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

• Published in: Medical physics (Lancaster) 2008-04, Vol.35 (4), p.1521-1531
• Main Authors: Hasenbalg, F., Fix, M. K., Born, E. J., Mini, R., Kawrakow, I.
• Format: Article
• Language: English
• Subjects: A CODES; ACCURACY; Algorithms; Applications; BEAMnrc; biomedical equipment; CHARGED-PARTICLE TRANSPORT; COLLIMATORS; COMPUTERIZED SIMULATION; Dose‐volume analysis; DOSIMETRY; GOLD; LINEAR ACCELERATORS; MONTE CARLO METHOD; Monte Carlo methods; Monte Carlo simulations; Multileaf collimators; Particle Accelerators; PHASE SPACE; Phase space methods; PHOTON BEAMS; Photons; Photons - therapeutic use; radiation therapy; Radiation treatment; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - methods; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Reproducibility of Results; Sensitivity and Specificity; Simulation; Software; Software Validation; Therapeutic applications, including brachytherapy; Thermodynamic properties; treatment head; VMC++
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2885372

BEAMnrc, a code for simulating medical linear accelerators based on EGSnrc, has been benchmarked 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.