E. Mehanna1, R. van Dams2, H. J. Mamon2, J. D. Mancias2, M. Lam2,3, S. Tanguturi4, M. A. Huynh2, V. Venkatachalam2, K. J. Fitzgerald2, R. H. Mak5, N. E. Martin2, Z. Han5, S. L. Chang6, B. McGregor7, T. K. Choueiri7, and J. E. Leeman5; 1Harvard Radiation Oncology Program, Boston, MA, 2Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, 3Department of Health Policy and Management, Harvard T.H. Chan School of Public Health, Boston, MA, 4Department of Radiation Oncology, Brigham and Women’s Hospital and Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 5Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, 6Brigham and Womens Hospital, Boston, MA, 7Dana Farber Cancer Institute, Boston, MA
Purpose/Objective(s): Renal cell carcinoma (RCC) has been historically viewed as a radioresistant tumor. However, novel radiation techniques, such as magnetic resonance-guided stereotactic body radiotherapy (MRgSBRT), enable the delivery of ablative doses of radiation while minimizing toxicity to surrounding organs, allowing for further exploration of the role of radiotherapy in RCC. In this study, we evaluated the safety and disease control outcomes of patients with metastatic RCC who underwent metastasis-directed MRgSBRT. Materials/
Methods: We performed a retrospective analysis of 44 patients who underwent MRgSBRT for RCC metastases at a single institution between 2019-2023. Endpoints were local control, freedom from distant progression, time to change in systemic therapy, overall survival, and toxicity. Disease progression was defined using RECIST criteria. Toxicity was graded using CTCAE v5.0. Outcomes were analyzed using the Kaplan-Meier method. Results: 44 patients underwent treatment for 64 lesions. All patients had an Eastern Cooperative Oncology Group status of 0-1. The most frequent histology was clear cell RCC (64%). 75% of patients had fewer than 5 metastatic lesions at the time of MRgSBRT. The most common metastatic sites treated were lymph nodes (28%), pancreas (25%), and adrenal glands (19%). Median lesion size prior to treatment was 2.2 cm (IQR 1.6-3.7). 94% of lesions were treated using daily adaptive planning. Radiation dose range was 40-54 Gy delivered in 3-5 fractions with 40 Gy in 5 fractions being the most common regimen (78%). At a median follow-up of 16.0 months (IQR 8.5-23.0), local control was 95.6% (95% CI 83.5-98.9), freedom from distant progression was 16.6% (95% CI 7.7-28.5), and overall survival was 78.0% (95% CI 62.9-87.6). The 2 local failure events observed were both pancreatic lesions, of clear cell and clear cell with rhabdoid histology. The median change in lesion size post-treatment was -0.45 cm (20% decrease from baseline). At median follow-up, 54.9% (95% CI 39.7-67.7) of patients continued either without systemic therapy or on the same systemic regimen as prior to MRgSBRT. Median time to change of systemic therapy post-MRgSBRT was 11.5 months (IQR 5.5-17.0). Among the 33 patients who did not receive systemic therapy prior to MRgSBRT, 72% remained off systemic therapy following treatment. There was no grade 3+ toxicity observed up to 3 months following treatment. Conclusion: MRgSBRT provides high rates of local control for metastasis-directed treatment of metastatic RCC and may allow for prolonged time without initiating or switching systemic therapy. Further investigations to explore factors that may predict response to radiotherapy are warranted.
