Abstract / Summary
Abstract Purpose Serial magnetic resonance imaging (MRI) demonstrates heterogeneous lesion evolution after stereotactic radiosurgery. We characterized longitudinal volumetric response phenotypes after Gamma Knife radiosurgery (GKRS) for breast cancer brain metastases and examined their association with 12-month lesion-level local control. Methods This single-center retrospective study included 80 patients, 182 GKRS-treated lesions, and 819 serial MRI records. Local control was assessed within a prespecified 10–14-month window. Lesions were classified as complete response/disappearance, partial regression, stable control, or progression. Baseline correlates of local failure were evaluated using Bayesian mixed-effects logistic regression, with patient-clustered generalized estimating equations used for sensitivity analysis. Results Local control was evaluable in 103 lesions and longitudinal phenotype in 154. The four phenotypes comprised 24 complete responses/disappearances, 59 partial regressions, 44 stable controls, and 27 progressions. In the prespecified Bayesian model, larger baseline whole-tumor volume and peritumoral edema were associated with higher odds of local failure, whereas higher BED₁₀ was inversely associated; clustered sensitivity estimates retained the same directions but were less precise. Progression phenotype was strongly associated with local failure after accounting for within-patient clustering (odds ratio 27.08, 95% confidence interval 7.11–103.20; p < 0.001) and remained associated when classification was restricted to the 10–14-month window. Conclusion Longitudinal volumetric MRI phenotypes capture heterogeneous post-GKRS lesion evolution and identify a progression pattern closely associated with local failure. This framework may complement standard local-control assessment during post-treatment surveillance.