Adjuvant Radiotherapy after Breast Conserving Treatment for Breast Cancer:A Dosimetric Comparison between Volumetric Modulated Arc Therapy and Intensity Modulated Radiotherapy

Background: Radiotherapy is an important treatment of choice for breast cancer patients after breastconservingsurgery, and we compare the feasibility of using dual arc volumetric modulated arc therapy (VMAT2),single arc volumetric modulated arc therapy (VMAT1) and Multi-beam Intensity Modulated Radiotherapy(M-IMRT) on patients after breast-conserving surgery. Materials and
Methods: Thirty patients with breastcancer (half right-sided and half left-sided) treated by conservative lumpectomy and requiring whole breastradiotherapy with tumor bed boost were planned with three different radiotherapy techniques: 1) VMAT1; 2)VMAT2; 3) M-IMRT. The distributions for the planning target volume (PTV) and organs at risk (OARs) werecompared. Dosimetries for all the techniques were compared.
Results: All three techniques satisfied the doseconstraint well. VMAT2 showed no obvious difference in the homogeneity index (HI) and conformity index(CI) of the PTV with respect to M-IMRT and VMAT1. VMAT2 clearly improved the treatment efficiency andcan also decrease the mean dose and V5Gy of the contralateral lung. The mean dose and maximum dose of thespinal cord and contralateral breast were lower for VMAT2 than the other two techniques. The very low dosedistribution (V1Gy) of the contralateral breast also showed great reduction in VMAT2 compared with the othertwo techniques. For the ipsilateral lung of right-sided breast cancer, the mean dose was decreased significantlyin VMAT2 compared with VMAT1 and M-IMRT. The V20Gy and V30Gy of the ipsilateral lung of the leftsidedbreast cancer for VMAT2 showed obvious reduction compared with the other two techniques. The heartstatistics of VMAT2 also decreased considerably compared to VMAT1 and M-IMRT.
Conclusions: Comparedto the other two techniques, the dual arc volumetric modulated arc therapy technique reduced radiation doseexposure to the organs at risk and maintained a reasonable target dose distribution.