Distributions of secondary particles in proton and carbon-ion therapy: a comparison between GATE/Geant4 and FLUKA Monte Carlo codes.

Monte Carlo simulations play a crucial role for in-vivo treatment monitoring based on PET and prompt gamma imaging in proton and carbon-ion therapies. The accuracy of the nuclear fragmentation models implemented in these codes might affect the quality of the treatment verification. In this paper, we investigate the nuclear models implemented in GATE/Geant4 and FLUKA by comparing the angular and energy distributions of secondary particles exiting a homogeneous target of PMMA. Comparison results were restricted to fragmentation of (16)O and (12)C. Despite the very simple target and set-up, substantial discrepancies were observed between the two codes. For instance, the number of high energy (>1 MeV) prompt gammas exiting the target was about twice as large with GATE/Geant4 than with FLUKA both for proton and carbon ion beams. Such differences were not observed for the predicted annihilation photon production yields, for which ratios of 1.09 and 1.20 were obtained between GATE and FLUKA for the proton beam and the carbon ion beam, respectively. For neutrons and protons, discrepancies from 14% (exiting protons-carbon ion beam) to 57% (exiting neutrons-proton beam) have been identified in production yields as well as in the energy spectra for neutrons.

A detailed Monte Carlo accounting of radiation transport in the brain during BNCT.

The collision type central to BNCT is (10)B(n, alpha)(7)Li, however, other types of nuclear reactions also take place in the patient. In addition to the major elements (H, C, N, O), minor elements such as Na, Mg, P, S, Cl, K, Ca and Fe present in body tissues also interact in neutron collisions. Detailed accounting of the above not only provides a better understanding of radiation transport in the human body during BNCT, but such knowledge affects the design of the facility, as well as treatment planning, imaging and verification for a given BNCT agent. Of the methods of investigation currently available, only Monte Carlo simulation could provide the detailed accounting and breakdown of the quantities required. We report Monte Carlo simulation of an anthropomorphic voxel phantom, the VIP-Man and show how these quantities change with different (10)B concentrations in the tumour, the blood and the remaining tissues. The (10)B biodistribution has been chosen to be the variable of interest, since it is not accurately known, is frequently approximated and is a crucial quantity upon which dose calculations are based.

Non-convergence of Geant4 hadronic models for 10 and 30 MeV protons in 18O and 14N.

We investigated Geant4 Monte Carlo simulation of protons interactions in (18)O and (14)N. With proton incident energies of 10 and 30 MeV, we compared the different Geant4 models available for proton inelastic collisions: the low-energy parameterisation, Bertini cascade and precompound models. The models produced different (1) combinations of secondary particles and (2) final states of secondary particles. The non-convergence suggests that the hadronic models, yet to be benchmarked for this energy range, are not ready for production-mode problem-solving.