Abstract

Objectives: The aim of this study was to evaluate the response of each brain metastasis lesion to frameless stereotactic radiosurgery (SRS) treatments by using a modified Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM).
    
Methods: This is a retrospective study of 87 patients with a total of 149 brain metastases lesions that were treated with frameless SRS from February 2015 to March 2017. The RANO-BM criteria are modified as following for each metastasis lesion: Complete Response (CR): Disappearance of the target lesion; Partial Response (PR): At least a 30% (or 3 mm for lesions with baseline longest diameters between 5 mm and 10 mm) decrease in the longest diameter of the target lesion (no PR for lesions less than 5 mm due to relative large measurement uncertainty); Progressive disease (PD): At least a 20% increase (or 3 mm for lesions with baseline longest diameters between 5 mm and 10 mm) in the longest diameter of the target lesion; Stable disease (SD): Neither sufficient shrinkage to qualify for partial response, nor sufficient increase to qualify for progressive disease. All measurements are based on T1 MR images with contrast. Follow up MR scans are from 2 to 16 months after treatments.

Results: Of the 95 patients treated during the study period, 7 patients did not have planning MRI or follow up MRI scans; the lesion of another patient was next to a surgical cavity. Those 8 patients were excluded from the study. 50 patients had single metastases lesions; 37 patients had 2 to 9 metastases lesions. A total of 149 lesions were studied. The results are 62 (41.6%) CR, 21 (14.1%) PR, 58 (38.9%) SD, and 8 (5.4%) PD.  

Conclusion: Our retrospective study shows a 94.6% local control (CR, PR and SD) rate to frameless SRS.