time Pearl number one.
Remember RTUG O529? 0529 again.
Can't emphasize it enough. This pivotal phase two trial
established dose painted IMRT with concurrent 5 FU and my toe,
(33:55):
my sin C as a safe and incredibly effective regimen for
anal cancer. The key take away the reason to
change practice is its demonstration of significantly
reduced acute grade 3 or higher GI and skin toxicity compared to
the historical 3 DCRT controls. Less toxicity.
And all this without sacrificingoncologic outcomes.
Same cancer control. That's the foundational evidence
(34:15):
for modern anal cancer radiotherapy.
Pearl #2 relates to SIB prescription for AT3 to T4 or
node positive patient like our missus Lee.
A standard dose painted IMRT plan typically delivers 54 grey
to the gross tumor and involved nodes. 54 GI to GTV.
And 45 grey to the elective nodes. 45 GI to elective CTV.
(34:38):
Usually over 30 fractions. This is your go to prescription
for definitive treatment and a very common board question
scenario. Excellent.
Earl #3 focuses on elective CTV coverage.
Remember that mnemonic, the comprehensive elective CTV for
anal canal cancer must include the primary tumor with its
margin, the entire anal canal itself, the adjacent rectum and
(34:59):
those critical nodal basins, themesorectal presacral, bilateral
internal iliac, bilateral external iliac, bilateral
obturator, and bilateral ingotallymph nodes.
My perineum is extremely obliging in going.
That's the one. Don't miss any of these as
inadequate coverage is a recipe for recurrence.
You have to know these regions. Pearl #4 is all about simulation
(35:20):
setup, the preferred setup for anal cancer.
IMRT is supine in a comfortable frog like position with a full
bladder and an empty rectum. Reproducibility is key and this
is vital especially for female patients.
Always remember that a vaginal dilator should be used during
both simulation and every treatment fraction to spare the
(35:40):
anterior vaginal wall from unnecessary dose and reduce long
term morbidity. Don't forget the dilator.
Crucial point and finally, Pearl#5 key OAR constraints for your
boards and perhaps even more importantly for clinical
practice, commit these to memory.
The small bowel constraint V20 less than 150CC.
Bowel V20150CC for. The femoral heads V 44, less
(36:04):
than 5%. Them heads V445 percent.
And for the bladder, V-35 less than 50%.
Bladder V 3550%. Mastering these constraints is
fundamental to safe and effective anal cancer planning,
protecting your patients from undue toxicity.
Know these numbers? Fantastic pearls.
Ready for a quick board blitz? Let's test these planning
concepts and see how well you'veintegrated this knowledge.
(36:25):
Imagine yourself in the hot seat, because these are exactly
the kind of questions you'll face.
All right, let's do case 1. You are contouring the elective
nodal volume for a patient with AT3NA squamous cell carcinoma of
the anal canal. Which of the following nodal
basins is not routinely includedin the standard elective CPV?
(36:46):
Is it a bilateral inguinal nodes, B bilateral internal
iliac nodes, C bilateral common iliac nodes, or D presacral
space? Think about that comprehensive
coverage we just discussed. OK, let's think about that one.
We talked about the comprehensive list, inguinal,
internal, iliac, external iliac,obturator, mesorectal,
presacral, common iliacs weren'ton that list.
(37:08):
So the best answer here without a doubt is C bilateral common
iliac nodes. And the the clinical reasoning
is straightforward. The standard elective CTV for
anal canal cancer is comprehensive indeed, including
the inguinal, external iliac, internal iliac, obturator,
mesorectal and pre sacral nodes.However, the common iliac nodes
are not routinely included in the elective volume because
(37:31):
their lymphatic drainage patterns are generally beyond
the direct regional spread of anal cancer.
In fact, if we find involvement of these nodes, it's typically
considered M1 disease, indicating distant metastatic
spread, which changes the staging and often the entire
treatment strategy from curativeto palliative intent.
Perfect reasoning. Excellent.
Let's move to case two. Another very practical scenario
(37:52):
encounter. A 50 year old woman is
undergoing simulation for anal cancer chemo radiation to
minimize dose to the anterior vaginal wall and reduce the risk
of long term sexual dysfunction.Which of the following
interventions is most appropriate during simulation
and treatment? Is it a prone positioning, B
placing A rectal balloon, C using a vaginal dilator, or D
(38:14):
instructing the patient to have an empty bladder?
OK. Minimizing dose to the anterior
vaginal wall, We talked about this specifically for Mrs. Lee.
Prone is mainly for bowel, rectal balloon is for prostate.
Empty bladder is the opposite ofwhat we want.
So the best answer here, and a crucial clinical practice point
for female patients has to be C using a vaginal dilator.
(38:35):
Why is that the best answer? The clinical reasoning is that
placing A vaginal dilator duringboth simulation and treatment
physically separates the vaginalwalls.
This action actively displaces the anterior wall specifically
away from the high dose region of the primary tumor and the
surrounding CTV, significantly reducing the dose it receives.
An empty bladder, conversely, would allow the small bowel and
(38:56):
potentially the uterus or vaginato fall into the high dose
field, increasing toxicity. A rectal balloon is a device
typically used for prostate cancer, not anal cancer, and
prone positioning, while useful for small bowel sparing and some
pelvic cases, doesn't directly address the vaginal wall dose as
effectively as a dilator in thisspecific context.
Yeah, the dilator is the specific tool for this job.
(39:18):
That's exactly right. Final question, Case 3A concept
you absolutely need to grasp forboth boards and practice.
According to the RTOG 0529 trial, what was the primary
benefit of using dose painted IMRT for anal cancer compared to
historical 3 DCRT techniques? Was it A improved 5 year overall
survival, B higher rates of pathologic complete response C
(39:40):
Significant reduction in acute grade 3 or higher
gastrointestinal and skin toxicities or DA shorter overall
treatment time? OK, RTOG 05/29 again.
What was its main point? Was it better survival?
No outcomes were similar, Betterpass CR?
Don't think so. Shorter time, no IMRT planning
can take longer. It has to be about side effects.
So the best answer clearly is C Significant reduction in acute
(40:03):
grade 3 or higher gastrointestinal and skin
toxicities. And the reasoning behind that?
The clinical reasoning is that the primary endpoint of RTOGO
529 was explicitly toxicity reduction.
