Verification of the multiple scattering and energy loss straggling algorithms for therapeutic light ion beams implemented in a semi-analytical pencil beam model and the MC code SHIELD-HIT; benchmark with experiments

The increased interest in radiation therapy with light ions calls for fast calculation of the dose distribution of narrow charged particle beams. In order to accurately calculate the physical dose and biological effect distribution of light ions in matter, a physical beam transport model has to be set up.A fast semi-analytical model used for calculation of energy deposition of narrow ion beams in water has been developed (Hollmark et al 2004, Hollmark et al 2007). The model applied the Fermi-Eyges theory for simultaneous calculation of multiple scattering and energy loss straggling of light ion beams traversing water. The developed semi-analytical algorithm incorporates the energy deposition kernels calculated by the Monte Carlo transport code SHIELD-HIT, in which ion scattering and energy straggling processes were suppressed. The analytical dose distributions are calculated by weighting the SHIELD-HIT calculated dose with analytical Gaussian multiple scattering and straggling distributions. Both primary and secondary particles are considered in this study. To evaluate the influence of the lightest secondary particles (nuclear charges Z=1 and Z=2) on the total lateral dose distribution, primary and secondary dose distributions are calculated separately.The multiple scattering and radial energy deposition of fragments produced along the ion path are calculated analytically as well as simulated by SHIELD-HIT. The results are verified against experimental data of the transverse energy deposition for clinical proton beams of energies 62 MeV from CATANA facility, LNS – INFN, Italy and 180 MeV from the TSL Laboratory, Uppsala, Sweden. The multiple scattering processes of primary carbon beams and their secondaries are discussed for experimental beams of 290 MeV/u (HIMAC, Chiba, Japan) and 400 MeV/u (GSI, Darmstadt, Germany).Hollmark et al. “Influence of multiple scattering and energy loss straggling on the absorbed dose distributions of therapeutic light ion beams: I. Analytical pencil beam model” Phys. Med. Biol. 49 pp. 3247-3265 (2004)Hollmark et al. “Influence of multiple scattering and energy loss straggling on the absorbed dose distributions of therapeutic light ion beams: II. Semi-analytical narrow beam model” manuscript (2007)