Adapting a generic BEAMnrc model of the BrainLAB m3 micro-multileaf collimator to simulate a local collimation device

Abstract

This work is focussed on developing a commissioning procedure so that a Monte Carlo model, which uses BEAMnrc's standard VARMLC component module, can be adapted to match a specific BrainLAB m3 micro-multileaf collimator (microMLC). A set of measurements are recommended, for use as a reference against which the model can be tested and optimized. These include radiochromic film measurements of dose from small and offset fields, as well as measurements of microMLC transmission and interleaf leakage. Simulations and measurements to obtain microMLC scatter factors are shown to be insensitive to relevant model parameters and are therefore not recommended, unless the output of the linear accelerator model is in doubt. Ultimately, this note provides detailed instructions for those intending to optimize a VARMLC model to match the dose delivered by their local BrainLAB m3 microMLC device.

Using narrow beam profiles to quantify focal spot size, for accurate Monte Carlo simulations of SRS/SRT systems

“…A series of Monte Carlo simulations were completed, using BEAMnrc and DOSXYZnrc [12,13], with established, geometrically and dosimetrically accurate models of the Varian iX linear accelerator, Millennium MLC and Brainlab m3 microMLC [14,15,16]. The film and water-equivalent phantom were modelled as a simple volume of water with voxels 0.1 cm thick in the beam-axis direction and 0.01 x 0.01 cm 2 across in the lateral directions.…”

The influence of field size on stopping‐power ratios in‐ and out‐of‐field: quantitative data for the BrainLAB m3 micro‐multileaf collimator

“…In this work we have constructed a model of the Varian 600C Clinac (Varian Medical Systems, Palo Alto, CA) with a mounted BrainLAB m3 micro‐multileaf collimator (MMLC) (BrainLAB, Feldkirchen, Germany) using BEAMnrc. The model was developed based on schematics provided by Varian Medical Systems and BrainLAB under nondisclosure agreements 23 , 24 . In this work, the model of the Varian 600C with MMLC was dosimetrically matched to measured data using percent depth‐dose curves, profiles, and scatter factors.…”

Design and experimental testing of air slab caps which convert commercial electron diodes into dual purpose, correction‐free diodes for small field dosimetry

“…All linear accelerator simulations were performed with the BEAMnrc Monte Carlo user code, 10 using a model of the Varian 21iX (Varian Medical Systems, Palo Alto) that had previously been commissioned in other studies for field sizes as small as 5 mm. 6,11,12 The incident electron fluence onto the target of this linear accelerator was modeled as centrally symmetric with a Gaussian distribution with a full-widthhalf-maximum (FWHM) equal to 1.2 mm. The electron spot size was tuned using the methodology of Cranmer-Sargison et al 13 All phantom simulations were performed using the EGSnrc ++ user code cavity.…”