Sub-Arc Gating Motion Tolerances for Single Target Cranial VMAT
Abstract
Purpose
Plan deliverability robustness was explored by identifying and gating motion-sensitive control point sequences in single-target cranial VMAT plans. A dose-informed, control-point-specific motion tolerance was tested for its performance in mitigating coverage loss compared to full-plan gating.
Methods
An in-house MATLAB application reconstructed thirty single-target cranial VMAT plans into static-field plans and simulated one hundred motion scenarios per plan by applying realistic 3D, control-point–specific motion traces. Control point motion sensitivity was quantified using the Euclidean distance (EucD) from the origin on a standard deviation–versus–mean plot of differences in area under the curve (AUC) of control point dose-volume histograms (DVHs). Sub-arcs for gating were defined by thresholding at the 10th–90th percentiles of EucD. Intrafraction motion simulations were calculated with a 1.0 mm motion tolerance for sub-arcs and full-plan gating. Variance in D99 (dose received by 99% of the planning target volume) was compared across scenarios using the Brown–Forsythe test (median-centered Levene).
Results
For all cases analyzed, full-plan gating reduced variance of D99 versus ungated delivery (variance ratios = 0.37 to 0.55, p < 0.05). Compared with full-plan gating, sub-arc gating at the 80th percentile of EucD (gating ~40% of control points in the plans) showed no statistical difference in D99 variance by the Brown–Forsythe test (α = 0.05).
Conclusion
Dose-informed sub-arc gating based on differences in AUC of control point DVHs may offer the same motion robustness compared to full-plan gating while significantly reducing the clinical burden of gating. Future work will evaluate coverage loss across tolerance levels and estimate interruption probability from motion trace statistics.