small bowel constraints

[Burt Radnolds]

I find small bowel constraints to be some of the most nebulous in our field with lots of variation, while also being a very important OAR and potential source of significant toxicity. What do you all like to use? V45? cc? %? max point dose? What do you constrain, bowel bag with large and small bowel? just small bowel? Say you had a post op gyn case with lots of bowel in pelvis that warranted extended field radiation with concurrent chemo, are there certain constraints that are a hard stop in regards to volume or point dose? Or would you just do your best and it is what it is?

---

Members don't see this ad.

 

[baculum1]

If you’re talking specifically about a definitive gyn case, getting brachy, EQD 0.02 cc bowel to like 66gy pt dose.

post op gyn case no nodes no gross disease, plus cuff brachy you shouldnt be seeing that high of bowel dose, would use like 45-50 gy pt max

 

[Burt Radnolds]

Im fairly at peace with what I would accept for point doses and am probably most interested in volumetric constraints such as V45 and if people have hard limits in that regard.

 

[baculum1]

Im fairly at peace with what I would accept for point doses and am probably most interested in volumetric constraints such as V45 and if people have hard limits in that regard.

would do best i can do to deliver plan

 

[Haybrant]

would do best i can do to deliver plan

This is a cop out answer often and it’s a slippery slope. Not always wrong though but you start seeing this argument with so many constraints for people that are very early in practice and can lead to a lot of issues

 

[FrostyHammer]

Given that the bowel moves so much, can anyone explain to me the point of contouring individual bowel loops (instead of bowel bag)? Honest question, I never understood why I heard of some centers doing that.

 

[scarbrtj]

Given that the bowel moves so much, can anyone explain to me the point of contouring individual bowel loops (instead of bowel bag)? Honest question, I never understood why I heard of some centers doing that.

Anyone who’s ever scrubbed in on an open laparotomy case knows this intimately. It’s oddly mesmeric.

 

[ramsesthenice]

If anyone has any compelling data supporting a particular V45 meaning anything please feel free to share. I for one don’t even look at it very often. I try to exclude as much bowel as I can from my target volumes and then make sure the dose distribution matches as closely as possible. For every case I expected to go horribly wrong but didn’t I can think of what looked to be a very benign case that went horribly wrong with significant issues by the time we got into the mid 30s.

As for the point dose I honestly don’t know anymore. I have treated a number of patients over the last couple years on bladder protocols which included small amounts of small bowel in the PTV expansions up into the high 60s without any issues yet (which still seems a little crazy to me).

Duodenum scares me a bit more and there I do try hard to stick to a V54 < 0.03 cc. That being said, the two major bleeds I have seen both had max point doses < 52 and should have been fine.

This is my convoluted way of saying I’m not aware of great data to answer the OPs question. I avoid as much as possible (I love probe positioning etc) but don’t compromise tumor coverage to meet artificial constraints. For cases like the OP described, if I have more than 1-2 cc of small (not large) bowel getting > 54 I will rescan after 36 or so and try to adapt the plan to bring it down but honestly it’s based more on first principle than hard data.

 

[Palex80]

60 Gy Dmax 0.01 cc for me. Some of my colleagues prefer something around 56-58 Gy.

But indeed, people who have done quite a few cervical cancer brachytherapy cases have seen quite high doses, exceeding those limits.
It can happen quite fast, bearing in mind that small bowel has already seen 50 Gy during the percutaneous part. If you are going to give 4 fractions of brachy on top, you are going over 54 Gy quite fast... I have actually seen a stenosis requiring laparotomy post RT for cervical cancer, cumulative dose was probably above 54 Gy (hard to tell if it was the individual small bowel loop, since it all moves so much).

It's quite sad that all the nice cervical brachytherapy consensus guidelines focus on sigma, rectum, bladder and totally neglect to adress the issue of small bowel.

We do know from the pancreas-field, where several trials have given up to 60 Gy using 3D-techniques, that terrible things do not happen. On the other hand most of these patients died within a year post-RT, so no hard data is coming from there on late-late toxicity.

Another issue to bear in mind is location.
Duodenum is certainly less "mobile" than a small bowel loop somewhere down the pelvis in a patient who has not had a laparotomy before.

 

[baculum1]

60 Gy Dmax 0.01 cc for me. Some of my colleagues prefer something around 56-58 Gy.

But indeed, people who have done quite a few cervical cancer brachytherapy cases have seen quite high doses, exceeding those limits.
It can happen quite fast, bearing in mind that small bowel has already seen 50 Gy during the percutaneous part. If you are going to give 4 fractions of brachy on top, you are going over 54 Gy quite fast... I have actually seen a stenosis requiring laparotomy post RT for cervical cancer, cumulative dose was probably above 54 Gy (hard to tell if it was the individual small bowel loop, since it all moves so much).

