Selection of arcs number of volumetric modulated arc therapy after modified mastectomy for breast cancer
Objective To study the effect of the number of arcs per field on the treatment plan of volumetric modulated arc therapy(VMAT)after modified mastectomy for breast cancer.Methods The plans of 15 patients with left breast cancer who received radiotherapy after modified mastectomy were selected.The target areas and organs at risk(OARs)were contoured on localized CT.The prescribed dose was 50 Gy/25 times to the target areas.The single arc(Arc1),double arcs(Arc2)and three arcs(Arc3)plans were designed by changing the number of arcs in a field in Monaco planning system on the same CT image sets.The dosimetry characteristics of target and OARs,monitor unit and the delivery time were compared among the three plans.Results Arc1 plan,Arc2 plan and Arc3 plan for 15 cases of breast cancer all were proved to meet the clinical requirements.Compared with Arc1 plan,the D2％and Dmean of target were lower,the D98％of target,Dmean and V5 of contralateral breast and Dmean of contralateral lung were higher in the Arc2 plan and Arc3 plan(P＜0.05),and the Arc2 plan and Arc3 plan achieved better conformity and homogeneity(P＜0.05).With the increase of arcs number,the monitor unit and the delivery time were increased(P＜0.05).Conclusion VMAT plan has the better target dose distribution with the increase of the number of arcs,while OARs low dose irradiation and treatment time are increased after modified mastectomy for breast cancer.Therefore,it is necessary to comprehensively consider the number of VMAT plan arcs based on clinical conditions.
Breast cancerVolumetric modulated arc therapyMonaco planning system
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