Anatomy-based parameter selection and efficiency-quality balance in radixact helical tomotherapy

OBJECTIVE: To investigate the effects of jaw width, pitch, and modulation factor (MF) on dose distribution quality and delivery efficiency in Radixact helical tomotherapy for targets with different anatomical characteristics.
Approach: Eighty patients were divided into four groups (n=20 each) based on target volume, shape complexity, and organ-at-risk (OAR) geometry: Group A (small volume/high gradient), Group B (medium volume/complex wrapping), Group C (medium volume/simple), and Group D (large volume/long-axis). Jaw width (1.0/2.5/5.0 cm), pitch (0.172-0.430), and MF (1.2-4.2) were optimized using a stepwise control variable approach. A composite efficiency-quality score (EQS) was developed for comprehensive evaluation of treatment plans. MAIN RESULTS: Dynamic jaw mode showed good longitudinal penumbra control, with both 2.5 cm and 5.0 cm settings achieving results comparable to 1.0 cm static mode (P > 0.05). Its impact was most pronounced for Group D, where 5.0 cm mode showed a 43.6% reduction in beam-on time compared to 2.5 cm mode, while maintaining similar plan quality. Pitch values had different impact across the groups. For group B, optimal pitch settings were critical to effectively navigate shape complexity and ensure adequate dose modulation. Furthermore, excessive MF (4.0) reduced the gamma pass rate to 89.2% for Group A, falling below the 90% clinical threshold. SIGNIFICANCE: Radixact physical parameters should be individualized based on specific target anatomy. The proposed EQS method and associated recommendations provide an anatomy-based approach to treatment planning optimization, attempting to balance delivery efficiency and plan quality.