The trial successfully demonstrated that dose painted
IMRT significantly reduced ratesof acute grade 3 or higher GI
and dermatologic toxicity when compared to the historical
(40:25):
control arm from RTOG 9811, which used 3 DCRT.
Importantly, oncologic outcomes like overall survival and local
control were found to be quite similar between the two
techniques. So the reduction in severe acute
toxicity was the key differentiator and immense
benefit of IMRT. It allowed us to deliver the
same powerful treatment with a far more tolerable experience
(40:46):
for the patient. That was a big win.
Absolutely nailed it. That concludes our board blitz
today. We've really translated our
clinical knowledge, all those facts and figures into a
practical step by step guide forcreating a modern, high quality
IMRT plan for anal cancer. You are now truly equipped, I
think, to handle the intricate technical aspects of simulation,
contouring and planning for thiscomplex disease.
(41:08):
From the initial setup to the final dose distribution, this
session should provide a solid foundation for your clinical
practice. Absolutely.
To recap our key takeaways from today, modern needle cancer
treatment absolutely relies on IMRT to deliver those precise
dose painted prescriptions. That's number one.
A successful and reproducible plan starts with a meticulously
(41:30):
executed supine frog leg simulation with a full bladder
and an emty rectum. Get the set U right first
crucial and remember that the elective CTV must always be
comrehensive, covering all at risk elvic and inguinal nodes.
Use that mnemonic to guide you and double check your contours.
Dose is precisely prescribed using a simultaneous integrated
boost or SIB approach, which is thoughtfully based on the TNN
(41:54):
stage of the disease, right. And as we discussed with Missus
Lee's case, this is often intelligently combined with the
sequential boost for adaptive planning and crucially, for
effective toxicity management, allowing the tumor to shrink and
the patient to tolerate the treatment better, especially in
bulky cases. All of this meticulous planning
is done while rigorously respecting critical oar
(42:15):
constraints for vital structureslike the small bowel, femoral
heads, bladder and external genitalia, all to minimize both
acute and late toxicities. This comprehensive approach is
what truly defines high quality care in anal cancer.
It's the whole package. Well said.
This brings our technical workshop on anal Cancer IMRT
planning to a close. For future discussions, we'll
(42:37):
continue our comprehensive Anal Cancer series.
We'll be synthesizing the recently published 2025 Astro
Clinical Practice Guideline in even more detail.
Looking forward to that. Reviewing the practical
management of both on treatment and late toxicities.
You know how to actually handle these issues when they arise.
Discussing evidence based followup strategies and looking ahead
(42:57):
to the exciting future directions of anal Cancer
Research, including emerging techniques and systemic
therapies, the prospect for continued improvement in patient
outcomes is very real. To put these concepts into
practice and master them for your oral boards, make sure to
complete practice oral boards atRadonk Smart learn.com.
It's Radons Smart learn.com. And be sure to subscribe to
(43:19):
Radonk Smart Review for our nextsession.
Thanks for tuning in and learning with us.
Welcome to the Radonk Smart Review GI Cancer series.
Today we're not just discussing,we're taking a practical, really
in depth workshop on how we safely and effectively deliver
radiation therapy for anal cancer.
You know, in our previous sessions, we've really explored
the clinical cases, delved into the intricate anatomy, dissected
(00:21):
the detailed staging, and of course, thoroughly reviewed
those landmark trials that fundamentally guide our
treatment regimens. Right, the foundations.
Exactly. Now the time has truly come to
bridge the gap from theory to practice, to focus on the how,
the intricate hands on details of treatment planning.
This is where the rubber meets the road, so to speak.
(00:42):
That's exactly for residents at all levels.
Whether you're just starting outor, you know, prepping for your
boards, mastering the art of IMRT planning for anal cancer
isn't just a desirable skill, it's absolutely crucial.
It's not simply about knowing what dose to prescribe based on
a guideline. It's about understanding the
precise methodology, the meticulous steps required to
(01:03):
ensure that prescription is delivered with well sub
millimeter precision, all while minimizing side effects to the
healthy surrounding tissues. Today, we're essentially
stepping into a virtual treatment planning suite
together, using a really complexpatient case as our guide to
truly walk you through the entire process, from simulation
(01:24):
to final dose evaluation. OK, let's unpack this.
When we talk about modern radiation for anal cancer, IMRT
is almost synonymous with it now.
It's pretty much the default. It is, but for those who maybe
weren't practicing during that shift, or perhaps are studying
for their exams, why exactly hasthis particular technique become
the unwavering standard of care?What was the compelling evidence
(01:46):
that truly made IMRT indispensable?
That's a vital question because understanding the why often
solidifies the how, doesn't it? It does.
The pivotal evidence which genuinely redefined the
landscape for anal cancer radiotherapy comes most notably
from the RTOG trial O 529. Yes, O 529.
Exactly. This phase two trial was without
(02:08):
a doubt a game changer for our field.
Before this we were often using older 3D conformal techniques
and while they were effective, they came with a significant
cost to the patient in terms of acute toxicity.
Right, the side effects were rough.
Very rough. RTOGO 529 clearly demonstrated
that IMRT significantly reduces acute gastrointestinal or GI and
(02:30):
skin toxicity when compared to those older 3D approaches.
And critically, this reduction in toxicity achieved without
compromising any oncologic outcomes, meaning we got the
same great cancer control with adramatically improved patient
experience during treatment. So same curates, fewer side
effects. Precisely.
This trial wasn't just about reducing a few side effects, it
(02:53):
fundamentally redefined our standard of care.
It proved we could achieve the same life saving outcomes with a
dramatically improved quality oflife for patients during
treatment. It was the moment we truly
understood that precision wasn'tjust about targeting the tumor,
but also about protecting the patient's immediate well-being
that really paved the way for IMRT to become, well,
(03:15):
indispensable. That's an incredible insight.
It's not just about immediate patient comfort during treatment
then, is it? It sounds like there are
broader, more systemic implications to this toxicity
reduction. Can you elaborate on that a bit?
Absolutely. While the the upfront cost of
implementing and delivering IMRTmay appear higher initially, you
(03:36):
know the technology, the planning expertise required, the
downstream benefits are actuallyquite substantial both for the
patient and the healthcare system.
