A Single-Institution Prospective Study To Evaluate the Safety and Efficacy of Real- Time Image-Gated Spot-Scanning Proton Therapy (RGPT) for Prostate Cancer

Kentaro Nishioka; Takayuki Hashimoto; Takashi Mori; Yusuke Uchinami; Rumiko Kinoshita; Norio Katoh; Hiroshi Taguchi; Koichi Yasuda; Yoichi M Ito; Seishin Takao; Masaya Tamura; Taeko Matsuura; Shinichi Shimizu; Hiroki Shirato; Hidefumi Aoyama

doi:10.1016/j.adro.2024.101464

A Single-Institution Prospective Study To Evaluate the Safety and Efficacy of Real- Time Image-Gated Spot-Scanning Proton Therapy (RGPT) for Prostate Cancer

Adv Radiat Oncol. 2024 Feb 8;9(5):101464. doi: 10.1016/j.adro.2024.101464. eCollection 2024 May.

Authors

Affiliations

¹ Radiation Oncology Division, Global Center for Biomedical Science and Engineering, Faculty of Medicine, Hokkaido University, Sapporo, Japan.
² Department of Radiation Oncology, Hokkaido University Hospital, Sapporo, Japan.
³ Department of Radiation Oncology, Hokkaido University Faculty of Medicine, Sapporo, Japan.
⁴ Data Science Center, Promotion Unit, Institute of Health Science Innovation for Medical Care, Hokkaido University Hospital, Sapporo, Japan.
⁵ Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan.
⁶ Department of Carbon Ion Radiotherapy, Osaka University Graduate School of Medicine, Osaka, Japan.

Abstract

Purpose: In real-time image-gated spot-scanning proton therapy (RGPT), the dose distribution is distorted by gold fiducial markers placed in the prostate. Distortion can be suppressed by using small markers and more than 2 fields, but additional fields may increase the dose to organs at risk. Therefore, we conducted a prospective study to evaluate the safety and short-term clinical outcome of RGPT for prostate cancer.

Methods and materials: Based on the previously reported frequency of early adverse events (AE) and the noninferiority margin of 10%, the required number of cases was calculated to be 43 using the one-sample binomial test by the Southwest Oncology Group statistical tools with the one-sided significance level of 2.5% and the power 80%. Patients with localized prostate cancer were enrolled and 3 to 4 pure gold fiducial markers of 1.5-mm diameter were inserted in the prostate. The prescribed dose was 70 Gy(relative biologic effectiveness) in 30 fractions, and treatment was performed with 3 fields from the left, right, and the back, or 4 fields from either side of slightly anterior and posterior oblique fields. The primary endpoint was the frequency of early AE (≥grade 2) and the secondary endpoint was the biochemical relapse-free survival rate and the frequency of late AE.

Results: Forty-five cases were enrolled between 2015 and 2017, and all patients completed the treatment protocol. The median follow-up period was 63.0 months. The frequency of early AE (≥grade 2) was observed in 4 cases (8.9%), therefore the noninferiority was verified. The overall 5-year biochemical relapse-free survival rate was 88.9%. As late AE, grade 2 rectal bleeding was observed in 8 cases (17.8%).

Conclusions: The RGPT for prostate cancer with 1.5-mm markers and 3- or 4- fields was as safe as conventional proton therapy in early AE, and its efficacy was comparable with previous studies.