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

Abstract

A model based on a specific phantom, called QuAArC, has been designed for the evaluation of planning and verification systems of complex radiotherapy treatments, such as volumetric modulated arc therapy (VMAT). This model uses the high accuracy provided by the Monte Carlo (MC) simulation of log files and allows the experimental feedback from the high spatial resolution of films hosted in QuAArC. This cylindrical phantom was specifically designed to host films rolled at different radial distances able to take into account the entrance fluence and the 3D dose distribution. Ionization chamber measurements are also included in the feedback process for absolute dose considerations. In this way, automated MC simulation of treatment log files is implemented to calculate the actual delivery geometries, while the monitor units are experimentally adjusted to reconstruct the dose-volume histogram (DVH) on the patient CT. Prostate and head and neck clinical cases, previously planned with Monaco and Pinnacle treatment planning systems and verified with two different commercial systems (Delta4 and COMPASS), were selected in order to test operational feasibility of the proposed model. The proper operation of the feedback procedure was proved through the achieved high agreement between reconstructed dose distributions and the film measurements (global gamma passing rates > 90% for the 2%/2 mm criteria). The necessary discretization level of the log file for dose calculation and the potential mismatching between calculated control points and detection grid in the verification process were discussed. Besides the effect of dose calculation accuracy of the analytic algorithm implemented in treatment planning systems for a dynamic technique, it was discussed the importance of the detection density level and its location in VMAT specific phantom to obtain a more reliable DVH in the patient CT. The proposed model also showed enough robustness and efficiency to be considered as a pre-treatment VMAT verification system.

Evaluation of machine log files/MC‐based treatment planning and delivery QA as compared to ArcCHECK QA

“…Similarly, Barbeiro et al. found log files reconstructed with ~3 times as many control points as the TPS agreed better with film than those reconstructed with the TPS’ discretization …”

“…times as many control points as the TPS agreed better with film than those reconstructed with the TPS' discretization. 26 Using 2-mm dose grid resolution and 1°control point spacing, computational cost for CS was 12 s per control point. This corresponds to 18 min for a 358°arc planned using 4 degree control point spacing or 72 min for a log file plan reconstructed using 1°control point spacing.…”

Assessment of radiation-induced secondary cancer risk in the Brazilian population from left-sided breast-3D-CRT using MCNPX

“…Indeed, Monaco TPS provides the MC and Collapsed Cone algorithms coupling. 42 Monaco addressed MC in Kernel evaluation; however, the Therma method of calculation remained. Therefore, Monaco may not be considered as a full implementation of MC for clinical applications.…”

Methodology for radiochromic film analysis using FilmQA Pro and ImageJ

“…These attributes have proven useful for a variety of clinical tasks such as dosimetry for total skin electron therapy [9,10] or total body irradiation [11]. RCF is also used in patient specific quality assurance (QA) measurements for delivery techniques such as volumetric modulated arc therapy (VMAT) [12] or stereotactic radiosurgery (SRS) [13,14] where high spatial resolution is necessary and has proven useful as a research tool in phantom and radiobiological studies to verify dosimetry in unconventional geometries that do not easily accommodate conventional dosimeters [15][16][17][18][19][20][21].…”