Model And Breast Cancer Cases Dosimetric Study On Volume Modulated Arc Radiotherapy (VMAT)

Objective: To assess the potential dosimetric advantages and drawbacksof volume modulated arc radiotherapy(VMAT) to difform model targets andarc shap targets of breast cancer after modified radical mastectomy comparedto 3D-CRT/sIMRT .Methods:1. Model targets were countered in a uniform density abdome phantom,including a cylinder with 5cm diameter, a ring with 7cm external diameterand 5cm internal diameter, a 90oarc with 2cm thickness. CRT/sIMRT andVMAT plans were designed and the dosimetric parameters based on DoseVolume Histograms were compared.2. 30 female patients with breast cancer underwent modified radicalmastectomy were selected for adjuvant radiotherapy. Conformal tangentialfields, 7-fields sIMRT and VMAT radiotherapy treatment plans weredesigned with encompassing the plan target volume (PTV) of the chest walland anterior supraclavicular area. A dose of 50Gy in 25 fractions wasprescribed. Comparing the targets coverage and Organs at risk (OARs) doseand treatment efficiency of the three types plan.Results:1. 2arc VMAT plan improve ring target conform number(CN) and reducephantom high-dose volume compared to 9f-CRT. As to arc target, 2 short arcVMAT plan have the best target CN and HI, and the lowest phantomhigh-dose volume among 7fields IMRT plan, 1arc VMAT plan, 2arc VMAT plan. 7fIMRT plan have the largest low-dose volume(V10%). All the VMATplan significantly reduce the treatment time than IMRT in all shap of tragets.2. At the same EUD of PTV, 2 arc based VMAT plan improve the targesCN and decrease the volume of normal tissue with high dose irradiation, butwith a bigger volume with low dose irradiation in ring shape targe and arcshape target. As to the breast target, VMAT and sIMRT plans get moreuniform targets dose distribution and higher CN 0.63, 0.67 compared to 0.44of 3-D CRT plans. Two short arcs have better dose uniform compared to onefull arc in VMAT. VMAT reduce ipsilateral lung(Ipsi-L) V20, V30, V40average as 8%, 10%, 11%, respectively. VMAT increase Ipsi-L average V5from 47% to 63%, and increase contralateral lung(Cont-L) V2.5 from 2% to13% compare to CRT. A larger volume of low irradiated dose level of normaltissue which include lung and heart generated in VMAT and sIMRT plans,especially in sIMRT plans. VMAT 152 (107～214) s reduced the treatmenttime significantly, compared with CRT 231(152～434)s and sIMRT485(432～550)s. The plan of sIMRT have the most MU value(757±143)compared with VMAT(450±46) and CRT(489±48).Conclusion: VMAT is a appropriate technology to difform model targetsfor irradiation. The VMAT plans generate more uniform and conformabletargets dose distributing and spare more highe-dose level normal tissuecompared to 3-D CRT and sIMRT. VMAT can improve targets dosedistribution and spare high dose volume of ipsilateral lung and heart.VMATshorter the treatment time, improving the work efficiency and confortingpaientens during treatment.VMAT apply to irradiation breast cancer aftermodified radical surgery is feasibility.