Think about it, severe acute toxicity, particularly GI and
dermatologic issues. They often lead to unscheduled
clinic visits, urgent hospitalizations, those critical
emergency department. Visits.
Yeah, those add up quickly. They really do.
(03:56):
Numerous studies have shown thatby significantly reducing these
severe toxicities, IMRT directlyreduces these associated
downstream costs. So in that sense, it truly makes
IMRT A valuable long term investment in comprehensive
patient care and from a broader perspective, a wise health
(04:17):
economic strategy. So a bit more investment upfront
saves money and hassle later. Exactly.
It's a classic example of spending a little more upfront
to save a lot more later, while also giving the patient a much,
much better experience through treatment.
That puts it into perspective. OK, before we jump into our
patient case, which I'm really looking forward to applying
these concepts to, let's establish the general principles
(04:37):
of modern anal cancer planning, specifically based on the new
American Society for Radiation Oncology or Astro guidelines.
The Astro guidelines. Right.
We'll start as always with target volume delineation or
contouring. When we're sitting down to
contour a patient's plan, what are the core components we
absolutely need to define OK? The two 2025 Astro guideline and
(04:58):
consensus atlases provide a veryclear and robust road map for
this, almost like a definitive playbook you could say.
First and foremost, we meticulously define the gross
tumor volume or GTV. This volume includes all visible
primary tumor, which we designate as GTV Dash P.
So if you see a palpable mass, an ulcer, or a lesion on
(05:20):
imaging, that's your GTV Dash P.What you can see or feel.
Exactly, Yeah. And then we also include any
involved regional nodes which welabel as GTV dash N.
Now it's important to be very specific here.
A node is generally considered gross disease if it is greater
than or equal to 1.5 centimeterson CT, or if it's PET positive
(05:40):
on the diagnostic imaging, or ofcourse if it's biopsy proven.
Clear criteria. Those are our unequivocal
criteria for gross nodal involvement.
Pretty standard stuff there. And then once we have that GTV
precisely defined, how do we build from that foundation to
create our clinical target volume or CTV?
That's where the margins come in, right?
Because we're not just treating what we see, but what might be
(06:01):
microscopically present nearby. That's absolutely right.
The CTV is designed to cover theGTV with an appropriate margin,
specifically accounting for thatmicroscopic extension we can't
see with our eyes or on routine imaging.
But it also includes all the necessary elective nodal regions
where there's a significant riskof subclinical disease even if
(06:22):
we don't see gross involvement there.
Got it. So the primary plus potential
spread. Exactly to be specific, the GTV
dash P, the primary tumor typically receives a generous
1.5 to 2.5 centimeter margin to encompass that potential
microscopic spread. 1.5 to 2.5 centimeters.
The GTV Dash N on the other hand, the involve nodes gets a
(06:43):
slightly tighter 1 to 1.5cm margin.
OK, one to 1.5 centimeters for nodes.
Right. This difference in margin
reflects the different patterns of microscopic spread from a
primary tumor versus a regional lymph node.
It's tailored. Makes sense.
And what about the comprehensiveelective CTV?
I know the Astro guideline has incredibly strong
(07:04):
recommendations here, making it a truly critical component for
anal cancer planning. This is where we ensure
recovering all those at risk regions, even if they're not
overtly involved because of those lymphatic drainage
patterns. This feels like a non negotiable
safety net. Indeed, this is truly a critical
concept and the Astro guideline makes a very strong explicit
recommendation. This comprehensive elective
(07:27):
volume must include the primary tumor with its appropriate
margin, the entire anal canal itself, the adjacent rectum
because of the direct extension and lymphatic pathways there,
and then a very specific non negotiable set of nodal basins.
This is where you know the detail really matters because
when we talk about comprehensivecoverage, we're not just
guessing. The Astra guideline lays out a
(07:48):
truly non negotiable checklist of nodal basins we must include,
almost like a safety net for microscopic disease.
OK, let's hear the list. So let's walk through those
critical regions. These include the mesorectal,
the presacral, the bilateral internal iliac, up the size, the
bilateral external iliac. Both sides again.
The bilateral obturator and the bilateral inguinot Lymphson
(08:10):
notes this extensive coverage isabsolutely non negotiable for
anal canal cancer as we know thelymphatic drainage can be quite
widespread and unpredictable, particularly down to those
inguinal regions. So you really have to cover the
pelvis, Andy the groins electively.
You absolutely do. If you miss one of these, you're
leaving a potential area for recurrence on the table.
(08:32):
It's that critical. There's a lot of nodal basins to
remember, especially under pressure.
For those of you studying or just wanting a quick recall
trick, here's a mnemonic that might help you keep track of
that comprehensive elective CTV nodal basins.
Oh, a mnemonic good idea. Yeah, think my perineum is
extremely obliging in going. So my other mazerectal perineum
(08:57):
for presacral is for internal iliac, extremely for external
iliac obliging for obturator andin going for inguinal.
My perineum is extremely obliging in going.
I like it. That's actually quite helpful.
Hopefully that sticks with you and helps you remember this
critical list. That's a fantastic mnemonic,
very helpful for remembering that extensive list and when I
(09:17):
know many residents will appreciate.
OK, shifting gears slightly, let's talk about dose and
fractionation. The Astro guideline endorses a
very precise risk adapted dosingstrategy that is based directly
on both the T stage and the end stage of the disease.
Right. It's not one-size-fits-all.
Not at all. How does this critical breakdown
of dosing look for the primary tumor depending on its size it's
(09:39):
T stage? OK.
For the dose of the primary tumor, we have a clear
stratification based on that T stage.
For clinical T1 to T2 tumors, which are generally smaller,
less bulky, the recommended doseis 45 to 50.4 Gray. 45 to 50.4
Kari. Right.
Typically delivered in 25 to 28 fractions.
This is usually sufficient for those smaller primary lesions.
(10:01):
However, for those larger, more advanced clinical T3 to T4
tumors where we have a higher tumor burden and potentially
more microscopic extension, a higher dose is recommended to
ensure adequate control 53.2 to 59.4 Gray. 53.2 to 59.4 Gray, so
a definite step up. A definite step up, yeah,
(10:21):
Usually delivered over 28 to 33 fractions.
The higher dose and slightly more fractions reflect the
increased challenge of eradicating a larger tumor.
Makes sense. More tumor needs more dose.
