Including the ischiorectal fossa in anal cancer - yay/nay?

[KHE88]

Australians say always include all of it.
American and British say do not include unless clear evidence of spread through levator and even then only some of it.

What's the answer? Does anyone actually follow the Australian advice and include the whole thing for every anal case? Doing something inbetween (giving more margin on muscle)?

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[RickyScott]

Australians say always include all of it.
American and British say do not include unless clear evidence of spread through levator and even then only some of it.

What's the answer? Does anyone actually follow the Australian advice and include the whole thing for every anal case? Doing something inbetween (giving more margin on muscle)?

wether you contour it or not as part of ctv, It is going to get a very substantial dose, way above 30 Gy needed for microscopic disease in anal cancer? So I don’t specifically contour it.
Edit- even if you tried, (assuming 1-1.5 cm expansion) would be hard to get the min dose below 40 in most cases to this area.

 

[xrthopeful]

i don't see why you would include it in CTV unless invaded.

i know people do though, but not purposefully. It's easier to do the expansion on the GTV and then not carve out of stuff, so that's why people 'cover' it haha (at least that I've seen in US)

 

[KHE88]

Read the Australian guidelines from Kachnic oddly enough and look at their contouring atlas. They specifically say to contour out the entire thing in every case because all historical 2-D data was based on blocks that covered it and state that it should always be covered until evidence, such as a patterns of failure analysis from 0529, demonstrates that it doesn't need to be:

Australasian Gastrointestinal Trials Group (AGITG) contouring atlas and planning guidelines for intensity-modulated radiotherapy in anal cancer - PubMed

These consensus planning guidelines and high-resolution atlas complement the existing Radiation Therapy Oncology Group (RTOG) elective nodal ano-rectal atlas and provide additional anatomic, clinical, and technical instructions to guide radiation oncologists in the planning and delivery of IMRT...

www.ncbi.nlm.nih.gov

I'll have to go back and look at the anal plans I've done, but I'd be surprised if the whole thing conincidentally is getting 36 gy, which is the minimum elective dose in anal IIRC, especially if using static fields.

I wasn't trained to do this and hadn't heard of it until I read these guidelines so I was wondering if anybody was actually doing this.
So, if you get Lisa Kachnic as your GI examiner on orals what are you gonna say?

 

[xrthopeful]

For Lisa - easy to say to follow the US guidelines which say to not cover

 

[scarbrtj]

Let me take you back to a very scary and practically Medieval time when IMRT was around but it had never really been used for anal. To Lisa’s credit she was one of the first proponents of IMRT for anal. Almost every cancer at one time or another had (an old crusty dinosaur sourpuss type) someone say “you can’t do IMRT for that disease.” Either the IMRT was going to cause Australian brushfire levels of toxicity or it was going to leave everyone’s cancer uncured.

The convert-from-2D rationale is a good rationale to cover it. The dose-spills-over-anyway is a good rationale not to cover it and this was a notion that evolved later after those dark, Medieval times and turns out to be true in a lot of disease sites. I cover it (electively to 36 Gy if no overt involvement). It’s probably impossible to tell in the clinic during tx (per patient complaints etc) who’s being covered and who’s being not covered, but it may be possible to tell by recurrence patterns after tx. You can’t fault someone for covering it, or not, until there’s good data about those recurrence patterns. If you’re such a smart cookie that you know your oral examiner’s preferences, I would recommend to say what the examiner wants to hear.

 

[KHE88]

Let me take you back to a very scary and practically Medieval time when IMRT was around but it had never really been used for anal. To Lisa’s credit she was one of the first proponents of IMRT for anal. Almost every cancer at one time or another had (an old crusty dinosaur sourpuss type) someone say “you can’t do IMRT for that disease.” Either the IMRT was going to cause Australian brushfire levels of toxicity or it was going to leave everyone’s cancer uncured.

The convert-from-2D rationale is a good rationale to cover it. The dose-spills-over-anyway is a good rationale not to cover it and this was a notion that evolved later after those dark, Medieval times and turns out to be true in a lot of disease sites. I cover it (electively to 36 Gy if no overt involvement). It’s probably impossible to tell in the clinic during tx (per patient complaints etc) who’s being covered and who’s being not covered, but it may be possible to tell by recurrence patterns after tx. You can’t fault someone for covering it, or not, until there’s good data about those recurrence patterns. If you’re such a smart cookie that you know your oral examiner’s preferences, I would recommend to say what the examiner wants to hear.

Interesting.

