Radiosurgery for Brain Metastases: Challenges in Imaging Interpretation after Treatment

Simple Summary Stereotactic radiosurgery is one of the main treatments for patients with brain metastases, with important achievements in terms of patient prognosis. Nevertheless, radiation treatment may induce brain changes, visible in neuroimaging, that are often difficult to distinguish from progressive disease. This review aims to provide an update on the innovative neuroimaging modalities to study brain changes after stereotactic radiosurgery, focusing on the differential diagnosis between the presence of disease and post-treatment effects.Abstract Stereotactic radiosurgery (SRS) has transformed the management of brain metastases by achieving local tumor control, reducing toxicity, and minimizing the need for whole-brain radiation therapy (WBRT). This review specifically investigates radiation-induced changes in patients treated for metastasis, highlighting the crucial role of magnetic resonance imaging (MRI) in the evaluation of treatment response, both at very early and late stages. The primary objective of the review is to evaluate the most effective imaging techniques for assessing radiation-induced changes and distinguishing them from tumor growth. The limitations of conventional imaging methods, which rely on size measurements, dimensional criteria, and contrast enhancement patterns, are critically evaluated. In addition, it has been investigated the potential of advanced imaging modalities to offer a more precise and comprehensive evaluation of treatment response. Finally, an overview of the relevant literature concerning the interpretation of brain changes in patients undergoing immunotherapies is provided.