And what about the lymph nodes? This is a crucial distinction.
How do we approach dosing for both the clinically involved
nodes where we see gross diseaseand then those elective volumes
where we're aiming for prophylaxis, trying to prevent
(10:43):
subclinical disease from emerging and at risk areas?
It's not the same dose for both,is it?
No, it certainly isn't for clinically involved nodes or N
positive disease, the ones we identified as GTVN.
These should receive a definitive curative dose of 50.4
to 54 grey. 50.4 to 54 grey, similar to the higher T stage
primary dose range. Exactly.
Usually delivered in 28 to 30 fractions.
(11:06):
This is to ensure we eradicate the gross disease in the lymph
nodes, treating them with the same intensity as the primary
tumor, essentially. And then for those elective
nodal volumes where our goal is prophylaxis to cover those at
risk areas that don't have grossdisease but are known pathways
to spread, what dose do they get?
Those at risk nodal regions where we're targeting
microscopic or subclinical disease should receive a
(11:29):
prophylactic dose. That range is 36 to 45 Gray. 36
to 45 Gray lower dose. Right, a lower dose typically
delivered in 20 to 30 fractions.This lower dose is sufficient
for microscopic disease while sparing healthy tissues from
unnecessary high dose radiation,which really helps reduce long
term toxicity. OK, that stratification is key.
(11:50):
Now with these Astro guidelines in mind and the elegance of
IMRT, we often utilize the simultaneous integrated Boost or
SIB approach. This is a very elegant technique
that allows for incredible efficiency by treating multiple
dose levels at once. Can you explain how these
different dose levels, the elective and the involved noodle
(12:10):
doses for instance, are delivered simultaneously within
a single plan using this SIB approach?
How does it work in practice? Right, the Seb for a node
positive patient utilizing an SIB approach, the guideline
recommends a dose of typically 40 to 42 Gray and 28 fractions
or alternatively 45 Gray and 30 fractions to the elective
volume. OK.
(12:31):
The prophylactic dose level. Exactly what's crucial here is
that this is delivered simultaneously with 50.4 to 54
Gray, also in 28 to 30 fractionsto the clinically positive lymph
nodes and the primary tumor. So delivering both doses every
single day. Every single day.
So in one treatment session, you're hitting multiple targets
with different precise dose levels.
(12:53):
This simultaneous delivery allows for incredible efficiency
in the treatment schedule, collapsing what might have been
two separate phases into one continuous course.
Much more convenient for the patient too.
Absolutely. It also ensures we deliver that
precise risk adapted dosing to each target volume within the
same overall treatment time frame.
It's a very smart way to achieveour dose goals, maximizing
(13:15):
therapeutic effect while maintaining a reasonable overall
treatment time. It requires sophisticated
planning, definitely, but offerssignificant clinical benefits.
Very elegant. Now let's take all these
foundational principles, the rationale for IMRT, the Astra
guidelines on contouring and dose and apply them to a real
world, highly complex scenario. We have Missus Lee, a 58 year
(13:37):
old woman. Can you walk us through her
story and her presentation really set the stage for the
planning challenge she presents.Certainly Missus Lee presents
with a quite large 7 centimeter ulcerated anal mass. 7
centimeters. Wow.
Yeah, quite bulky. What makes her case particularly
challenging and relevant to our discussion today is that this
(13:57):
mass extends directly into the lower vagina, indicating local
advancement. OK, so T3 at least.
Right biopsy confirmed that thisis human papilloma virus, or HPV
positive squamous cell carcinoma, a common type but
with a significant local extent that demands A robust approach.
And what did her comprehensive staging workup reveal?
(14:18):
Was there any distant spread or,more relevant to our discussion
today, extensive nodal involvement that would
complicate our planning? Her comprehensive staging
workup, which included APETCT, revealed concerning findings
beyond just the primary tumor. Specifically, she has a right
external iliac lymph node that is involved.
OK, pelvic node. Along with bilateral inguital
(14:39):
lymph nodes that are also clearly involved.
Both groins too. Yeah.
So this multi station nodal disease combined with her
already bulky primary tumor result in a clinical stage of
clinical T3N1CT3. N1C.
Correct. This is indeed a complex case
with a bulky primary and multi level nodal involvement, and it
will truly challenge our treatment planning approach,
(15:01):
requiring very careful consideration of precision at
every step. This isn't your straightforward
T1N0 case. This is where thoughtful
planning truly shines. Absolutely.
So, given Missus Lee's complex presentation with that bulky
primary and multi station nodal involvement, let's walk through
the plan for her step by step, starting with simulation best
(15:21):
practices. What are the key considerations
we need to keep in mind for her setup to ensure not only
reproducibility but also the most accurate dose delivery
possible for such an extensive target?
OK, simulation for Missus Lee. We'll simulate her supine with
her arms positioned comfortably on her chest, and she'll be
immobilized securely in a vac lock bag.
Standard supine setup. Exactly.
(15:42):
Supine positioning is standard for IMRT and anal cancer, and
for good reason. It offers the highest level of
reproducibility, which is absolutely essential for precise
daily treatments day after day for many weeks.
It's also specifically necessaryfor adequately treating her
involved inguinal nodes, which can be particularly challenging
to target accurately in other positions due to potential
(16:03):
positional shifts or patient discomfort.
So supine is the go to. Any special positioning
requirements for the lower body?I can imagine with a tumor
extending into the vagina and inguinal nodes, you'd want to
manage skin folds and ensure consistent geometry down there.
Yes, definitely. This is a subtle but critical
detail. Will utilize A specialized knee
(16:24):
and ankle fixation device to maintain a comfortable frog leg
position for her lower extremities.
OK, the frog leg position, why is that important?
This particular position is critical because it helps to
pull the upper thighs slightly away from the perineum, which
minimizes skin folds in that sensitive.
Area. Oh right, skin dose.
Exactly. If not addressed, these folds
(16:45):
can significantly impact dose distribution to the target
volumes, creating areas of overall underdosing and
dramatically increased skin toxicity, which is already a
significant concern in this area.
It's about creating the cleanest, most predictable
anatomy for treatment delivery. Makes sense.
And what about those standard bladder and rectum protocols?
We know those are often key for managing pelvic treatments and
(17:07):
protecting critical organs at risk.
