P2.01-98 Single-Isocenter Volumetric-Modulated Arc Radiosurgery for Non-Small-Cell Lung Cancer Patients with Multiple Brain Metastases

Abstract

Radiosurgery for multiple brain metastases (BMs) in patients with non-small-cell-lung cancer (NSCLC) is a well-established treatment option. However, only 1–4 BMs can be treated by conventional linear-accelerator-based radiosurgery because the treatment time becomes longer as the number of BMs increases. Advanced volumetric modulated arc therapy combined with image-guided radiotherapy enables the realization of single-isocenter volumetric-modulated arc radiosurgery (VMAR), a novel irradiation technique. VMAR irradiates multiple BMs simultaneously using only one isocenter and within a short treatment time. Here we report our initial experience with VMAR. The clinical records of 19 patients with 115 BMs from NSCLC were retrospectively analyzed. All patients were treated by VMAR for multiple BMs from October 2015 to September 2017 at our institution and received follow-up magnetic resonance imaging at least once after VMAR. The median patient age was 69 years. The median Karnofsky Performance Scale score was 90; five patients had been previously treated with whole-brain radiotherapy. The histology of the primary tumor was squamous-cell carcinoma in one patient and adenocarcinoma in 18 patients; 12 patients had either an EGFR or ALK alteration. A planning target volume (PTV) was created by expanding the contrast-enhanced lesion with a 1- or 2-mm margin. The median peripheral prescribed dose was 28 Gy, delivered in five fractions. All lesions were set to be covered by ≥99.5 % of the prescribed dose. The median follow-up period was 8.5 (range, 1.7–29.9) months. The median number of PTVs was four (range, 2–18). The median PTV was 0.49 (range, 0.13–13.49) cm3, and the median total PTV 8.3 (range, 1.52–18.87) cm3. The median PTV was significantly smaller in patients with than without genetic alterations to their tumor. The probabilities of local control, overall survival, and developing new BMs at 12 months were 100%, 68.4%, and 51.1%, respectively. Acute adverse events included grade 2 alopecia in four patients and seizure in one patient. The number of PTVs in patients with grade 2 alopecia was more than six. Two patients developed grade 2 central nervous system necrosis as a late adverse event. No grade 3 or higher toxicities were noted. While VMAR achieves good local control, the development of temporary alopecia remains to be addressed. More cases and a longer- follow-up period are required to verify the efficacy of VMAR.