Men with localized prostate cancer may receive either photon-based intensity-modulated radiotherapy (IMRT) or proton beam therapy (PBT). The XXXXX trial (NCT01617161), demonstrates the feasibility of performing a large, multicenter phase 3 randomized trial comparing IMRT to PBT for localized prostate cancer. Here, we report baseline features of patients enrolled on this trial and present strategies to improve feasibility of other similar trials.

Patients with low- or intermediate-risk prostate cancer were randomized to either PBT or IMRT with stratification by institution, age, use of rectal spacer, and fractionation schedule (conventional fractionation: 79.2 Gy in 44 fractions vs. moderate hypofractionation: 70.0 Gy in 28 fractions). The primary endpoint is a change from baseline bowel health using the EPIC score 24 months after radiotherapy. Secondary objectives include treatment-related differences in urinary and erectile functions, adverse events, and efficacy endpoints.

Between 07/2012 and 11/2021, 450 patients were successfully accrued. Patients were randomized to either PBT (N=226) or to IMRT (N=224); 13 were ineligible or withdrew prior to treatment. The median age of 437 analyzed patients was 68 years (range 46-89). 41% of patients had low-risk and 59% had intermediate-risk disease. 49% of patients were treated with conventional fractionation and 51% with moderately hypofractionation. For patients receiving PBT, 48% used a rectal balloon, 44% a rectal spacer, and 5% both. For patients receiving IMRT, 46% used a rectal balloon, 42% a rectal spacer, and 5% both. PBT and IMRT arms were balanced for baseline variables.

Despite significant challenges, the XXXXX trial demonstrated that, with targeted recruitment approaches, multicenter collaboration, payer engagement, and protocol updates to incorporate contemporary techniques, it is feasible to perform a large phase III randomized clinical trial to assess whether PBT improves outcomes. We will separately report primary results and continue to monitor participants for longer followup and secondary endpoints.