Radiation necrosis risk assessment after stereotactic radiation therapy for brain metastasis

Objective: To investigate factors influencing the occurrence of radiation necrosis (RN) in patients receiving fractionated stereotactic radiotherapy (fSRT) for brain metastases. Patients and Methods: Forty patients underwent linear accelerator-based fSRT from January 2018 to December 2023. RN and treatment response were monitored using magnetic resonance imaging (MRI), with toxicity graded by the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and oncological response was evaluated by the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Results: At a median follow-up of 12 months, RN occurred in 4 (10%) patients. Two patients had asymptomatic grade 1 RN, while two required steroids for grade 2 RN. Univariate analysis showed significant factors for RN: history of repeated fSRT (p=0.020), >1 metastatic lesion (p=0.022), age (p=0.016), and brain V30 (p=0.022). Multivariate analysis confirmed that repeated fSRT (p=0.02) and age (p=0.002) were significant. Conclusion: Radiation necrosis is a major concern in fSRT for brain metastases. Repeated fSRT, multiple metastatic lesions, age, and higher brain V30 values increase RN risk. Individualized treatment planning, especially considering dose-volume parameters, may help reduce this risk. Larger prospective studies are needed to confirm these findings and optimize RN mitigation strategies.