36 Gy in a sequential boost mode?
If doing SIB would you also take it to 42 or less? I have not used less than 150s. If covering it I would be tempted to use something lower (based on exactly nothing -- I suppose really all I would be doing is improving homogeneity in the volume). However, I agree that excess toxicity from treating the IRF is probably minimal. I wouldn't even expect much of a hit to bone marrow.

 

[Burt Radnolds]

Well Kachnic was the first author on 0529 and last author on the Australasian guidelines, the first omitting and the latter including. If you are savvy enough to be aware of the discrepency in these publications, its not going to matter what you say to the oral board examiner, as either is SOC in my book. FWIW, I hedge and cover about half of it.

 

[xrthopeful]

Would love know if anyone has ever seen an isolated IRF recurrence. I’ve never heard of it

 

[Burt Radnolds]

Would love know if anyone has ever seen an isolated IRF recurrence. I’ve never heard of it

I have seen a positive node in the IRF up front. Interestingly I saw a biopsy proven isolated IRF failure in a bladder cancer case. SBRTd it and NED 2 years out now.

 

[scarbrtj]

Interesting.

36 Gy in a sequential boost mode?
If doing SIB would you also take it to 42 or less? I have not used less than 150s. If covering it I would be tempted to use something lower (based on exactly nothing -- I suppose really all I would be doing is improving homogeneity in the volume). However, I agree that excess toxicity from treating the IRF is probably minimal. I wouldn't even expect much of a hit to bone marrow.

All the elective stuff gets 36/20, and that includes fossa; rescan and replan at some later point but fuse original scans (and contour original size-volumes of gross disease 'cause there can be considerable radiographic response even at ~30 Gy dose of course), then treat the gross disease volumes to gross disease dose-of-choice based on stage etc.

EDIT: And certainly the fossa XRT no more of a hit to marrow than the 5FU/MMC.

Would love know if anyone has ever seen an isolated IRF recurrence. I’ve never heard of it

Probably meaning covering it is a bit meaningless... probably.

 

[Palex80]

Would love know if anyone has ever seen an isolated IRF recurrence. I’ve never heard of it

I have only seen recurrences in the skin around the anus, several cms beyond the anal margin. These areas would have been included within the "standard" portals of 3D ap/pa radiation therapy. And I presume that if you include the entire IRF in your CTV you would also get relevant dose to those skin areas too.

I do not really see the rationale in treating the IRF unless you have a tumor which is substantially invading the muscles and you think it may spread there. Some cms of IRF are "incidentally" irradiated anyway when you add your PTV margin for your typical volumes anyways...

 

[dsh]

I personally use these contouring/planning guidelines which are reasonable: http://analimrtguidance.co.uk/National-Guidance-IMRT-Anal-Cancer-V4-Jan17.pdf

Outcomes using this approach here: https://www.redjournal.org/article/S0360-3016(19)33898-2/fulltext

 

[seper]

I always cover IRF in T3 and T4 disease on the side of the tumor.

 

[Krukenberg]

I personally use these contouring/planning guidelines which are reasonable: http://analimrtguidance.co.uk/National-Guidance-IMRT-Anal-Cancer-V4-Jan17.pdf

Outcomes using this approach here: https://www.redjournal.org/article/S0360-3016(19)33898-2/fulltext

I know there are a couple of GI specialists here. What does everyone think of these UK contouring guidelines? Seems like the big difference is a) the boost volume expansion is 1cm plus whole anal canal), and b) 40 Gy in 28 fx to the elective nodes. The more reasonable boost volume and lower elective dose appeal to me, but I’m nervous doing <150 cGy fractions. The results look good though, and to my knowledge the RTOG has never published patterns of failure analysis from 0529 while the UK has (see above).

 

[GI_RadOnc]

Great discussion! I'm on the original 0529 paper having the privilege to work with Drs. Kachnic and Myerson and getting my first taste of how 'the sausage is made' with clinical trials. The volumes and expansions were the subject of much debate between the different generations creating the study!

I don't routinely include the ischiorectal fossa. Neither does the most current US protocols; such as Jennifer Dorth's EA2182.

Besides for the history of 2D->3D excellently discussed by scarbrtj; the other helpful piece today is CT/PET to help define volumes. The recommended 1 cm expansions in the UK guidelines are perfectly adequate in this era; are are used in EA2182 as well.

With regard to the low dose per fraction.. as far as I know, there hasn't been any downside to this from any institutional standpoint or cooperative group standpoint.