Max small bowel point dose

[Gfunk6]

During residency, I've been taught that max small bowel point dose is 50.4 Gy. This was mainly based on Emami's original data. However, when I recently re-reviewed the QUANTEC paper on small bowel/stomach dose constraints, the max dose restriction appears to have mysteriously vanished. Specifically:

. . . if the entire volume of peritoneal space in which the small bowel can move is delineated, the volume receiving >45 Gy should be <195 cc when possible. Such a limit likely also reduces late toxicity risk, although this correlation is not established. The volume of small bowel receiving higher doses should also be minimized.

In recent RTOG trials, the max dose ceiling appears to have been lifted:

From RTOG 0848 (post-op pancreatic adenocarcinoma):

Max dose < 54Gy; D15% < 45Gy (no more than 15% of the organ can receive more than 45Gy)

From 0524 (concurrent chemoXRT for muscle-invasive bladder cancer):

Bowel: All attempts should be made to keep< 300cc's of the volume of the bowel receiving a dose greater than 45 Gy.

So under an 'ideal' scenario (no prior abdominal surgery, no adhesions) what is your comfort zone for max small bowel dose?

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[medgator]

I've been OK with point doses of 55 Gy in practice using the quantec and rtog constraints you've referenced. The small bowel becomes an issue with some of the bladder rectal and pancreas plans where I've had to go to or above 54 Gy

 

[Cancerdancer]

Best guideline I've found is this paper from MDACC showing association of duodenal toxicity when volume >55 Gy exceeds 1 cc.

PMID: 23200173

 

[deleted4401]

Good data. Sort of fits the mindset that most people have for this - max dose of 54-55.

 

[Palex80]

54-55 Gy for me too... I've worked with protons in an institution, which regularly gives 60+ Gy to little volumes of small bowel. The point there is, that it's a moving structure, so you may very well not hit the same part of bowel daily and have very little to non-dose to the adjoining small bowel segments, which may receive the full dose on another day.

Side-point:

What is your management in cases of HDR-brachytherapy in cervix cancer concerning small bowel?
Published guidelines give constraints for rectum/sigma & bladder, but no guideline mentions small bowel. Small bowel can often get in the way and if you have already prescribed 45-50 Gy of EBRT, it can become tough to follow the 54-55 Gy constraint for small bowel, bearing in mind that you often have higher doses / fraction with brachytherapy. This issue has become an increasing "problem" after the introduction of image guided brachytherapy-planning, especially if you use MRI-fusion where you can usually distinguish small bowel and sigma better than purely on CT.

 

[CUBuffsgrad98]

54-55 Gy for me too... I've worked with protons in an institution, which regularly gives 60+ Gy to little volumes of small bowel. The point there is, that it's a moving structure, so you may very well not hit the same part of bowel daily and have very little to non-dose to the adjoining small bowel segments, which may receive the full dose on another day.


Agreed, the point dose may be higher than what we think due to it being a moving structure. Any constraint has some hand waving to it, based on imaging, technology, set up error, etc, etc. On top of that, the dose constraints (see QUANTAC) are simply saying that by hitting 'x' dose, the risk is 10%, or 15% or 50% or whatever it may be. Note, even at these constraints it is NEVER zero. Being in private practice, Im not willing to push beyond RTOG or QUANTAC limitations, however in academic medicine, it may be acceptable.

Here is a question/case I had: Guy in his 30's, has a large spinal column neuroma. Resected once, had RT, new mass and growing fast. Neurosurg says no more surgery (not sure why). It is compressnig the cord. Lets assume all 2nd opinions say no more surg. Do you reirradiate to a high dose, knowing the better than 50% risk of damaging the cord (cumulative dose), but also knowing that doing nothing will mean 100% risk of cord compression and progression? In other words, at what point do the risks of treatment outweigh the risks of protecting normal tissue, but allowing tumor to go undercovered (or not covered at all)?

 

[Palex80]

If you can't control microscopic tumor (I assume it was completely resected and you irradiated it in the adjuvant setting during the first series) with an adequate dose (50 Gy?), then you are not going to control macroscopic tumor with less dose this time around.

You'll merely cause side effects without any true benefit to the patient.

I wouldn't treat and would rather try to find someone to operate this poor soul.

 

[deleted4401]

That's a good point, but it also depends on interval ... If it was controlled for 4 months vs 4 years - different option for each case. What was does the dose to the cord the first time? You might be able to SBRT it fairly safely depending on the interval of prior treatment and total dose received.

Is anyone else having a hard time saying SABR? I know I have not been able to.
S

 

[CUBuffsgrad98]

If you can't control microscopic tumor (I assume it was completely resected and you irradiated it in the adjuvant setting during the first series) with an adequate dose (50 Gy?), then you are not going to control macroscopic tumor with less dose this time around.

