Cerebral Radionecrosis Following Stereotactic Irradiation of Skull Bone Metastases: A Diagnostic Pitfall to Be Aware of

We report an unusual case of brain radionecrosis following fractionated stereotactic radiotherapy (FSRT) delivered to a calvarial metastasis in a patient with metastatic luminal A breast cancer. A 40-year-old woman developed three subcentimetric brain lesions during follow-up, initially interpreted as new metastases and treated with FSRT. Subsequent radiological progression and advanced imaging suggested radionecrosis, which was confirmed histologically after surgical resection. Retrospective dosimetric analysis revealed that all lesions arose within the high-dose isodose region of the previously irradiated skull metastasis, despite compliance with established brain dose constraints. This case highlights a previously unreported risk of brain radionecrosis after stereotactic irradiation of skull bone metastases and underscores the need for caution in treatment planning and imaging interpretation.