Evaluating The Impact Of Respiratory Motion On Risk Organ Dosimetry In Radiotherapy Of Non-small Cell Lung Cancer Based On 4D-CT

Research purposeIn this study,IGTV was generated by GTV which delineated from images of 10 breathing phases of 4D-CT,PTV was generated by external expansion of IGTV,and then designed radiotherapy plan on AIP images.The plan based on AIP images was performed on to 10 breathing phases using deformable registration,and the dose comparison and dosimetric analysis of lung,spinal cord and other organs at risk were carried out.Materials and MethodsThe clinical and imaging data(including 3D-CT and 4D-CT images)of 22 patients with non-small cell lung cancer(NSCLC)which did not undergo surgery from January2018 to October 2018 were collected.All patients were fixed with a unified body position and fixator and then underwent conventional CT and 4D-CT scans.Among them,there were 11 patients whose tumors were completely located in the lung,11 patients whose tumors were partly in contact with the chest wall,10 patients with lung cancer in the upper and middle lobes,and 2 patients with lung cancer in the lower lobes.According to the ICRU 62 report,the images of 22 patients were processed as follows: a senior radiotherapist delineated GTV on 10 breathing phases of 4D-CT,then GTV generated IGTV,and then radiotherapy plan was designed on the AIP images.Deformation on the AIP images were registered on 10 breathing phases.The dose comparison and dosimetric analysis of lung,spinal cord and other organs at risk will provide some reference for the design and evaluation of planning for radiotherapy of non-small cell lung cancer.ResultsDuring a complete respiratory cycle,the lung dose and body dose in the end-inspiratory phase of T0(0%)were the smallest;the lung dose and body dose in the endexpiratory phase of T5(50%)were the largest.With the breathing movement,the change trend of lung volume was opposite to that of lung dose and body dose,and the change range was larger than that of the latter.There were significant differences in lung volume and lung dose and body dose between the intrapulmonary tumors group and the middle lobe tumors group(P < 0.05).There was no significant difference in lung volume and lung,body dose between the marginal tumors group and the upper lobe tumors group(P > 0.05).There was no significant difference between the maximum dose of spinal cord and the maximum dose of body(P > 0.05).ConclusionsBy comparing the dosimetry of different breathing phases of patients,it can be concluded that there were some dosimetric differences between them,which indicates that respiratory exercise has a certain effect on dosage.The current three-dimensional dose calculation does not take into account the time factor,so the time factor should be taken into account in the future dose calculation,so as to make the patient’s dose more accurate,and provide the basis for individualized precise radiotherapy.