Toxicity at 1 year after Stereotactic Body Radiotherapy in 3 Fractions for Localized Prostate Cancer.

Abstract

PURPOSE\nTo assess the toxicity profile of prostate cancer stereotactic radiotherapy (SBRT) in 3 fractions.\n\n\nMETHODS AND MATERIALS\nThis is a prospective, multicenter phase II toxicity study enrolling patients with low to favorable intermediate risk prostate cancer. Before simulation 3-4 fiducial markers along with a rectal spacer were placed. The target (prostate only) was prescribed 40 Gy, while the maximum dose to the urethra was limited to 33 Gy with the highest priority at planning; less stringent objectives were placed on the bladder whose filling was controlled via a Foley catheter. Treatment was delivered every other day. Toxicity was prospectively scored with CTCAE and several PROs collected. The maximum allowed prevalence rate of grade 2+ GU toxicity at 1 year was set at 15% and the study was sized accordingly.\n\n\nRESULTS\nBetween November 2015 to May 2019, 59 patients were enrolled by 3 participating Institutions. Acute gastrointestinal (GI) toxicity was occasional and mild, while 11.9% and 1.7% developed acute GR2 and GR3 GU toxicity, respectively. No patient had persistent treatment-related GR2+ GU toxicity at 12 months after SBRT, and thus the null hypothesis is rejected. We observed a clinically relevant worsening of both IPSS and ICIQ-SF scores at 12 months compared to baseline. Moreover, we found a strong association between all selected bladder dose/volume metrics at planning and ICIQ-SF worsening at 12 months, while for IPSS, the correlation with bladder dose metrics was marginal.\n\n\nCONCLUSIONS\nAt 12 months, the toxicity profile of SBRT in 3 fractions is acceptable.