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The relative biological effectiveness (RBE) calculations used during the planning of ion therapy treatments are generally based on the microdosimetric kinetic model (MKM) and the local effect model (LEM). The Mayo Clinic Florida MKM (MCF MKM) was recently developed to overcome the limitations of previous MKMs in reproducing the biological data and to eliminate the need for ion-exposed in vitro data as input for the model calculations. Since we are considering to implement the MCF MKM in clinic, this article presents (a) an extensive benchmark of the MCF MKM predictions against corresponding in vitro clonogenic survival data for 4 rodent and 10 cell lines exposed to ions from 1H to 238U, and (b) a systematic comparison with published results of the latest version of the LEM (LEM IV). Additionally, we introduce a novel approach to derive an approximate value of the MCF MKM model parameters by knowing only the animal species and the mean number of chromosomes. The overall good agreement between MCF MKM predictions and in vitro data suggests the MCF MKM can be reliably used for the RBE calculations. In most cases, a reasonable agreement was found between the MCF MKM and the LEM IV. [ABSTRACT FROM AUTHOR]

Objective. Treatment planning based on computer simulations wasproposed to account for the increased relative biological effectiveness (RBE) of proton radiotherapy beams near to the edges of the irradiated volume. Since silicon detectors could be used to validate the results of these simulations, it is important to explore the limitations of this comparison. Approach. Microdosimetric measurements with a MicroPlus Bridge V2 silicon detector (thickness = 10 μ m) were performed along the Bragg peak of a clinical proton beam. The lineal energy distributions, the dose-mean values, and the RBE calculated with a biological weighting function were compared with PHITS simulations (microdosimetric target = 1 μ m water sphere), and published clonogenic survival in vitro RBE data for the V79 cell line. The effect of the silicon-to-water conversion was also investigated by comparing three different methodologies (conversion based on a single value, novel bin-to-bin conversions based on SRIM and PSTAR). Main results. Mainly due to differences in the microdosimetric targets, the experimental dose-mean lineal energy and RBE values at the distal edge were respectively up to 53% and 28% lower than the simulated ones. Furthermore, the methodology chosen for the silicon-to-water conversion was proven to affect the dose-mean lineal energy and the RBE10 up to 32% and 11% respectively. The best methodology to compensate for this underestimation was the bin-to-bin silicon-to-water conversion based on PSTAR. Significance. This work represents the first comparison between PHITS-simulated lineal energy distributions in water targets and corresponding experimental spectra measured with silicon detectors. Furthermore, the effect of the silicon-to-water conversion on the RBE was explored for the first time. The proposed methodology based on the PSTAR bin-to-bin conversion appears to provide superior results with respect to commonly used single scaling factors and is recommended for future studies. [ABSTRACT FROM AUTHOR]

Abstract Due to their common use for dose measurements in space and hadron therapy facilities, it is of fundamental importance to know the efficiency of luminescent detectors for measuring a wide range of particles and energies. However, due to experimental limitations it is often not possible to irradiate the detectors with very high energies, less common isotopes or exotic particles. Furthermore, the efficiency determination at low energies is biased with associated large uncertainties in range, linear energy transfer and dose. This paper presents the recently developed Microdosimetric d(z) Model able to assess the relative efficiency of thermoluminescent detectors for measuring different radiation qualities by relating the simulated dose probability distribution of the specific energy in nanometric targets with an experimentally determined response function. The model was tested in case of LiF:Mg, Ti (MTS) and LiF:Mg,Cu,P (MCP) thermoluminescent detectors exposed to charged particles from 1H to 132Xe in the energy range 3–1000 MeV/u. A comparison with experimentally determined efficiency results showed a very good agreement in case of calculations performed in a simulated target size of 40 nm. This validated model can be used to assess detector efficiency to exotic particles, unavailable radiation qualities and energies at ground level accelerators or complex mixed fields. The assumptions behind the model, its methodology and results are discussed in detail. Furthermore, a systematic investigation on the effect of simulation parameters on the calculated efficiency values is included in the manuscript. Highlights • A model based on microdosimetry was developed for predicting TLD efficiency. • LiF:Mg, Ti and LiF:Mg,Cu,P efficiency was determined for particles from 1H to 132Xe. • The determined efficiencies depend on the site size of the calculations. • For a site size of 40 nm, very good agreement with experimental data was found. [ABSTRACT FROM AUTHOR]

