| Objective To simulate the set-up errors,and to explore the dosimetry effects of set-up errors to lung and heart in radiation therapy for breast cancer patients.Methods Moving the centre of beam, simulate the linear set-up error of three axis,the set-up errors value were 2mm、3mm、5mm、7mm、9mm. When we move the centre of beam to direction of tumor,recalculate the dose of lung and heart,if the value was 2mm, the new plan named X2. When we move the centre of beam to direction of normal breast,recalculate the dose of lung and heart,if the value was 2mm, the new plan named X-2.when simulate others value,the new plans named X3、X-3、X5、X-5……When we move the centre of beam to direction of head,recalculate the dose of lung and heart,if the value was 2mm, the new plan named Y2. When we move the centre of beam to direction of foot,recalculate the dose of lung and heart,if the value was 2mm, the new plan named Y2. when simulate others value,the new plans named Y3、Y-3、Y5、 Y-5……When we move the centre of beam to direction of chest,recalculate the dose of lung and heart,if the value was 2mm, the new plan named Z2. When we move the centre of beam to direction of back,recalculate the dose of lung and heart,if the value was 2mm, the new plan named Z2. when simulate others value,the new plans named Z3、Z-3、 Z5、 Z-5……Results For the whole lung V20,the value of Y-5、Y-7、Y-9、Z5、Z7、Z9 was increased;For the lung V20 of affected side, the value of X-5、X-7、X-9、Y-5、 Y-7、Y-9、Z5、Z7、Z9 was increased,the value of new plan was exceed the limited dose;The MLD of affected side was increased by 65%、11.55%、 17.15%、7.5%、12.5%、17.8%、23.1%、8.0%、11.48%、10.7%。For the heart V30, the value of X-3、X-5、X-7、X-9、Y-5、Y-7. Y-9 was increased; the value of X-7、X-9、Y-9 was exceed the limited dose; For the heart V40, the value of Y-7、Y-9 was increased; The MHD of X-5、X-7、X-9、Y-5、Y-7、Y-9 was increased by 51cGy.79cGy.107cGy.85cGy.125cGy.171cGy。Conclusion ① If the set-up error in trouble side’s derection. posterior derection. inferior derection were more than 5mm, the lung V20 of trouble side would exceed the limited dose.If the set-up error in trouble side’s derection. anterior derection more than 3mm or inferior derection more than 5mm,the MLD of trouble side would significant increase.②If the set-up error in trouble side’s derection. anterior derection more than 5mm,the MHD of trouble side would significant increase. ③ The set-up error more than 5mm should be corrected in trouble side’s derection. anterior derection. inferior derection.For the patients at high risk of developing RILI,the threshold value of correction was 3mm in trouble side’s derection and anterior derection.Objective To analyze radiotherapy setup errors of breast cancer suffers when they are fixed at the head-shoulder-truncus vacuum bags and using kilovoltage cone beam computed tomography(CBCT), and providing foundation for the Clinical Target Volume (CTV) enlarging to the Planing Target Volume(PTV).Methods Breast cancer radiotherapy setup errors were analyzed using CBCT. The patients were immobilized by the head-shoulder-truncus vacuum bags. We collected the data of the linear and rotational setup errors. Three capital letters(X,Y&Z) take the place of three axis line such as:left-right, cranio-caudal and superior-inferior, and Xr,Yr and Zr represent rotational errors that around the X,Y&Z axises. The statistics were used for estimate fit or unfit of the fixed method of head-shoulder-truncus vacuum bags. According to the formula Mptv=2.5Σ+0.7δ, the Mptv was calculated.Results We analyzed total 265 CBCT scans from 53 patients. For the linear setup errors, the systematic errors of group were X=2.5mm, Y=2.3mm and Z=1.9mm,the random errors of group were X=2.5mm Y=2.2mm and Z=2.2mm. In accordance with formula,the Mptv were recommended as X=8.0mm,Y=7.3mm and Z=6.3mm; about the rotational errors, the systematic errors of group were Xr=1.03,Yr=1.l and Zr=0.95 degrees, and the random errors of group were Xr=0.79, Yr=1.15 and Zr=0.72 degrees.Conclusion The head-shoulder-truncus vacuum bag has good setup accuracy. The data of setup errors which measured by CBCT provide references for CTV enlarge to PTV, and increase the precision in breast cancer radiotherapy. |
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