Right, we will adhere to a full bladder, empty rectum protocol.
This is crucial. A full bladder helps displace
the small bowel superiorly and anteriorly out of the high dose
treatment field which is vital for reducing GI toxicity later
on. Get the bowel out of the way.
Precisely. An empty rectum, conversely,
(17:29):
helps minimize rectal wall dose,especially as the primary tumor
is often directly adjacent to it.
We'll also place a radiopaque marker at the anal verge.
The BB marker. Yep, the BB marker.
This is a very simple but incredibly effective trick for
accurate daily setup and for clearly outlining the inferior
border of our target volumes, ensuring we don't miss any of
the primary down low. And given her vaginal
(17:51):
involvement, anything specific there?
Yes, absolutely right. Given her vaginal involvement, a
crucial step for Missus Lee willbe to use a vaginal dilator
during both simulation and everysingle treatment fraction.
A dilator during treatment. Yes, this physically displaces
the uninvolved vaginal tissue away from the high dose region,
helping disparate from unnecessary radiation and
(18:12):
significantly reducing the risk of late toxicities like vaginal
stenosis, which can severely impact a patient's quality of
life. Super important.
Wow. OK, that's a key intervention.
And for imaging, what will we acquire to ensure we have the
most precise anatomical information for contouring,
especially with her complex neural involvement?
We will acquire ACT scan with intravenous contrast.
(18:34):
The contract helps us clearly delineate vessels, bladder and
importantly identify and confirmpotentially involved lymph nodes
with better precision. And then we will meticulously
fuse her diagnostic PTCT scan with this simulation CT.
TT, fusion critical. Absolutely critical for precise
contouring, especially for identifying and defining her
(18:54):
metabolically active gross disease in both the primary
tumor and the involved lymph nodes.
It gives us that physiological correlate to our anatomical CT,
ensuring we are hitting the trueextent of the tumor.
You really need both. OK, great setup.
Moving on to contouring Missus Lee's plan itself, how do we
approach defining her GTV's and CTV's?
Given her complex presentation with both a bulky primary tumor
(19:17):
and multistation nodal involvement, this seems like
where the planning really gets intricate.
It does. This is where the art meets the
science. For her GTV's, we'll precisely
contour her 7 centimeter primarytumor, which we designate as GTV
dash P. This is our starting point for
the highest dose. GTVP the primary.
Right. Additionally, we'll contour her
(19:37):
involved right external iliac lymph node and her bilateral
inguinal lymph nodes, all designated as GTV dash N.
GTVN the positive nodes. Exactly.
These are the areas of gross visible metabolically active
disease that absolutely need definitive doses Now For her CT
DS, given her extensive nodal involvement and the need for
(19:57):
comprehensive coverage of microscopic disease will define
three distinct CT VS to manage the different dose levels we
plan to deliver. Three CT VS OK break that down
for us. This multi tiered approach
allows for tailored dosing to different risk levels.
So CTV 1 is what we call the upper elective pelvis.
CTV 1 upper pelvis. This volume covers the upper
(20:19):
pelvic nodes at risk, extending cranially from L5S1 down to the
bottom bottom of the SI joint. This comprehensive volume
includes the presacral space anda 7mm margin around the internal
and external iliac vessels. OK.
It's designed to scoop up any potential microscopic disease in
those higher pelvic noble chainsthat are still at risk, even if
(20:39):
not grossly involved. And how about CTU 2?
Where does that pick up and whatdoes it encompass for Misses
Lee, especially concerning the primary tumor in those lower
nodes? Right.
CTV 2 is the lower pelvis and inguinal nodes volume.
This volume starts precisely at the bottom of the SI joint and
extends inferiorly, encompassingeverything below that point that
needs to be treated to an elective dose.
(20:59):
So from the SI joint down. Correct.
It's designed to encompass the entire mesorectum, a critical
emphatic drainage area, the remaining pelvic nodes that are
at risk and crucially, the bilateral inguinal nodal basins,
as well as the entire primary tumor volume and its associated
GTV dash P margin. Wow, so CTV 2 covers the
(21:20):
primary, the lower pelvis and the groins.
Exactly This ensures A comprehensive coverage of the
primary site and the lower regional drainage, recognizing
the dual lymphatic pathways of the anal canal.
It's a big volume. And then CTV three, I imagine
this is where we concentrate thehighest dose, the boost volume
targeting her known gross disease.
(21:40):
How is that specifically definedfor Mrs. Lee, considering both
her primary tumor and her involved lymph nodes?
Exactly right. CTV 3 is indeed the high risk
boost volume. This is where we focus our
highest dose to the known gross disease.
We create it by taking her GTVP,that 7 centimeter primary tumor
and adding a 1.5cm margin aroundit.
GTVP plus 1.5 centimeters. Correct.
(22:02):
This is our target for definitive local control.
We also include her GTVN, her involved lymph nodes with a 1cm
margin. GTB N + 1 centimeter.
Right. This volume, derived from CTV 3
and expanded to a PTV will be the target for our highest
definitive dose. It's the bullseye for maximum
tumor killing. OK. 3 distinct C2 VS driving 3PT
(22:25):
VS. Now for the critical part,
prescribing misses Lee's dose. Given our clinical T3N1C
disease, which is quite advancedand complex, what specific dose
approach are we taking for her and how does it integrate those
different PT VS derived from theCT VS we just defined to deliver
tailored doses to different risklevels?
Good question for Missus Lee, given her bulky and extensive
(22:48):
disease, we'll use a specific combination of a simultaneous
integrated boost or SIB followedby a sequential boost.
OK, a hybrid approach, SC plus sequential boost.
Exactly. It's a hybrid approach,
meticulously tailored for these more complex and larger cases,
allowing for both efficient initial treatment and adaptive
dose escalation. It's about being smart with how
we deliver the radiation, especially with large tumors.
(23:10):
How does that breakdown phase byphase?
So in phase one, which is the SIB phase over 25 fractions. 25
fractions for phase one. Right.
We will simultaneously deliver 40 Grays in 1.6 Gray fractions
to PTV, one which covers her upper elective pelvic notes.
OK 40 dray in 1.6 dray fractionsto PTV 1.
