Electron Paramagnetic Resonance Dosimeter Research Articles

Towards liquid EPR dosimetry using nitroxides in aqueous solution.

Objective. Water-equivalent dosimeters are desirable for dosimetry in radiotherapy. The present work investigates basic characteristics of novel aqueous detector materials and presents a signal loss approach for electron paramagnetic resonance (EPR) dosimetry.Approach. The proposed principle is based on the radiation dose dependent annihilation of EPR active nitroxides (NO·) in aqueous solutions. Stable nitroxide radicals (3-Maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (MmP), 3-Carbamoyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (CmP)) in aqueous solutions containing dimethyl sulfoxide (DMSO) as an additive were filled in glass capillaries for irradiation and EPR readout. Radiation doses ranging from 1 to 64 Gy were applied with a clinical 6 MV flattening filter free photon beam. EPR readout was then performed with a X-band benchtop spectrometer. The dose response, temporal stability and reproducibility of the samples' EPR signal amplitudes as well as the influence of the nitroxide concentration between 10 and 160μM on the absolute signal loss were investigated using MmP. CmP was used to examine the dependence of the dose response on DMSO concentration between 0 and 10 vol%. An indirect effect model was fitted to the experimental data assuming irradiation induced radical reactions as the underlying mechanism.Main results. For an initial MmP concentration of 20μM, absolute EPR signal loss is linear up to a dose of 16 Gy with a yield G(-NO·) of approximately 0.4μmol J-1. Within five weeks upon sample irradiation to doses between 0 and 32 Gy relative EPR signal fluctuations were on average (126 readouts) below 1% (1σ). For c(MmP) ≥ 20μM, absolute signal loss is only weakly dependent on c(MmP), whereas it increases strongly with increasing c(DMSO) in the range 0-5 vol%. An indirect effect model is applicable to describe the reaction mechanism resulting in the observed dose response curve.Significance. Liquids consisting of nitroxides in aqueous solution and small amounts of DMSO (2 vol%) show promising basic characteristics for application as water-equivalent EPR dosimeter materials in radiotherapy. The EPR signal loss is based on an indirect effect mediated by diffusing radicals originating from the radiolysis of the water/DMSO mixture.

Review of nanomaterial advances for ionizing radiation dosimetry.

There are a wide range of applications with ionizing radiation and a common theme throughout these is that accurate dosimetry is usually required, although many newer demands are provided by improved features in higher range, multi-spectral and particle type detected. Today, the array of dosimeters includes both offline and online tools, such as gel dosimeters, thermoluminescence (TL), scintillators, optically stimulated luminescence (OSL), radiochromic polymeric films, gels, ionization chambers, colorimetry, and electron spin resonance (ESR) measurement systems. Several future nanocomposite features and interpretation of their substantial behaviors are discussed that can lead to improvements in specific features, such as (1) lower sensitivity range, (2) less saturation at high range, (3) overall increased dynamic range, (4) superior linearity, (5) linear energy transfer and energy independence, (6) lower cost, (7) higher ease of use, and (8) improved tissue equivalence. Nanophase versions of TL and ESR dosimeters and scintillators each have potential for higher range of linearity, sometimes due to superior charge transfer to the trapping center. Both OSL and ESR detection of nanomaterials can have increased dose sensitivity because of their higher readout sensitivity with nanoscale sensing. New nanocrystalline scintillators, such as perovskite, have fundamentally important advantages in sensitivity and purposeful design for key new applications. Nanoparticle plasmon coupled sensors doped within a lower Zeff material have been an effective way to achieve enhanced sensitivity of many dosimetry systems while still achieving tissue equivalency. These nanomaterial processing techniques and unique combinations of them are key steps that lead to the advanced features. Each must be realized through industrial production and quality control with packaging into dosimetry systems that maximize stability and reproducibility. Ultimately, recommendations for future work in this field of radiation dosimetry were summarized throughout the review.

Investigation of the dosimetric properties of potassium hydrogen tartrate using EPR

Use of electron paramagnetic resonance (EPR) in radiation dosimetry means more accurate and reliable evaluation of radiation doses. The search for new dosimeter material is continuing to overcome some drawbacks of available ones. In current work potassium hydrogen tartrate is presented as a new EPR dosimeter material where its radiation dose dependency, effects of the change in microwave power and modulation amplitude on the peak-to-peak intensity were studied. Response of potassium hydrogen tartrate to gamma radiation was studied in two ranges: the first starts at 1.4 Gy and ends at 84.2 Gy, and the second from 42.1 Gy to 2415.6 Gy. Calibration curves were obtained with associated combined uncertainties range from 0.5% and up to 27.4% for the first peak and from 0.5% up to 10.2%, for the second peak. Calibration curves were plotted and compared to alanine. Time dependence of the EPR spectra of the radiation-induced radicals was monitored over short term (10 h) and long-term (28 days) following irradiation.

