Dosimetric Superiority of a Novel Spiral VMAT over Conventional VMAT for Hippocampal-Avoidance Whole-Brain Radiotherapy
Abstract
Purpose
Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) presents a dosimetric challenge in sculpting steep dose gradients to spare critical neural structures. This study evaluated a novel Spiral Volumetric Modulated Arc Therapy (SVMAT) technique against conventional VMAT for HA-WBRT, focusing on plan quality, organ sparing, and dose fall-off characteristics.
Methods
In this retrospective planning study, paired SVMAT and conventional VMAT plans were generated for ten patients with multiple brain metastases. All plans adhered to identical dose prescriptions (whole-brain PTV: 30 Gy in 10 fractions) and stringent organ-at-risk constraints (hippocampus Dmax <17 Gy, lens Dmax <5 Gy). The key innovation of the SVMAT technique lies in the synchronization of continuous gantry rotation with longitudinal couch movement, enabled by the NeuRT Aurora platform and DeepPlan 1.3, to generate a helical delivery path. This design aims to enhance fluence modulation freedom for complex cases. Conventional VMAT plans were created using Varian Eclipse 13.5. Plan quality was comprehensively assessed using the conformity index (CI), homogeneity index (HI), critical dose-volume parameters for the hippocampus and lenses, and quantitatively evaluated dose fall-off gradients.
Results
Both techniques achieved clinically acceptable and comparable target coverage for the whole-brain PTV. However, SVMAT demonstrated statistically superior critical organ sparing. It significantly reduced the maximum dose to the hippocampus by 6.3% (16.76 ± 1.40 Gy vs. 17.88 ± 3.32 Gy, p=0.014) and showed a trend toward reducing the maximum lens dose. Furthermore, SVMAT plans yielded better dose conformity (CI) and significantly steeper dose fall-off gradients at the hippocampal-PTV boundary, indicating a more rapid dose reduction outside the target volume.
Conclusion
For HA-WBRT, the novel SVMAT technique provides dosimetrically superior plans to conventional VMAT, offering enhanced hippocampus sparing and sharper dose gradients through its unique helical delivery. These advantages support its potential to better preserve neurocognitive function in patients.