It's quite sad that all the nice cervical brachytherapy consensus guidelines focus on sigma, rectum, bladder and totally neglect to adress the issue of small bowel.

We do know from the pancreas-field, where several trials have given up to 60 Gy using 3D-techniques, that terrible things do not happen. On the other hand most of these patients died within a year post-RT, so no hard data is coming from there on late-late toxicity.

Another issue to bear in mind is location.
Duodenum is certainly less "mobile" than a small bowel loop somewhere down the pelvis in a patient who has not had a laparotomy before.

Now with volumetric planning for hdr cervix brachy stenosis are prob less common than LDR brachy giving 40gy to pt A. You have a chance to try to minimize risk with inverse planning. But yes routinely would see 60+ gy to bowel point dose without giving myself an ulcer. Rationale as Scar said is that when you see bowel snaking around the abdomen in an open case you realize the bowel is constantly moving and a specific point is very unlikely to truly see that cumulative dose.

 

[ramsesthenice]

60 Gy Dmax 0.01 cc for me. Some of my colleagues prefer something around 56-58 Gy.

But indeed, people who have done quite a few cervical cancer brachytherapy cases have seen quite high doses, exceeding those limits.
It can happen quite fast, bearing in mind that small bowel has already seen 50 Gy during the percutaneous part. If you are going to give 4 fractions of brachy on top, you are going over 54 Gy quite fast... I have actually seen a stenosis requiring laparotomy post RT for cervical cancer, cumulative dose was probably above 54 Gy (hard to tell if it was the individual small bowel loop, since it all moves so much).

It's quite sad that all the nice cervical brachytherapy consensus guidelines focus on sigma, rectum, bladder and totally neglect to adress the issue of small bowel.

Once I switched to MR-guided volume optimized delivery I came to appreciate just how much more small bowel was getting blasted than I would have thought. Not every case, not even most cases, but maybe 20% you will regularly have a loop sneak into the 4-6 Gy lines which, as you said, is after getting at least 45 EBRT. Still gives me chills to sign those plans the nightmares have subsided

If you read the EMBRACE2 documents (maybe it was 1, I’m not 100%) closely they do at least indirectly address the small bowel. They don’t give formal constraints because in RETRO-EMBRACE they simply couldn’t find any statistically significant correlations because clinically-significant small bowel injuries were too infrequent. Same for sigmoid, but they rationalize its the same organ as the colon so should have the same radio sensitivity in theory and thus has the same constraints. I think these are some of the most relevant studies because they are the largest series which get realistic image-based volumetric bowel data.

at the end of the day, even for bladder and rectum the recommendation from ABS and ESTRO is that if all else fails despite optimization don’t compromise tumor coverage to meet normal tissue constraints. In those instances, I always have a detailed conversation with the patient after fraction 1 about the difficulty I am having keeping the doses as low as I would like and that this means the chances of the really bad things we talked about (like fistula formation) are probably a little higher than we first thought. I can’t recall a single time anyone ever said anything other than do what you have to do to beat this thing.

 

[baculum1]

Yes back in the empirical loading Non-CT LDR days you’d just load 15-10-10 and a 10 in each ovoid and call it a day. When deparments got their first CTs they noticed some of these patients were loaded with perforated uterus, or their bowel dose ended up being quite high. these patients ended up correlating with SBO. One of those inconvenient things about knowing now with CT. Like you said, EMBRACE data suggests one should try to give the dose to target to achieve cure if that is the goal. Now that we are prescribing to a volume rather than point A, we are certainly dose de-escalating to some points...pluses and minuses

 

[seper]

In doing cervical implants, the total D1cc of 70 Gy (a/b=3) is sometimes acceptable.

 

[evilbooyaa]

For bowel EBRT there's no hard numbers, but I try to keep V45 < 5-10% (it's always a soft constraint) and was initially V30 < 30%. I, over time, discovered that certain cases I could do V25 < 25% and still maintain coverage. That being said, it's probably one of the most nebulous constraints without great data. I don't bother with bowel loops.

Again, not really supported by data, but if you don't constrain it at all the algorithm won't push the dose at all.

For Cervical HDR we draw and monitor 0.1cc of small bowel for every fraction, especially if we think it's a piece of bowel 'stuck' to the uterus or whatever. We'll inflate bladder with saline and re-scan if it's falling anterior to the uterus to push it out of the way.. We won't accept a lower D90 for it, but we monitor it as part of our optimization.