SU‐E‐T‐485: Validation of Acuros XB Dose Calculations in SBRT Lung Planning with Monte Carlo Methods

Purpose: The Acuros XB (AXB) Advanced Dose algorithm (Varian Medical Systems) represents a dramatic shift in clinical photon dose calculation methodology from pencil‐beam superposition/convolution methods. Early studies evaluating the accuracy of the algorithm in lung have found good agreement with both measurement and Monte Carlo based dose calculations. In this study, a dosimetric validation of Acuros is performed for clinical SBRT lung planning cases using Monte Carlo (MC) calculations as a benchmark. Methods: MC simulations using BEAMnrc/DOSXYZnrc were carried out for 8 AXB calculated 6/10 MV arc plans delivered on a TrueBeamTM STx linac in high‐dose‐rate flattening filter free mode. Clinical planning constraints were applied in each case with plans normalized to achieve 95% PTV coverage. Metrics used in the evaluation include: maximum and minimum GTV/PTV dose, PTV isodose coverage, conformity and dose profile comparisons. To understand the impact of moving toward to AXB calculations in SBRT lung planning, calculations using the Analytical Anisotropic Algorithm (AAA) are presented for each plan. Results: For both 6 and 10MV energies, consistent mean GTV dose and PTV isodose coverage was observed for AXB and MC calculations. GTV mean dose was observed to deviate by