This study compared PBS toxicity rates with those of passive scattering/uniform scanning (PS/US) in a prospective multicenter registry. For low-to-intermediate risk patients treated with PS/US (n = 1105) or PBS (n = 238), this study found that acute grade ≥2 GI toxicity in PBS did not significantly differ from that with PS/US (2.9% and 2.1%, respectively; P = 0.47), but acute grade ≥2 GU toxicity was significantly higher with PBS (21.9% and 15.1%; P < 0.01).

Late grade ≥2 GI and GU toxicities did not differ significantly between groups. This is the first multi-institutional comparative effectiveness evaluation of PBT techniques in prostate cancer, and the authors concluded that differences in acute GU toxicity warrant further evaluation with prospective data.