Dosimetric Impact of Simultaneous and Separate Planning with Fixed/Iris Collimators on Brain Doses in Multiple Brain Metastases
Abstract
CyberKnife
®
stereotactic radiosurgery enables frameless, image-guided treatment of multiple brain metastases. Collimator type (Fixed vs. Iris) and planning strategy (Simultaneous vs. Separate) may influence low-dose normal brain exposure, plan quality, and treatment delivery efficiency.
The objective of the study was to compare the dosimetric performance of different collimator types and planning strategies in patients with three or four brain metastases under standardized planning conditions.
Twenty patients were retrospectively replanned using four treatment configurations: Fixed Separate, Fixed Simultaneous, Iris Separate, and Iris Simultaneous. All plans were generated using identical prescription doses and planning objectives. Dosimetric evaluation included normal brain V8, V10, V12 (volumes receiving ≥8 Gy, ≥10 Gy, and ≥12 Gy), mean brain dose (Vmean), Paddick conformity index (PCI), and gradient index (GI). Comparisons were performed using Friedman and Wilcoxon signed-rank tests. Estimated treatment time was recorded for all plans.
Significant differences were observed for V8 (
P
= 0.039), Vmean (
P
= 0.019), and PCI (
P
< 0.001), whereas V10 (
P
= 0.180), V12 (
P
= 0.103), and GI (
P
= 0.420) showed no significant differences among the planning approaches. Median dosimetric values tended to favor Iris Simultaneous planning for reducing low-dose normal brain exposure. The significant PCI difference was primarily attributable to lower conformity in the Iris Separate…
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