2067 - Superior Hippocampal Sparing with Spiral VMAT in Whole-Brain Radiotherapy: A Dosimetric Comparison
Presenter(s)
Y. Gao1, Z. Wang1, and L. Zhao2; 1Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China, 2StateKey Laboratory of Holisticntegrative Managementof Gastrointestinal Cancersand Department of RadiationOncology,Xijing Hospital,Fourth Military MedicalUniversity, Xi'an, China
Purpose/Objective(s): Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) seeks to balance tumor control with neurocognitive preservation. Delivering the required steep dose gradients around the hippocampus remains technically challenging. This study dosimetrically compares a novel spiral volumetric modulated arc therapy (SVMAT) technique against conventional VMAT for HA-WBRT.
Materials/Methods: In this retrospective planning study, paired SVMAT and VMAT plans were generated for ten patients with multiple brain metastases. All plans adhered to identical prescriptions (whole-brain PTV: 30 Gy/10 fractions) and RTOG 0933-derived constraints (hippocampus Dmax <17 Gy, D100% <10 Gy; lens Dmax <5 Gy). The SVMAT technique employs continuous gantry rotation with synchronized longitudinal couch movement to create a helical dose delivery trajectory. SVMAT plans were optimized using a ring-gantry linac with helical delivery capability, while VMAT plans were generated using a conventional C-arm linac. Plan quality was assessed via conformity index (CI), homogeneity index (HI), dose-volume parameters, and quantitatively evaluated dose fall-off gradients at the hippocampal-PTV interface.
Results: Both techniques achieved comparable target coverage (PTV D95 ˜ 30 Gy). However, SVMAT demonstrated significantly superior organ sparing: it reduced the maximum hippocampus dose by 6.3% (16.76±1.40 Gy vs. 17.88±3.32 Gy, p=0.014) and showed a trend toward lower lens dose. SVMAT also yielded better CI and significantly steeper dose fall-off gradients (2.8±0.3 Gy/mm vs. 2.0±0.4 Gy/mm, p<0.05), indicating 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 dosimetric advantages support its potential to better preserve neurocognitive function and improve the therapeutic ratio for patients undergoing whole-brain radiotherapy.