There is an increased worldwide interest in radiation therapy with proton and heavier ions and several clinical ion therapy facilities are in use. Accurate evaluation of the dose delivered to tissue and estimation of biological effects in ion beams, require correct knowledge of the physics of ion interaction with matter. Such studies are also of importance for evaluation of biologically equivalent doses delivered to astronauts in long-term manned interplanetary missions.
Proton and heavy charged particle beams produce secondary radiation from beam fragmentation processes and nucleus–nucleus interactions in the structural materials of accelerator or space station, as well as in the human body. These secondaries consist of a variety of particle types like neutrons, protons, heavier ions, photons and electrons within broad energy ranges up to several GeV. They are characterized by a wide range of LET and can be a source of significant biological doses to healthy tissues.
Due to the very complex interaction pathways of high energy heavy charged ions in the shielding materials and the human body, computation methods using 3-D Monte Carlo (MC) particle transport codes provide unique and very useful tool in simulating therapeutic beams and evaluations of radiation environment around spacecraft.
The capability and accuracy of any MC hadron transport code depend critically upon the model used to describe elastic and inelastic nuclear interactions of light and heavy ions, and on the cross section data for production of secondary particles. Recently, several MC hadron transport codes have significantly improved the implemented nuclear models for secondary particle production in the ion energy range 0 – 1 GeV/A.
In these studies a capability of the SHIELD-HIT, MCNPX and GEANT4 MC codes to simulate radiation field around proton/ion facility and space station will be discussed. The code features will be presented and implemented nuclear models discussed. MC calculations using these codes will be compared with experiments and theoretical evaluations using other MC techniques.
Some deficiencies in the descriptions of nuclear inelastic interactions of high energy ions with tissue equivalent materials are still noticed for all analyzed codes. Generally better agreement for heavier target material is observed. There is a need both for extensive theoretical studies to validate the physical models implemented in the MC codes for hadron transport and for further development of these codes.