A simulation study of a novel spiral volumetric modulated arc therapy for enhanced dose delivery efficiency and
Kuo Li1, Wei Zhang2, Xingmin Ma1
1Department of Radiation Oncology Physics & Technology, Cancer Hospital of Shandong First Medical University, Jinan, China.
Background:
Conventional volumetric modulated arc therapy (VMAT) is limited by its longitudinal field size for large targets, often requiring multiple isocenters, while Helical Tomotherapy (HT) offers superior longitudinal conformity but suffers from prolonged treatment times due to its narrow fan beam.
Purpose:
This simulation study proposes a novel spiral volumetric modulated arc therapy (SVMAT) technique designed to bridge this gap by synergizing continuous couch movement with dynamic MLC modulation.
Methods:
The SVMAT technique was implemented on a model of ring-gantry linac with dual-layer staggered MLC. Its core is a direct aperture optimization algorithm that discretizes the delivery path into finite projections, concurrently optimizing MLC aperture, monitor unit weight, gantry angle, and couch position. A comprehensive dosimetric and efficiency comparison was conducted against state-of-the-art VMAT and HT plans for three clinically challenging scenarios: hippocampal-sparing whole-brain radiotherapy (HS-WBRT), bilateral breast radiotherapy (BBRT), and craniospinal irradiation (CSI), including a pediatric subgroup.
Results:
SVMAT demonstrated comparable or superior target coverage and conformity index to VMAT and HT across all cases. Its most significant advantage was in organ-at-risk (OAR) sparing. For HS-WBRT, SVMAT significantly reduced the maximum (Dmax) and mean (Dmean) doses to the hippocampus compared to both VMAT and HT (p < 0.05). For BBRT, SVMAT notably reduced the heart Dmean (4.78 ± 0.86 Gy vs. 9.47 ± 3.44 Gy) for VMAT. In CSI, SVMAT reduced the lens Dmax by over 33% and the heart Dmean by 36.1%. Also, the pediatric CSI analysis confirmed these benefits, with SVMAT significantly reducing doses to developing organs. Regarding efficiency, SVMAT's beam on time was significantly shorter than HT's across all plans (reductions of 33.1% to 55.3%) and was comparable to the multi-isocenter VMAT in CSI.
Conclusions:
The SVMAT technique successfully integrates the dynamic delivery of VMAT with the longitudinal integration and single-isocenter capability of HT. By offering enhanced OAR sparing and reduced treatment times, SVMAT represents a significant advancement in radiotherapy, showing immense potential for improving outcomes, especially in vulnerable populations such as pediatric patients.
