Plan Comparison of Left Breast Postmastectomy Radiotherapy: Halcyon IMRT and VMAT Plan vs. Truebeam Fixed-Jaws Plan

Abstract

The purpose of this work is to provide a Varian Halcyon planning solution for left breast postmastectomy radiotherapy by comparing the plan quality of Varian Truebeam plan with Halcyon plan. Ten patients who previously received left breast postmastectomy intensity-modulated radiotherapy (IMRT) on Truebeam were retrospectively selected and replanned using Halcyon. The planning target volume (PTV) included chest wall and supraclavicular region, and the prescribed dose was 50 Gy in 25 fractions (2 Gy/F). In addition to the original Truebeam fixed-jaws IMRT (IMRT_T), a Halcyon IMRT (IMRT_H) plan and a Halcyon volumetric-modulated arc therapy (VMAT_H) plan were designed for each patient. The conformity index (CI) and homogeneity index (HI) of the PTVs, and the dose of organs at risk were calculated and compared. Statistical significance was performed using the LSD-t test or Wilcoxon signed-rank test with a significance level of 0.05. The V20 and V30 of ipsilateral lung, the V20, V30 and Dmean of heart, and CI of target area in IMRT_H plan were significantly lower than those in IMRT_T plan (P<0.05). No significant difference was found in the V5, V10 and Dmean of ipsilateral lung, the V5 and Dmean of contralateral lung, the V5 and Dmean of contralateral breast, HI of PTV (P>0.05), but the Dmean of left humeral head in IMRT_H plan was significantly higher than that of IMRT_T plan (P<0.05). All the metrics mentioned above showed higher level in VMAT_H plan than the IMRT_T plan and IMRT_H plan (P<0.05), except for HI (P>0.05) and Dmean of left humeral head (P>0.05 when compared to IMRT_H plan). The IMRT_H plan acts better in OAR sparing and PTV conformity than the IMRT_T plan, while the VMAT-H plan can only parallel the other two techniques in HI. The IMRT_H plan is promising in treating left breast postmastectomy patients with dosimetric improvements.