Long-Term Safety and Efficacy of SAbR for Metastatic RCC.

Abstract

Metastasis-directed stereotactic ablative radiation (SAbR) in metastatic renal cell carcinoma (mRCC) has been shown to prolong time to systemic therapy start/change. However, there is a paucity of data on the durability of local control by SAbR and long-term side effects, limiting its investigation in prospective trials. Here we report the long-term local control rates of SAbR for mRCC, focusing on factors that lead to local failure where dose escalation may be beneficial. We retrospectively reviewed 354 metastatic RCC patients who received SAbR to 902 lesions between 2005 and September 2021. Acute and late adverse events and their Common Terminal Criteria for Adverse Events (CTCAE) v. 5.0 grades were collected. RECIST v. 1.1 was used to evaluate treatment response. LC was estimated using the cumulative incidence function, with death as a competing risk. Local control (LC) was calculated using the Kaplan-Meier method. Lesions were followed for a median of 16 months; 136 lesions had >36 months of follow-up. The most common radiation prescription was 36 Gy in 3 fractions, and the median biological effective dose was 72 Gy10. 3-year local control was 80% (95% CI 75, 83). 3-year LC differed according to lesion location, ranging from 65% (95% CI 52, 75) in the spine to 93% (95% CI 80, 98) in the lungs. Radiation-induced adverse events were experienced by 101 patients: 79 had an acute (≤90 days of SAbR) grade 1-2 toxicity; 20 had an acute grade 3-4 toxicity; 59 had a late grade 1-2 toxicity; 15 had a late grade 3-4 toxicity. The most common acute grade 1-2 toxicity was pain (n = 32), followed by nausea (n = 22) and fatigue (n = 16). There were 7 occurrences of acute grade 3-4 pain, 4 of nausea, and 2 fractures. The most common late grade 1-2 toxicity was fracture (n = 16), followed by pain (n = 15) and pneumonitis (n = 12). Hyperglycemia was the only late grade 3-4 toxicity that occurred more than once (n = 2). SAbR offers durable LC of mRCC lesions with an acceptable toxicity profile. LC was affected by treated lesion location, with bone (including long bones and ribs) and spine locations experiencing less durable LC, corresponding to locations that received lower-BED treatments.