When do you consider replanning patient if body contour is off on CBCT but PTV is aligned to prostate?

When reviewing the CBCT for a prostate case, I first look at the PTV. I make adjustments as necessary. Then, I look at the rectum. If anteriorly, it approximates what it looked like at simulation, I proceed with treatment. If it appears substantially off, I may consider having the patient come down and empty bowel if possible. How much is substantial? This is subjective, but I have less tolerance for an SBRT case and more for a convention case. I worry much less about the bladder, but as long as it’s close, I have not found untoward issues with acute/late toxicity. That balloon is resistant!

The concern for the body contour is minimal for VMAT cases. With rotational treatments, it will even out. There is no reason for large weight changes. ...

Not a GU specialist but we frequently encounter this issue in H&N where body contour changes are more pronounced due to weight loss. If there is any question, run a verification plan using the existing plan with new body contour from CBCT. Dosi can density override such that any contour gain becomes soft tissue density or any contour loss becomes air density. VMAT is exceptionally robust and the plan usually hangs together quite well. That avoids resim unless truly needed.

I agree with Dr. @Dr. First Last. I haven't come across a case yet where I have replanned a prostate cancer patient due to changes in body habitus, but that is because they generally maintain a stable weight. I have done so for a number of other cancer types. I do look when I review each CBCT because it could be possible, and big changes in setup could, in theory, affect the attenuation of the beams. In cases, more typically non-prostate, where there is change of body contour, I rely on my physicist to review and determine whether there is a significant delivered dose change. However, without us looking she or he wouldn't know to evaluate, so it is a great example of partnership between the physician and physicist!

Thank you everyone for your input and expertise. This was the first prostate patient I have had to replan due to body change. The patient started developing covid-like symptoms the day we were to start him. His treatment ended up being delayed and interestingly enough, he decided to get in shape for his prostate cancer treatment (working out and doing 100 sit-ups a day). He lost weight and a couple of belt sizes. I did end up replanning. But his case provoked me to ask this question as I wanted to see what everyone thinks given on my literature review, there was minimal data on this subject.