| Zhu Zhipeng,Li Guihua,Li Xiangde,et al.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[J].Chinese Journal of Radiological Medicine and Protection,2024,44(11):953-959 |
| 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 |
| Received:March 25, 2024 |
| DOI：10.3760/cma.j.cn112271-20240325-00100 |
| KeyWords:Nasopharyngeal carcinoma Volumetric modulated arc therapy Systematic error of multi-leaf collimator leaf position Dosimetry Complexity |
| FundProject:广西壮族自治区卫健委自筹课题(Z-A20230603,Z-A20230606) |
| Author Name | Affiliation | E-mail | | Zhu Zhipeng | Department of Radiation Oncology, Second Affiliated Hospital of Guangxi Medical University, Nanning 530000, China | | | Li Guihua | Department of Radiation Oncology, Second Affiliated Hospital of Guangxi Medical University, Nanning 530000, China | | | Li Xiangde | Department of Radiation Oncology, Second Affiliated Hospital of Guangxi Medical University, Nanning 530000, China | | | Qin Wen | Department of Radiation Oncology, Frist Affiliated Hospital of Guangxi Medical University, Nanning 530012, China | | | Zheng Lianrong | Department of Radiation Oncology, Second Affiliated Hospital of Guangxi Medical University, Nanning 530000, China | 845150703@qq.com |
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| 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 T1-4N1M0 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 T1 and T2 stage NPC and 71 Gy in 33 fractions for patients with T3 and T4 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 cm3 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 T4 NPC displayed higher sensitivity to the D98% of PGTV than those with stage T1, T2 and T3 NPC (Z = -3.12, -2.86, -2.59, P < 0.05), patients with stage T3 NPC exhibited lower sensitivity to the D0.1 cm3 of optic chiasm than those with stage T1 and T2 NPC (Z = -2.92, -2.72, P < 0.05), and patients with stage T4 NPC manifested lower sensitivity to the D0.1 cm3 of chiasma than those with stage T1 and T2 NPC (Z = -3.51, -3.25, P < 0.05). The relationship between the sensitivity of MU/Gy and PGTV D98% was y=-3.020+0.025x (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 T4 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 T4 stage NPC, and it is recommended that the systematic errors should be less than 0.42 mm. |
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