Dosimetric Study Of Simultaneous Addition Of VMAT And TOMO To Tumor Bed After Left Breast Conserving Surgery

Objective:To study and analyze the dosimetric difference of target area and organ-at-risk between two radiotherapy techniques,VMAT and TOMO,simultaneously increasing the tumor bed after breast-conserving surgery for left breast cancer,and provide dosimetry reference basis for clinical selection of treatment plan.Methods:Thirty cases of left breast cancer breast-conserving surgery patients（with silver clip on the tumor bed）who were admitted to our department from May 2016 to May 2019 were selected,all of whom were female.Collect clinical case data of patients,mainly including age,general condition,tumor location（left breast,quadrant）and size,surgical method（breast-conserving surgery）,pathological type,pathological stage（TNM staging）,etc.The target area was delineated strictly in accordance with uniform standards for all enrolled patients,and the VMAT plan and TOMO plan were designed for each patient.Analyze and compare the differences in the dosimetry of the target areas and organs at risk of the two plans,especially the differences in the low-dose areas of cardiac substructure and organs at risk.Results:1.Target dosimetry:（1）PTV:there were significant differences in D₉8,D50 and HI between the two plans（P<0.05）,and the hi value of VMAT plan was higher than that of TOMO plan;there was no significant difference in D₂ and CI between the two plans（P>0.05）.（2）PGTV:there were significant differences in D₂,D₉8 and hi between the two plans（P<0.05）,and the hi value of VMAT plan was higher than that of TOMO plan;there were no significant differences in D50 and CI（P>0.05）.2.Dosimetry of organs at risk:（1）left and right lung:there were significant differences in V₅,V₁0,V₁5,V₂0,V₄0,D_mean of left lung and V₅,V₁0,D_mean of right lung between the two plans（P<0.05）.In VMAT plan,V₄0 of left lung was higher than those of TOMO plan,and other indexes were lower than that of TOMO plan;there was no significant difference in V₃0 of left lung between the two plans（P>0.05）.（2）heart:there were significant differences in heart V₅,V₁0,V₃0,V₄0 and D_mean between the two plans（P<0.05）,among which VMAT plan was lower than TOMO plan in V₅,V₁0 and D_mean,while V₃0 and V₄0 were higher than TOMO plan;there was no significant difference in V₁5 and V₂0 between the two plans（P>0.05）.（3）cardiac substructure:①Left Atrium（LA）:there was significant difference between the two plans in D_mean（P<0.05）,VMAT plan was significantly lower than TOMO plan.②Left Ventricle（LV）:there were significant differences in V₅,V₁0,V₃0 and V₄0 between the two plans（P<0.05）.VMAT plan was lower than TOMO plan in V₅ and V₁0,and higher than TOMO plan in V₃0 and V₄0;there was no significant difference in V₁5,V₂0 and D_mean between the two plans（P>0.05）.③Right Atrium（RA）:there was significant difference between the two plans in D_mean（P<0.05）,VMAT plan was significantly lower than TOMO plan.④ Right Ventricle（RV）:there were significant differences in V₅,V₁0,V₁5 and D_mean between the two plans（P<0.05）,while VMAT plan was lower than TOMO plan;there was no significant difference in V₂0,V₃0 and V₄0 between the two plans（P>0.05）.⑤ Left Anterior Descending Coronary Artery（LAD）:there were significant differences in V₅,V₁0 and V₁5 between the two plans（P<0.05）,VMAT plan was lower than TOMO plan;there was no significant difference in V₂0,V₃0,V₄0 and D_mean between the two plans（P>0.05）.⑥Left Circumflex ramus（LCX）:there was significant difference in D_mean between the two plans（P<0.05）.VMAT plan was significantly lower than TOMO plan.⑦Right Coronary Artery（RCA）:D_mean of the two plans was statistically significant（P<0.05）,VMAT plan was significantly lower than TOMO plan.（4）Right Breast:there were statistically significant differences in V₅,V₁0 and D_mean between the two plans（P<0.05）,and VMAT plan was lower than TOMO plan（P<0.05）,and（5）Spinal Cord:there were statistically significant differences in D₂ between the two plans（P<0.05）,and VMAT plan D₂ was significantly lower than TOMO plan（P<0.05）.Conclusion（s）:1.The target dose distribution of VMAT and TOMO can meet the requirement of prescription dose.2.The homogeneity index of TOMO is better than that of VMAT,but there is no statistical difference between the two in conformal index.TOMO is slightly better than VMAT in the target area distribution of postoperative radiotherapy for left breast cancer.3.TOMO reduces the high-dose exposure volume of the lung,heart and its substructures,while increasing its low-dose exposure volume.The low-dose area of VMAT is relatively better.4.VMAT is superior to TOMO in the protection of contralateral breast.