Comparison of dosimetric impacts of the systematic errors of a multi-leaf collimator on volumetric modulated arc therapy plans for different T stages of nasopharyngeal carcinoma
10.3760/cma.j.cn112271-20240325-00100
- VernacularTitle:多叶准直器位置系统误差对不同T分期鼻咽癌容积旋转调强放疗计划的剂量影响研究
- Author:
Zhipeng ZHU
1
;
Guihua LI
;
Xiangde LI
;
Wen QIN
;
Lianrong ZHENG
Author Information
1. 广西医科大学第二附属医院放疗科，南宁 530000
- Keywords:
Nasopharyngeal carcinoma;
Volumetric modulated arc therapy;
Systematic error of multi-leaf collimator leaf position;
Dosimetry;
Complexity
- From:
Chinese Journal of Radiological Medicine and Protection
2024;44(11):953-959
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To investigate the differences in dosimetric impacts of the systematic errors induced by the leaf positions of a multi-leaf collimator (MLC) on the volumetric modulated arc therapy (VMAT) for patients with different T stages of nasopharyngeal carcinoma (NPC).Methods:A total of 44 patients with T 1-4N 1M 0 NPC were selected to design the VMAT plans using the Pinnacle planning system as the initial plans. The prescribed doses to the primary gross tumor volume (PGTV) were 68-70 Gy in 33 fractions for patients with T 1 and T 2 stage NPC and 71 Gy in 33 fractions for patients with T 3 and T 4 stage NPC. The prescribed doses to other target volumes were identical. In the initial plan files, a systematic error ranging from ±0.2 to ±1 mm was introduced to the position of each MLC leaf, leading to an increase or decrease in the subfield area. Then, potential error plans at the positions of MLC leaves during VMAT treatment were simulated. Dose evaluation indices involved target volumes and organs at risk (OARs). The indices related to target volumes consisted of the D98% of PGTV and PGTVnd, while those concerning OARs included the D0.1 cm 3 of the brainstem, spinal cord, and optic chiasm. Results:After the systematic errors induced by the positions of MLC leaves were introduced, the sensitivity range of each dose index range was (3.87%-9.87%)/mm ( R2 = 0.932-0.998, P < 0.01). Specifically, patients with stage T 4 NPC displayed higher sensitivity to the D98% of PGTV than those with stage T 1, T 2 and T 3 NPC ( Z = -3.12, -2.86, -2.59, P < 0.05), patients with stage T 3 NPC exhibited lower sensitivity to the D0.1 cm 3 of optic chiasm than those with stage T 1 and T 2 NPC ( Z = -2.92, -2.72, P < 0.05), and patients with stage T 4 NPC manifested lower sensitivity to the D0.1 cm 3 of chiasma than those with stage T 1 and T 2 NPC ( Z = -3.51, -3.25, P < 0.05). The relationship between the sensitivity of MU/Gy and PGTV D98% was y=-3.020+ 0.025 x ( r = 0.80, P < 0.05). Conclusion:The MU/Gy in the plans increased with the T stage of NPC, and the D98% of PGTV was more significantly affected by the systematic errors induced by the positions of MLC leaves. After the systematic errors induced by the positions of MLC leaves were introduced into the VMAT plans, doses to patients with T 4 stage NPC changed more significantly than those to patients with other T stages of NPC. Therefore, stricter quality control of leaf positions is required for patients with T 4 stage NPC, and it is recommended that the systematic errors should be less than 0.42 mm.