(23:30):
Concurrently, within the very same daily treatment, we will
deliver 45 Gray in 1.8 Gray fractions to PTV 2 her lower
pelvis and elective inguinal nodes, which also includes the
primary tumor area. Got it. 45 GI in 1.8 Gray
fractions to PTV 2, so slightly higher dose per fraction to the
(23:51):
lower volume. Correct.
This sets the stage by covering all at risk and lower risk gross
disease areas upfront, and it treats the majority of the
field, including the primary, toa substantial dose.
OK. That's phase one.
Then after that initial phase, you mentioned a sequential
boost. How does phase two work and what
is its specific target, especially considering the
tumor's likely response to the initial treatment?
(24:12):
Right, for Phase 2, the sequential boost after
completing the 1st 25 fractions of the SIB phase, we will
deliver a sequential boost only to PTV 3 only.
PTV 3 the high risk volume. Exactly that highest risk volume
covering her gross primary tumorand involved nodes.
Based on the initial GT VS plus margins, she will receive an
additional 10.8 Gray delivered in six fractions of 1.8 Gray.
(24:36):
10.8 G and six fractions to PTV 3.
Correct. This means the highest
definitive dose is concentrated on the gross disease after an
initial phase of treatment, allowing for tumor shrinkage and
precise retargeting if needed. Though often planned upfront
this way, it's an adaptive strategy built in in a sense.
So we add those doses up, what does that bring her total
cumulative dose to her gross disease, both the primary tumor
(24:58):
and the involved nodes covered by PTV 3 by the very end of her
treatment course? OK, so PTV 3 was part of PTV 2
initially, right? So it received 45-D in 25
fractions during phase one. Then it gets the additional 10.8
Gigi boost in phase two, right? So 45 + 10.8 that brings the
total cumulative dose to a grossdisease to 55.8 Gray. 55.8 G
(25:19):
total. Exactly.
And this dose falls perfectly within the Astro recommended
range of 53.2 to 59.4 Gray for her T3 primary tumor and her
involved nodes. So we're delivering a highly
effective and guideline concordant definitive dose with
this approach. Excellent.
A common and very good question often arises, especially when
(25:40):
talking about these multi phase plans.
Why not just use a single SIB for the entire treatment course,
hitting all targets with their final doses from day one?
You know, just plan 40 to PTV 145 to PTV 2 and 55.8 to PTV 3
all simultaneously for say 31 fractions.
Why do we opt for this hybrid sib plus sequential boost
(26:02):
approach, especially for complexand bulky presentations like
Mrs. Lees? There has to be a compelling
clinical rationale behind this added complexity.
That's an excellent question, and one that often comes up in
practice. There are indeed three very
compelling clinical reasons why this hybrid approach is often
superior, particularly for complex and bulky presentations
like misses. Lee's is not just about
complexity for complexity's sake.
(26:24):
It's deeply rooted in patient safety and treatment efficacy.
OK, what are those three reasons?
1st and perhaps most importantly, is for toxicity
management. OK.
Imagine starting with the absolute highest dose per
fraction on a large ulcerated tumor like the seven centimeter
mass misses Lee has from day one.
This can cause a truly severe acute reaction in the patient.
(26:45):
Think intense skin breakdown, painful GI issues.
Yeah, a big flare up early. On exactly this dramatically
increases the risk of a treatment break, which we
absolutely want to avoid as breaks can compromise overall
oncologic outcomes. The initial SIB phase with
slightly lower daily fractions to the highest dose volume 1.8
grand instead of otentially higher if boosting from day one,
(27:08):
acts as a more tolerable induction period, right?
This allows the timber to start shrinking significantly, often
reducing its size and the associated inflammation.
This means that when we deliver the final highest boost dose
sequentially, it's going to a smaller, more manageable volume,
which in turn significantly reduces the likelihood and
severity of acute toxicity. It's about building tolerance
(27:29):
and letting things cool down a bit first.
So it's almost like you're training for a marathon by
starting with shorter runs before building up to the full
distance. You wouldn't just throw someone
into a marathon without preparation.
Exactly. And similarly you wouldn't blast
a large sensitive tumor with theabsolute maximum dose per
fraction from day one. It's a phased approach to allow
the body to adapt and the tumor to respond, making the entire
(27:52):
journey more tolerable for the patient.
That analogy really makes sense.Exactly.
That analogy perfectly captures the essence of it.
It's about a measured adaptive response, a strategic approach
to ensure a stronger finish withless acute pain along the way.
OK, reason 1, Toxicity management.
What's the second reason? Second, there's the aspect of
(28:13):
DOS symmetric feasibility. Can the computer even do it?
Pretty much creating a plan withthree or even more simultaneous
dose levels, all needing to meetspecific target coverage and
organ at risk or OAR constraintscan be extremely challenging, if
not downright impossible for thetreatment planning system to
optimize. Sometimes the complex dose
(28:35):
gradients and overlapping volumes required to deliver say
40 grey, 45 grey and 55.8 grey all simultaneously while sparing
critical organs like the bowel, bladder, femoral heads, it can
make it incredibly difficult to achieve all objective
simultaneously without compromise.
You might have to sacrifice OAR sparing or target coverage
(28:58):
somewhere. Exactly.
The hybrid approach, by separating the highest boost
into a sequential phase, simplifies the planning problem
considerably for the dosimetrists and physicists.
It makes it much more achievabledose symmetrically and often
leads to a higher quality plan overall, meeting all constraints
more reliably. OK, so it's just easier to plan.
Well, reason 3. And 3rd, and this is perhaps the
(29:19):
most elegant and clinically powerful reason, is for adaptive
radiotherapy. An adaptive OK.
The sequential boost is a powerful intrinsic form of
adaptive radiotherapy. Think about it.
After the first five weeks of treatment, misses Lee's tumor
will have likely shrunk significantly.
The initial radiation and concurrent chemotherapy will
have done their work. The final boost, that critical
(29:40):
highest dose, is then planned onthis smaller residual tumor
volume. Ideally we'd rescan and replan
the boost based on the new anatomy.
True adaptive planning. Right, that's the ideal form.
But even if planned upfront as asequential boost to the original
PTV 3, you're still delivering that highest dose after the bulk
of the tumor has responded. This adaptive strategy,
(30:03):
especially if replanned, spares a significant amount of normal
healthy tissue from the highest cumulative dose, which is
absolutely crucial for reducing the risk of late toxicity,
things like chronic bowel issues, bladder dysfunction or
long term sexual dysfunction. So concentrating the final punch
on a smaller target. Exactly.
