Physical and biophysical properties of proton tracks of energies 1 keV to 300 MeV in water

Abstract

Purpose: To investigate physical and biophysical properties of proton tracks 1 keV–300 MeV using Monte Carlo track structure methods.

Materials and methods: We present model calculations for cross sections and methods for simulations of full-slowing-down proton tracks. Protons and electrons were followed interaction-by-interaction to cut-off energies, considering elastic scattering, ionisation, excitation, and charge-transfer.

Results: Model calculations are presented for singly differential and total cross sections, and path lengths and stopping powers as a measure of the code evaluation. Depth-dose distributions for 160 MeV protons are compared with experimental data. Frequencies of energy loss by electron interactions increase from ∼3% for 10 keV to ∼77% for 300 MeV protons, and electrons deposit >70% of the dose in 160 MeV tracks. From microdosimetry calculations, 1 MeV protons were found to be more effective than 5–300 MeV in energy depositions greater than 25, 50, and 500 eV in cylinders of diameters and lengths 2, 10, and 100 nm, respectively. For lower-energy depositions, higher-energy protons are more effective. Decreasing the target size leads to the reduction of frequency- and dose-mean lineal energies for protons <1 MeV, and conversely for higher-energy protons.

Conclusions: Descriptions of proton tracks at molecular levels facilitate investigations of track properties, energy loss, and microdosimetric parameters for radiation biophysics, radiation therapy, and space radiation research.

Keywords:

• Monte Carlo simulation
• track structure
• proton
• cross sections
• microdosimetry

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.