A Monte Carlo tool for evaluating VMAT and DIMRT treatment deliveries including planar detectors

Abstract

The aim of this work is to describe and validate a new general research tool that performs Monte Carlo (MC) simulations for volumetric modulated arc therapy (VMAT) and dynamic intensity modulated radiation therapy (DIMRT), simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system. The tool is generalized to handle either entrance or exit detectors and provides the simulated dose for the individual control-points of the time-dependent VMAT and DIMRT deliveries. The MC simulation tool was developed with the EGSnrc radiation transport. For the individual control point simulation, we rotate the patient/phantom volume only (i.e. independent of the gantry and planar detector geometries) using the gantry angle in the treatment planning system (TPS) DICOM RP file such that each control point has its own unique phantom file. After MC simulation, we obtained the total dose to the phantom by summing dose contributions for all control points. Scored dose to the sensitive layer of the planar detector is available for each control point. To validate the tool, three clinical treatment plans were used including VMAT plans for a prostate case and a head-and-neck case, and a DIMRT plan for a head-and-neck case. An electronic portal imaging device operated in 'movie' mode was used with the VMAT plans delivered to cylindrical and anthropomorphic phantoms to validate the code using an exit detector. The DIMRT plan was delivered to a novel transmission detector, to validate the code using an entrance detector. The total MC 3D absolute doses in patient/phantom were compared with the TPS doses, while 2D MC doses were compared with planar detector doses for all individual control points, using the gamma evaluation test with 3%/3 mm criteria. The MC 3D absolute doses demonstrated excellent agreement with the TPS doses for all the tested plans, with about 95% of voxels having γ <1 for the plans. For planar dosimetry image comparisons, we defined an acceptable pass rate of >90% of percentage pixels with γ <1. We found that over 90% of control points in the plans passed this criterion. In general, our results indicate that the simulation tool is suitable for accurately calculating both patient/phantom doses and planar doses for VMAT dose delivery. The tool will be valuable to check performance and advance the development of in vivo planar detectors for use in measurement-based VMAT dose verification. In addition, the tool can be useful as an independent research tool for VMAT commissioning of the TPS and delivery system.

A comparison of the JO-IMRT dose distribution calculated by the SOURCE 8 and 20 in the DOSXYZnrc for head-and-neck cancer

“…al. (26) used SOURCE 20 in DOXYZnrc to calculating the dynamic IMRT dose distribution for head and neck patient that found the same our result.…”

Two‐dimensional in vivo dose verification using portal imaging and correlation ratios

“…(18,19) Pure simulation and mixed simulation/empirical methods can provide very accurate results, but require highly specific mathematical models for both the accelerator and the EPID. As well, the long calculation times can render them inapplicable to clinical routine (up to 336 hours for a single volumetric modulated arc therapy plan (20) ).…”

3D VMAT Verification Based on Monte Carlo Log File Simulation with Experimental Feedback from Film Dosimetry

“…In order to cover both type of uncertainties commented above, some works proposed MC simulation of linac log files recorded during treatment delivery [6, 13, 14]. The dose distribution discrepancy introduced between the discretized plan and the continuous delivery was assessed by incorporating DynaLog files into MC simulations for RapidArc QA [6].…”