Dosimetric Comparison Of Different Position Immobilization Devices In Adjuvant Radiotherapy For Modified Breast Cancer

OBJECTIVE:To study the setup error of adjuvant radiotherapy patients after modified radical mastectomy by using Kv-CBCT on the linear accelerator.The influence of the setup error to dose distribution of PTV and OAR was assessed by simulating the error causing by different position immobilization,in order to evaluate the application of breast board,thermoplastic film and vacuum pad placement in breast cancer radiotherapy.METHODS:From November 2015 to January 2017,32 breast cancer patients afer modified radical mastectomy were enrolled in our study.Including10 cases of breast board group;10 cases of heat thermoplastic film group;12cases of vacuum pad group.The first 5 times of error data of every cases were collected.Changing the IMRT plan's isocenter position according to the error data in the Pinnacle radiotherapy planning system to get a new simulation plan.The setup error data,and the difference between the new simulation plan dose and the original planned dose were compared.RESULTS:1.The three position immobilization devices comparison:the setup error?2.63±1.94?mm vs?2.77±1.95?mm vs?2.04±1.81?mm in the X-axis?left and right?directions,and the difference between the three groups was no significance.Y-axis?superior-inferior??3.82±2.43?mm vs?2.60±1.84?mm vs?2.78±2.50?mm,Z-axis?anterior-posterior??3.72±3.05?mm vs?1.91±1.55?mm vs?1.70±1.43?mm.The setup error of the thermoplastic film group and the vacuum pad group was significantly less than the breast board group?P=0.000?P=0.000?.There was no significant difference between the former two groups.There was no significant difference between the three groups in Dmax.As Dmean?-2.28±3.02?%vs?-0.59±1.13?%vs?-0.93±1.19?%,change in the thermoplastic film group and the vacuum pad group were significantly less than the breast board group?P=0.000?P=0.016?,the no significant difference between the former two groups.D₉₅?-7.55±9.67?%vs?-2.43±3.37?%?-5.89±5.13?%,V_100%?-8.16±11.44?%vs?-2.61±4.91?%vs?-5.73±6.41?%,the rangeability of thermoplastic film group was smaller than that of the breast board group and vacuum pad group,And there was no significant difference between the latter two.V_105%?-5.99±7.24?%vs?-3.03±3.58?%vs?-4.58±3.67?%There was a significant difference between breast board group and thermoplastic film group.3.OAR dosimetric comparison of the three groups on the ipsilateral lung Dmean,Dmax and contralateral breast Dmean,ipsilateral lung V20 volume were all lower than the original plan,and the difference between groups were not statistically significant.The Dmax of spinal cord?15.17±40.64?%vs?-3.58±15.05?%vs?1.57±17.62?%,the breast board group was significantly higher than thermoplastic film and vacuum pad group,And there was no significant difference between the latter two groups.CONCLUSIONS:In the commonly used position immobilization method of radiotherapy for breast cancer,the thermoplastic film and the vacuum pad are smaller than the traditional breast board in direct comparison with the setup error on longitudinal and vertical direction.In further dosimetric analysis,the dose changing of the thermoplastic film in the PTV Change is smaller than vacuum pad.