How long after prostate radiation do you recommend waiting for routine screening colonoscopy?

Good question. In this regard, I would say that the timing would depend on the nature of the acute reaction in the area of the rectum adjacent to the prostate. This may be patient dependent. Further, the local reaction erythema can last for weeks to months depending on the reaction. Also, if it's >12 months post RT, depending on the intensity of the acute reaction in this irradiated area, some patients developed telangiectasias there too. GI guys will biopsy this area/site as well -> potential fistula.

So GI MDs must be educated to these potential realities before, and have an open relationship to the Rad Onc MD as well.

But for the rest of the colon regardless post RT period a colonoscopy should not be an issue.

The problem I have found i...

We prefer to have one within 3 years of starting so that another won’t be necessary for 2-3 years or more post RT. We have a form letter for the GI doc asking them not to biopsy an area of radiation proctitis.

This is an important topic we all face in the clinic. Given the high doses delivered for prostate, we know the risks are high when colorectal biopsies are performed thereafter.

Given the wide range of scenarios and doses for malignancy within the pelvis (45-54Gy for GYN, various dosing schema for bladder, palliative doses for pain/bleeding, or even different hypofractionated regimens for prostate) I am curious what the experts thoughts are. Obviously there are different clinical settings for expected survival etc, but is there a dose below which you are less concerned?