Stereotactic Radiosurgery for Multiple Brain Metastases: A Dose-Volume Study

Abstract

A substantial number of cancer patients develop brain metastases, which often present as multiple lesions. Stereotactic radiosurgery (SRS) can be used to treat brain metastases, with some incidental dose to the healthy brain. This study evaluated the effect of the number and combined volume of metastatic lesions on the dosimetric quality and the deliverability of a small sample of SRS test treatments. Five simulated static conformal arc treatments of 4–12 brain metastases were planned for linac-based multi-isocentre delivery to a head phantom. Film measurements were used to verify dose calculation and treatment delivery accuracy. Several of the treatment plans were considered clinically acceptable when local dose prescriptions (14–18 Gy) were used, but when the prescription dose to all metastases was increased to match the RTOG 0320 recommended value of 24 Gy, no plans resulted in a V12 less than 10 cm3. Agreement between planned and measured dose was poorest for the treatments of 10 and 12 metastases, due to increased disagreement in out-of-field regions. Using the multi-isocentre static conformal arc method, it is possible to deliver treatments to relatively large numbers (at least 12) and total volumes (at least 8 cm3) of brain metastases without excessive radiation doses being delivered to the healthy brain, provided that reduced prescription doses are acceptable.