2056 - 4p Non-Coplanar Stereotactic Body Radiation Therapy: Dosimetric Evaluation of VMAT Configurations for Recurrent Head and Neck Tumors
Presenter(s)
S. Dong1, W. Hu1, J. Wang1, and Z. Zhang2; 1Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, Shanghai, China, 2Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China
Purpose/Objective(s): This study aimed to evaluate the dosimetric benefits and treatment efficiency of different beam configurations in 4p non-coplanar volumetric modulated arc therapy (VMAT) for stereotactic body radiotherapy (SBRT) in recurrent head and neck tumors
Materials/Methods: A retrospective analysis was conducted on 100 patients with recurrent head and neck tumors treated with SBRT. Treatment plans were created using the uRT-linac 506c linear accelerator and uRT-TPS (United Imaging, China) under standardized optimization conditions. Dosimetric assessments were performed across configurations with varying numbers of non-coplanar beams (1–7, figure 1), ensuring consistent treatment couch angles for each scenario. Metrics included 50% dose spillage volume index (R50 = V50/VPTV, where V50 is the total volume receiving 50% or more of the prescription dose, and VPTV is the volume of the PTV) and maximum, minimum, and mean dose for target coverage. The relationship between R50 and tumor volume was analyzed for each configuration. Treatment efficiency was evaluated by comparing the execution time for each plan.
Results: Tumor volumes ranged from 0.67 cm³ to 30.88 cm³, with a median of 5.06 cm³. As shown in figure 2, adding a single non-coplanar beam significantly reduced R50 compared to coplanar VMAT (mean reduction: 0.51±0.12). The lowest R50 value (4.07±1.19, p=0.03) was achieved with three non-coplanar beams, after which further beam increases yielded diminishing returns. R50 was inversely correlated with tumor volume, with the strongest correlation in coplanar VMAT (slope = -5.56). Increasing the number of non-coplanar beams raised the maximum target dose by 6.69%±1.02% while minimally affecting the mean (3.66%±0.50%) and minimum (0.24%±0.16%) doses. Treatment time increased proportionally with beam number, from 159.37 seconds (0 non-coplanar beams) to 437.07 seconds (7 non-coplanar beams).
Conclusion: Beam configuration in 4p non-coplanar SBRT significantly influences dose conformity, with optimal dosimetric performance observed at three non-coplanar beams. However, these benefits must be balanced against increased treatment time and elevated maximum target doses. Clinical decision-making should consider both dosimetric advantages and treatment efficiency to achieve optimal outcomes.