Study Of T-shaped Oral Fixator For Nasopharyngeal Carcinoma And The Prediction Model Of Lung Dosimetry For Thoracic Esophageal Carcinoma In Radiotherapy

Radiotherapy,especially intensity-modulated radiotherapy,is the primary treatment for nasopharyngeal carcinoma.Accurate treatment can guarantee the efficacy.However,accurate treatment is difficult because of the complexity of target and diversity of organs at risk.In the course of radiotherapy,little position change will result in a decrease in the accuracy of the treatment.On the other hand,radiation pneumonia is a common complication in esophageal carcinoma radiotherapy,which limit the target dose and affect the therapeutic effect.We need to pay attention to prevention and reduce radioactive pneumonia.The knowledge of radiotherapy technology and equipment are reviewed at the beginning of the research.This paper introduces the factors which affects the positioning accuracy of nasopharyngeal carcinoma and the factors which relates to the radiation pneumonia after radiotherapy for esophageal carcinoma.The application of self-made T-shaped oral fixator in radiotherapy for nasopharyngeal carcinoma and the prediction model of lung dose in radiotherapy for coplanar IMRT were discussed respectively.(1)The self-made T-shaped oral fixator is used to control rotation errors of neck and reduces setup errors in radiotherapy for nasopharyngeal carcinoma.In radiotherapy,the position fixation is an important guarantee for precision radiotherapy.The targets of nasopharyngeal carcinoma are complex and there are more important organs at risk,and the rotation errors are difficult to control.The self-made T-shaped oral fixator is used in this study.Patients who are not used and used the oral fixator are divided into group A and group B,then the six-dimensional setup errors and the change of dose cover for targets and organs at risk in two groups are compared.The ratio of rotation errors ≤2° is raised from 88.7%,83.5%,80.5%of Group A to 98.4%,95.3%,96.9%of Group B,and the rotation errors are significantly decreased;The mean values of GTVnx-D98%、GTVnd-D98%、CTV1-D95%、CTV1-D95%in group A were 2.20,1.74,1.96 and 1.83 times of those in group B,respectively,the mean values of the relative deviation of the volume dose in the target are significantly reduced.This verifies the self-made T-shaped oral fixator reduces rotation errors and guarantees radiotherapy accuracy for nasopharyngeal carcinoma.(2)A lung volume prediction model of lung dosimetry for esophageal carcinoma of coplanar intensity modulated radiotherapy was established,which combined with the correlation between the target volume and dose,the lung volume and the Expansion-Overlapped Volume Histogram.In radiotherapy for esophageal carcinoma,normal lung tissue is inevitably irradiated,and then radiation pneumonitis is caused.The incidence and severity are closely related to lung dose.How to evaluate the plan for a given target and prescribed dose and predict the lung dose become the focus of attention.In this paper,through a high-quality esophageal carcinoma plan with known curative effect,the geometric relationship characteristics of the target and organs at risk are extracted,and the characteristic relationship is fitted to the model.The results showed that the absolute errors of the predicted values of V5,V10,V20,and V30 were less than 2.3,2.3,1.6,and 0.9%,respectively,and the absolute error of Dmean was less than 31.7cGy.It shows that the model can predict the reasonable range of lung dose for esophageal carcinoma intensity modulation plan based on the given target,prescribed dose,and the spatial position relationship of the target and lung.The model can control the quality of the designed plan,guarantee the plan quality of the intensity-modulated plan used for treatment effectively,thereby preventing radiation pneumonia.