Assessment of microscopic ion beam field variation using fluorescent nuclear track detectors

Abstract Fluorescent Nuclear Track Detectors (FNTDs) feature superior, submicron spatial resolution that allows for single particle track detection. However, when assessing particle fluence from measured track positions, discrimination of actual fluence patterns from stochastic fluctuations due to spatial randomness in particle arrival can only be done at considerably lower resolution. This work quantifies the spatial limits of fluence-based dosimetry of (heavy) charged particles and presents the tools to detect deviations from homogenous 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 tenths 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%.