Effect of Incoming Particle Energy and Ionization Cluster Size On the G-Value of Hydrated Electrons
A Bui*1, L Childress2, J Sankey2, J Seuntjens13, S A Enger134(1) Medical Physics Unit, McGill University, Montreal, QC, CA, (2) Department of Physics, McGill University, Montreal, QC, CA (3) Research Institute of the McGill University Health Centre, Montreal, QC, CA, (4) Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, QC, CA
Presentations
TH-D-TRACK 5-6 (Thursday, 7/29/2021) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]
Purpose: To accurately calculate absorbed dose to water in hydrated electron (e⁻(aq)) dosimetry, the radiation chemical yield (i.e. G-value) of hydrated electrons, G(e⁻(aq)), must be precisely determined. The relationship between the G-value, linear energy transfer (LET), and ionization cluster size were also investigated for better understanding of factors affecting the G-value using Geant4-DNA.
Methods: Different scenarios were investigated using Geant4-DNA track structure Monte Carlo toolkit. In scenario A, a 10 x 4 x 2 cm³ phantom of liquid water was placed at SSD 70 cm and irradiated with monoenergetic electron beams of different incoming energies from 1 keV to 1 MeV. G(e⁻(aq)) and the G-value of all generated species with respect to incoming energy were scored. In scenario B, the relation between G(e⁻(aq)) and cluster size was investigated by irradiating a 0.1 x 0.1 x 0.1 cm³ water phantom with electron point sources of energies from 0.01 keV to 1 MeV, starting at the center of the volume.
Results: The time-evolution of the G-value showed good agreement with previous simulations and experiments. It was observed that as the incoming electron energy decreases (i.e. higher LET), G(e⁻(aq)) generally decreases, and its rate of change over time becomes steeper. For 1 MeV electron beams, the initial G(e⁻(aq)) at 1 picosecond was calculated to be 4.1±0.1. Moreover, we observed a negative correlation between G(e⁻(aq)) and cluster size as a function of incoming electron energy. The results indicated that cluster size had a pattern similar to that of LET, which has been shown to remain relatively constant as the incoming electron energy increases.
Conclusion: As the incoming electron energy increases to tens of MeV, G(e⁻(aq)) will remain relatively constant, since it decreases with increasing cluster size and LET. This is beneficial, as Geant4-DNA can only simulate electron interactions up to 1 MeV.
Funding Support, Disclosures, and Conflict of Interest: Funding support: Research Institute - McGill University Health Centre (RI-MUHC). No disclosures and conflicts of interest.
Handouts
Keywords
Ionizing Radiation, Monte Carlo, Radiation Therapy
Taxonomy
TH- External Beam- Electrons: Computational dosimetry: Monte Carlo
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