My SBRT was 5 fractions of 7.25 GU per fraction (36.25 total to entire prostate and proximal seminal vesicles) with a boost to the tumor to a total of 40GU. This focal boost SBRT treatment plan is fairly new having been implemented within the last 3-4 years.

When I had my MRI taken 7 days after my Barrigel rectal spacer placed my RO ordered very thin image "slices" taken. I think the image was sliced every 1mm. This enabled him to visualize my urethra as it passed through my prostate. He then fused my CT, MRI and PSMA PET and was able to visualize the tumor's position with respect to the urethra. Having that positioned they can either do urethral sparing ( lower radiation dose to the urethra) or urethral steering where they ensure no area of the urethra receives a "hot-spot" dosage that would exceed the whole gland dosage. When they treatment plan the radiation they put a bullseye on the tumor, and then have concentric isotonic rings representing the specific dose in each ring. With the prostate being the size of a walnut those "rings", are small. Any overlap would cause a higher dose in that area. Using the "steering" they make sure the urethra receives the whole gland dose of 36.25, but no more. Urethral sparing lowers the dosage to the urethra below the whole gland amount and may lead to less than optimal results if any cancer cells approximate or invade the urethra.

Steering within SBRT is fairly new, here is a paper from September 2023.

Please let me know if you have any additional questions.

Stay Strong Brother!