The effect of stereotactic ablative radiotherapy on time to change of systemic therapy in extra-cranial renal cell carcinoma metastases.

Abstract

533 Background: Renal cell carcinoma (RCC) has traditionally been refractory to radiotherapy with conventional fractionation, although recent evidence suggests a response to higher doses per fraction. We evaluated local control of extra-cranial metastases from RCC treated with stereotactic ablative radiotherapy (SABR). Methods: RCC patients with extra-cranial metastases treated with SABR were retrospectively enrolled from a single institution between 2005 and 2015. A total of 188 lesions were identified from 91 patients. Radiation (8-60Gy) was delivered in 1-5 fractions (fx) using stereotactic guidance. Local control (LC) was determined by imaging according to RECIST 1.1. Results: Median age at the time of treatment was 62.4 years. Metastases were detected in bone (39.9%), lung (14.9%), liver (9.6%), lymph nodes (11.7%) and other sites (23.9%). Ninety-seven (51.6%) lesions reached curative intent while 91 (48.4%) only reached palliative intent. The most common radiation regimens were 20Gy/1fx, 30Gy/3fx, and 40Gy/5fx. One-year overall survival was 76.5% with a median follow up of 10.7 months. Patients treated with curative SABR showed a 2-fold median survival as compared to those treated with palliative therapy (3.97 year vs 1.43 year, p<0.05). LC rates at 1 and 2 years were 91.4% and 89.7%, respectively. For the patients that failed, median time to local failure was 6.6 months. LC at 1 year significantly improved when treatment was curative (96.1% vs 84.9%, p<0.05), while it decreased in a re-irradiation setting (94.8% vs 46.7%, p<0.05). The median biological equivalent dose (BED) for the lesions that failed was 103Gy, corresponding to 6Gy x 5fx, and was significantly lowered compared to controlled lesions (BED 134Gy). Although 79% of patients developed new lesions within 1 year following SABR, 34.8% did not switch systemic therapy. Switching systemic therapy was delayed in patients treated with curative as compared to palliative SABR (13.4 vs 2.5 months, p<0.05). Conclusions: SABR improved LC of extra-cranial RCC metastases and delayed change to systemic therapy. SABR may complement systemic therapy to improve outcome in the present patient population.