Prospective superficial EPR in-vivo dosimetry study during hypofractionated radiotherapy of breast cancer patients treated with helical tomotherapy

BackgroundIn-vivo dosimetry (IVD) is a patient specific measure of quality control and safety during radiotherapy. With regard to current reporting thresholds for significant occurrences in radiotherapy defined by German regulatory authorities, the present study examines the clinical feasibility of superficial electron paramagnetic resonance (EPR) IVD of cumulative total doses applied to breast cancer patients treated with helical intensity-modulated radiotherapy (tomotherapy).MethodsIn total, 10 female patients with left- or right-sided breast cancer were enrolled in this prospective IVD study. Each patient received a hypofractionated whole breast irradiation. A total median dose of 42.4 Gy in 16 fractions (5 fractions per week) was prescribed to the planning target volume. The treatments were completely delivered using helical tomotherapy and daily image guidance via megavoltage CT (MVCT). For each patient, three EPR dosimeters were prepared and placed at distinct locations on the patient’s skin during the delivery of all fractions. Two dosimeters were placed next to the ipsilateral and contralateral mammilla and one dosimeter was placed ventrally to the thyroid (out-of-primary-beam). The total doses delivered to the dosimeters were readout after all fractions had been administered. The measured total dose values were compared to the planned dose values derived from the treatment planning system (TPS). Daily positional variations (displacement vectors) of the ipsilateral mammilla and of the respective dosimeter were analyzed with respect to the planned positions using the daily registered MVCT image.ResultsAveraged over all patients, the mean absolute dose differences between measured and planned total dose values (± standard deviation (SD)) were: 0.49 ± 0.85 Gy for the ipsilateral dosimeter, 0.17 ± 0.49 Gy for the contralateral dosimeter and -0.12 ± 0.30 Gy for the thyroid dosimeter. The mean lengths of the ipsilateral displacement vectors (± SD) averaged over all patients and fractions were: 10 ± 7 mm for the dosimeter and 8 ± 4 mm for the mammilla.ConclusionSuperficial EPR IVD is suitable as additional safeguard for dose delivery during helical tomotherapy of breast cancer. Despite positional uncertainties in clinical routine, the observed dose deviations at the ipsilateral breast were on average small compared to national reporting thresholds for total dose deviations (i.e. 10%/4 Gy). EPR IVD may allow for the detection of critical dose errors during whole breast irradiations.

Possible use of food grade Isomalt material as an EPR dosimeter

Abstract The feasibility of using Isomalt “the food grade substance” as electron paramagnetic resonance (EPR) material in monitoring the absorbed dose has been studied. Isomalt was prepared in two forms (powder and rods). The sensitivity of Isomalt to gamma rays exceeded by increasing the absorbed dose. The prepared powder can be used in monitoring the absorbed dose in the dose range up to 22 kGy, whereas the rods can be used in the range from 5 to 50 kGy (almost double the allowed powder range). After irradiation two signals were recorded using the EPR technique addressed as S1 and S2 with (g) factor valued by 2.01 ± 0.002 and 1.993 ± 0.002 respectively. This dosimeter offers negligible humidity effect during irradiation, short and long term stabilities were investigated as well. The obtained results may qualify the Isomalt substance to be used as dose monitoring in low and moderate irradiation doses.

Suitability of superficial electron paramagnetic resonance dosimetry for in vivo measurement and verification of cumulative total doses during IMRT: A proof of principle

PurposeThe present study investigates superficial in vivo dosimetry (IVD) by means of a previously proposed electron paramagnetic resonance (EPR) dosimetry system aiming at measuring and verifying total doses delivered by complex radiotherapy treatments. In view of novel regulatory requirements in Germany, differences between measured and planned total doses to the EPR dosimeters are analyzed and compared to reporting thresholds for significant occurrences. MethodsEPR dosimeters, each consisting of one lithium formate monohydrate (LFM) and one polycrystalline l-alanine (ALA) pellet, were attached to the surface of an anthropomorphic head phantom. Three head and neck treatments with total target doses ranging from 30 to 64Gy were fully delivered to the phantom by helical tomotherapy. During each treatment, eight EPR dosimeters were placed at distinct spots: (i) within or next to the planning target volume (PTV), (ii) near to organs at risk including the parotids and the lenses, (iii) at the thyroid lying out-of-field. EPR read out was always performed after all fractions were delivered. EPR results were compared to thermoluminescence dosimeter (TLD) measurements and to the planned total doses derived from the treatment planning system (TPS). Planned total doses to the EPR dosimeters ranged from about 2 to 64Gy. ResultsBy taking uncertainties into account, the measured and planned doses were in good agreement. Exceptions occurred mainly at the thyroid (out-of-field) and lenses (extreme sparing). The maximum total dose difference between EPR results and corresponding planned doses was 1.3Gy occurring at the lenses. Remarkably, each LFM and ALA pellet placed within or next to the PTV provided dose values that were within ±4% of the planned dose. Dose deviations from planned dose values were comparable for EPR and TLD measurements. ConclusionThe results of this proof of principle study suggests that superficial EPR-IVD is applicable in a wide dose range and in various irradiation conditions – being a valuable tool for monitoring cumulative total doses delivered by complex IMRT treatments. EPR-IVD in combination with helical tomotherapy is suitable to reliably detect local dose deviations at superficial dosimeter spots in the order of current national reporting thresholds for significant occurrences (i.e. 10%/4Gy).

