Biaxially rotational noncoplanar radiotherapy vs. coplanar radiotherapy: A planning study for non-small-cell lung cancer.

The objective of this study was to evaluate the dosimetric characteristics and clinical utility of radiotherapy plans using the Dynamic Swing Arc (DSA) technique on the OXRAY (Hitachi Ltd., Tokyo, Japan) system for stage III non-small-cell lung cancer (NSCLC). This study involved a retrospective analysis of 26 patients with stage III NSCLC treated with non-stereotactic volumetric modulated arc therapy (VMAT). We generated DSA plans and conventional coplanar VMAT plans with identical optimization parameters. After contouring targets and organs at risk using three separate computed tomography images acquired under free breathing, inhalation, and exhalation conditions, the dose-volume parameters, including percent volume receiving ≥20 Gy (V20Gy), V5Gy, and mean lung dose for normal lungs, as well as spinal cord, heart, and esophagus doses, were evaluated. The parameters of total monitor units (MUs) and beam-on time (BoT) were also compared. Statistical significance was assessed using the Wilcoxon signed-rank test. Compared with conventional coplanar VMAT, the DSA plans significantly reduced normal lungs doses, with median V20Gy reducing from 19.18% to 16.46% (p < 0.001). DSA plans also reduced other lung dose metrics, including V5Gy and mean lung dose, while maintaining target coverage and homogeneity. A reduction in the median spinal cord (D0.03cc) of approximately 4 Gy in the DSA plan (p < 0.05), indicated greater sparing compared with other organs at risk. Total MU and BoT were higher in DSA plans (734.90 vs. 634.92 MU, respectively; 158.0 vs. 124.5 s, respectively; p < 0.001). However, the increase in BoT of several tens of seconds is small relative to the overall treatment time, including patient setup (approximately 10-15 min), and can be considered clinically acceptable. DSA plans on the OXRAY system for stage III NSCLC maintained target dose coverage and enabled significant sparing of normal lung tissue, including V20Gy. Despite modest increases in MU and BoT, clinical efficiency and accuracy were minimally affected. These results indicate that DSA may be a clinically valuable option for radiotherapy in stage III NSCLC with improved normal tissue protection.