SU‐E‐T‐693: Should We Use RapidArc (VMAT) for Breast Treatments? A Dosimetric Comparison of IMRT Versus VMAT Optimization in Whole Breast Irradiation of Early Stage Breast Cancer

Abstract

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 whole left breast patient's plans (either RapidArc plan or IMRT) previously treated were the subjects of this study. Eclipse v 11.0.47 was used to create the alternative plans for each case using the same CT images, contours, energy, Linac and normalization. The prescription dose to the planning target volume was 50 Gy in 25 fractions. All plans were normalized such that 100% of the dose covered 95% of planning target volume (PTV). Results: V10, V20 and Dmean Gy of left lung differ significantly between the two plans (p‐value <0.0001, =0.0473 and <0.0001 respectively). However, V30 Gy does not (p‐value 0.463). V25, D33 and Dmean Gy of heart differ significantly between the two plans (p‐value =0.034, <0.0001 and 0.01 respectively). However V10 Gy does not (p‐value 0.058). V5 of both right breast and right lung differs significantly between the two plans (p‐value <0.0007 and =0.0112, respectively). Dmean of both right breast and right lung differs significantly between the two plans (p‐value <0.0001 for both). The mean conformity index did not differ significantly, p‐value 0.142. There was a significant difference between the mean MUs of the two plans as well, p‐value <0.0001. Conclusion: Mean doses to left lung, heart, right lung and right breast were significantly different in RapidArc than IMRT plans. IMRT treatment delivery was faster than RapidArc in terms of the total monitor units used (mean of 382 vs 707 respectively). In fact, since it was observed that both plans have the same mean of conformity index, IMRT is not only faster but also safer regarding not irradiating the organs at risk.