By adapting to the tumors response, either implicitly or
(30:25):
explicitly, we improve her long term quality of life and make
the entire treatment more precise and personalized.
It's a truly patient centric approach.
Toxicity management. Does symmetric feasibility and
adaptive radiotherapy. Three very strong reasons for
the hybrid approach in complex cases.
Got it now, once the plan is designed and the doses are
(30:45):
rescribed, we absolutely must ensure it's safe.
This is where quality assurance and meticulous checking of oar
constraints come in. What are the critical organ at
risk or OAR constraints we're meticulously checking for in
anal cancer planning to minimizethose acute and late toxicities
you just mentioned. These are the numbers we live
by, right? Absolutely.
(31:06):
Patient safety is paramount and radiation oncology and in anal
cancer planning we have very specific non negotiable
constraints to meet for various OA Rs.
These aren't just suggestions, they're critical thresholds we
must respect. OK, let's run through the key
ones bowel. For the stomach, bowel and
duodenum, collectively the sensitive upper GI tract that
could dip into the field, we strictly limit the volume of
(31:27):
bowel receiving 20 Gray or V20 to be less than 150 cubic
centimeters. These two of me less than 150CC.
OK, right. And additionally, the dose
maximum, the hottest spot anywhere in the bowel, should be
less than 54 Gray. D Max less than 54 Gray.
Got it. This helps to prevent severe
acute GI reactions and avoid long term strictures or
(31:48):
ulceration. Very important constraint.
OK. What about the bladder?
It's right there in the pelvis. For the bladder, our constraint
is that the volume receiving 35 Gray or V-35 should be less than
50%. V-35 less than 50%, correct.
This helps preserve bladder function and minimizes the risk
of radiation cystitis, which canbe a persistent and irritating
(32:10):
side effect down the road. Makes sense.
The femoral heads are also oftenpartially in the field for these
treatments, especially with inbital node coverage, and we
need to protect bone integrity to prevent long term mobility
issues. Absolutely.
For the femoral heads, we aim for the volume receiving 44 Gray
or V44 to be less than 5%. V 44 less than 5%, that's a
(32:31):
tight constraint. It is, and it's crucial for
minimizing the risk of a vascular necrosis or significant
long term hip issues that could impact ambulation and quality of
life. We really want to avoid that if
at all possible. Definitely.
And finally, what about the external genitalia and perineum?
Very sensitive area, lots of potential for skin reaction and
(32:51):
late effects. Right.
For the external genitalia and perineum, which are very
sensitive to acute skin reactions and potential long
term fibrosis or sexual dysfunction, we constrain the
volume receiving 30 Gray or V30 to be less than 50%.
V30 Less than 50% for genitalia and perineum, correct.
Meeting all these constraints istruly vital for minimizing both
(33:12):
acute and late toxicities and maintaining the patient's
quality of life far beyond the completion of treatment.
It's about treating the cancer effectively and safely.
All right, having walked throughthat intricate plan for Mrs. Lee
and a critical safety checks, what are the absolute undeniable
must knows that our listeners, especially those cramming for
boards, should lock into memory?Let's distill this into some
(33:35):
high yield clinical pearls that are practically guaranteed to
show up on an exam or be crucialin clinic.
OK, clinical pearls time Pearl number one.
Remember RTUG O529? 0529 again.
Can't emphasize it enough. This pivotal phase two trial
established dose painted IMRT with concurrent 5 FU and my toe,
(33:55):
my sin C as a safe and incredibly effective regimen for
anal cancer. The key take away the reason to
change practice is its demonstration of significantly
reduced acute grade 3 or higher GI and skin toxicity compared to
the historical 3 DCRT controls. Less toxicity.
And all this without sacrificingoncologic outcomes.
Same cancer control. That's the foundational evidence
(34:15):
for modern anal cancer radiotherapy.
Pearl #2 relates to SIB prescription for AT3 to T4 or
node positive patient like our missus Lee.
A standard dose painted IMRT plan typically delivers 54 grey
to the gross tumor and involved nodes. 54 GI to GTV.
And 45 grey to the elective nodes. 45 GI to elective CTV.
(34:38):
Usually over 30 fractions. This is your go to prescription
for definitive treatment and a very common board question
scenario. Excellent.
Earl #3 focuses on elective CTV coverage.
Remember that mnemonic, the comprehensive elective CTV for
anal canal cancer must include the primary tumor with its
margin, the entire anal canal itself, the adjacent rectum and
(34:59):
those critical nodal basins, themesorectal presacral, bilateral
internal iliac, bilateral external iliac, bilateral
obturator, and bilateral ingotallymph nodes.
My perineum is extremely obliging in going.
That's the one. Don't miss any of these as
inadequate coverage is a recipe for recurrence.
You have to know these regions. Pearl #4 is all about simulation
(35:20):
setup, the preferred setup for anal cancer.
IMRT is supine in a comfortable frog like position with a full
bladder and an empty rectum. Reproducibility is key and this
is vital especially for female patients.
Always remember that a vaginal dilator should be used during
both simulation and every treatment fraction to spare the
(35:40):
anterior vaginal wall from unnecessary dose and reduce long
term morbidity. Don't forget the dilator.
Crucial point and finally, Pearl#5 key OAR constraints for your
boards and perhaps even more importantly for clinical
practice, commit these to memory.
The small bowel constraint V20 less than 150CC.
Bowel V20150CC for. The femoral heads V 44, less
(36:04):
than 5%. Them heads V445 percent.
And for the bladder, V-35 less than 50%.
Bladder V 3550%. Mastering these constraints is
fundamental to safe and effective anal cancer planning,
protecting your patients from undue toxicity.
Know these numbers? Fantastic pearls.
Ready for a quick board blitz? Let's test these planning
concepts and see how well you'veintegrated this knowledge.
(36:25):
Imagine yourself in the hot seat, because these are exactly
the kind of questions you'll face.
All right, let's do case 1. You are contouring the elective
nodal volume for a patient with AT3NA squamous cell carcinoma of
the anal canal. Which of the following nodal
basins is not routinely includedin the standard elective CPV?
