Stereotactic Ablative Radiotherapy (SABR) for Large Renal Tumors: A Retrospective Case Series Evaluating Clinical Outcomes, Toxicity, and Technical Considerations

Objectives: Metastatic renal cell carcinoma represents a clinical scenario where aggressive treatment to the primary tumor (ie, cytoreductive nephrectomy) is associated with a survival benefit. We hypothesized that stereotactic ablative radiotherapy (SABR) could be a safe alternative local modality for inoperable metastatic renal cell carcinoma patients. Our study objectives were to report on technical considerations, toxicity, and clinical outcomes of our institutional experience with renal SABR. Materials and Methods: Patients who underwent renal SABR at our institution between January 2008 and June 2015 were reviewed. Toxicity was quantified using the Common Terminology Criteria for Adverse Events version 4.0. Radiographic response was evaluated using the Response Evaluation Criteria in Solid Tumors classification. Median overall survival and follow-up were calculated using the Kaplan-Meier and reverse Kaplan-Meier methods, respectively. Results: We identified 11 patients that met study criteria. SABR was directed to the tumor or whole kidney in 5 fractions to a dose of 25 to 40 Gy. Median tumor diameter and planning target volume were 9.5 cm (range, 7.5 to 24.4) and 819.3 cm3 (range, 313.4 to 5704.3), respectively. Median follow-up was 3.9 years (95% confidence interval, 0.6-4.9). Five cases of grade 1 toxicity were reported. In the patient with the largest target, grade 2 diarrhea and probable grade 3 nausea were observed. In patients with available follow-up imaging (7/11), stable disease (n=5), partial response (n=1), and progressive disease (n=1) were observed. Median overall survival was 20.4 months (95% confidence interval, 2.30-N/A). Conclusions: In this small cohort, renal SABR was delivered with minimal toxicity. A prospective study is underway at our institution to determine maximum tolerable and optimal dosing (NCT02264548).

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