Error Analysis Of Contrast CT Scan On Contouring Of Gross Tumor Volume In Three Dimensional Conformal Radiotherapy Of Lung Cancer

Objectives:To explore the methods of improving the accuracy and consistency of delineating gross tumor volume(GTV) by the contrast CT scan,and to analyze the error of delineating GTV and find up a method to amend it.Methods:We selected 15 cases of lung cancer patients,which were confirmed by pathological diagnosis,including 5 cases of peripheral lung cancer and 10 cases of central lung cancer.Seven of these 15 cases have hilum of lung invasion.Firstly,non-contrast scan was performed in all 15 cases,and then subjected to contrast-enhanced scan.Axial cuts were usually taken from the apex to the base of lung,with a field of view(FOV) 480mm and a matrix size of 512×512.These images were transferred to the radiation therapy treatment planning workstation eighteen times.The gross tumor volume(GTV) was delineated by adjusting the window width and window level of the images. The target volume used for planning(PTV) includes the gross tumor volume (GTV),involved nodes,treatment setup error and motion of the tumor due to breathing.The treatment plans were designed by three radiotherapic physicians independently,who have different qualifications and experiences. We measured the volume of GTV and V90,and calculated the conformal index and mean dose of risk organs with non-contrast and contrast-enhanced.We calculated CV of all the above mentioned indicators.Results:These were no significant difference between non-contrast and contrast-enhanced image in the respects such as the volume of GTV,the volume of V90 and the conformal index(P＞0.05).But there were significant differences between CV of GTV of non-contrast and contrast-enhanced (P＜0.01).The impact of window width and level is not significant(P＞0.05), when the gross tumor volume was delineated.The mean dose of risk organ have significant differences between non-contrast and contrast-enhanced (P＜0.05).There were 2%dose increase between contrast-enhanced image and non-contrast image.Conclusions:1.Contrast-enhanced scan can improve the accuracy and consistency of delineating GTV,when the tumor invaded hilum of lung.2.When we make radiotherapy plan by conventional fraction,the error for contrast-enhanced scan is not significant,however,this could not be neglected in non-conventional fraction.3.The impact of window width and level has no significant difference between non-contrast and contrast-enhanced.Impact of subjective factors can be decreased at 1000W and -750L.