Dosimetric Comparison Of VMAT And IMRT Radiotherapy Combined With Tissue Compensation Membrane In Hypofractionated Radiotherapy For Breast Cancer After Modified Radical Mastectomy

Objective: To analyze and compare the dosimetry difference between conformal tailored tissue compensation membrane and untailored tissue compensation membrane using VMAT and IMRT technology in hypofractionated radiotherapy for breast cancer after modified radical mastectomy,to provide guidance and reference for choosing a more optimized treatment mode of clinical postoperative adjuvant radiotherapy.Methods: From December 2021 to March 2023,20 breast cancer patients(10 patients with left breast cancer and 10 patients with right breast cancer)who received hypofractionated radiotherapy for breast cancer after modified radical mastectomy in Jiangxi Provincial Cancer Hospital were collected.The target volume included the affected chest wall and supraclavicular lymph node drainage area.Three different plans were designed for each patient:(1)VMAT plan A: The chest wall target volume of PTV was expanded 1cm outside the left and right planes,and the skin area was subtracted as the compensation membrane of the conformal trimming virtual tissue,and the VMAT rotational treatment plan was formulated.(2)VMAT plan B: The chest wall target volume was expanded by 7 cm stereoscopically,the lateral boundary was not more than the edge of the plastic pad,and the upper boundary was not more than the clavicular head.After the skin was subtracted,an untrimmed virtual tissue compensation membrane of about 30x30 cm~2 was formed,and the VMAT treatment plan was formulated.(3)IMRT plan C: the tissue compensation membrane was replicated on the basis of VMAT plan A to obtain the same conformal tissue compensation membrane as VMAT plan A,and then the traditional static IMRT plan was formulated.The thickness of the three tissue compensation membrane was 0.5 cm.In this thesis,we refer to the three plans as VMAT plan A,VMAT plan B,and IMRT plan C,respectively.The conformity and homogeneity of dose distribution in the target volume and the dose distribution of organs at risk were compared and evaluated among the three plans.Results:(1)For VMAT plan A,the addition of conformal tissue compensation membrane can improve the dose distribution of the target volume.The conformity index and homogeneity index of the target volume dose are better than those of VMAT plan B and IMRT plan C.(2)For patients with left breast cancer after modified radical mastectomy,the mean dose of heart,V30 Gy,V20Gy,V10 Gy,and V5 Gy of VMAT plan A were better than those of VMAT plan B(P<0.05).Compared with IMRT plan C,the mean dose of heart in VMAT Plan A was significantly reduced(P<0.05).For patients with right breast cancer after modified radical mastectomy,the heart dose in VMAT plan A was similar to that in VMAT plan B and IMRT plan C(P>0.05).(3)For patients with left breast cancer after modified radical mastectomy,the V30 Gy,V20Gy,and V10 Gy of the affected lung in VMAT plan A were better than those in VMAT plan B and IMRT plan C(P<0.05).The mean dose and V5 Gy of the affected lung in VMAT plan A were better than those in IMRT plan C(P<0.05),but similar to those in VMAT plan B(P>0.05).For patients with right breast cancer,there was no significant difference between VMAT plan A and VMAT plan B(P>0.05).The mean dose,V30 Gy,V20Gy,and V10 Gy of the affected lung in VMAT plan A were significantly better than those in IMRT plan C(P<0.05).(4)All three plans could meet the dose limitation requirements of left anterior descending(LAD),right coronary artery(RCA),contralateral lung,contralateral breast and spinal cord.Conclusions: Compared with the IMRT plan and the VMAT plan with untrimmed tissue compensation membrane,VMAT plan with conformal trimming tissue compensation membrane can not only significantly improve target volume dose distribution,target volume dose conformity index and homogeneity index,but also reduce the radiation dose to organs at risk.The correct and reasonable use of conformal trimming tissue compensation membrane for volumetric modulated arc therapy has higher value in the clinical treatment of patients with hypofractionated radiotherapy for breast cancer after modified radical mastectomy.