Single particle tracking uncertainties in ion imaging

TL;DR

This study uses Monte Carlo simulations to analyze and optimize the spatial resolution and path uncertainty in ion imaging single particle tracking systems, providing guidelines for hardware design to improve clinical dose calculations.

Contribution

It offers a comprehensive simulation-based comparison of path uncertainties in ion imaging, highlighting how system parameters affect achievable spatial resolution and pixel spacing.

Findings

Helium ions enable sub-millimetre pixel spacing in large phantoms.

Detector material budget should be below 0.25-0.75% for desired resolution.

Position resolution of 100 μm is necessary for sub-millimetre pixel spacing with helium ions.

Abstract

An extensive comparison of the path uncertainty in single particle tracking systems for ion imaging was carried out based on Monte Carlo simulations. The spatial resolution as function of system parameters such as geometry, detector properties and the energy of proton and helium beams was investigated to serve as a guideline for hardware developments. Primary particle paths were sampled within a water volume and compared to the most likely path estimate obtained from detector measurements, yielding a depth-dependent uncertainty envelope. The maximum uncertainty along this curve was converted to a conservative estimate of the minimal radiographic pixel spacing for a single set of parameter values. Simulations with various parameter settings were analysed to obtain an overview of the reachable pixel spacing as function of system parameters. The results were used to determine intervals of detector material budget and position resolution that yield a pixel spacing small enough for clinical dose calculation. To ensure a pixel spacing below 2 mm, the material budget of a detector should remain below 0.25 % for a position resolution of 200 $\mathrm{\mu m}$ or below 0.75 % for a resolution of 10 $\mathrm{\mu m}$. Using protons, a sub-millimetre pixel size could not be achieved for a phantom size of 300 mm or at a large clearance. With helium ions, a sub-millimetre pixel spacing could be achieved even for a large phantom size and clearance, provided the position resolution was less than 100 $\mathrm{\mu m}$ and material budget was below 0.75 %.