Research On The Dosage And Location Of Tangent Field Radiation For Chest Wall After Operation Of Breast Cancer

OBJECTIVE: 1. To discuss the semifield isocenter tangent radiation for chest wall after operation of breast cancer and define the location of isocenter. 2. Through the establishment of mathematics model of semifield distance and effective treatment depth,we can obtain the effective treatment depth experience formula of semifield isocenter tangent radiation for the chest wall .Materials and Methods: From Aug. 2005 to Dec. 2006, we researched on the 25 patients of our hospital who had received radical operation of breast cancer. 1. We carried out the normal simulation location of semifield isocenter tangent radiation for chest wall after operation of breast cancer. Though 3 dimentional laser system, we determined the central point of the isocenter radiation with the help of simulator. 2. We carried out the CT simulation location through the post-operation breast cancer patients and worked out the radiotherapy treatment plan for chest wall target area,chest wall and inner mammary lymph node drainage area with 3-D TPS. Then we measured related factors and established the model. Through the method of statistics, we studied the relations among chest wall tangent field radiation, semifield distance inside and outside tangent field and effective treatment depth. Results: After the 3-D laser semifield isocenter location , the SSD from the inside and outside of tangent field was almost equal, which showed that the origin was located in the middle point of radiation axis. There were 25 patients who had received 3D laser light location, the average deviation value between the origin and the middle point of axis was 0.54cm, standard deviation was 0.19cm. Meanwhile after we carried out CT simulation location according to 3-D laser conditions, we found that the EPID verification image was less than +-3mm .2. The experience formula of tangent semifield isocenter in chest wall radiotherapy was : Y=0.7X-1.9(X value range: 7.9cm-12.1cm). related factor(r)=0.7738, hypothesis test t=5.3254, p=0.0000. So we thought that there was a linear relation between the independent variable X and attributive variable Y. The effective treatment depth experience formula of semifield isocenter tangent radiation for chest wall and inner mammary lymph drainage target area was:Y=0.5X-0.8(X value range :9.3cm-13.4cm), related factor(r)=0.6384, hypothesis test t=3.615, p=0.0018, so we thought that there was a linear relation between the independent variable X and attributive variable Y. 3. The average entrance dosage and standard deviation we had obtained from the two reference points were respectively: chest wall target areas 114.7mu, 6.0915mu, 1.2183mu; 113.68mu, 7.2728mu, 1.4546mu. T test showed t=0.3994, p=0.6914. Chest wall and inner mammary lymph drainage target area were: 112.36mu,5.0652mu;111.68mu,6.8418mu, T test showed t=0.3994,p=0.6914. We thought that the average values of the two groups was almost equal. Conclusion: We carry out the radiotherapy location of tangential field for chest wall after operation of breast cancer through 3-D laser method . In this way we can locate the origin at the middle point of field distance quickly and accurately. Meanwhile 2. When we work out the normal modulation location of semifield isocenter radiation and measure the dosage, dosage needs to be corrected for a part of lung tissue in the field, semifield or a quarter of the field (irregular radiation field) because of irregular and sinuous chest wall. The accurate results can not be obtained by hand computation. We can compute the effective treatment depth through our experience formula. So we can obtain the accurate entrance dose. 3. There is no statistical or clinic significance in the difference of entrance dose when we carry out breast cancer tangent field radiation for the chest wall with the two different doses.