Should we use RapidArc (VMAT) for breast radiotherapy? A Dosimetric comparison of IMRT versus VMAT optimization

Purpose: The purpose of this study is to compare the dose-volumetric results of intensity modulated
radiation therapy (IMRT) with RapidArc (RA Varian Medical Systems, Palo Alto, CA) for whole breast
irradiation. Methods: 25 patients previously treated for whole left breast (either RapidArc plan or IMRT)
were the subjects of this planning study. Eclipse v 11.0.47 was used to make all retrospective plans using
the same contours, energy, machine and normalization. Prescription dose to the planning target volume
was 5000 Gy in 25 fractions. All plans were normalized such that 100% covered 95% of planning target
volume (PTV). Results: V10, V20 and Dmean Gy of left lung significantly differed between the two plans
(p-value <0.0001, =0.0473 and <0.0001 respectively), but V30 Gy did not (p-value 0.463). V25, D33 and
Dmean Gy of heart significantly differed between the two plans (p-value =0.034, <0.0001 and 0.01
respectively), but V10 Gy did not (p-value 0.058). V5 of both right breast and right lung significantly
differed between the two plans (p-value <0.0007 and =0.0112, respectively). Also Dmean of both right
breast and right lung significantly differed between the two plans (p-value <0.0001 for both). The mean
conformity index did not significantly differ, p-value 0.142. There was a significant difference between the
mean MUs of the two plans as well, p-value <0.0001.