The Dosimetric Study Of IMRT And TOMO Fixed Field Irradiation Simultaneous Integrated Boost For Patients Receiving Breast-conserving Surgery Of Left Breast Cancer With Tumor Bed

Objective:The study compares the dosimetric characteristics of the two radiotherapy techniques,IMRT and TOMO fixed field irradiation(TomoDirect)on the tumor bed after breast-conserving surgery for left breast cancer,in the target area and organs at risk,and provides a reference for clinical selection of radiotherapy techniques.Methods:Twenty-eight patients who were diagnosed at the Radiotherapy Center of the Third Affiliated Hospital of Kunming Medical University from May 2016 to May 2018 and whose tumor beds were marked by silver clips after breast-conserving surgery for left breast cancer were selected.Collect the patient’s clinical data,including the patient’s general condition,age,quadrant location of the lesion,specific pathological type,TNM staging,etc.After delineating the target area and organs at risk in 28 cases according to the unified delineation standard,the IMRT plan and the TD plan were designed for the same patient.Finally,analyze and compare the dosimetry differences between the two plans in target areas and organs at risk,especially the dosimetry differences in cardiac substructures.Results:1.Target area dosimetry:Both IMRT and TD plans can meet the dose requirements of the target area.The D2 and D98 of the two plans PGTV are significantly different(P<0.05).The D2 of IMRT is higher than TD,and D98 is lower than TD;There was no statistically significant difference between the two at D50 P>0.05)。The differences in D98 and D50 of PTV between the two plans were statistically significant(P<0.05),and the D98 and D50 of the IMRT plan were lower than those of the TD plan;there was no statistically significant difference between the two in D2(P>0.05).Comparing the CI and HI of the two plans between PGTV and PTV,the CI of the IMRT plan is higher than that of the TD plan(P<0.05),that is,the fitness of the IMRT plan is better;the HI of the TD plan is lower than the IMRT plan(P<0.05),that is,the uniformity of the TD plan is better than that of the IMRT plan.2.Dosimetry of organs at risk:(1)Left and right lungs:V5,V10,V15,V20,V30,V40 and Dmean in the left lung of the two plans are significantly different(P<0.05).The average values of V5,V10,V15,V20,V30,V40,and Dmean of the left lung in the IMRT plan are lower than those of the TD plan.The Dmean difference in the right lung was statistically significant(P<0.05).The mean Dmean of the right lung of the TD plan was significantly lower than that of the IMRT plan,and there was no difference between the two in terms of V5 and V10(P>0.05).(2)Heart:The two plans have statistically significant differences in cardiac V5,V10,V15,V30,and V40(P<0.05).The V5,V10,and V15 of the heart in the IMRT plan are lower than the TD plan,and V30 and V40 are higher than the TD plan.There is no significant difference between V20 and Dmean(P>0.05).(3)Right breast:V5,V10,and Dmean of the two plans have significant differences in the right breast(P<0.05),and the above values in the TD plan are all lower than the IMRT plan.(4)Spinal cord:There is a significant difference in spinal cord D2 between the two plans(P<0.05),and the spinal cord D2 in the TD plan is lower than the IMRT plan.(5)Heart substructure:left and right atria(LA,RA):the two plans have significant differences on the Dmean of the left and right atria(P<0.05);The Dmean of the left and right atrium of the TD plan is significantly lower than that of the IMRT plan.Left ventricle(LV):The V5,V10,V15,and Dmean of the left ventricle in the IMRT plan were lower than those of the TD plan,while V20,V30,and V40 were higher than those of the TD plan,and the difference was statistically significant(P<0.05).Right ventricle(RV):The V5,V10,V15 and Dmean of the right ventricle in the IMRT plan were lower than the TD plan,while V30 and V40 were higher than the TD plan,and the difference was statistically significant(P<0.05);There is no significant difference between the two plans at V20 of the right ventricle(P>0.05).Left anterior descending branch(LAD):V5,V10,and V15 of LAD in MRT plan are lower than TD plan,but V40 is higher than TD plan,the difference is statistically significant(P<0.05);There is no significant difference between the two at V20,V30 and Dmean(P>0.05).Left circumflex branch(LCX):The Dmean of LCX in the TD plan is lower than the IMRT plan(P<0.05).Right coronary artery(RCA):The Dmean of RCA in the TD plan was lower than that of the IMRT plan(P<0.05).Conclusions:1.In the implementation of radiotherapy for patients undergoing breast-conserving breast cancer on the left side,both IMRT and TomoDirect can achieve good coverage of the target area.IMRT is better than TomoDirect in terms of target area conformity,but in terms of target area uniformity,Inferior to TomoDirect.2.In terms of organs at risk,IMRT has obvious advantages over TomoDirect in terms of protecting the affected lung.IMRT is also more advantageous than TomoDirect in the protection of low-dose areas of the heart,left and right ventricles,and left anterior descending branch,while TomoDirect has more advantages than IMRT in the protection of high-dose areas of the heart,left and right ventricles,and left anterior descending branch.The average dose of TomoDirect in left and right atrium,left circumflex artery and right coronary artery is lower than IMRT.TomoDirect protects the right breast and spinal cord better than IMRT.