Dosimetric and delivery-time impacts of Jaw width, Pitch, and modulation factor in Radixact TomoHelical planning: An anatomy-stratified analysis

Abstract

Objective To evaluate the dosimetric and delivery-time effects of Jaw width, Pitch, and modulation factor (MF) in Radixact TomoHelical planning across different anatomical scenarios, and to develop anatomy-stratified practical guidance for parameter selection. Methods Eighty cases were stratified into four anatomical groups according to target length, geometric complexity, and spatial relationship to organs at risk. Using the same patient dataset, prescription, and optimization framework, a single-variable control approach was used to compare Jaw modes, Pitch values, and MF settings. Plan quality and efficiency were evaluated using nCI, HI, dose-spread-related metrics, organ-at-risk dose, LOT, and BoT. Representative cases also underwent longitudinal dose profile analysis. Results Dynamic Jaws generally improved longitudinal dose control and reduced cranial-caudal dose spill compared with static Jaws. Wider Jaws improved efficiency, but their dosimetric trade-off was more pronounced in complex and long-span cases. Increasing Pitch shortened BoT but could increase longitudinal dose fluctuation, particularly in long-span targets. Pitch 0.287 provided a favorable and relatively robust balance in most complex or long-span scenarios, whereas larger Pitch values remained feasible in selected anatomically regular cases when efficiency was prioritized. Increasing MF improved conformity, but the benefit diminished beyond MF 2.5, while BoT continued to increase. Overall, Groups A and C more often benefited from a 5.0 cm dynamic Jaw combined with a larger Pitch and low-to-moderate MF. Groups B and many Group D cases more commonly favored a 2.5 cm dynamic Jaw with Pitch 0.287 and MF 2.5-3.0, although a 5.0 cm dynamic Jaw remained an efficiency-oriented option in selected long-span cases. Conclusion Optimal Radixact TomoHelical parameters depend on target length, geometric complexity, and organ-at-risk distribution. These findings support scenario-dependent parameter adjustment in Radixact TomoHelical planning, with particular attention to longitudinal dose control in long-span or anatomically complex targets.