RADT-21. LINEAR ACCELERATOR BASED RADIOSURGERY WITH DYNAMIC CONFORMAL ARCS FOR PATIENTS WITH MULTIPLE BRAIN METASTASES: A PROSPECTIVE COHORT STUDY

Abstract

Abstract PURPOSE Linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) is gaining popularity as an alternative due to its high delivery efficiency and improved accessibility. This study focuses on the radiosurgery protocol of a single institution, utilizing single-isocenter multi-target SRS treatment with an inverse-optimized dynamic conformal arc technique. Materials & METHODS A prospective cohort study was conducted from August 2020. The study protocol was approved by the Research Ethics Committee. Patients with brain tumors referred for SRS were treated based on the indications. Prescription doses were determined by target size and radiation oncologists. The protocol included a 1-2 mm expansion of tumors for the planning target volume (PTV), with a requirement of at least 85% PTV coverage. At least three non-coplanar arcs are needed. Competing risk survival analysis was used to assess the cumulative incidence of failure. RESULTS A total of 57 patients with 190 brain tumors underwent SRS in this study. 12 patients (21.1%) received at least 2 radiation courses for recurrent lesions. Tumor sizes ranged from 0.45 to 8.0 cm (median 1.41 cm). The maximal dose relation ranged between 71.5% and 91.4% (median 81.6). The conformal index ranged from 1.08 to 2.19 (median 1.19), and the dose gradient index ranged from 2.19 to 6.95 (median 3.59). The 1-year cumulative incidence of local failure and intracranial distant failure rates were 10.8% and 35.6%, respectively. CONCLUSION LINAC-based SRS using dynamic conformal arcs achieves optimal tumor coverage and a high dose gradient with ease. It demonstrates a low rate of local failure, effectively protects normal brain tissue, and allows for the postponement of whole brain radiotherapy, enabling patients to maintain a normal quality of life. In conclusion, LINAC-based SRS with dynamic conformal arcs may be a beneficial treatment option for brain metastases, even with a high lesion count, particularly in institutions equipped with LINAC.