Fluence-based dosimetry of proton and heavier ion beams using single track detectors

Abstract

Due to their superior spatial resolution, small and biocompatible fluorescent nuclear track detectors (FNTDs) open up the possibility of characterizing swift heavy charged particle fields on a single track level. Permanently stored spectroscopic information such as energy deposition and particle field composition is of particular importance in heavy ion radiotherapy, since radiation quality is one of the decisive predictors for clinical outcome. Findings presented within this paper aim towards single track reconstruction and fluence-based dosimetry of proton and heavier ion fields. Three-dimensional information on individual ion trajectories through the detector volume is obtained using fully automated image processing software. Angular distributions of multidirectional fields can be measured accurately within ±2° uncertainty. This translates into less than 5% overall fluence deviation from the chosen irradiation reference. The combination of single ion tracking with an improved energy loss calibration curve based on 90 FNTD irradiations with protons as well as helium, carbon and oxygen ions enables spectroscopic analysis of a detector irradiated in Bragg peak proximity of a 270 MeV u(-1) carbon ion field. Fluence-based dosimetry results agree with treatment planning software reference.

Alpha particle spectroscopy using FNTD and SIM super‐resolution microscopy

“…The true energy distribution can therefore reasonably be expected to be broader than the simulation is showing. Nevertheless, for both imaging modalities the proposed method showed a better energy resolution than would likely be achievable using track width or track intensity based methods for alpha radiation (Sykora et al ., ; Klimpki et al ., ). It is however important to note that the method proposed in this work is only applicable for tracks ending within the FNTD, which is only the case for (very) low‐energy ions, whereas the other methods can be used for all types of tracks.…”

“…The increased resolution can also be used for better detection of secondary particles in clinical carbon beams. Due to the low fluorescence intensity and often large angle of incidence of these secondary particles, their numbers are often underestimated when using CLSM for FNTD read‐out (Klimpki et al ., ). SIM is therefore considered an excellent competitor for high‐resolution FNTD read‐out, especially with the possibility of fast image acquisition and real‐time SIM reconstruction in combination with automatic surface plane detection (Akselrod et al ., ).…”

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

“…For dosimetry, LET determination with FNTDs still suffers from uncertainties in the order of 20 % due to inter-detector fluctuation of sensitivity [Klimpki et al, 2016], which increases the dose uncertainty accordingly.…”

“…Beside well-established methods such as plastic nuclear track detectors (e.g. CR-39 [Durrani, 2008, Sinenian et al, 2011) or (silicon-based) semiconductor devices ([Eisaman et al, 2011, Renker andLorenz, 2009]), Fluorescent Nuclear Track Detectors (FNTDs) together with confocal laser scanning [Akselrod and Sykora, 2011] are currently studied as fluence-based dosimeters [Klimpki et al, 2016].…”

A 3D feature point tracking method for ion radiation

“…The expected fluence in the FNTD was 1.25x10 6 cm -2 , which corresponds roughly to the scenario of a cell study with 1 alpha track per 10 µm diameter cell. The FNTD was read-out using a Carl Zeiss LSM710 with a 63x 1.40 oil-immersion objective and two fiber-coupled, photon-counting APDs (Klimpi et al 2015).…”