Dosimetry Comparison Of IMRT Vs VMAT On Target Area Radiotherapy In Supraclavicular Combined With Thoracic Wall For Left Breast Cancer After Radical Mastectomy

Objective:This study compared the dosimetric differences between IMRT and VMAT radiotherapy techniques in the target areas(supraclavicular combined with thoracic wall)and organs at risk for left breast cancer after radical mastectomy to provide a date basis for the selection of postoperative radiotherapy technology for breast cancer patients,the observation of long-term adverse effects of radiotherapy and to improvement of long-term quality of life of patients.Methods:By selecting 20 cases of breast cancer patients after radical mastectomy of left breast cancer treated in our department from 2016 to 2017.Clinical data of patients were collected,including age,general condition,tumor site(left breast,quadrant),pathological type,disease stage(TNM stage),surgical method(modified radical mastectomy),chemotherapy regimens and treatment course etc.Patients' informed consent was obtained for this study.Two radiotherapy plans(IMRT and VMAT)were designed for each patient.supraclavicular combined with thoracic wall target area were delineated according to the standards of tumor hospital of Chinese academy of medical sciences.The dosimetry characteristics of the target area and OAR of the two kinds of radiotherapy plans were compared and analyzed,especially the dosimetry characteristics in the healthy side of the breast.thyroid,right lung and L-head of humerus.Finally,to explore the relative advantages and disadvantages of the two technologies in the radiotherapy after radical mastectomy of the left breast cancer.Results:1.Target area dosimetry:there were significant differences in Dmean,D2,D50,D9s,CI and HI between the two plans(P<0.05).The Dmean,D50,D95 and Cl values in the VMAT plan were higher than those in the IMRT plan,but the D2 and HI values in the VMAT plan were lower than those in the IMRT plan.V105(%)of PTV in VMAT's plan was also higher than that in IMRT(P<0.05).2.OAR dosimetry:(1)left lung,right lung and all-lung:There were significant differences in Vs(%),V10(%),V20(%),V3(%)and Dmean between the two kinds of plans(P<0.05).The mean values of Vs(%),V10(%),V20(%)and Dmean of the left lung in VMAT's plan were lower than those in IMRT's plan,while the mean values of V5(%),V10(%),V20(%)and Dmean of the right lung in VMAT's plan were significantly higher than those in IMRT's plan,and the mean values of V20(%)?V30(%)of the whole lung in VMAT's plan were lower than those in IMRT's plan.While,the mean values of V5(%),V10(%)and Dmean of the whole lung were higher than those of IMRT.(2)Heart:there are significant differences between the two plans in Vs(%),V10(%),V20(%),V30(%)and V40(%)(P<0.05),and the values in IMRT plan are higher than those in VMAT plan.(3)right breast:in the two plans,V5(%),V10(%),V20(%)and Dmean mean VMAT are higher than IMRT,and the difference is statistically significant(P<0.05).(4)thyroid gland:there was no significant difference between the two plans in left thyroid gland V45(%)and V50(%)(P>0.05),and VMAT's left thyroid gland V45(%)and Dmean were lower than IMRT.The right thyroid V20(%)and Dmean mean VMAT were lower than IMRT.The mean values of VMAT in total thyroid gland V20(%),V30(%),V40(%)and Dmean were lower than those in IMRT,but there was no significant difference in V45(%)and V50(%).(5)L-head humerus:the mean values of VMAT V30(%),V40(%),V50(%)and Dmean were all lower than IMRT.(6)cord:there was no significant difference in the mean D2 of cord between the two plans.Conclusion:The IMRT plan target area of the combined supraclavicular and thoracic wall regions was more uniform than that of VMAT for the left breast cancer after radical mastectomy,but the conformal of VMAT in the target area was better than that of IMRT.VMAT has advantages over IMRT in the protection of the OAR at heart and the right humerus head.VMAT has smaller the high-dose area of the lung than IMRT,but VMAT has significantly larger in the low-dose area of the lung than IMRT.VMAT is also less protective of the right breast than IMRT.The thyroid was irradiated at a higher dose volume in both radiotherapy programs.Overall VMAT and IMRT combined with supraclavicular and chest wall areas after left radical mastectomy have their own advantages and disadvantages in target area and organ at risk dosimetry.