Long‐term outcomes in patients treated with proton therapy for localized prostate cancer

Masaru Takagi,Takashi Daimon,Nobukazu Fuwa,Dongcun Jin,Yusuke Demizu,Masao Murakami,Yasue Niwa,Kazuki Terashima,Tomoaki Okimoto,Osamu Fujii

doi:10.1002/cam4.1159

Abstract

The aim of this retrospective study was to report long‐term clinical outcomes in patients treated with proton therapy (PT) for localized prostate cancer. Between 2001 and 2014, 1375 consecutive patients were treated with PT. Patients were classified into prognostic risk groups based on the National Comprehensive Cancer Network criteria. Freedom from biochemical relapse (FFBR), cancer‐specific survival (CSS) and incidence of late gastrointestinal (GI)/genitourinary (GU) toxicities were calculated. Multivariate analysis was performed to identify clinical prognostic factors for FFBR and late toxicities. The median follow‐up period was 70 months (range, 4–145 months). In total, 99% of patients received 74 Gy (relative biologic effectiveness [RBE]); 56% of patients received neoadjuvant androgen deprivation therapy. For the low‐, intermediate‐, high‐, and very high‐risk groups, 5‐year FFBR was 99% (95% confidence intervals [CI], 96–100%), 91% (95% CI, 88–93%), 86% (95% CI, 82–89%), and 66% (95% CI, 53–76%), respectively, and 5‐year CSS was 100% (95% CI, 100–100%), 100% (95% CI, 100–100%) , 99% (95% CI, 97–100%), and 95% (95% CI, 94–98%), respectively. Patient age, T classification, Gleason score, prostate‐specific antigen, and percentage of positive cores were significant prognostic factors for FFBR. Grade 2 or higher GI and GU toxicities were 3.9% and 2.0%. Patient age was a prognostic factor for both late GI and GU toxicities. This study represents the largest cohort of patients treated with PT for localized prostate cancer, with the longest follow‐up to date. Our results demonstrate that the biochemical control of PT is favorable particularly for high‐ and very high‐risk patients with lower late genitourinary toxicity and indicates the necessity of considering patient age in the treatment protocols.

Highlights

Prostate cancer (PCa) is the second most common cancer in men [1]
Patients were classified into four risk groups as defined by the National Comprehensive Cancer Network (NCCN) criteria according to T classification, Gleason score (GS), and the prostate-specific antigen (PSA) level at diagnosis excepting the very low-risk group [10]
According to NCCN risk groups, 249 (18%), 602 (44%), 449 (33%), and 75 (5.5%) of patients were classified as low-, intermediate, high, and very high-risk groups, respectively

Summary

Introduction

Prostate cancer (PCa) is the second most common cancer in men [1]. The treatment for localized PCa is selected based on a consideration of the patient age, risk group, and other factors [2]. Due to prostate-specific antigen (PSA) screening, an increasing proportion of patients are being diagnosed with localized PCa and are candidates for definitive external beam radiotherapy (EBRT) [3]. Proton Therapy for Prostate Cancer randomized controlled trials (RCTs) and several single- institution studies have confirmed the advantage of high- precision EBRT to achieve optimal biochemical control and a low rate of toxicity in patients with localized PCa [4,5,6,7,8,9]. The physical characteristics of proton beam therapy include a Bragg peak and reduced lateral scatter, which enable more conformal dose distribution compared with that of X-ray-based radiotherapy. The results of RCTs directly comparing PT with modern X-ray-based radiotherapy have not been reported, and nonrandomized studies have reported mixed results

Methods

Results

Conclusion