Predictive value of perilesional edema volume in melanoma brain metastasis response to stereotactic radiosurgery

Background and aim: Stereotactic radiotherapy (SRT) is an established treatment for melanoma brain metastases (MBM). Recent evidence suggests that perilesional edema volume (PEV) might compromise the delivery and efficacy of radiotherapy to treat BM. This study investigated the association between SRT efficacy and PEV extent in MBM. Materials and methods: This retrospective study reviewed medical records from January 2020 to September 2023. Patients with up to 5 measurable MBMs, intracranial disease per RANO/iRANO criteria, and on low-dose corticosteroids were included. MRI scans assessed baseline neuroimaging, with PEV analyzed using 3D Slicer. SRT plans were based on MRI-CT fusion, delivering 18-32.5 Gy in 1-5 fractions. Outcomes included intracranial objective response rate (iORR) and survival measures (L-iPFS and OS). Statistical analysis involved decision tree analysis and multivariable logistic regression, adjusting for clinical and treatment variables. Results: Seventy-two patients with 101 MBM were analyzed, with a mean age of 68.83 years. The iORR was 61.4%, with Complete Response (CR) in 21.8% and Partial Response (PR) in 39.6% of the treated lesions. PEV correlated with KPS, BRAF status, and treatment response. Decision tree analysis identified a PEV cutoff at 0.5 cc, with lower PEVs predicting better responses (AUC = 0.82 sensitivity: 86.7%, specificity:74.4%,). Patients with PEV ≥ 0.5 cc had lower response rates (iORR 44.7% vs. 63.8%, p < 0.001). Median OS was 9.4 months, with L-iPFS of 27 months. PEV significantly impacted survival outcomes. Conclusions: A more extensive PEV was associated with a less favorable outcome to SRT in MBM.