Microdosimetry of radiation field from a therapeutic C-12 beam in water: A study with Geant4 toolkit

作者：Burigo Lucas^*; Pshenichnov Igor; Mishustin Igor; Bleicher Marcus

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2013, 310: 37-53.

DOI：10.1016/j.nimb.2013.05.021

• Theory and algorithms in physics of heavy-ion therapy
• Microdosimetry
• Monte Carlo applications
• Simulation

We model the responses of Tissue-Equivalent Proportional Counters (TEPC) to radiation fields of therapeutic C-12 beam in a water phantom and to quasi-monoenergetic neutrons in a PMMA phantom. Simulations are performed with the Monte Carlo model for Heavy Ion Therapy (MCHIT) based on the Geant4 toolkit. The shapes of the calculated lineal energy spectra agree well with measurements in both cases. The influence of fragmentation reactions on the TEPC response to a narrow pencil-like carbon beam with its width smaller than the TEPC diameter is investigated by Monte Carlo modeling. It is found that the total lineal energy spectra are not very sensitive to the choice of the nuclear fragmentation model used by MCHIT. The calculated frequency-mean lineal energy differs from the data on the axis of a therapeutic beam by less than 10% and by 10-20% at other TEPC positions. Following the validation of MCHIT with quasi-monoenergetic neutron beams the contributions to lineal energy spectra from secondary neutrons produced by C-12 nuclei in water are estimated. As found, the neutron contribution at 10 cm distance from the beam axis amounts to similar to 50% close to the entrance to the phantom and decreases to similar to 25% at the depth of the Bragg peak and beyond it. The presented results can help in evaluating biological out-of-field doses in carbon-ion therapy.

• 出版日期2013-9-1