(36:46):
Is it a bilateral inguinal nodes, B bilateral internal
iliac nodes, C bilateral common iliac nodes, or D presacral
space? Think about that comprehensive
coverage we just discussed. OK, let's think about that one.
We talked about the comprehensive list, inguinal,
internal, iliac, external iliac,obturator, mesorectal,
presacral, common iliacs weren'ton that list.
(37:08):
So the best answer here without a doubt is C bilateral common
iliac nodes. And the the clinical reasoning
is straightforward. The standard elective CTV for
anal canal cancer is comprehensive indeed, including
the inguinal, external iliac, internal iliac, obturator,
mesorectal and pre sacral nodes.However, the common iliac nodes
are not routinely included in the elective volume because
(37:31):
their lymphatic drainage patterns are generally beyond
the direct regional spread of anal cancer.
In fact, if we find involvement of these nodes, it's typically
considered M1 disease, indicating distant metastatic
spread, which changes the staging and often the entire
treatment strategy from curativeto palliative intent.
Perfect reasoning. Excellent.
Let's move to case two. Another very practical scenario
(37:52):
encounter. A 50 year old woman is
undergoing simulation for anal cancer chemo radiation to
minimize dose to the anterior vaginal wall and reduce the risk
of long term sexual dysfunction.Which of the following
interventions is most appropriate during simulation
and treatment? Is it a prone positioning, B
placing A rectal balloon, C using a vaginal dilator, or D
(38:14):
instructing the patient to have an empty bladder?
OK. Minimizing dose to the anterior
vaginal wall, We talked about this specifically for Mrs. Lee.
Prone is mainly for bowel, rectal balloon is for prostate.
Empty bladder is the opposite ofwhat we want.
So the best answer here, and a crucial clinical practice point
for female patients has to be C using a vaginal dilator.
(38:35):
Why is that the best answer? The clinical reasoning is that
placing A vaginal dilator duringboth simulation and treatment
physically separates the vaginalwalls.
This action actively displaces the anterior wall specifically
away from the high dose region of the primary tumor and the
surrounding CTV, significantly reducing the dose it receives.
An empty bladder, conversely, would allow the small bowel and
(38:56):
potentially the uterus or vaginato fall into the high dose
field, increasing toxicity. A rectal balloon is a device
typically used for prostate cancer, not anal cancer, and
prone positioning, while useful for small bowel sparing and some
pelvic cases, doesn't directly address the vaginal wall dose as
effectively as a dilator in thisspecific context.
Yeah, the dilator is the specific tool for this job.
(39:18):
That's exactly right. Final question, Case 3A concept
you absolutely need to grasp forboth boards and practice.
According to the RTOG 0529 trial, what was the primary
benefit of using dose painted IMRT for anal cancer compared to
historical 3 DCRT techniques? Was it A improved 5 year overall
survival, B higher rates of pathologic complete response C
(39:40):
Significant reduction in acute grade 3 or higher
gastrointestinal and skin toxicities or DA shorter overall
treatment time? OK, RTOG 05/29 again.
What was its main point? Was it better survival?
No outcomes were similar, Betterpass CR?
Don't think so. Shorter time, no IMRT planning
can take longer. It has to be about side effects.
So the best answer clearly is C Significant reduction in acute
(40:03):
grade 3 or higher gastrointestinal and skin
toxicities. And the reasoning behind that?
The clinical reasoning is that the primary endpoint of RTOGO
529 was explicitly toxicity reduction.
The trial successfully demonstrated that dose painted
IMRT significantly reduced ratesof acute grade 3 or higher GI
and dermatologic toxicity when compared to the historical
(40:25):
control arm from RTOG 9811, which used 3 DCRT.
Importantly, oncologic outcomes like overall survival and local
control were found to be quite similar between the two
techniques. So the reduction in severe acute
toxicity was the key differentiator and immense
benefit of IMRT. It allowed us to deliver the
same powerful treatment with a far more tolerable experience
(40:46):
for the patient. That was a big win.
Absolutely nailed it. That concludes our board blitz
today. We've really translated our
clinical knowledge, all those facts and figures into a
practical step by step guide forcreating a modern, high quality
IMRT plan for anal cancer. You are now truly equipped, I
think, to handle the intricate technical aspects of simulation,
contouring and planning for thiscomplex disease.
(41:08):
From the initial setup to the final dose distribution, this
session should provide a solid foundation for your clinical
practice. Absolutely.
To recap our key takeaways from today, modern needle cancer
treatment absolutely relies on IMRT to deliver those precise
dose painted prescriptions. That's number one.
A successful and reproducible plan starts with a meticulously
(41:30):
executed supine frog leg simulation with a full bladder
and an emty rectum. Get the set U right first
crucial and remember that the elective CTV must always be
comrehensive, covering all at risk elvic and inguinal nodes.
Use that mnemonic to guide you and double check your contours.
Dose is precisely prescribed using a simultaneous integrated
boost or SIB approach, which is thoughtfully based on the TNN
(41:54):
stage of the disease, right. And as we discussed with Missus
Lee's case, this is often intelligently combined with the
sequential boost for adaptive planning and crucially, for
effective toxicity management, allowing the tumor to shrink and
the patient to tolerate the treatment better, especially in
bulky cases. All of this meticulous planning
is done while rigorously respecting critical oar
(42:15):
constraints for vital structureslike the small bowel, femoral
heads, bladder and external genitalia, all to minimize both
acute and late toxicities. This comprehensive approach is
what truly defines high quality care in anal cancer.
It's the whole package. Well said.
This brings our technical workshop on anal Cancer IMRT
planning to a close. For future discussions, we'll
(42:37):
continue our comprehensive Anal Cancer series.
We'll be synthesizing the recently published 2025 Astro
Clinical Practice Guideline in even more detail.
Looking forward to that. Reviewing the practical
management of both on treatment and late toxicities.
You know how to actually handle these issues when they arise.
Discussing evidence based followup strategies and looking ahead
(42:57):
to the exciting future directions of anal Cancer
Research, including emerging techniques and systemic
therapies, the prospect for continued improvement in patient
outcomes is very real. To put these concepts into
practice and master them for your oral boards, make sure to
complete practice oral boards atRadonk Smart learn.com.
It's Radons Smart learn.com. And be sure to subscribe to
(43:19):
Radonk Smart Review for our nextsession.
Thanks for tuning in and learning with us.
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