SBRT-d up.

Top Line: We’re about to see the perfect storm for mass adoption of prostate stereotactic radiation (SBRT).

The Study: Favorable large-scale data has started flowing, and it’s brevity and non-invasiveness are popular with both patients and the RO-APM. We’ve already seen the encouraging HYPO-RT-PC results demonstrating no difference in cancer outcomes and a nominal uptick in grade 2+ GU toxicity with the 6.1 Gy x 7 = 42.7 Gy Scandinavian regimen. Here we get a taste of the acute toxicity outcomes from the PACE-B trial where 874 men with low (<10%) or favorable intermediate risk (>90%) prostate cancer were randomized to receive either: [1] 7.25 Gy x 5 = 36.25 Gy (SBRT) or [2] either 3.1 Gy x 20 = 62 Gy (hypofractionated, HF) or 2 Gy x 39 = 78 Gy (conventionally fractionated, CF). Importantly, androgen deprivation was not allowed. The primary outcome of this planned sub-study was the rate of “RTOG” grade 2+ toxicities at 12 weeks, which was not statistically different: 27% for CF/HF and 23% for SBRT. Only 1% and 2% of patients in both arms had grade 3+ GI or GU toxicity, respectively. There was, however, an almost doubling of “CTCAE” acute toxicity with SBRT, mainly driven by grade 2 events. Why this difference? Besides highlighting the subject nature of selecting toxicity measures, CTCAE tends to have lower-threshold grade 2 events. Perhaps most importantly, there were no differences in patient-reported EPIC scores. So, is prostate SBRT “ready for take-off” as the external beam radiation standard of care? It’s definitely on the tarmac.

TBL: Acute toxicity after prostate SBRT was comparable to fractionated treatment in the randomized PACE-B trial. | Brand, Lancet Oncol 2019