Monte Carlo simulation techniques are widely used in medical physics. One can distinguish between general purpose Monte Carlo codes which can be applied to a wide range of problems and Monte Carlo codes that are specialized for specific purposes. VERIQA applies the SciMoCa^TM Monte Carlo code which is a specialized code developed for the efficient calculation of radiation treatment dose.

For dose calculation, the Monte Carlo principle is used to predict the absorbed energy by simulating the individual transport of particles passing through matter. Monte Carlo therefore applies the knowledge of the patient geometry derived from imaging and the physical knowledge of particle interactions gained from experimental data. The sophisticated simulation of physical interactions is the reason why Monte Carlo is often considered the gold standard for dose calculation in radiation therapy.

A crucial aspect of accurate Monte Carlo simulations is the precise definition of the particle origin. In radiotherapy, the particle origin is described in linac-specific beam models that simulate the accelerator head.  

VERIQA RT MonteCarlo 3D applies is a specialized Monte Carlo code derived from the EGSnrc/XVMC/VMC++ Monte Carlo code family. It keeps deviations in the toughest artificial situations to a maximum of 2% compared to general purpose Monte Carlo codes. Due to its unique virtual beam modelling and optimized use of sophisticated variance reduction techniques, it maximizes efficiency and minimizes non-Gaussian noise.

VERIQA is an independent dose calculation tool. It is best suited for evaluating full 3D dose distributions for quality assurance purposes. By calculating dose in 3D, it provides dose information in millions of points. However, the traditional method of patient plan quality assurance is based on single point dose and Monitor Units (MU) as a measure of the released radiation.

For this reason, in addition to 3D dose evaluation, VERIQA provides a secondary point dose/MU check based on the independent Monte Carlo calculated dose in a specific dose point.

VERIQA does not use GPU base dose calculation. For the efficient simulation of the accelerator head and variable collimators, variance reduction techniques can be applied to great benefit. Variance reduction techniques come with an overhead in terms of memory management and at some cost in terms of code complexity. Both factors are a greater problem for a GPU architecture, which is specialized for executing the same set of instructions in parallel on many data entities (SIMD, single instruction, multiple data), than for a CPU architecture (MIMD, multiple instructions, multiple data). VERIQA is designed to be versatile and work with very diverse accelerator head geometries. It has a finely balanced suite of variance reduction techniques to couple the accelerator head model with the patient model. Therefore, the code executes preferentially on the CPU architecture.

VERIQA`s Monte Carlo algorithm was extensively benchmarked against EGSnrc. It was validated for materials between mass densities
of 0.25 g/cm³ and 8.0 g/cm³ and photon energies between 1 MeV and 25 MeV. The validation of the linac beam models was based on dose measurements under controlled conditions. Furthermore, comparison to measurements of realistic treatment plans served the purpose of comprehensive end-to-end testing.

Standard Beam Models:

Standard beam models can be used for linacs calibrated based on reference data sets provided by the linac vendors. These references are often referred to as golden beam data sets. In theory, all linacs tuned to golden beam data have the same dosimetric characteristics.

VERIQA’s standard beam models were created based on golden beam measurements and can be used for the dose calculation of linacs calibrated to golden beam data.  

Custom Beam Models:

Custom beam models can be applied for all linacs. VERIQA’s customized beam models are tailored to the specific characteristics of an individual linac based on water phantom and MLC measurements provided by the customer. The measurements are reviewed by PTW experts and used to create beam models meeting the highest quality standards.

Each VERIQA linac head is simulated with a type- and energy- specific beam model. VERIQA beam models are created by PTW experts based on water phantom and MLC calibration measurements. Beam models can either be provided as standardized or customized beam models.