RTAD-05 LOCAL RECURRENCE AND RADIONECROSIS WITH 3-FRACTION STEREOTACTIC RADIOTHERAPY FOR POSTOPERATIVE CAVITIES AND INTACT BRAIN METASTASES: A PROSPECTIVE REGISTRY STUDY
Pranav Samineni, Sandeep Purohit, Shyam Tanguturi, Yujue Tan, Nayan Lamba, Diana Shi, Daphne Haas-Kogan, Patrick Wen, Ayal Aizer, Rifaquat RahmanAbstract
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.