RTAD-05 LOCAL RECURRENCE AND RADIONECROSIS WITH 3-FRACTION STEREOTACTIC RADIOTHERAPY FOR POSTOPERATIVE CAVITIES AND INTACT BRAIN METASTASES: A PROSPECTIVE REGISTRY STUDY
TL;DR
Three-fraction SRT was associated with higher rates of radionecrosis in postoperative cavities relative to 5-fraction regimens and larger targets (>2cm vs. <2cm) were associated with higher rates of RN.
Abstract
Abstract Objective Stereotactic radiotherapy has been increasingly used for brain metastases though differences between single fraction and hypofractionated regimens remain incompletely defined. We performed a lesion-level competing-risk analysis to evaluate cumulative incidence of radiation necrosis (RN) and local recurrence (LR) for intact brain metastases and postoperative cavities treated with 3-fraction SRT. Materials/Methods: Patients treated with 3-fraction SRT were enrolled onto a prospective registry at our institution between 2021-2024. Gross totally resected metastases were treated with 24Gy in 3 fractions, targeting the cavity; for intact metastases or residual and/or recurrent disease after surgery, 27Gy in 3 was utilized. Outcomes included symptomatic RN, radiographic RN, and local recurrence based upon RANO-BM criteria. Cumulative incidence functions (CIFs) were estimated with death as a competing risk. We compared cumulative incidence functions with institutional historical benchmarks for 5-fraction stereotactic radiotherapy (25Gy for cavities, 30Gy for intact metastases): 18-month LR was 7.6%[95%CI:5.1-10.9] for cavities and 4.1%[95%CI:2.3-6.8] for intact metastases; respective 18-month RN rates were 4.3% [95%CI:2.4-7.0] and 8.3% [95%CI:5.4-11.9]. Results Among 110 lesions from 81 patients treated on the prospective registry (range 1-5 metastases per patient), 56 (51%) were postoperative cavities and 54 (49%) were intact lesions. Median size of cavities and intact lesions was 27mm and 16mm, respectively. Eighteen-month LR was 5.4% (95%CI: 0-11.5%) for cavities and 3.7% (95%CI: 0-8.9%) for intact metastases. The 18-month RN rate was 19.2% (95%CI 7.7-30.6%) for cavities and 14.4% (95% CI: 4.2-24.6%) for intact metastases. Amongst RN cases, 55% were symptomatic, and median time to RN was 15.8 months for postoperative cavities and 8.8 months for intact metastases. Larger targets (>2cm vs. <2cm) were associated with higher rates of RN (HR 3.50, 95% CI: 1.05-11.1, p = 0.041) on univariable analysis. Conclusion Three-fraction SRT was associated with higher rates of radionecrosis in postoperative cavities relative to 5-fraction regimens.