You'll merely cause side effects without any true benefit to the patient.

I wouldn't treat and would rather try to find someone to operate this poor soul.

I agree that he needs surgery. It was my partners case from about a month ago, so Im not overly familiar with all the details. Overall what Im suggesting is how much do these tolerance doses need to be respected? What is the outcome without treatment? Staying under tolerance may mean there is only a 10% or 15%, or whatever is estimated by QUANTAC, risk, but risk still exists. Is it worth going over these arbitrary limits (and thus risk is 20 or 30%) in order to gain better chance at tumor control? I think "yes" in many cases, but Im also too chicken to do it in a private practice setting.

 

[medgator]

Is anyone else having a hard time saying SABR? I know I have not been able to.
S

Me either. I just keep thinking of star wars

 

[Palex80]

What dose did the cord receive during the first treatment?

 

[evilbooyaa]

So... it's been 3.5 years. Where are people at now with this concept?

Node positive cervical cancer for definitive chemoRT followed by HDR Brachy - B/L external iliac nodes next to bowel. Was hoping to go to 55GY (2.2 SIB x 25) to these 2 areas but they're not going to meet bowel constraints (be it point dose 55Gy or anything similar in concept).

Chickening out and going 50/25. Constraint to dosimetry of point dose < 52Gy. Any evidence for toxicity data based on the more mobile parts of intestine (like not duodenum)? Do you just punt point doses and go V45 195cc? Attending is old school too and has no desire to break a 50Gy point dose for small bowel, so this might all be for naught anyways, but I'd be interested in what other places are doing.

 

[Reaganite]

I do what you said--55 in 25 SIB. I watch bowel near the target day-to-day on CBCT and also really stress full bladder to get bowel out of pelvis. If moving around, I don't stress or change plan. Don't let the initial CT sim fool you. In cases where bowel didn't seem to be moving (which I've seen maybe twice), I prioritized alignment to that area on daily CBCTs, ensured rapid dose fall off across the piece bowel, and cautioned patient on increased risk of SBO. Personally, I'm not sure we really have a handle on the true tolerance of a small piece of bowel, particularly with modern techniques such as CBCT and IMRT that allow extremely accurate alignment with rapid dose fall off. I mean, what's worse: treating the whole circumference of a piece of bowel to 50 Gy or treating the surface to 60Gy, but perhaps ensuring the mid point of the bowel only gets 60-70% of that, and the contralateral side even less?

 

[Mandelin Rain]

Definitive bladder treatment is always the problem. You're taking the structure to 64Gy with small bowel literally sitting on it.

In olden days, you just treated it blissfully unaware of what the DVH looked like. With 3D planning though, you know the small bowel will almost assuredly get full (or nearly full) dose. You can try to have them empty the bladder (which usually doesn't work well due to dysfunction) or cone down to a smaller area, but realistically there's not much to do. I usually just take a hard swallow and hope the bowel sloshes around a bunch day-to-day.

 

[seper]

I really dislike going > 1.8 Gy per day for abdominal and pelvic tumors. Hypofx causes more diarrhea. I therefore do not treat node positive cervical cancer with SIB IMRT, but use sequential boost instead.

 

[medgator]

I really dislike going > 1.8 Gy per day for abdominal and pelvic tumors. Hypofx causes more diarrhea. I therefore do not treat node positive cervical cancer with SIB IMRT, but use sequential boost instead.

I dose paint large, involved nodes up to 2 Gy a day. Otherwise I agree, I like to keep things at 2 or less below the diaphragm

 

[seper]

yep there is phase 1 study on 2.2 Gy for rectal cancer, which was shut down due to diarrhea


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[Mandelin Rain]

Second analysis of RTOG 9406 showing worse late GI toxicity with the dose escalated 2 Gy arm vs the others. Obviously different planning and localization that what we do today.

 

[Palex80]

In my opinion the main problem with SIB in pelvic tumors when treating involved nodes too lies in the precision of delivering the SIB to the right place.
Due to rotational shifts I often find myself having to use bigger PTV-margins just to make sure that the boost lands at the right spot.
It's quite frustrating to fuse CBCT in long target volumes, which generally is the case if you are treating for example a cervical cancer with presacral nodes.

 

[evilbooyaa]

Fair point, Palex. Could you get away with that by focusing the fusion to the lymph nodes and ensuring PTV45 at least covers the gross tumor in the cervix? Given the margins we place around the cervix on IMRT plans, I'd imagine with proper immobilization any rotation shift would be miniscule compared to bladder/bowel differences day in and out.

Ended up sticking with 50/25 on the case I discussed. I suppose it's better than the 3DCRT for some amount of dose escalation beyond 45. V45 for bowel ended up being high too (approx. 215cc) as the patient is extremely skinny, but attending was okay with it as it was still better than 3D.