The Dosimetric Effect Of The Angle Change After Electron Beam Irradiation For The Patients After Breast Surgery

Objective: The standard manikins model and the MCNP5 Monte Carlo code was used to simulate the female patients’ left breast cancer. To study the dosimetric change of target region and sensitive organs in electron beam irradiation of the rotational angle change after breast surgery.Methods: The standard manikins model was used to simulate the female patients’ left breast cancer, and wa-li-an 23 EX medical electron accelerator was used to irradiate model’ target region at the horizontal position. The energy of electron beamwas 6Me V, the irradiative dosimetry of target was 2 Gy, the thermoluminescence dose meterwas used to measureirradiation dose.(1)The standard manikins model was set on accelerator tableat the horizontal positionand applied 0.5 mm tissue equivalent bolus.The model was irradiate in left breast target region, the dose of chest wall, two lungs and heart was measured, and 0°group was set as control group. The 350°、355°、5°、10° rotational angle change was set as experimental group, they dose of chest wall, two lungs and heart were also measured.(2) The MCNP5 Monte Carlo code was used to simulate the female patients’ left breast cancer. The irradiation was set 350°、355°、0°、5°、10° rotational angle change. The dosimetric effect of chest wall, two lungs and heart was measured and analysed.Results:(1)The simulation results of standard manikins model:(1)After set 350°、355°、0°、5°、10° rotational angle change, the dose of chest wall had no significant change(t=0.323,P>0.05;t=0.248,P>0.05;t=0.562,P>0.05;t=0.312,P>0.05), the dose change of chest wall in two sides at 355° group was higher than the middle parts, but the differences have no significant change(t=1.418, P>0.05).(2)The dose of sensitive organs increased, the dose of the same lung,heart and the contralateral lung in control group was 0.79±0.15 Gy, 0.66±0.15 Gy and 0.21±0.08 Gy, and in 5°rotational angle change group was1.06±0.23 Gy,0.82±0.18 Gy and 0.31±0.11 Gy,the differences have significant change(t=2.42,P<0.05;t=1.52,P>0.05;t=3.14,P<0.05).(2) The simulation results of Monte Carlo:(1) The gap between monte carlo calculation and The 3 d water tank of wa-li-an 23 EX medical electron acceleratorwas less than 3%, the fitting result was good(2)After the set of 350°,355°,0°,5° and 10°rotational angle change, the highest dose of chest wall was 0°control group, the dose of 355 ° group, 350 ° group, 10 ° group, 5 ° group in turn reduced.(3)The irradiation dose of sensitive organs were all increased in rotation angle group. Two lungs and heart near the radiation field, their dose and the dose change were large. the dose of 0° control group, 350° group, 355° group, 10° group, 5° group of the same lung was in turn increased, the dose of 0° control group, 355° group, 350°, 10° group, 5° group of the heart was in turn increased, the dose of the contralateral lung was less affected.Conclusions:(1) The rotational angle change had no significant effect on the irradiation dose of target region, 355 °, 350 °, 0 °, 10 °, 5 °rotational angle change can meet the target dosage requirements;(2) 355 °, 350 °, 5°, 10° rotational angle change degrade the irradiation dose of target organs’ edge, the cold spot caused by radiation angle change could not be ignored;(3) 5 °rotational angle change significantly increased the irradiation dose of the same and contralateral lung, while the rest angle could avoid endangering organs, thus reduced the radiation dose of endangering organs, the irradiation way of avoid 5 °rotational angle change is worth optimizing and learning.