Verification of rebuild-up effect on superficial cardiac lesion of ventricular tachycardia using 3-D printed phantom in volumetric-modulated arc therapy planning.

The aim of the study was to evaluate dose distributions on the superficial cardiac lesion surrounded by low-density lungs. Volumetric modulated arc therapy (VMAT) technique was applied to optimize the dose distribution using the anisotropic analytic algorithm (AAA) and Acuros XB algorithm (AXB) using the 3-D printed cardiac phantom. We used four full and half arcs with 6-MV and 15-MV photons to investigate the rebuild-up effect near the planning target volume (PTV). Depending on the calculation algorithm (AAA vs. AXB) for full arcs plans, V of PTV differed by 27% for 6-MV and 29% for 15-MV, and D for 6-MV and 15-MV shows 24% and 30%, respectively. The maximum doses in the AXB plans on PTV were 5.1% higher than those in AAA plans at 6-MV, and 3.8% higher at 15-MV. In addition, half arcs treatment plans showed a very similar tendency with full arcs plans. Film dosimetry showed significant differences from the planned results in the AAA plans. Particularly, the dose mismatch occurred between the cardiac PTV and the left lung interface. In the case of 6-MV plans calculated by AAA, the maximum dose increased from 4.1 to 7.7% in the PTV. Furthermore, it showed that 50% of the width of dose profiles was reduced by 1.3 cm in the 6-MV plan. Conversely, in the case of the plans using the AXB algorithm, the maximum dose increased by 2.0-5.0%. In contrast to the AAA algorithm, the dose patterns at the interface demonstrated a good agreement with the plans. Dose fluctuation on the interface between superficial cardiac lesions and low-density lungs can lead to an error in the estimation of accurate dose delivery for the case of VT SBRT.