Comparative Analysis of Arc Geometrical Configurations and Jaw Tracking for Peripheral Low-Dose Bath in Whole Breast VMAT
Chanyoung Park, Jun-Bong Shin, Semie Hong, Jeong-Woo LeeIntroduction
Minimizing low-dose radiation spillage to surrounding organs at risk (OARs) is a critical consideration in whole breast irradiation (WBI) using volumetric modulated arc therapy (VMAT). While VMAT improves dose conformity and delivery efficiency, its continuous arc delivery may increase the “low-dose bath” in normal tissues. This study compared the dosimetric impact of arc geometry and jaw tracking under controlled planning conditions to characterize their effects on low-dose exposure.
Methods
In this retrospective dosimetric study, VMAT plans were generated for 30 breast cancer patients (15 left-sided and 15 right-sided). Four arc configurations were evaluated: conventional-arc VMAT (two and four arcs), tangential-arc VMAT (TA-VMAT), and hybrid-arc VMAT (HA-VMAT). Each configuration was planned with and without jaw tracking using identical objectives. Dose–volume histogram (DVH) parameters were analyzed for the planning target volume (PTV) and OARs, including the ipsilateral/contralateral lungs, heart, left anterior descending coronary artery (LAD), liver, and contralateral breast.
Results
All techniques achieved comparable target coverage. Arc configuration substantially affected OAR dose distribution. Compared with conventional-arc VMAT, TA-VMAT reduced contralateral lung and breast exposure by 60–70%, while HA-VMAT yielded intermediate results. Notably, tangential arc restriction increased ipsilateral lung dose, particularly in right-sided cases, and increased LAD dose in left-sided cases. Jaw tracking provided additional dose reductions in selected OAR metrics, although the magnitude and statistical significance of these changes varied across arc configurations.
Conclusions
The findings suggest that peripheral low-dose exposure in whole-breast VMAT is influenced by arc configuration, while jaw tracking may provide additional dose reduction in selected OAR metrics. Considering both beam geometry and delivery-level leakage control may help reduce unnecessary OAR exposure.