A Pooled Toxicity Analysis of Moderately Hypofractionated Proton Beam Therapy and Intensity-Modulated Radiation Therapy in Early Stage Prostate Cancer Patients.

Abstract

PURPOSE\nData comparing moderately hypofractionated intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT) are lacking. We aim to compare late toxicity profiles of patients with early stage prostate cancer treated with moderately hypofractionated PBT and IMRT.\n\n\nMATERIALS AND METHODS\nThis multi-institutional analysis included patients with low- or intermediate-risk biopsy-proven prostate adenocarcinoma from 7 tertiary referral centers treated from 1998 to 2018. All patients were treated with moderately hypofractionated radiation, defined as 250 - 300 cGy per daily fraction given over 4-6 weeks, and stratified by use of IMRT or PBT. Primary outcomes were late genitourinary (GU) and gastrointestinal (GI) toxicity. Adjusted toxicity rates were calculated using inverse probability of treatment weighting, accounting for race, NCCN risk group, age, pretreatment IPSS (GU only) and anti-coagulant use (GI only).\n\n\nRESULTS\nA total of 1850 patients were included, 1282 IMRT (median follow-up 80.0 months) and 568 PBT (median follow-up 43.9 months). Overall toxicity rates were low, with the majority of patients experiencing no late GU (56.6%, n=1048) or late GI (74.4%, n=1377) toxicity. No difference was seen in the rates of late toxicity between the groups, with late Grade 3+ GU toxicity of 2.0% vs 3.9%, OR 0.47 (0.17-1.28) and late Grade 2+ GI toxicity of 14.6% vs 4.7%, OR 2.69 (0.80-9.05) for the PBT and IMRT cohorts respectively. On multivariable analysis, no factors were significantly predictive of GU toxicity and only anti-coagulant use was significantly predictive of GI toxicity (OR 1.90, p=0.008).\n\n\nCONCLUSIONS\nIn this large, multi-institutional analysis of 1850 early-stage prostate cancer patients, treatment with moderately hypofractionated intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT) resulted in low rates of toxicity. No difference was seen in late GI and GU toxicity between the modalities over long term follow up. Both treatments are safe and well-tolerated.