Summary: This repository presents a comprehensive longitudinal dataset comprising of 185 imaging studies (magnetic resonance imaging and computed tomography scans) from 40 patients diagnosed with metastatic brain cancer, with the dataset featuring detailed segmentations of 65 brain metastases, along with pre-treatment radiotherapy dosage distribution maps (RT plan). The dataset includes manual segmentations that encompass three distinct regions in the brain: the enhancing tumor region, the edema and the necrotic core, thus, providing a comprehensive representation of tumor morphology for advanced analysis. The data available in this repository aims to support research and evaluation of automatic brain metastases detection, lesion segmentation, disease assessment, treatment planning, and the development of pertinent predictive and prognostic tools. Acknowledgements: This study was financially supported by the Cyprus Cancer Research Institute through the PROTEAS project (Call: Bridges in Research Excellence CCRI_2020_FUN_001; Grant ID: CCRI_2021_FA_LE_105) and has been approved by the Cyprus National Bioethics Committee (ID: EEBK/ΕΠ/2021/72).