4 Weeks Versus 5 Weeks of Hypofractionated High-dose Radiation Therapy as Primary Therapy for Prostate Cancer: Interim Safety Analysis of a Randomized Phase 3 Trial

Purpose: Hypofractionated radiation therapy (HFRT) for localized prostate cancer is safe and effective. The question that remains is which hypofractionation schedule to implement. We compared 2 different HFRT regimens in the present study.

Methods and materials: From June 2013 to July 2016, 160 patients with prostate cancer were randomly assigned (1:1), within this single-center phase III trial, to 56 Gy (16 fractions of 3.5 Gy; arm A) or 67 Gy (25 fractions of 2.68 Gy; arm B). Randomization was performed using computer-generated permuted blocks, stratified by previous transurethral resection of the prostate and the presence of a dominant intraprostatic lesion. Treatment allocation was not masked, and the clinicians were not blinded. The primary endpoint was acute gastrointestinal (GI) toxicity, assessed using the Common Terminology Criteria for Adverse Events, version 4.0, and Radiation Therapy Oncology Group toxicity scale. An interim analysis of acute toxicity was planned at 160 patients to prove the safety of both treatment regimens. If ≥22 of 72 patients had grade ≥2 GI toxicity, the study arm would be rejected. The study is registered at ClinicalTrials.gov (NCT01921803).

Results: In arm A, 20 patients (26%) and 1 patient (1%) developed acute grade 2 and grade 3 GI toxicity. In arm B, 16 patients (20%) reported acute grade 2 GI toxicity. In arm A, 42 (55%) and 5 (6%) patients developed acute grade 2 and grade 3 urinary toxicity. In arm B, 40 (49%) and 7 (9%) patients reported acute grade 2 and grade 3 urinary toxicity. Toxicity peaked during radiation therapy and resolved in the months after radiation therapy.

Conclusions: With acute grade ≥2 GI toxicity reported in 21 of 77 patients in arm A and 16 of 82 patients in arm B, both treatment arms can be considered safe.