Top Line: Stereotactic body radiation (SBRT) is now a mainstay treatment for prostate cancer, but considerable debate remains surrounding the optimal dose and interfraction time interval to maximize the therapeutic window.
The Story: Here we have 5-years results of a prospective phase 2 trial that randomized 165 evaluable men across nine European centers to prostate SBRT delivered every other day (EOD) versus weekly. Why weekly? The thought was interval normal tissue repair would decrease toxicity while tumor reoxygenation could even improve efficacy. Approximately two-thirds (64%) had intermediate risk disease followed by low (22%) and high (15%) risk. The target was the prostate +/- seminal vesicles at physician discretion with a 0.5 cm (0.3 cm posterior) PTV expansion prescribed 36.25 Gy in 5 fractions with simultaneous 32.5 Gy to a urethral PRV with a catheter in place at time of sim. Short-course ADT was given when indicated beginning two months prior to SBRT initiation. At a median follow-up of 6.5 years, there was no difference in survival free from biochemical recurrence (92-93%). Same goes for rates of experiencing grade 2+ GU toxicity (21-22%), grade 2+ GI toxicity (8-11%), or grade 3+ erectile dysfunction (28-30%) within 5 years.
TBL: Whether prostate SBRT is delivered every other day versus weekly doesn’t appear to impact efficacy or toxicity at 5 years. | Zilli, Int J Radiat Oncol Biol Phys 2023
The Story: Here we have 5-years results of a prospective phase 2 trial that randomized 165 evaluable men across nine European centers to prostate SBRT delivered every other day (EOD) versus weekly. Why weekly? The thought was interval normal tissue repair would decrease toxicity while tumor reoxygenation could even improve efficacy. Approximately two-thirds (64%) had intermediate risk disease followed by low (22%) and high (15%) risk. The target was the prostate +/- seminal vesicles at physician discretion with a 0.5 cm (0.3 cm posterior) PTV expansion prescribed 36.25 Gy in 5 fractions with simultaneous 32.5 Gy to a urethral PRV with a catheter in place at time of sim. Short-course ADT was given when indicated beginning two months prior to SBRT initiation. At a median follow-up of 6.5 years, there was no difference in survival free from biochemical recurrence (92-93%). Same goes for rates of experiencing grade 2+ GU toxicity (21-22%), grade 2+ GI toxicity (8-11%), or grade 3+ erectile dysfunction (28-30%) within 5 years.
TBL: Whether prostate SBRT is delivered every other day versus weekly doesn’t appear to impact efficacy or toxicity at 5 years. | Zilli, Int J Radiat Oncol Biol Phys 2023