Evaluation of new lesions and symptoms after gamma knife radiosurgery for brain metastases: a retrospective cohort study

Symptomatic new lesions that appear after gamma knife radiosurgery (GKRS) for brain metastases have not been thoroughly described. Among 238 patients who underwent a single session of GKRS without whole-brain radiotherapy or surgery for brain metastases between 2009 and 2014, a total of 165 (69.3%) patients underwent follow-up magnetic resonance imaging (MRI). Their electrical health records were reviewed retrospectively. The median age was 68 years, and 62.4% patients were men. The median number of brain metastases was 2. The most frequent primary organ site was the lung (71.5%). Then, we evaluated predictors for the symptoms of new lesions. New lesions and leptomeningeal dissemination were observed in 101 (61.2%) and 23 (14.2%) patients, respectively. The median number of new lesions was 2; moreover, 20 of 101 patients (19.8%) with new lesions had tumours with the largest diameters of > 1 cm. Among 101 patients with new lesions, 13 were symptomatic (12.9%). Patients with larger new lesions (> 1 cm of the largest diameter) experienced symptoms more frequently (odds ratio 7.6, P < 0.01). Symptoms resolved after salvage GKRS in seven of 11 patients who abided by the recommended follow-up MRI schedule. No significant risk factors were found for symptoms of new lesions. The incidence of symptomatic new lesions that appeared after GKRS was low, and more than half of the patients showed improvements in their symptoms after salvage GKRS. However, careful MRI-based assessments and salvage GKRS are critical for the quality of life.