GEANT4 Tuning For pCT Development

Abstract

Abstract. Proton beams in medical applications deal with relatively thick targets like the human head or trunk. Thus, the fidelity of proton computed tomography (pCT) simulations as a tool for proton therapy planning depends in the general case on the accuracy of results obtained for the proton interaction with thick absorbers. GEANT4 simulations of proton energy spectra after passing thick absorbers do not agree well with existing experimental data, as showed previously. Moreover, the spectra simulated for the Bethe-Bloch domain showed an unexpected sensitivity to the choice of low-energy electromagnetic models during the code execution. These observations were done with the GEANT4 version 8.2 during our simulations for pCT. This work describes in more details the simulations of the proton passage through aluminum absorbers with varied thickness. The simulations were done by modifying only the geometry in the Hadrontherapy Example, and for all available choices of the Electromagnetic Physics Models. As the most probable reasons for these effects is some specific feature in the code, or some specific implicit parameters in the GEANT4 manual, we continued our study with version 9.2 of the code. Some improvements in comparison with our previous results were obtained. The simulations were performed considering further applications for pCT development. The interest in proton computed tomography (pCT) development is now reopened with the spread of the proton beam treatment [1]. The idea is to use the same medical proton therapy beam for diagnosis with pCT, i.e. for tumor localization and data acquisition for further irradiation planning. Potentially it can improve the quality of proton therapy and decrease the dose delivered to patients. The Monte Carlo simulations have a successful history in varied fields of study and could also be a helpful instrument in the case of pCT.

The comparison of GEANT 4.8.2 and 4.9.2 results for the 25MeV protons in thick polyethylene

“…Thus, the fidelity of proton computed tomography (pCT) simulations as a tool for proton therapy planning depends in the general case on the accuracy of results obtained for the proton interaction with thick absorbers. As we previously showed it, the GEANT4 simulations of proton energy spectra after thick absorbers do not agree well with existing experimental data [2,3,4]. Moreover, the spectra simulated for the Bethe-Bloch domain showed an unexpected sensitivity to the choice of low-energy electromagnetic models during the code execution.…”

“…In order to make a correct comparison of the spectra with different number of protons, all the spectra were reduced to the discrete Probability Density Functions (PDF) by using (2), where N i is the number of protons in the i-th energy range -from E i to E i +δE, and N 0 is the total number of protons in the spectrum.…”