Dosimetric evaluation of lung treatment plans produced by the Prowess Panther system using Monte Carlo simulation

Purpose: This study evaluated the accuracy of lung dose calculation done by the fast photon effective (FPE) and the collapsed cone convolution (CCC) algorithms of the Prowess Panther treatment planning system (TPS) using Monte Carlo (MC) simulation. Materials and methods: A set of treatment plans of test cases including an acrylic phantom, the QUASAR multi-purpose body phantom, and one lung cancer patient, were created the system to assess the accuracy of the FPE and CCC algorithms. The DICOM-RT files of the plans were imported to the EGSnrc-based Monte Carlo simulation for dose calculations. The plans generated by the TPS and Monte Carlo simulation were compared using relative dose error comparison and 3D gamma index. The gamma index, using global methods, was implemented in PTW-VeriSoft with 3%/3 mm, 2%/2 mm criteria. Results: There was a good agreement between Monte Carlo-simulated and TPS-calculated doses for both the QUASAR multipurpose body phantom and one lung cancer patient. However, discrepancies for the FPE algorithm were found to be 10% in the inhomogeneous medium such as the lung. Conclusions: The FPE algorithm may not accurately predict the dose distributions in and near the inhomogeneous structures. Monte Carlo simulation and CCC algorithm are more accurate than the FPE algorithm in calculating the dose in an inhomogeneous medium. The FPE and CCC algorithms must be validated before clinical implementation of the system.