Would you irradiate the prostate in a patient with SpaceOAR in the incorrect location but not invading rectum or prostate?

I would treat without delay if the SpaceOAR gel is not invading the rectum. It is common to see gel placements that are not ideally placed, and we have not seen any unusual or unexpected side effects/complications from this. We still see a dosimetric advantage in our treatment plans, even with a suboptimal SpaceOAR gel placement.

Unless the patient is very symptomatic due to poor placement of the SpaceOAR, or you cannot meet normal tissue dose constraints due to anatomic distortion created by the placement, I would proceed with treatment. SpaceOAR placements are often not perfect, especially when one is learning the procedure. You may still derive some benefit of rectal dose reduction, at least on the right side. There have been reports of fistulas developing when the gel is injected into the rectum, but this does not appear to be the case here.

No matter how many gel placements one has performed, some will not result in the ideal “pancake” geometry between the prostate and anterior rectal wall. Experience will lessen this frequency but will not eliminate it, since variables such as unexpected fibrosis or gland size/shape can sometimes dominate the flow of the gel into position. However, even a suboptimal geometry will likely result in an improved DVH for the rectum. The uncommon scenario of gel within the rectal wall would be different, as it would create a risk for fistula formation. Perhaps that would best be handled by delaying irradiation until this dissolves (using ADT if the risk level warrants that), then re-assessing therapy options at that point. Immediate conversion to s...