gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Monte Carlo calculations of dose to medium and dose to water for carbon ion beams in various media

Meeting Abstract

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  • author R. Herrmann - Department of Physics and Astronomy, University Aarhus, Denmark
  • J. Petersen - Aarhus University Hospital, Aarhus, Denmark
  • N. Bassler - Department of Physics and Astronomy, University Aarhus, Denmark

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog087

doi: 10.3205/09ptcog087, urn:nbn:de:0183-09ptcog0877

Veröffentlicht: 24. September 2009

© 2009 Herrmann et al.
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Background: In clinical practice the quantity dose to water (Dw) is used as a reference standard for dosimeters and treatment planning systems. Treatment planning systems usually rely on analytical representation of the particle beam, which are normally expressed as dose with respect to water.

The dose to medium (Dm) ay however differ from Dw, due to the different particle spectrum and stopping power found herein. Monte Carlo particle transport codes are capable of directly calculating dose to medium (Dm), and was for instance recently investigated by Paganetti 2009 for various proton treatment plans. Here, we quantisize the effect of dose to water vs. dose to medium for a series of typical target materials found in medical physics.

Material and methods: The Monte Carlo code FLUKA [Battistioni et al. 2007] is used to simulate the particle uence spectrum in a series of target materials exposed to carbon ion beams. The scored track-length uence spectrum i for a given particle i at the energy E, is multiplied with the mass stopping power for target material for calculating Dm. Similarly, Dw is calculated by multiplying the same uence spectrum with the mass stopping power for water. This represents the case that our \detector" is an in nitesimal small non-perturbing entity made of water, where charged particle equilibrium can be assumed following the Bragg-Gray cavity theory. Dw and Dm are calculated for typical materials such as bone, brain, lung and soft-tissues using the PSTAR, ASTAR stopping power routines available at NIST ( and MSTAR ( provided by H. Paul et al.

Results: For a pristine carbon ion beam we encountered a maximum deviation between Dw and Dm up to 8% for bone. In addition we investigate spread out Bragg peak con gurations which dilutes the effect, and other tissue like materials. However, ideally further comparisons between Dw and Dm have to be done for real treatment plans using CT-scans in order to quantisize the clinical consequences.