Article

A particle track-repeating algorithm for proton beam dose calculation.

Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
Physics in Medicine and Biology (Impact Factor: 2.92). 04/2005; 50(5):1001-10. DOI: 10.1088/0031-9155/50/5/022
Source: PubMed

ABSTRACT A particle track-repeating algorithm has been developed for proton beam dose calculation for radiotherapy. Monoenergetic protons with 250 MeV kinetic energy were simulated in an infinite water phantom using the GEANT3 Monte Carlo code. The changes in location, angle and energy for every transport step and the energy deposition along the track were recorded for the primary protons and all secondary particles. When calculating dose for a patient with a realistic proton beam, the pre-generated particle tracks were repeated in the patient geometry consisting of air, soft tissue and bone. The medium and density for each dose scoring voxel in the patient geometry were derived from patient CT data. The starting point, at which a proton track was repeated, was determined according to the incident proton energy. Thus, any protons with kinetic energy less than 250 MeV can be simulated. Based on the direction of the incident proton, the tracks were first rotated and for the subsequent steps, the scattering angles were simply repeated for air and soft tissue but adjusted properly based on the scattering power for bone. The particle step lengths were adjusted based on the density for air and soft tissue and also on the stopping powers for bone while keeping the energy deposition unchanged in each step. The difference in nuclear interactions and secondary particle generation between water and these materials was ignored. The algorithm has been validated by comparing the dose distributions in uniform water and layered heterogeneous phantoms with those calculated using the GEANT3 code for 120, 150, 180 and 250 MeV proton beams. The differences between them were within 2%. The new algorithm was about 13 times faster than the GEANT3 Monte Carlo code for a uniform phantom geometry and over 700 times faster for a heterogeneous phantom geometry.

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    • "To fully exploit the potential advantages of IMPT, one must have a fast and accurate dose calculation algorithm. In recent years, a number of such algorithms have been proposed (Deasy 1998, Li et al 2005, 2008, Petti 1992, 1996, Russell et al 2000, Schaffner et al 1999, Soukup et al 2005, Szymanowski and Oelfke 2002), most of which are of the pencil beam type. For most pencil beam algorithms, the doses deposited from the pencil beams are described as the product of a central axis term, which is basically the depth–dose distribution 'Bragg curve' of a broad beam (or scanning pencil beam), and an off-axis term, which describes the lateral dose distribution. "
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