Having your SBRT and brachy boosting it, too.

Top Line: Men with higher risk prostate cancer have a higher risk of occult disease spread outside the prostate.

The Study: At the same time, a prostate brachytherapy (PBT) boost allows for higher dose escalation than external beam radiation radiation (EBRT) alone. In order to escalate dose while still covering potential occult spread outside the prostate, some advocate for combining EBRT and PBT. For men with intermediate-risk disease, the EBRT component often includes just the prostate and seminal vesicles. So, why not give the EBRT component with a stereotactic (SBRT) approach? In this pilot study from MSKCC, men with NCCN intermediate-risk prostate cancer, a prostate volume <60cc, and an IPSS of ≤15 indeed received both. They were first allowed to receive ADT for cytoreductive purposes for up to 6 months. PBT consisted of a Pd-103 implant with a prescription dose of 100 Gy. One month later, they received 5 Gy x 5 = 25 Gy SBRT to the prostate and seminal vesicles +0.5 cm (0.3 cm posteriorly). By 12 months, 25% of men experienced grade 2 urinary toxicity, which is comparable to the rate seen when EBRT alone is conventionally fractionated, and <10% was ongoing at 2 years. There was no grade 3 toxicity. Bowel toxicity was also low and infrequent: grade 2 occurred in 5%. Finally, freedom from biochemical failure was 100% at 3 years.

TBL: LDR brachytherapy followed by SBRT is a promising way to deliver combined modality radiation for intermediate-risk prostate cancer. | Kollmeier, Int J Radiat Oncol Biol Phys 2020