Investigating the ionization potential and stopping power of water and compare with NIST data

Introduction: Since the human body contains mostly water, the knowledge of depth dose profile of charged particles in this stopping medium is of great importance for an accurate treatment planning. It is known that the range of energetic ions depends on the mean ionization potential ( -value) of the stopping medium. It is the goal of the present paper to perform a systematic study on the sensitivity of the Bragg curve to different -values reported in the literature. As a working tool we employed numerical Monte Carlo simulations based on the Geant4 computer code.Methods: In this study, GATE code was used to compute absorbed dose and fluence of protons in the energy range of 30-250 MeV. A water phantom (40*40*40 cm3) was modeled in a vacuum world volume (5*5*5 m3). In our previous study, we examined the accuracy of different physics and our proposed physics-list in proton therapy applications was QGSP_BIC_EMY and here we used it. We examined the ionization potential values from 70-80 eV and we compared the precision in computing the range with NIST data. Also, in this study, we compared the obtained stopping power values from simulation in all energies with NIST data.Results:The calculated difference diagram for all ionization potential values is plotted in energy terms. The NIST continuous slowing down approximation (CSDA) range in 100 MeV is equal to 77.18 mm. We observed that the proton range is heavily influenced by the ionization potential of the environment, and with increasing the amount of I from 70-80 eV, the proton range has decreased significantly. It was observed that this difference in the amount of 76 eV reaches its lowest value. Therefore, the ionization potential of water was determined 76 eV. We also observed the agreement between the NIST data and the stopping power obtained from the simulation within ±2% in all energies.Conclusion: In this study, we investigated different amounts of water ionization potential and proposed optimal amounts of ionization potential. We also conclude that the amount of stopping power obtained from simulation does not differ significantly with NIST data.