Dosimetry study of nasopharyngeal carcinoma based on Halcyon accelerator fixed-field intensity-modulated radiation therapy

Objective: Halcyon accelerator applies the flattening filter (FF)-free mode instead of the lead gate and FF treatment mode for traditional C-type accelerators. We aimed at comparing and analyzing the quality and delivery of nasopharyngeal carcinoma (NPC) plans between Halcyon and VitalBeam (VB) accelerators in fixed-field intensity-modulated radiation therapy (IMRT). Methods: The IMRT plans for thirty patients with NPC who had received radiotherapy were optimized using the VB (Plan VB) and Halcyon (Plan H) accelerators. Quality assurance verification was then conducted. The dose coverage of the planning target volume (PTV) and organs at risk (OARs), monitor units (MUs), and delivery time were analyzed for each plan. Results: All PTV and OAR indexes of Plan H and Plan VB met the clinical requirements. In the exposure dose of bilateral optic nerves between Plan H and Plan VB, no difference was found. The maximum dose of the lens, brainstem, spinal cord were 1.13 Gy, 1.36 Gy, 1.35 Gy, 2.82 Gy lower than the plan using VB , and the mean dose of the parotid glands were 3.82 Gy, 5.56 Gy lower than the plan using VB respectively, and an insignificant difference was found in the brainstem (P > 0.05). The MU for Plan H (22.92 +/- 1.58 Gy) was higher than that for Plan VB (19.69 +/- 4.52 Gy), and the difference was significant (P < 0.05). Conclusions: The treatment plans designed by Halcyon can meet clinical requirements with better protection for OARs and show advantages over VB in the dosimetry of NPC IMRT plans.