Radiation-associated Second Primary Cancers After Iodine-125 Low-Dose-Rate Brachytherapy for Localized Prostate Cancer

Background Low-dose-rate brachytherapy with iodine-125 (LDR-BT) is an established curative radiation treatment modality for localized prostate cancer (PCa). This study aimed to evaluate the long-term incidence of radiation- associated secondary primary cancer (RASPC) after LDR-BT in Japanese patients with localized PCa and identify predictive factors associated with RASPC. Methods and materials: We retrospectively reviewed the clinical records of 478 consecutive patients with localized PCa who underwent LDR-BT at the Gifu University Hospital. This study’s primary endpoint was RASPC incidence, including bladder and rectal/anal cancers. The secondary endpoint was the identification of risk factors for LDR-BT that predicted RASPC development. Results After a median follow-up period of 105 months, RASPC developed in 13 patients (2.7%). Bladder cancer and rectal/anal canal cancer were observed in seven (1.5%) and six (1.3%) patients, respectively. Multivariate analysis showed that a biologically effective dose (BED) ≥ 197 Gy was associated with increased risk of RASPC (hazard ratio 4.145; 95% confidence interval 1.108–15.498; p  = 0.035). Conclusions RASPC incidence after LDR-BT was relatively low; BED ≥ 197 Gy was identified as an independent significant predictor for developing RASPC. Adequate tumor control can be achieved through appropriate radiation dose administration; carefully planned long-term follow-up may be beneficial for RASPC early detection.