Dosimetric comparison between biaxially rotational dynamic radiation therapy and volumetric modulated arc therapy for locally advanced non-small cell lung cancer.

Background: Radiotherapy device (OXRAY) using an O-ring-type linear accelerator system was developed in Japan. In this study, we aimed to compare dose distributions using biaxially rotational dynamic radiation therapy (BROAD-RT) with the OXRAY system and conventional coplanar volumetric modulated arc therapy (VMAT) in patients with locally advanced non-small cell lung cancer (LA-NSCLC). Methods: Ten patients with LA-NSCLC who received radiotherapy (60 Gy in 30 fractions) at the National Cancer Center Hospital East were selected for this study. Dose distributions in the planning target volume (PTV), lungs, heart, left anterior descending coronary artery region (LADR), and oesophagus were compared using two novel virtual plans (BROAD-RT and VMAT). Both plans were analysed using paired t-tests. Results: The mean [standard deviation (SD)] of Lungs-V20 (%) and Lungs-V5 (%) values were 21.64 (5.15) and 54.67 (9.95) for BROAD-RT and 26.76 (5.80) and 59.97 (12.40) for VMAT, respectively. Lungs-V20 was significantly improved with BROAD-RT compared with that with VMAT (P=0.001), while Lungs-V5 was not (P=0.10). The dose-volume parameters for the heart (Heart-V40), LADR (LADR-V15), and oesophagus (Oesophagus-V50 and Oesophagus-V60) were also significantly improved in BROAD-RT compared with those in VMAT (P=0.009, 0.006, 0.006, and 0.005, respectively) without worsening the PTV dose coverage. However, the mean (SD) of Lungs-V1 (%) value, which indicates the extent of very low-dose distribution, was 97.38 (3.98) for BROAD-RT and 90.84 (10.00) for VMAT. Lungs-V1 was significantly worse with BROAD-RT compared with that with VMAT (P=0.01). Conclusions: BROAD-RT improved key metrics of dose-volume parameters of the lungs, heart, LADR, and oesophagus in patients with LA-NSCLC. However, it resulted in an increased volume of lung tissue irradiated with very low doses, such as in Lungs-V1.