Nanodosimetric cluster size distributions of therapeutic proton beams

Abstract

Abstract-As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC's proton research beam lines.

Experimental Validation of Track Structure Models

“…4 shows that the distributions produced by the MC simulation are in satisfactory agreement with the experimental data for all particle kinds with the notable exception of electrons. The difference between experimental and simulation results for protons and alpha particles on average does not exceed 15% and can be attributed to both experimental statistical and systematic errors as well as to uncertainties in MC calculations as discussed in detail in (7,12). For electrons the difference is much bigger: more than 200% for non-zero cluster sizes at impact parameter values of 0 and 21 nm.…”

“…A dedicated Monte Carlo (MC) particle track structure code (7,11,12) was used to simulate the experimental data. It utilizes a compilation of experimental ionization cross sections of protons and alpha particles, experimental electron interaction cross sections for elastic scattering, excitation, and ionization to transport primary high-energy protons, alpha-particles or electrons, as well as secondary electrons with energies down to 10 eV in propane.…”

Nanodosimetry-based quality factors for radiation protection in space

“…Since experimental data for a larger range of heavy ions and LET values are scarce, we performed Monte Carlo simulations of the experimental nanodosimetric data for protons, helium and carbon ions, as well as 100 keV electrons, the latter used as low-LET reference radiation. The Monte Carlo code developed at the PTB for that purpose has been extensively validated in comparison with experimental nanodosimetric data with protons and helium ions [10,13,14]. For heavier ions, the code remains to be validated as experimental data do not exist at this time.…”

“…Ion clusters are then transformed into ion-signal pulse trains based on the experimentally measured location-vs.-drift time relationship. The code has been benchmarked against experimental data with good agreement [10,[13][14][15].…”