D. Huang1, C. Lynch1, L. M. Serra1, R. F. Sweis2, W. M. Stadler2, R. Z. Szmulewitz2, P. H. ODonnell2, P. J. Chang3, S. E. Eggener4, A. L. Shalhav4, S. Liauw1, and S. P. Pitroda1; 1Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL, 2Department of Medicine, Section of Hematology/Oncology, University of Chicago, Chicago, IL, 3Department of Radiology, University of Chicago, Chicago, IL, 4Department of Surgery, Section of Urology, University of Chicago, Chicago, IL
Purpose/Objective(s): Stereotactic Ablative Body Radiotherapy (SABR) is an effective treatment for localized renal cell carcinoma (RCC). However, the role of primary site SABR for locally recurrent or metastatic RCC has not been established. Here, we report the outcomes of primary SABR across a heterogeneous cohort of localized, recurrent, and metastatic RCC patients treated at our institution. Materials/
Methods: All RCC patients treated with SABR in 1-5 fractions to the kidney or to the nephrectomy bed at our institution were included for analysis. Patients were deemed either medically inoperable or high risk for dialysis due to poor baseline renal function. Local control (LC), overall survival (OS), and freedom from distant failure (FFDF) were estimated using the Kaplan-Meier method. Our primary outcome was LC, which was evaluated using RECIST v1.1. Toxicities were reported according to the CTCAE v5.0. Estimated glomerular filtration rate (eGFR) was assessed at baseline and at 1-year post-SABR. Univariable and multivariable linear modeling were used to test the association of 1-year post-SABR eGFR with the following clinical and treatment-related features: age, race, Charlson comorbidity index (CCI), planning target volume, ipsilateral kidney volume, and baseline eGFR. Results: From March 2018 to July 2023, 42 patients with RCC received primary site SABR. The median follow-up was 26 (range 6-65) months. Median age was 73 (range 47-93) years. Median CCI was 8 (range 5-14). By disease extent, 28 (67%) patients had localized and 14 (33%) patients had metastatic RCC. Seven (17%) tumors were locally recurrent after prior surgery or ablation. Median tumor size was 4.5 (range 1.8-12.9) cm. Median biologically equivalent dose using an alpha/beta ratio of 10 was 93.6 (range 60-112.5) Gy. Two-year LC was 100%, and 3-year LC was 93.8% (95% CI 82.6%-100%). Two-year OS was 74.7% (95% CI 61.6%-90.7%). Among 28 patients with initially localized disease, 2-year FFDF was 96.4% (95% CI 89.8%-100%). Ten (24%) patients experienced acute grade 1-2 GI toxicity, with no acute grade 3+ toxicities. Two (4.8%) patients developed late grade 3+ GI toxicity. Among 29 patients with an intact ipsilateral kidney who were not on dialysis pre-SABR, the median baseline eGFR was 48 (range 22-101) mL/min/1.73 m2. At 1-year post-SABR, the median eGFR decline was 3 mL/min/1.73 m2. No patients required dialysis within 1 year post-SABR. Only baseline eGFR was significantly associated with eGFR change at 1 year with a predicted drop of 9 mL/min/1.73 m2 in 1-year eGFR for every 10 mL/min/1.73 m2 decrease in baseline eGFR (p < 0.001). Conclusion: This analysis demonstrates excellent LC rates across patients with localized, recurrent, and metastatic RCC treated with SABR. Treatment was well tolerated, with minimal associated eGFR decline. These findings support the efficacy and safety of primary SABR for recurrent and metastatic RCC.
