A detailed dosimetric comparative study of IMRT and VMAT in normal brain tissues for nasopharyngeal carcinoma patients treated with radiotherapy

Kainan Shao; Shuang Zheng; Yajuan Wang; Xue Bai; Hongying Luo; Fenglei Du

doi:10.3389/fradi.2023.1190763

A detailed dosimetric comparative study of IMRT and VMAT in normal brain tissues for nasopharyngeal carcinoma patients treated with radiotherapy

Front Radiol. 2023 May 18:3:1190763. doi: 10.3389/fradi.2023.1190763. eCollection 2023.

Authors

Kainan Shao^#¹, Shuang Zheng^#², Yajuan Wang¹, Xue Bai¹, Hongying Luo^{1

3}, Fenglei Du¹

Affiliations

¹ Department of Radiation Physics, Zhejiang Cancer Hospital, Hangzhou, China.
² School of Media and Design, Hangzhou Dianzi University, Hangzhou, China.
³ Faculty of Nuclear Science and Technology, University of South China, Hengyang, China.

^# Contributed equally.

Abstract

Background: Radiotherapy (RT) is the primary treatment for nasopharyngeal carcinoma (NPC). However, it can cause implicit RT-induced injury by irradiating normal brain tissue. To date, there have been no detailed reports on the radiated exact location in the brain, the corresponding radiation dose, and their relationship.

Methods: We analyzed 803 Chinese NPC patients treated with RT and used a CT brain template in a Montreal Neurological Institute (MNI) space to compare the group differences in RT dose distribution for different RT technologies (IMRT or VMAT).

Results: Brain regions that received high doses (>50 Gy) of radiation were mainly located in parts of the temporal and limbic lobes, where radioactive damage often occurs. Brain regions that accepted higher doses with IMRT were mainly located near the anterior region of the nasopharyngeal tumor, while brain regions that accepted higher doses with VMAT were mainly located near the posterior region of the tumor. No significant difference was detected between IMRT and VMAT for T1 stage patients. For T2 stage patients, differences were widely distributed, with VMAT showing a significant dose advantage in protecting the normal brain tissue. For T3 stage patients, VMAT showed an advantage in the superior temporal gyrus and limbic lobe, while IMRT showed an advantage in the posterior cerebellum. For T4 stage patients, VMAT showed a disadvantage in protecting the normal brain tissue. These results indicate that IMRT and VMAT have their own advantages in sparing different organs at risk (OARs) in the brain for different T stages of NPC patients treated with RT.

Conclusion: Our approach for analyzing dosimetric characteristics in a standard MNI space for Chinese NPC patients provides greater convenience in toxicity and dosimetry analysis with superior localization accuracy. Using this method, we found interesting differences from previous reports: VMAT showed a disadvantage in protecting the normal brain tissue for T4 stage NPC patients.

Keywords: CT brain template; cognition; dosimetry; nasopharyngeal carcinoma; radiotherapy.

Grants and funding

This study was supported by the Medical Health Science and Technology Project of Zhejiang Provincial Health Commission (No. 2021PY040) and Zhejiang Provincial Basic Public Welfare Research Project (No. LGF22H160070).