Research On The Correlation Of Breast Structure And Setup Error And The Influence Of Setup Error On The Margin

Radiation therapy,chemotherapy and surgery are the three major methods of cancer treatment.About 70% of cancer patients need to receive radiation therapy.Patients with thoracic tumors will have the problem of setup errors during radiotherapy.Setup errors are divided into systematic errors and random errors,which are inevitable.The current clinical method to reduce the impact of setup errors is to broaden a certain margin on the basis of the clinical target volume to form the planned target volume.The traditional external margin is calculated based on the three-dimensional setup errors of X,Y,and Z.For precision radiotherapy,it is necessary to consider precision and individualization,so how to obtain a more accurate external radiotherapy margin is particularly important for the development of radiotherapy technology.Based on this,this article will systematically study from three aspects:(1)Effect of breast thickness,volume and BMI on radiotherapy setup error of breast cancer.Selectting 118 patients,and compare the CBCT images scanned before the radiotherapy with the positioning CT images,acquired the setup errors of the three directions of X-axis,the Y-axis,the Z-axis.The breast thickness and breast volume were measured via the Ray Station plan system,and BMI was calculated.The experimental results show that the breast volume,thickness and BMI are related to the setup error of X-axis,the relevant sequence is the breast volume(r=0.522)> BMI(r=0.454)>breast thickness(r=0.368).Partial correlation analysis shows that breast volume is the dominant factor among the three influencing factors.(2)Research on the external radiation margin of precision radiotherapy for thoracic tumors based on the setup errors of Helical Tomotherapy.Select the setup errors data of 4308 MVCT of 219 patients with thoracic tumors based on Helical Tomotherapy.Analysis of the frequency,error incidence and the average setup errors data of three chest tumors,all of which reflect the asymmetry of the coaxial anisotropy.The experimental results show that the calculation of the margin from six directions is more accurate.The margin of lung cancer,esophageal cancer and breast cancer in the left,right,head,foot,abdominal and dorsal directions are respectively(4.2,5.1,7.6,7.0,5.4 and 4.0)mm,(3.6,4.1,5.8,6.5,4.1 and 2.8)mm and(5.3,4.5,7.3,6.9,7.7and 3.8)mm.(3)The effect of bolus placement error on radiotherapy dosimetry of breast cancer.Ten patients with left breast cancer after modified radical resection are randomly selected and given 50Gy/25 fractions of radiotherapy.The VMAT radiotherapy plan is designed through Raystation planning system,and all parameters of the original plan are kept unchanged.A total of 120 new plans are obtained by moving bolus 5mm,10 mm and 15 mm in the four directions of head(H),foot(F),right(R)and underarm(O),respectively,to simulate the effect of bolus placement error in actual treatment on the dose distribution in the PTV and the OARs.Choose the V50 of PTV,V30,V40 and Dmean of the heart,V20 and Dmean of the left lung,and V5 of the whole lung etc.The results show that the placement error of bolus have little effect on the dose of PTV and the OARs.Therefore,the placement error within 15 mm in the four directions is allowed during the placement of bolus.