External border zone may be correlated with radiation necrosis after radiosurgery in metastatic brain tumor

Radiation necrosis (RN) after stereotactic radiosurgery (SRS) in brain metastases has been extensively evaluated, and RN is correlated with various risk factors. However, no study comprehensively analyzed the correlation between RN and the border zones of the brain that are vulnerable to ischemia. We hypothesized that patients with tumors in the border zone are at high risk of RN. Hence, the current study aimed to assess the correlation between border zone lesions and RN, with consideration of other predetermined factors. This retrospective study included 117 patients with 290 lesions who underwent Gamma Knife® stereotactic radiosurgery (SRS). Radiological and clinical analyses were performed to identify factors possibly correlated with RN. Notably, the lesion location was classified into two groups (border zone and non-border zone) based on the blood supply. In total, 22 (18.8%) patients with 22 (7.5%) lesions developed RN. Univariate analysis revealed a significant correlation between RN and external border zone lesions, second course of SRS administered at the same site of the previous SRS, prescribed dose, and tumor volume. Multivariate analysis showed that border zone lesions, second course of SRS at the same site of the previous SRS, and tumor volume were significantly correlated with RN. Patients with tumors in the border zone are at high risk of RN. The potential risks of RN can be attributed hypothetically to hypoperfusion. Hence, the association between RN and border zone lesions seems reasonable.