MET-05 PRELIMINARY REPORT OF RADIOTHERAPY FOR BRAIN METASTASES FROM GASTRO-INTESTINAL CANCERS USING MASK SYSTEM OF LEKSELL GAMMA KNIFE ICON

OBJECT: Leksell Gamma Knife Icon enables us to apply new methods of immobilization using mask fixation and the option of fractionated treatment. This provides exceptional accuracy and precision of radiosurgery, making it a possibility for many more disease types and many more patients to be treated. METHODS: We retrospectively analyzed 50 patients (71 times) with brain metastases from gastro-intestinal cancers who underwent Gamma Knife Icon using mask fixation between September 25th, 2017 and June 30th, 2019 at Rakusai Shimizu Hospital. Patients with small, few, newly diagnosed, and non-eloquent area tumors were treated in a single session. If the tumor volume was larger than 5.0 ml, recurrence, or the location was in an eloquent area, we applied a fractionated schedule. If the tumor number was large, we selected a multisession schedule. The most common origin was colon (19 patients), followed by rectum (11), stomach (7), esophagus (5) and others (8). RESULTS: 13 cases were treated in a single session, 53 with fractionation, and five with multiple sessions. We selected fractionated schedules as follows; 7.0 Gy x 5Fr (5–10 ml), 4.2Gy x 10Fr (10-20ml), 3.7Gy x 10Fr (20-30ml), 3.2Gy x 10Fr (30ml-) for malignant tumors, and 2.7Gy x 10Fr for benign tumors. Median tumor number was two (1–40) and median tumor size was 8.1 (0.03–67.5) ml. Median survival times after Icon treatment was 13.5 months and local control rate after 6-month Icon treatment was 80%. CONCLUSIONS: Although these results are limited to short periods, survival rates, local control rates and qualitative survival rated in patients unsuitable for stereotactic radiosurgery, such as those with large, recurrent, and eloquent site lesions, were within the acceptable ranges.