Carbon Ion Radiotherapy for Prostate Cancer; a nationwide survey of the Japan Carbon-ion Radiation Oncology Study Group (J-CROS 1501)

Introduction of the study; Multi-institutional analysis of the patients with prostate cancer who have received carbon ion radiotherapy (CIRT) as the prospective study in each institute of the Japan Carbonion Radiation Oncology Study Group (J-CROS) was carried out. Methodology; Data of patients enrolled in prospective clinical trials performed at National institute of radiological science, Gunma university heavy ion medical center and Ion beam therapy center, SAGA-HIMAT foundation were retrospectively analyzed. CIRT dose and fractionations were 66-63Gy(RBE)in 20 fractions, 57.6Gy(RBE) in 16 fractions or 51.6Gy(RBE) in 12fractions.All patient risks were reclassified according to the D'Amico risk classification. A short-term (6 months) androgen deprivation therapy (ADT) and a long-term ( 24 months) ADT were combined with CIRT for the intermediate-risk group and the high-risk group, respectively. ADT was not combined in low-risk group. The biochemical failure was defined as a rise of >2.0 ng/mL above PSA nadir (Phoenix definition). Results; Between December 2003 and December 2014, the total number of enrolled patients from all three institutions was 2157. The number of patients in low-risk, intermediate-risk, and high-risk groups were 263, 679, and 1215, respectively. A total of 1754 patients (82%) underwent ADT. The median follow-up periods of surviving patients was 29 months. The five-year biochemical relapse-free survivals (bRFS) in low risk, intermediate-risk, and high-risk patients were 92%, 89%, and 92%, respectively. The ten-year bRFS in low-risk, intermediate-risk, and high-risk patients were 77%, 70%, and 79%, respectively. The five-year local control rates (LCR) and cause-specific survivals (CSS) in low-risk, intermediaterisk, and high-risk patients were 98%, 96%, and 99% for LCR, respectively, and 100%, 100%, and 99% for CSS, respectively. The incidence of grade (G) 2 and G3 late toxicities were 4.5% and 0% for the bladder, and 0.5% and 0% for the rectum, respectively. Conclusion; Analysis of the first multiinstitutional data on CIRT for prostate cancer suggested that the treatment outcomes of CIRT were favorable, especially in high-risk group patients. (author)