Laser Interstitial Thermal Therapy for Brain Metastases: Imaging Guidelines for Clinical Trials and Practice

Laser interstitial thermal therapy (LITT) is a local surgical treatment for brain metastases (BM). Here, we present and discuss the main radiologic findings and challenges related to LITT-treated BM. Prior to LITT, imaging features are useful for prognostic stratification and patient selection, as well as treatment planning. During the LITT session, intra-procedural imaging is acquired immediately at the beginning of the procedure for tumor delineation, during the ablation to monitor treatment using MR thermometry, and immediately post-LITT to evaluate the ablated region. Images obtained during the LITT procedure are useful to estimate extent of ablation, either by analyzing the real-time thermometry data or by comparing pre- and post-ablation images. In the months following LITT, follow-up scans exhibit characteristic imaging patterns for responding versus progressing lesions, which should be accounted for during post-LITT surveillance. In light of these patterns, and considering the strategies adopted by previous LITT studies, we propose dedicated criteria for local radiologic response and local radiologic progression in clinical trials, by adapting the RANO-BM criteria for local therapies to a "dual baseline" framework dedicated to LITT treated BM. Finally, we provide suggestions for the adoption of standardized post-LITT imaging protocols based on the current consensus.