What’s all the fossa ‘bout prostate SBRT?

In this phase 1 trial, 24 men with indications for postoperative radiation received extreme hypofractionation (aka SBRT) to the prostate fossa with fiducials and a full bladder. The CTV was pretty standard with an additional PTV margin of 3 mm. Hypofractionation schemes escalated from 3.6 Gy x 15 (54 Gy) → 4.7 Gy x 10 (47 Gy) → 7.1 Gy x 5 (35.5 Gy) with each conforming to the same constraints. The rectum was divided into anterior, lateral, and posterior walls with decreasing maximum dose thresholds, respectively. Of note, all patients were treated daily with not even one acute grade 3 toxicity. At 10 weeks, grade 2 GI toxicity was only 8% even with 5 fractions. At the same time point, sphincter tone of the trialists was markedly reduced. TBL: Acute toxicity with post-op extreme hypofractionation to the prostate fossa appears safe in this small dose-escalation study. | Ballas, Int J Radiat Biol Phys 2018