Abstract
BACKGROUND: Recent advancements in radiotherapy technology have made it possible to implement single-isocenter noncoplanar volumetric modulated arc therapy (NC-VMAT) for stereotactic radiosurgery (SRS) of multiple brain metastases (BMs). This study aimed to demonstrate the dosimetric feasibility of combining coplanar-only single-isocenter VMAT with the "Treat" function as a potential alternative to conventional single-isocenter NC-VMAT for intracranial multitarget SRS. METHODS: Eleven patients with 2-6 BMs previously treated with conventional single-isocenter NC-VMAT SRS were retrospectively selected. In NC-VMAT, the collimator angle of each arc was manually adjusted to mitigate the "island blocking" problem. For comparison, each NC-VMAT plan was replanned via coplanar-only single-isocenter VMAT combined with the "Treat" function of the RayStation treatment planning system with a fixed collimator angle of 0°, referred to as TREAT-CO-VMAT, of which each arc only irradiated a single target. Plan comparisons between two plan techniques were performed regarding the gradient index (GI), conformity index (CI), normal brain tissue (NBT) dose exposure, absolute dose volume (V(10%)-V(100%)), homogeneity index (HI), beam-on time (BOT), monitoring units (MUs) and delivery accuracy. RESULTS: Compared with the NC-VMAT plan, the TREAT-CO-VMAT plan achieved comparable median CI and HI but with a significantly improved GI [median (range): 5.09 (4.13-6.75) vs. 8.72 (5.06-12.45), P=0.003]. It also provided better NBT sparing, with lower median V(12Gy) and D(mean) but at the cost of a substantial increase in MUs [median (range): 13,840 (8,014-18,809) vs. 4,661 (3,131-5,862), P=0.003] and a slightly longer BOT [median (range): 10.10 (5.95-14.23) vs. 6.89 (4.94-8.24) min, P=0.004]. Additionally, TREAT-CO-VMAT resulted in a significantly lower median V(10%)-V(50%), along with a higher median gamma passing rate, showing an approximate 2% increase for both the 2%/2 mm and 2%/1 mm criteria. CONCLUSIONS: TREAT-CO-VMAT provides high-quality treatment plans and accurate delivery for SRS in patients with 2-6 BMs, making it a promising alternative to conventional NC-VMAT.