Sigma constraints

[Palex80]

Advertisement - Members don't see this ad

I was wondering: Do you use sigma constraints in prostate RT?
The RTOG protocols dont demand you to contour sigma separately and do not state any constraint.
What would you use? I thought about extrapolating some constraints from cervix-brachytherapy guidelines, but I'd like to hear what you guys think.

 

[medgator]

Sigmoid colon? No

 

[Brim]

Rarely is the sigmoid an issue... Your case must have some pretty twisted anatomy.

But, FWIW, the RTOG contouring guideline for nodal RT for prostate cancer (RTOG GU Radiation oncology specialists reach consensus on pelvic lymph node volumes for high-risk prostate cancer. - PubMed - NCBI)(Lawton 2009) lists their constraints as:

(Fig 3) DVH constraints
"Large bowel: Same as rectum"

Curiously, their rectal constraints are, "Same as large bowel."

Okay, not really. 🙂
They use 50 Gy ≤ 50% and 70 Gy ≤ 20%.

Of course, what's not stated is what they contoured as large bowel.... Obviously if you contour the whole damn colon from cecum to rectum, it will make your V50 and V70 look better.

 

[w00tz]

At my institution, some attendings will treat sigmoid like small bowel, but most see view it as something between small bowel and rectum. Generally we will tell the dosimetrists that it is like small bowel when they plan, but will be less stringent when it comes to plan review. No one here treats sigmoid the same as rectum.
We will sometimes treat less of the SVs as a result. Interested to see what others do as well.

 

[medgator]

At my institution, some attendings will treat sigmoid like small bowel, but most see view it as something between small bowel and rectum. Generally we will tell the dosimetrists that it is like small bowel when they plan, but will be less stringent when it comes to plan review. No one here treats sigmoid the same as rectum.
We will sometimes treat less of the SVs as a result. Interested to see what others do as well.

Much closer to rectum in terms of function and tolerance than it is to small bowel imo if we are going to consider them on a spectrum

 

[Palex80]

Well, the case Im battling with is a biochemical recurrence with a macroscopic recurrent / residual tumor in the area of the seminal vesicles. Id like to push the dose to 70+ Gy, but the sigmoid colon is practically on top of those seminal vesicles. We attempted prone positioning and bladder feeling, but it didnt change much. It just seems that this patient has a lower recto-sigmoid-junction than other patients do.
GEC-ESTRO-constraints for cervix brachytherapy treat sigma just like rectum, meaning D2cc should receive a max dose of 70 Gy EQD2