Dosimetry Comparison Of The Plan Design And Heart Substructure In Different Radiotherapy Ways After Breast Conserving Therapy Of The Left Breast Cancer

Background and purpose: Common radiotherapy technologies for the whole breast irradiation after the breast conserving therapy of the breast cancer include conventional tangent wedge field irradiation(TW),three-dimension conformal radiotherapy(3D-CRT)and intensity modulated radiotherapy(IMRT),etc and the uneven dose distribution in the breast is caused for the conventional tangent field radiotherapy due to irregular shape of the thorax and the breast,serious complication in the short and long terms is also caused because the organs at risk such as heart and lung,etc are also subject to irradiation of large dosage,and though the irradiation dosage of the organs at risk is reduced by the three-dimension conformal radiotherapy compared with the tangent field radiotherapy,there is no obvious difference for the short-term effect;the conformal property of the target volume and the evenness of the dosage are increased and the radioactive harm to organs such as heart and lung,etc is reduced by the reverse intensity modulated radiotherapy compared with the three-dimension conformal radiotherapy.The purpose of the paper is to compare the two intensity modulated radiotherapy ways,namely the dosimetry difference between “field in field” intensity modulated radiation therapy(FIF-IMRT)and 6 field-intensity modulated radiation therapy(6F-IMRT),and count the differences in aspects of dose distribution and volume of the target volume,organs at risk and the substructure of heart,etc for the two plans so as to pinpoint the clinical application value of the two methods and seek the optimal radiotherapy scheme for the radiotherapy treatment of the breast cancer after the breast conserving therapy.Methods: twenty patients whose pathological stages were T1-2,N0 and M0,with the left breast cancer after the breast conserving therapy,treated in the hospital were selected and their breast volume was203cm3-580cm3.Positioning scanning was conducted with the GE16 16 rows helical CT machine scanning layer was 2.5mm thick;then CT scan image was obtained and then transmitted to the American Varian Eclipse 11 radiotherapy plan system through the network.The outlining and modification of the target volume were respectively conducted by two doctors in charge and professors in the department of the radiotherapy to determine the clinical target volume(CTV),plan target volume(PTV)and the organs at risk(OARs)and then the two treatment plans of FIF-IMRT and 6F-IMRT were respectively formulated by the same physicist;all the prescribed dose was set at 50 Gy for conventional segmented irradiation(2Gy/time,5times/week).The two plans were normalized with the 50 Gy absorbed dose of 95%PTV volume.Self-control study was conducted through the dose volume histogram(DVH)to compare the dose evenness index(HI),conformity index(CI)of the target volume,irradiation dose and volume of the organs at risk for the two treatment plans.Result: Target dose distribution: 95% of target volume of two groups all can reach the requirement of prescribed dose,Dmax and volume V105 and V98 in FIF-IMRT were lower than that in IMRT.CI in IMRT was obviously higher than that in FIF-IMRT,but there's no obvious difference was seen for HI in two groups.OARs dose distribution: for Dmax and Dmean of the right side of lung in FIF-IMRT were lower than that in IMRT.For the left side of lung Dmean and low-dose irradiated volume in FIF-IMRT were obviously lower than that in IMRT,no obvious difference was seen for V40 and Dmax in two groups.Heart and its substructure dose distribution: Dmean?V5and V10 of heart in FIF-IMRT were lower than that in IMRT,and no obvious difference was seen for V20 and V40 in two groups.Dmean?V5 and V10 of left ventricle(LV)in FIF-IMRT were lower than that in IMRT,no obvious difference was seen for V15 and V20 in two groups.Dmean?V5 and V10 of left anterior descending(LAD)in Group FIF-IMRT were lower than that in Group IMRT,no obvious difference was seen for V20 and V30 in two groups.Dmean and V5 of heart anterior wall tissue(AMT)in FIF-IMRT were lower than that in IMRT,no obvious difference was see for V10 and V20 in two groups.For right side of mammary glands,Dmax ?Dmin and Dmean in FIF-IMRT were lower than that in IMRT.Conclusion:1.The target dose distribution of two radiation therapies FIF-IMRT and IMRT all can reach the requirement of prescription.2.The Conformity index of IMRT was better than that of FIF-IMRT.3.FIF-IMRT can decrease the low-dose irradiated volume of OARs that can bring benefits to a patient,which was a cost-effective radiation therapy.