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| Three Dimensional Analysis of the Effects of Two Different Body Surface Labeling Methods on Cervical Vertebra Positioning Errors and Organ Dose at Risk in Patients with Nasopharyngeal Carcinoma Undergoing Intensity-modulated Radiotherapy |
| ZHONG Qing-chu, LIN Chu-yan, HUANG Ying-ping, et al |
| Cancer Center of Sun Yat-sen University/State Key Laboratory of Oncology in South China/Collaborative Innovation Center for Cancer Medicine/Guangdong Provincial Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy,Guangzhou Guangdong 510060 |
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Abstract 【Objective】To undertake three dimensional analysis of the effect of two different body surface labeling methods on cervical vertebra positioning error and organ endangering dose in patients with nasopharyngeal carcinoma undergoing intensity modulated radiotherapy.【Methods】From January 2019 to June 2020, 32 patients who were pathologically diagnosed as nasopharyngeal carcinoma in the Cancer Prevention and Treatment Center of Sun Yat-sen University were selected and divided into two groups according to the time of treatment, with 16 cases in each group. Group B patients fixed the facial mask with a conventional three-point marking method. The Group A added a positioning point between the left and right clavicular heads of patients on the basis of the Group B to guide the positioning of the neck of patients. Each patient underwent cone beam CT (CBCT) scanning once a week, and a total of 6 sets of CBCT images were obtained. Through the registration of CBCT images and positioning CT images, the positioning errors of 6 cervical vertebrae (C1~C6) of the patient in the three-dimensional direction were analyzed.In the ECLIPSE 15.5 planning system, according to the size of positioning error, the bed transfer parameters in the center of the target area were adjusted to simulate the positioning error, the dose distribution was recalculated, and the dose to the cervical spinal cord of the organ at risk was obtained.【Results】There was no significant difference between the two groups in the positioning errors of C1, C2, C3 in the left and right, head foot and front and rear directions (P>0.05), but there was a significant difference between C4, C5, C6 in the left and right, head foot and front and rear directions (P<0.05). Compared with the group B, the group A can reduce 1.4~3.3 mm, 0.7~3.3 mm and 1.5~3.1 mm in the left and right, head and foot, front and rear directions, and the increase of cervical spinal cord uptake is significantly reduced. 【Conclusion】The 4-point marking method can improve the positioning accuracy of cervical vertebra in patients with nasopharyngeal carcinoma and reduce the irradiation of cervical spinal cord.
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Received: 05 May 2022
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2022, Vol. 39 
