(P108) Local Control and Toxicity of Reirradiation With Pulsed Low-Dose-Rate Radiation

Abstract

To evaluate the efficacy and toxicity of reirradiation using pulsed low-dose-rate (PLDR) technique. We evaluated patients treated with reirradiation using PLDR between 2009-2016 at a single institution. Toxicity was graded based on CTCAE4.0 and local control was assessed using RECIST1.1. Kaplan-Meier estimation and Cox proportional hazard model were used for univariate analysis (UVA). Multivariate analysis was not performed due to the small number of events. Thirty-nine patients were treated to 41 sites with PLDR reirradiation, with a median follow-up of 8.8 months (range 0.5-64.7 months). Targets included 25 thoracic, 3 abdominal, and 13 pelvic. Thirty-six were symptomatic, including 20 with pain. The intent was palliative in 87%. The median time between the first course of radiation and reirradiation was 26.2 months. The median doses of the first and second courses of radiation were 50.4 Gy and 50 Gy. Five patients (13%) received concurrent systemic therapy. Of the 39 patients, 9(23%) developed G2+ acute/subacute toxicity, most commonly skin (5/9). None developed G4+ acute/subacute toxicity. The only late G2+ toxicity was 1 patient with G2 skin toxicity. On UVA, toxicity was not significantly associated with dose of the first course of radiation or reirradiation, time interval between the two courses of radiation, or reirradiation site. Of the 41 sites treated with PLDR, 32 were assessed for local control. Local control rates were 85% at 6 months and 76% at 12 months. Local control was not significantly associated with the dose of reirradiation, reirradiation site, or concurrent systemic therapy on UVA. Of the 36 symptomatic sites, 6(15%) achieved complete symptomatic relief and 19(46%) achieved partial relief. Pain improved in 14/20 (70%) patients. Based on this retrospective study, reirradiation with PLDR is effective and well-tolerated. Assessment of late toxicity was limited by the relatively short follow up in this cohort.