Dosimetry of automatic non-coplanar volumetric-modulated arc therapy for nasopharyngeal carcinoma

Abstract

Objective

To evaluate the dosimetric quality of radiotherapy plans for nasopharyngeal carcinoma (NPC) using HyperArc (HA) technology.

Methods

A retrospective analysis was conducted on 20 patients with initially diagnosed NPC who had received TomoTherapy (TOMO) treatment. Treatment plans were redesigned using HA technology on the Eclipse planning system. Dosimetric parameters and verification passing rates were collected to assess the dosimetric quality of target coverage and organ-at-risk (OAR) sparing in both sets of plans. Paired t-tests or Rank-Sum tests were used to compare the dosimetric parameters between the two plans.

Results

For the planning target volumes (PTVs), the target coverage in both plans reached 95%. Compared with the TOMO plans, the HA plans exhibited a steeper dose fall-off for PTV_69.75Gy (P ​< ​0.05). However, the conformity index (CI) of the HA plans (0.75) was slightly lower than that of the TOMO plans (0.81, P ​< ​0.05). The homogeneity index (HI) was better in the TOMO plans, with statistically significant differences for PTV_69.75Gy and PTV_55.80Gy (P ​< ​0.05). Moreover, the HA plans had better sparing, particularly for the optic chiasm, optic nerves, and parotid glands (P ​< ​0.05), while no statistically significant differences were observed for other critical structures such as the brainstem, spinal cord, and temporal lobes (P ​> ​0.05). Additionally, the average beam-on time for the HA plans (252 ​s) was shorter than that of the TOMO plans (326 ​s, P ​< ​0.05). The mean gamma passing rate at 3%/2 ​mm for all plans exceeded 98%.

Conclusions

Radiotherapy plans for NPC based on HA technology exhibit excellent dosimetric quality, providing good target coverage, rapid dose fall-off, and effective protection of adjacent critical organs.