Abstract Lithium fluoride thermoluminescent radiation detectors with different dopant concentrations (7LiF:Mg,Ti and 7LiF:Mg,Cu,P) were exposed to 1H and 4He ions at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in order to investigate their response to energetic light charged particles. Computer simulations with the Monte Carlo code PHITS were performed for a better interpretation of the experimental data. The results were compared with literature efficiency data and with the results of a recently developed microdosimetric efficiency model. In case of the main peak signal of 7LiF:Mg,Ti detectors, the determined efficiency values are in good agreement with previous investigations. Discrepancies in the efficiency of high temperature signal due to well-known non-linearity effects are reported. For 7LiF:Mg,Cu,P detectors, an anomalous thermoluminescence behavior in the low temperature part of the signal was found and discussed. Depending on the light quantification process, differences up to 30% in the dose assessment can be obtained, affecting also the relative efficiency determination process. An explanation of this phenomenon as a consequence of local migration of the charged carriers between the low temperature peaks and the main peak is presented. The implications of these findings on the use of LiF:Mg,Cu,P detectors in radiation environments characterized by the presence of 1H and 4He ions (i.e. space and proton therapy) are discussed. In order to avoid the occurrence of this anomalous behavior, it is advised to pre-heat the detectors after energetic light particle exposures. Highlights • LiF:Mg,Ti and LiF:Mg,Cu,P thermoluminescent detectors were exposed to 1H and 4He ions. • An anomalous low temperature behavior was found for LiF:Mg,Cu,P detectors. • This can affect the dose assessment process with LiF:Mg,Cu,P detectors up to 30%. [ABSTRACT FROM AUTHOR]

Passive radiation detectors based on the optically stimulated luminescence of anion-defective aluminum-oxide doped with carbon (Al 2 O 3 :C) are commonly used for personal, environment and medical dosimetry. However, their luminescence efficiency in measuring a certain type of radiation is strongly affected by the pattern of energy deposition at the nanoscale and the corresponding possible saturation of trapping, luminescent or competitive centers within the detector. To better understand the results of the measurements and to further exploit their use in complex radiation environments, including space and clinical particle beams, the efficiency of the detectors should be known for a wide variety of particles and particle energies. In this work, radiation transport simulations using the Monte Carlo code PHITS are coupled with the Microdosimetric d(z) Model to calculate the efficiency of the blue emission (F centers) of Al 2 O 3 :C (Luxel) optically stimulated luminescent detectors in case of exposures to ions from 1H to 132Xe. The model was initially developed to describe the response of differently doped thermoluminescent detectors based on lithium fluoride. This study represents the first application of the Microdosimetric d(z) Model to a different material (aluminum oxide) and a different phenomenon (optically stimulated luminescence). The results of the theoretical calculations were compared to experimentally determined efficiency data and good agreement (average relative deviation ∼ 6%) was found in case of simulations performed using radiation sensitive targets with a diameter of approximately 100 nm. Furthermore, the possibility of determining the optimal target size by using only a subset of the available data was proven successful. • The relative efficiency of Al 2 O 3 :C OSL detectors was theoretically calculated. • The theoretical results are in very good agreement with the experimental data. • The optimal radiation-sensitive target diameter was found to be ∼100 nm. • The target diameter can be determined by using a subset of the available data. • The relative efficiency depends strongly on both the particle type and the LET. [ABSTRACT FROM AUTHOR]

