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The response of Al2O3:C optically stimulated luminescence detectors (OSLDs) was investigated in a 250 MeV pencil proton beam. The OSLD response was mapped for a wide range of average dose rates up to 9000 Gy s−1, corresponding to a ∼150 kGy s−1 instantaneous dose rate in each pulse. Two setups for ultra-high dose rate (FLASH) experiments are presented, which enable OSLDs or biological samples to be irradiated in either water-filled vials or cylinders. The OSLDs were found to be dose rate independent for all dose rates, with an average deviation <1% relative to the nominal dose for average dose rates of (1–1000) Gy s−1 when irradiated in the two setups. A third setup for irradiations in a 9000 Gy s−1 pencil beam is presented, where OSLDs are distributed in a 3 × 4 grid. Calculations of the signal averaging of the beam over the OSLDs were in agreement with the measured response at 9000 Gy s−1. Furthermore, a new method was presented to extract the beam spot size of narrow pencil beams, which is in agreement within a standard deviation with results derived from radiochromic films. The Al2O3:C OSLDs were found applicable to support radiobiological experiments in proton beams at ultra-high dose rates.

Ionization quenching in organic scintillators is usually corrected with methods that require careful assessment of the response relative to that of an ionization chamber. Here, we present a framework to compute ionization quenching correction factors (QCFs) from first principles for organic plastic scintillators exposed to ions. The tool solves the kinetic Blanc equation, of which the Birks model is a simplified solution, based on amorphous track structures models. As a consequence, ionization quenching correction factors can be calculated relying only on standard, tabulated scintillator material properties such as the density, light yield, and decay time. The tool is validated against experimentally obtained QCFs for two different organic plastic scintillators irradiated with protons with linear energy transfers (LETs) between 5-[Formula: see text]. The QCFs computed from amorphous track structure models and the BC-400 scintillator properties deviate less than 3% from the Birks model for LETs below [Formula: see text] and less than 5% for higher LETs. The agreement between experiments and the software for the BCF-12 scintillator is within 2% for LETs below [Formula: see text] and within 10% for LETs above, comparable to the experimental uncertainties. The framework is compiled into the open source software [Formula: see text] available for download. [Formula: see text] enables computations of QCFs in organic plastic scintillators exposed to ions independently of experimentally based quenching parameters in contrast to the Birks model. [Formula: see text] can improve the accuracy of correction factors and understanding of ionization quenching in scintillator dosimetry.

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Dosimetry with ionization chambers in clinical ion beams for radiation therapy requires correction for recombination effects. However, common radiation protocols discriminate between initial and general recombination and provide no universal correction method for the presence of both recombination types in ion beams of charged particles heavier than protons. Here, we present the open source code IonTracks, where the combined initial and general recombination effects in principle can be predicted for any ion beam with arbitrary particle-energy spectrum and temporal structure. IonTracks uses track structure theory to distribute the charge carriers in ion tracks. The charge carrier movements are governed by a pair of coupled differential equations, based on fundamental physical properties as charge carrier drift, diffusion, and recombination, which are solved numerically while the initial and general charge carrier recombination is computed.The algorithm is numerically stable and in accordance with experimentally validated theories for initial recombination in heavy ion tracks and general recombination in a proton beam.IonTracks is validated against the Jaffé's and Boag's theory of recombination in pulsed beams of multiple ion species. IonTracks is able to calculate the correction factor for initial and general recombination losses in parallel-plate ionization chambers. Even if only few experimental data on recombination effects in ionization chambers are available today, the universal concept of IonTracks is not limited to the ions investigated here. Future experimental investigations of recombination in pulsed and possibly also continuous ion beams may be conducted with IonTracks, which ultimately may lead to a more precise prediction of recombination factors in complex radiation fields.

The ion recombination is examined in parallel-plate ionization chambers in scanning proton beams at the Danish Centre for Particle Therapy and the Skandion Clinic. The recombination correction factor k s is investigated for clinically relevant energies between 70 MeV and 244 MeV for dose rates below 400 Gy min −1 in air. The Boutillon formalism is used to separate the initial and general recombination. The general recombination is compared to predictions from the numerical recombination code IonTracks and the initial recombination to the Jaffé theory. k s is furthermore calculated with the two-voltage method (TVM) and extrapolation approaches, in particular the recently proposed three-voltage (3VL) method. The TVM is in agreement with the Boutillon method and IonTracks for dose rates above 100 Gy min −1 . However, the TVM calculated k s is closer related to the Jaffé theory for initial recombination for lower dose rate, indicating a limited application in scanning light ion beams. The 3VL is in turn found to generally be in agreement with Boutillon's method. The recombination is mapped as a function of the dose rate and proton energy at the two centres using the Boutillon formalism: the initial recombination parameter was found to be A = (0.10 ± 0.01) V at DCPT and A = (0.22 ± 0.13) V at Skandion, which is in better agreement with the Jaffé theory for initial recombination than previously reported values. The general recombination parameter was estimated to m 2 = (4.7 ± 0.1) • 10 3 V 2 nA −1 cm −1 and m 2 = (7.2 ± 0.1) • 10 3 V 2 nA −1 cm −1 . Furthermore, the numerical algorithm IonTracks is demonstrated to correctly predict the initial recombination at low dose rates and the general recombination at high dose rates.

The objective of this study was to improve the precision of linear energy transfer (LET) measurements using $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4–6.5) $$\hbox {keV}\, \upmu \hbox {m}^{-1}$$ keV μ m - 1 range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV ($$F^+$$ F + -center) emission bands of $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

Ionization quenching in ion beam dosimetry is often related to the fluence-or dose-averaged linear energy transfer (LET). Both quantities are however averaged over a wide LET range and a mixed field of primary and secondary ions. We propose a novel method to correct the quenched luminescence in scintillators exposed to ion beams. The method uses the energy spectrum of the primaries and accounts for the varying quenched luminescence in heavy, secondary ion tracks through amorphous track structure theory. The new method is assessed against more traditional approaches by correcting the quenched luminescence response from the BCF-12, BCF-60, and 81-0084 plastic scintillators exposed to a 100 MeV pristine proton beam in order to compare the effects of the averaged LET quantities and the secondary ions. Calculations and measurements show that primary protons constitute more than 92 % of the energy deposition but account for more than 95 % of the luminescence signal in the scintilllators. The quenching corrected luminescence signal is in better agreement with the dose measurement when the secondary particles are taken into account. The Birks model provided the overall best quenching corrections, when the quenching corrected signal is adjusted for the number of free model parameters. The quenching parameter k B for the BCF-12 and BCF-60 scintillators is in agreement with literature values and was found to be k B = (10.6 ± 0.1) × 10 −2 µm keV −1 for the 81-0084 scintillator. Finally, a fluence threshold for the 100 MeV proton beam was calculated to be of the order of 10 10 cm −2 , corresponding to 110 Gy, above which the quenching increases non-linearly and the Birks model no longer is applicable.