Linac-based radiosurgery for multiple brain metastases: A quality assurance and feasibility study.

Abstract

2077 Background: The classical treatment for multiple brain metastases is whole brain radiotherapy (WBRT). For patients with 1-3 brain metastases stereotactic radiosurgery (SRS) results in better response, similar survival and less short and long term toxicity such as neurocognitive dysfunction than WBRT. For patients with > 3 metastases there is little prospective data of SRS partly due to the technical and logistic difficulties of delivering SRS to multiple metastases. We present a new SRS planning program (MMM) that allows the planning and delivery of linac-based SRS to up to 10 brain metastases simultaneously in less overall time than for WBRT. Methods: Between August 2014 and August 2016, patients referred for RT with 2 or more brain metastases were offered treatment with MMM. System QA included ArcCheck diode array and film dosimetry and gel dosimetry based on a patient derived phantom. Individual QA included replanting treatment arcs on an independent system. Results: 94 patients with 2-10 (median 5) metastases and a combined volume of 0.01-8.64 cc were treated. Planning time including image fusion, target delineation and RT plan generation required on average 20 minutes minutes. SRS was delivered using 4-5 (is more 7-10 since return arcs do not address the same targets) non-coplanar arcs and a single isocenter at the center of mass of the metastases. Treatment time to deliver 18-24 Gy to all metastases was 25 mins (beam on time ~6 minutes) for a total time of 45 minutes. This is the same as the time for each individual metastasis on earlier planning systems and compares to 20 minutes planning time and 12 mins delivery time for each of 10 fractions for a conventional 2 field WBRT plan WBRT (total 140 minutes). At 6 months follow up, 88% of treated metastases had decreased in size, 10% were stable and 2% grew. Acute toxicity was mild except for one patient with intractable seizures. Conclusions: Linac based SRS for multiple brain metastases is efficient, requiring the same resources as for treatment of a single metastasis and less resources than for WBRT, with a high rate of local control. Appropriate equipment is available in most radiotherapy departments which will allow more prospective studies of SRS for multiple metastases.