The Microdosimetric d(z) Model was used in combination with simulated microdosimetric specific energy probability distributions for monoenergetic 1H and 4He ions (energy range = 0.1–1000 MeV/n, target size range = 1–2000 nm) to investigate the possibility of modeling the relative efficiency of two optical absorption (OA) bands (4.77 and 5.08 eV) in the OA energy spectra of LiF:Mg,Ti (TLD-100) thermoluminescent detectors. This work represents the first application of the model to a physical system other than thermally- and optically-stimulated luminescence. The 4.77 eV OA trap is populated by electrons liberated during irradiation and its experimental OA relative efficiency was successfully predicted using a target size of 9 nm in the simulations. On the other hand, the model was not able to reproduce the values of the experimentally-observed proton induced OA efficiency above unity for the 5.08 eV OA band associated with the F centers in LiF:Mg,Ti (electron occupied Fluoride vacancy). The F centers are initially present in the LiF lattice but are also created by the irradiation. Since the absence of defect creation by the irradiation is a necessary condition of the microdosimetric model, the discrepancy between the model results for the F band and the experimental data was not unexpected. The calculations for both OA bands are presented as a function of the particle energy and the simulated microdosimetric target size and will be useful in further applications of the model OA relative efficiencies for charged particles. • The relative OA efficiency of LiF:Mg,Ti detectors was calculated for two OA bands. • 4.77 eV OA band: the model agrees with the experimental data for a 9 nm target. • 5.08 eV OA band: as expected, the model cannot reproduce the experimental data. [ABSTRACT FROM AUTHOR]

The relative efficiency of the two most commonly used 7LiF:Mg,Ti (MTS-7) and 7LiF:Mg,Cu,P (MCP-7) thermoluminescent detectors was calculated using the Microdosimetric d(z) Model for negative muons, positive muons, negative pions, positive pions, negative kaons, positive kaons and neutral kaons with energies spanning from 2 keV to 1 GeV. The needed microdosimetric specific energy probability density distributions were obtained by performing Monte Carlo radiation transport simulations using the computer code PHITS in the optimal 40 nm site size. The obtained efficiency values were found to be strongly affected by the particle type, its energy and the detector, ranging from 0.25 to 1.08. Possible correlations with average microdosimetric quantities such as the frequency- and dose-mean specific energy were discussed in detail. Finally, the effect of including the nominal dopant concentrations in the simulations used for the assessment of the microdosimetric spectra was proven to play a marginal role in the computation of the relative efficiency values, in agreement with what was found in previous studies for ions, photons, electrons, positrons and mixed particle fields. • Specific energy density distributions for muons, pions and kaons were simulated using PHITS. • The obtained spectra were used as input to the Microdosimetric d(z) Model. • The efficiencies of 7LiF:Mg,Ti (MTS-7) and (MCP-7) detectors were theoretically calculated. • The efficiency values depend strongly on the detector, the particle type and its energy. [ABSTRACT FROM AUTHOR]

7LiF:Mg,Cu,P (MCP-7) thermoluminescent detectors were exposed at nine positions within a 60 MeV pristine proton Bragg peak to investigate the possibility of counteracting the occurrence of their low temperature anomalous behavior (strong increase in the relative intensity of the peak 3 after exposure to energetic charged particles, Parisi et al., 2018 a) by using the post-irradiation pre-readout thermal protocol of 120 °C for 30 min. Simulations with the Monte Carlo radiation transport code PHITS were performed in order to determine the absorbed dose, the LET and the specific energy density distributions within the detector volume as a function of its position along the Bragg peak. The experimentally determined efficiency values for the main peak signal agreed with the results of the Microdosimetric d(z) Model with an average deviation of 2.4%. The consistency of the results supports the hypothesis that the light signal of the main peak 4 partly arises from trapped charge carriers previously giving rise to the neighboring low-temperature peak 3 and that the non-standardized post-irradiation procedure is the reason for the spread in the experimentally determined proton efficiency data present in literature. Thus, for a correct dose assessment and to mitigate possible low temperature anomalies in the glow curve structure of LiF:Mg,Cu,P detectors, it is strongly advised to always employ the recommended preheat protocol of 30 min at 120 °C. • Using an optimal pre-heat protocol, LiF:Mg,Cu,P efficiency to protons was determined. • A very good agreement with theoretical efficiency values was found. • The low temperature anomalous behavior was successfully counteracted. • The phenomenon was explained as charge carrier migration from peak 3 to peak 4. [ABSTRACT FROM AUTHOR]