Although prostate cancer control using radiotherapy is dose-dependent, dose-volume effects on late toxicities in organs at risk, such as the rectum and bladder, have been observed. Both protons and carbon ions offer advantageous physical properties for radiotherapy, and create favorable dose distributions using fewer portals compared with photon-based radiotherapy. Thus, particle beam therapy using protons and carbon ions theoretically seems suitable for dose escalation and reduced risk of toxicity. However, it is difficult to evaluate the superiority of particle beam radiotherapy over photon beam radiotherapy for prostate cancer, as no clinical trials have directly compared the outcomes between the two types of therapy due to the limited number of facilities using particle beam therapy. The Japanese Society for Radiation Oncology organized a joint effort among research groups to establish standardized treatment policies and indications for particle beam therapy according to disease, and multicenter prospective studies have been planned for several common cancers. Clinical trials of proton beam therapy for intermediate-risk prostate cancer and carbon-ion therapy for high-risk prostate cancer have already begun. As particle beam therapy for prostate cancer is covered by the Japanese national health insurance system as of April 2018, and the number of facilities practicing particle beam therapy has increased recently, the number of prostate cancer patients treated with particle beam therapy in Japan is expected to increase drastically. Here, we review the results from studies of particle beam therapy for prostate cancer and discuss future developments in this field.

International journal of urology : official journal of the Japanese Urological Association. 2019 Jul 08 [Epub ahead of print]

Hitoshi Ishikawa, Hiroshi Tsuji, Shigeyuki Murayama, Mikio Sugimoto, Nobuo Shinohara, Satoru Maruyama, Motohiro Murakami, Hiroki Shirato, Hideyuki Sakurai

Department of Radiation Oncology, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan., Hospital of the National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan., Division of Proton Therapy, Shizuoka Cancer Center Hospital, Shizuoka, Japan., Department of Urology, Faculty of Medicine, Kagawa University, Takamatsu, Kagawa, Japan., Department of Urology, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan., Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Hokkaido, Japan.