Highlights
- •w-Values are a source of uncertainty in reference dosimetry for hadrontherapy.
- •MDM-Ion is a Monte Carlo code developed for swift ions transport in liquid water.
- •w-Values shown to be independent of both particle charge and energy.
- •Electronic excitation and Auger electron emission strongly affect the results.
- •w-Values in liquid water should be used as a benchmark for microdosimetry.
Abstract
Purpose
To develop a particle transport code to compute w-values and stopping power of swift ions in liquid water and gases of interest for
reference dosimetry in hadrontherapy. To analyze the relevance of inelastic and post-collisional
processes considered.
Methods
The Monte Carlo code MDM was extended to the case of swift ion impact on liquid water
(MDM-Ion). Relativistic corrections in the inelastic cross sections and the post-collisional
Auger emission were considered. The effects of introducing different electronic excitation
cross sections were also studied.
Results
The stopping power of swift ions on liquid water, calculated with MDM-Ion, are in
excellent agreement with recommended data. The w-values show a strong dependence on the electronic excitation cross sections and on
the Auger electron emission. Comparisons with other Monte Carlo codes show the relevance
of both the processes considered and of the cross sections employed. W and w-values for swift electron, proton, and carbon ions calculated with the MDM and MDM-Ion
codes are in very close agreement with each other and with the 20.8 eV experimental
value.
Conclusion
We found that w-values in liquid water are independent of ion charge and energy, as assumed in reference
dosimetry for hadrontherapy from sparse experimental results for electron and ion
impact on gases. Excitation cross sections and Auger emission included in Monte Carlo
codes are critical in w-values calculations. The computation of this physical parameter should be used as
a benchmark for micro-dosimetry investigations, to assess the reliability of the cross
sections employed.
Keywords
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Article info
Publication history
Published online: June 28, 2021
Accepted:
June 4,
2021
Received in revised form:
May 5,
2021
Received:
January 29,
2021
Identification
Copyright
© 2021 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
