Reirradiation of locally recurrent prostate Cancer: a review of prospective evidence and delineation and planning strategies from the reirradiation Collaborative group (ReCOG).

There is considerable uncertainty regarding the optimum approaches to target volume and organ at risk (OAR) delineation and tolerances to reirradiation for locally recurrent prostate cancer. To address these uncertainties, we undertook a literature review of treatment planning approaches of stereotactic body radiotherapy (SBRT) or brachytherapy reirradiation in published and ongoing prospective studies. Twenty published and 11 ongoing studies were identified. No phase 3 clinical trials were identified. Both focal and whole gland with/without simultaneous integrated boost approaches to target volume delineation were used. SBRT dose-fractionation schedules ranged from 25 to 42.5Gy in 5 fractions and 36-38Gy in 6 fractions with varying approaches to target objectives. Brachytherapy studies utilised both low dose rate and high dose rate approaches and employed a range of dose-fractionation schedules. Approaches to OAR delineation and constraints were heterogenous. No published and only 1 ongoing study utilises cumulative OAR constraints. Acceptable rates of genitourinary and gastrointestinal toxicities were observed in the majority of studies although some studies reported relatively high rates of severe toxicity events. The relatively short follow-up of some published series may underestimate the incidence of late toxicities. There remains uncertainty regarding optimum dose-fractionation schedules, target volumes and OAR constraints and how these influence toxicity. Prostate reirradiation using SBRT or brachytherapy can be used for treatment of locally recurrent prostate cancer. Treatment is recommended within prospective studies or registries with robust target definition, treatment delivery and comprehensive assessment of toxicity so that evidence to optimise treatment can be generated.