Real-world comparative outcomes and toxicities after definitive radiotherapy using proton beam therapy versus intensity-modulated radiation therapy for prostate cancer: a retrospective, single-institutional analysis

This retrospective study aimed to compare the clinical outcomes of intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT). A total of 606 patients diagnosed with prostate cancer between January 2008 and December 2018 were included. Of these patients, 510 received PBT up to a dose of 70-78 Gy (relative biological effectiveness) and 96 patients received IMRT up to a dose of 70-78 Gy. The median follow-up period was 82 months (range: 32-140 months). Patients in the PBT group had significantly higher 7-year rates of biochemical relapse-free survival (bRFS) and disease-free survival (DFS) rates: 95.1% for PBT vs 89.9% for IMRT (P = 0.0271) and 93.1% for PBT vs 85.0% for IMRT (P = 0.0019). After matching analysis, 94 patients were assigned to both groups, and the PBT group showed significantly higher 7-year bRFS and DFS rates: 98.9% for PBT vs 89.7% for IMRT (P = 0.023) and 93.4% for PBT vs 84.6% for IMRT (P = 0.022), respectively. In the subgroup analysis of intermediate-risk patients, the PBT group showed a significantly higher 7-year bRFS rate (98.3% for PBT vs 90.5% for IMRT; P = 0.007). The V60 of the bladder in the PBT group (18.1% ± 10.1%) was higher than that in the IMRT group (14.4% ± 7.6%) (P = 0.024). This study found that the treatment outcomes of PBT potentially surpassed those of IMRT specifically concerning bRFS and DFS in real-world settings. However, it should be noted that attention is warranted for late bladder complication of PBT.