Secondary monitor unit calculations for VMAT using parallelized Monte Carlo simulations

Abstract

We have developed a fast and accurate in‐house Monte Carlo (MC) secondary monitor unit (MU) check method, based on the EGSnrc system, for independent verification of volumetric modulated arc therapy (VMAT) treatment planning system dose calculations, in accordance with TG‐114 recommendations. For a VMAT treatment plan created for a Varian Trilogy linac, DICOM information was exported from Eclipse. An open‐source platform was used to generate input files for dose calculations using the EGSnrc framework. The full VMAT plan simulation employed 107 histories, and was parallelized to run on a computer cluster. The resulting 3ddose matrices were converted to the DICOM format using CERR and imported into Eclipse. The method was evaluated using 35 clinical VMAT plans of various treatment sites. For each plan, the doses calculated with the MC approach at four three‐dimensional reference points were compared to the corresponding Eclipse calculations, as well as calculations performed using the clinical software package, MUCheck. Each MC arc simulation of 107 particles required 13–25 min of total time, including processing and calculation. The average discrepancies in calculated dose values between the MC method and Eclipse were 2.03% (compared to 3.43% for MUCheck) for prostate cases, 2.45% (3.22% for MUCheck) for head and neck cases, 1.7% (5.51% for MUCheck) for brain cases, and 2.84% (5.64% for MUCheck) for miscellaneous cases. Of 276 comparisons, 201 showed greater agreement between the treatment planning system and MC vs MUCheck. The largest discrepancies between MC and MUCheck were found in regions of high dose gradients and heterogeneous densities. By parallelizing the calculations, point‐dose accuracies of 2‐7%, sufficient for clinical secondary checks, can be achieved in a reasonable amount of time. As computer clusters and/or cloud computing become more widespread, this method will be useful in most clinical setups.

Enhanced optimization of volumetric modulated arc therapy plans using Monte Carlo generated beamlets

“…The EO process is based on doses calculated for VMAT plans using MC algorithms. In most cases, the plan dose values agree well with those calculated by the TPS 18 . The EO also requires the calculation of DVH’s for the VMAT plans, which also generally agree with the TPS DVHs.…”

“…In most cases, the plan dose values agree well with those calculated by the TPS. 18 The EO also requires the calculation of DVH's for the VMAT plans, which also generally agree with the TPS DVHs. However, this study found some instances in which there were differences between the EO and Eclipse DVH's.…”

“…Another study involved comparison of an MC method to Eclipse's Analytical Anisotropic Algorithm (AAA) for VMAT calculations, and found absolute dose value agreement to within 3%. 18 However, these studies compared the deliverable VMAT plan doses. Although it is difficult to evaluate directly, the pencil-beam algorithm used by Eclipse during the optimization process will be much less accurate than the MC or AAA methods.…”

Validation of a secondary dose check tool against Monte Carlo and analytical clinical dose calculation algorithms in VMAT

“…Sophisticated commercial computer algorithms for secondary dose or Monitor Unit (MU) calculation are becoming available. 34,35 These software packages provide useful dosimetric tools especially in treatment centers with many available treatment machines and a large number of patients treated per day. Among the most used, Mobius3D (Varian/Mobius Medical Systems, Houston, TX, USA) 36 performs a full recalculation of the dose on the patient computed tomography (CT) dataset based on an independent Collapsed Cone Convolution Superposition (CCCS) algorithm; 37,38 the open-source toolkit GATE 39 is a Geant4based 40 MC platform typically used for dose calculations and features 3D simulation and parallel computation 41 ; MUCheck is an EGSnrc-based 42 MC calculation system used as secondary MU check method for VMAT plans.…”

“…Among the most used, Mobius3D (Varian/Mobius Medical Systems, Houston, TX, USA) 36 performs a full recalculation of the dose on the patient computed tomography (CT) dataset based on an independent Collapsed Cone Convolution Superposition (CCCS) algorithm; 37,38 the open-source toolkit GATE 39 is a Geant4based 40 MC platform typically used for dose calculations and features 3D simulation and parallel computation 41 ; MUCheck is an EGSnrc-based 42 MC calculation system used as secondary MU check method for VMAT plans. 35 In this study, the recently released SciMoCa software package (version 1.4.2, Scientific RT GmbH, Munich, Germany), 43 a MC secondary dose check and plan verification software, is validated against a CCCS algorithm and, to our knowledge for the first time, against a widely used MC software. The CCCS algorithm is implemented in the Pinnacle 3 TPS, 44 while the MC calculations are available in the Monaco TPS, 45 which are used to generate the primary treatment plans.…”