Predictive Factors of Micrometastases in Metastatic Brain Tumors Treated with Gamma Knife Radiosurgery

Objective: Whether to administer or omit adjuvant whole brain radiotherapy (WBRT) in conjunction with stereotactic radiosurgery (SRS) in the initial management of patients with newly diagnosed brain metastases is still up for debate. The ability to predict micrometastases will aid in the decision making process for these patients. In this study, we analyzed factors predictive of micrometastases after gamma knife radiosurgery (GKRS). Materials and Methods: We retrospectively reviewed clinical and imaging data of 172 patients with metastatic brain tumors who underwent GKRS from July 2012 to July 2013. The study included patients with MRIs taken at both the time of GKRS and 3 months after GKRS. The overall distant brain failure (newly detected metastatic lesions) observed on MRIs taken 3 months after SRS was estimated. Factors such as the primary origin of metastases, CCRTx, EGFR (in lung cancer), volume and number of metastases, status of systemic disease, and delayed MRI were analyzed. Results: A total of 128 patients were enrolled in this study. Lung cancer was most common as a primary disease (80 patients, 62.5%). Among the patients enrolled, 76 patients (95%) were NSCLC and four patients (5%) were SCLC. In NSCLC patients (76), 30 patients were EGFR mutation positive and 42 patients were negative. Status of the primary disease was stable in 73 patients (57.0%), progressive in 55 patients (42.9%). Eighty-nine patients (62.1%) underwent combined systemic chemotherapy. Mean number of metastatic brain lesions at the time of planning the MRI was 3.67 (from 1 to 22) and mean total tumor volume at planning was 9.05cm3. For brain tumors originating from lung cancer, a greater number of metastatic lesions suggested a tendency towards micrometastases 3 months after GKRS, with statistically significant differences (p＜0.05). Factors such as CCRTx, EGFR (in lung cancer), volume of brain metastases, status of systemic disease, and delayed MRI were not statistically significant. Conclusions: This study shows predictive factors associated with micrometastases of metastatic brain tumors previously treated with GKRS. Patients with brain metastases originating from lung cancer, more than four metastases should be taken into consideration in the decision making of initial treatment and follow-up management.prohibitio