University of Wisconsin Carbone Cancer Center Madison, WI
C. Harari1, M. M. Basree1, E. J. Abel2, D. Shapiro2, C. Glide-Hurst1, S. G. Zhao1, R. Hutten1, N. J. Hurst Jr1, G. M. Cooley Jr1, J. M. Floberg1, and M. F. Bassetti1; 1Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, 2University of Wisconsin Department of Urology, Madison, WI
Purpose/Objective(s): Historically, radiation therapy has played a limited role in the definitive management of renal cell carcinoma (RCC). However, stereotactic body radiotherapy (SBRT) has emerged as a promising treatment alternative for RCC, particularly when surgery is not feasible, offering precision radiation delivery with limited toxicity profiles. We present outcomes for patients with RCC treated definitively with SBRT at our institution over a five-year period. Materials/
Methods: A retrospective analysis identified 22 patients diagnosed with RCC who underwent SBRT as definitive management between October 2017 - December 2023. All patients were treated with radiotherapy alone and had no prior RCC-directed therapies. Radiotherapy treatment planning was performed using four-dimensional CT for patients treated with conventional linac and gated 0.35T MR-linac for patients treated with adaptive MRI guidance. Clinical data including toxicity profiles, survival data, local and distant progression data were evaluated. Results: Mean age was 73.6 years old (54-97 years old). Average greatest RCC tumor dimension was 4.9 cm (range 2.9-10.1cm) with only 18% of patients having cT1a tumors. The majority of patients had grade 2 disease (82%) and clear cell histology (77%). The most common dose/fractionation schedule was 50 Gy in 5 fractions (64% of patients). 73% of patients were treated using an MR-linac with an average of 3 inter-fraction adaptations and 63% of total fractions adapted. SBRT demonstrated a low acute toxicity profile with only 3 patients reporting nausea and 1 patient reporting fatigue. Long term toxicity was minimal in our limited follow up with median 1-year decrease in eGFR of 7 ml/min (95% CI 2.6-11.4). Local-regional progression was noted in 2 of 22 (91% local control) based on increase in radiographic size on follow up imaging. Neither of the 2 patients with progression have required further therapy. Metastatic progression occurred in 1 patient (96% freedom from distant failure). Cancer specific survival in this population was 100%. Median follow-up was 28.2 months. Median DFS and OS have not yet been reached. Conclusion: In our cohort, SBRT is a promising, effective, and well-tolerated treatment modality for RCC in cases where surgical intervention is not feasible, specifically in older patients unable to undergo surgery or for patients with larger RCC tumor volumes. This is among the larger reported series of RCC patients treated with adaptive MRI guided SBRT. With excellent rates of disease control and low toxicity profiles, SBRT appears valuable to consider as a non-invasive definitive management option for RCC patients. The high percentage of adaptive fractions shows that MRI guidance may help further reduce risk of toxicity while facilitating further dose escalation and warrants further investigation.
