RADT-46. Radiosurgery Dose Reduction for Brain Metastases on Immunotherapy (Radremi): A Prospective Pilot Study
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Abstract
BACKGROUND: The combination of immunotherapy and single-fraction stereotactic radiosurgery (SRS) for treatment of metastatic brain disease has yielded symptomatic radiation necrosis rates as high as 16%. The aim of this study was to evaluate the toxicity of dose reduced stereotactic radiosurgery (SRS) in patients receiving concurrent immune checkpoint inhibitors (ICI).
METHODS: RADREMI is a prospective, single arm, phase 1 pilot study evaluating adults with 1-10 brain metastases on MRI receiving ICI within 30 days of treatment. SRS was delivered using dose reduction: 18 Gy for lesions 0-2 cm, 14 Gy for lesions 2.1-3 cm, and 12 Gy for lesions 3.1-4 cm. Patients were evaluated at 6-months with regard to symptomatic radiation necrosis, defined as a 6-month rate of clinical symptomatology requiring steroid administration, bevacizumab, and/or operative intervention concomitant with advanced and routine brain imaging findings consistent with radiation necrosis.
RESULTS: Between 2019 and 2023, 18 eligible patents were entered with 12 evaluated. All patients were treated within the 18 Gy cohort. The median follow up was 13.82 months. The median number of brain metastases treated was 1.5 (inner quartiles 1, 3) with up to 7 lesions treated. The proportion of patients who experienced symptomatic radiation necrosis by 6 months was calculated with the 95% confidence interval tested against a historical proportion of 16%. The incidence of symptomatic radiation necrosis at 6 months was 1 of 12 (0.083; 95% CI: 0.002, 0.385; p-value 0.234) following SRS.
CONCLUSIONS: Our findings of dose reduced SRS with concurrent ICI unfortunately did not have statistical significance regarding symptomatic radiation necrosis. This was likely due to the small number of evaluable patients. The secondary endpoint of local control is currently under review. Dose reduced SRS with concurrent ICI warrants further studies to evaluate toxicity and local control.