VMC++ versus BEAMnrc: A comparison of simulated linear accelerator heads for photon beams

Division of Medical Radiation Physics, Insel Hospital, University of Berne, Berne 3010, Switzerland.
Medical Physics (Impact Factor: 2.64). 04/2008; 35(4):1521-31. DOI: 10.1118/1.2885372
Source: PubMed


BEAMnrc, a code for simulating medical linear accelerators based on EGSnrc, has been bench-marked and used extensively in the scientific literature and is therefore often considered to be the gold standard for Monte Carlo simulations for radiotherapy applications. However, its long computation times make it too slow for the clinical routine and often even for research purposes without a large investment in computing resources. VMC++ is a much faster code thanks to the intensive use of variance reduction techniques and a much faster implementation of the condensed history technique for charged particle transport. A research version of this code is also capable of simulating the full head of linear accelerators operated in photon mode (excluding multileaf collimators, hard and dynamic wedges). In this work, a validation of the full head simulation at 6 and 18 MV is performed, simulating with VMC++ and BEAMnrc the addition of one head component at a time and comparing the resulting phase space files. For the comparison, photon and electron fluence, photon energy fluence, mean energy, and photon spectra are considered. The largest absolute differences are found in the energy fluences. For all the simulations of the different head components, a very good agreement (differences in energy fluences between VMC++ and BEAMnrc <1%) is obtained. Only a particular case at 6 MV shows a somewhat larger energy fluence difference of 1.4%. Dosimetrically, these phase space differences imply an agreement between both codes at the <1% level, making VMC++ head module suitable for full head simulations with considerable gain in efficiency and without loss of accuracy.

  • [Show abstract] [Hide abstract]
    ABSTRACT: This article reviews Monte Carlo Treatment Planning—An Introduction: Report 16 of the Netherlands Commission on Radiation Dosimetry
    No preview · Article · Nov 2008 · Medical Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In teletherapy VMC++ is known to be a very accurate and efficient Monte Carlo (MC) code. In principle, the MC method is also a powerful dose calculation tool in Brachytherapy or for orthovoltage radiotherapy. However, VMC++ is not validated for the low energy range of this application. Thus, this work aims in the validation of the VMC++ MC code for photon beams in the low energy range, i.e. between 20 and 1000 keV. Dose calculations were performed in a 40x40x40 cm3 water phantom with two 4 cm thick slabs of bone and lung. Dose distributions of mono-energetic (ranging from 20 - 1000 keV) 10x10 cm2 sized parallel beams as well as a 10x10 cm2 sized parallel beam using the energy spectrum for Iridium- 192 were calculated. A voxel size of 4x4x4 mm3 was used for all dose calculations. The resulting dose distributions were compared with those calculated using EGSnrc, which is used as golden standard in this work. At energies between 100 keV and 1000 keV, EGSnrc and VMC++ calculated dose distributions agree within a statistical uncertainty of about 1% (1σ). At energies ≤ 50 keV beams, local dose differences for doses > 10% of Dmax of up to 4% occur when VMC++ and EGSnrc are compared. Turning off Rayleigh scattering, binding effects for Compton scattering and the atomic relaxation after photoelectric absorption in EGSnrc (not implemented in VMC++) leads to an agreement between both MC codes within 2% (local dose difference). Although further improvements for very low energies in accuracy of VMC++ could be achieved by implementing these interactions, this MC Code is able to calculate dose distributions for Ir-192 brachytherapy within statistical uncertainty.
    Full-text · Article · Jan 2009 · IFMBE proceedings
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this work is to revisit the impediments and characteristics of fast Monte Carlo techniques for applications in radiation therapy treatment planning using new methods of utilizing pregenerated electron tracks. The limitations of various techniques for the improvement of speed and accuracy of electron transport have been evaluated. A method is proposed that takes advantage of large available memory in current computer hardware for extensive generation of precalculated data. Primary tracks of electrons are generated in the middle of homogeneous materials (water, air, bone, lung) and with energies between 0.2 and 18 MeV using the EGSnrc code. Secondary electrons are not transported, but their position, energy, charge, and direction are saved and used as a primary particle. Based on medium type and incident electron energy, a track is selected from the precalculated set. The performance of the method is tested in various homogeneous and heterogeneous configurations and the results were generally within 2% compared to EGSnrc but with a 40-60 times speed improvement. In a second stage the authors studied the obstacles for further increased speed-ups in voxel geometries by including ray-tracing and particle fluence information in the pregenerated track information. The latter method leads to speed increases of about a factor of 500 over EGSnrc for voxel-based geometries. In both approaches, no physical calculation is carried out during the runtime phase after the pregenerated data has been stored even in the presence of heterogeneities. The precalculated data are generated for each particular material and this improves the performance of the precalculated Monte Carlo code both in terms of accuracy and speed. Precalculated Monte Carlo codes are accurate, fast, and physics independent and therefore applicable to different radiation types including heavy-charged particles.
    Full-text · Article · Mar 2009 · Medical Physics
Show more