Assessment of Microscopic Ion Beam Field Variation using Fluorescent Nuclear Track Detectors

TL;DR

This study evaluates the spatial resolution limits of Fluorescent Nuclear Track Detectors in detecting microscopic variations in ion beam fluence, highlighting the scale at which dose heterogeneities can be reliably identified.

Contribution

It introduces quantitative tools to assess the detectability of fluence deviations in FNTD measurements and defines spatial thresholds for accurate dosimetry.

Findings

Deviations in fluence below 5% are undetectable on scales smaller than several tens of millimeters.

Read-out areas larger than 0.2 mm are necessary to detect small fluence differences.

Detection of sub-percent dose variations requires spatial scales exceeding 0.2 mm.

Abstract

Fluorescent Nuclear Track Detectors (FNTDs) offer a superior, sub-micrometer spatial resolution that allows for single particle track detection. However, when assessing particle fluence from the measured track positions, discrimination of actual fluence patterns from stochastic fluctuations is necessary due to spatial randomness in particle arrival. This work quantifies the spatial limits of fluence-based dosimetry of (heavy) charged particles and presents the use of tools to detect deviation from homogenous (true) fluence in measured data. It is found that deviations in fluence (and hence dose) on a percent level cannot be detected in a carbon beam on scales smaller than several tens of a millimeter even when using dose levels of 1 Gy. For typical fluences measured with FNTDs, read-out area side-lengths should be larger than 0.2 mm to detect fluence differences of less than 5 %.