A dual natural lithium formate/L-alanine EPR dosimeter for a mixed radiation field in a boron neutron capture therapy irradiation facility

Standard commercial L-alanine pellets and specially prepared natural lithium formate monohydrate powder samples of specific granulometry were irradiated in a 60Co gamma-ray irradiation plant and in the mixed field (thermal neutrons and gamma photons) of a boron neutron capture therapy (BNCT) experimental facility. The γ-doses applied with the 60Co source range from 0.1 to 50 kGy, while those in the BNCT facility go from ~7 Gy to 150 Gy. The thermal neutron fluences range from 1012 neutrons cm−2 to 2 1013 neutrons cm−2. The irradiation of materials promotes the creation of stable electronic defects (generally free radicals) which constitute paramagnetic centers that can be detected and quantified by electron paramagnetic resonance (EPR). After irradiation, the EPR characterization of the samples was performed by determining the EPR intensity of the spectrum relative to a reference standard constituted by Mn2+ impurities diluted into a MgO single crystal. As expected, L-alanine has revealed to be largely insensitive to thermal neutrons fluence in the investigated range. On the contrary, it is shown that the EPR intensity of irradiated natural lithium formate monohydrate powders is clearly sensitive to thermal neutrons and has a linear dependence with the γ-dose. We propose a dual dosimeter by combining L-alanine pellets and formate powders that would allow to determine the γ-dose and thermal neutron fluence in a selected position of the BNCT irradiation facility. Moreover, we demonstrate that the 6Li enrichment that has been proposed in the literature to enhance the performance of lithium-based EPR dosimeters is not crucial in our case. Instead, the natural isotopic abundance of lithium is large enough to obtain a satisfactory sensibility to thermal neutrons in our BNCT facility for fluencies  >1012 neutrons cm−2.

Verification of lithium formate monohydrate in 3D-printed container for electron paramagnetic resonance dosimetry in radiotherapy

The nondestructive dosimetry achieved with electron paramagnetic resonance (EPR) dosimetry facilitates repetitive recording by the same dosimeter to increase the reliability of data. In precedent studies, solid paraffin was needed as a binder material to make the lithium formate monohydrate (LFM) EPR dosimeter stable and nonfragile; however, its use complicates dosimetry. This study proposes a newly designed pure LFM EPR dosimeter created by inserting LFM into a 3D-printed container. Dosimetric characteristics of the LFM EPR dosimeter and container, such as reproducibility, linearity, energy dependence, and angular dependence, were evaluated and verified through a radiation therapy planning system (RTPS). The LFM EPR dosimeters were irradiated using a clinical linear accelerator. The EPR spectra of the dosimeters were acquired using a Bruker EMX EPR spectrometer. Through this study, it was confirmed that there is no tendency in the EPR response of the container based on irradiation dose or radiation energy. The results show that the LFM EPR dosimeters have a highly sensitive dose response with good linearity. The energy dependence across each photon and electron energy range seems to be negligible. Based on these results, LFM powder in a 3D-printed container is a suitable option for dosimetry of radiotherapy. Furthermore, the LFM EPR dosimeter has considerable potential for in vivo dosimetry and small-field dosimetry via additional experiments, owing to its small effective volume and highly sensitive dose response compared with a conventional dosimeter.

A new EPR dosimeter based on glutamic acid for radiation processing application.

L-Glutamic acid (L-GA) pellets (3.8mm × 4mm) and powder dosimeters were studied in the dose range of 0.1-150kGy using the electron paramagnetic resonance (EPR) technique. The EPR spectra of irradiated L-GA pellets showed an EPR signal with eight lines, and the intensity of the signal increased with an increase of absorbed dose. The results obtained in terms of the energy-absorption coefficients suggest a similar performance of the L-GA pellets as compared to alanine pellets. The value of the temperature coefficient for the L-GA pellets during irradiation was around - 0.08%/°C which is lower than that reported for alanine dosimeter, 0.14%/°C. The influence of humidity on the pellet response was found to be negligible; i.e., the increase in response was only about 2% for a relative humidity of up to 94%. The response of L-GA powder reached stability 4h after irradiation and continued to be stable until 47days after irradiation. In contrast, the response of the L-GA pellet dosimeter reached stability 22h after irradiation and continued to be stable until 8days after irradiation. For routine applications, the L-GA pellet dosimeter should be analyzed during the stable period after irradiation, to minimize the uncertainties in dose assessment. The overall two-sigma uncertainties in absorbed dose estimation were 5.1% and 3.9% for the dose ranges of 0.1-15kGy and 15-150kGy, respectively. It is concluded that L-GA pellets represent a promising dosimeter material for quantification of radiation doses in food irradiation, medical sterilization and polymer modification.

A Brief Review-EPR Dosimetry and the Use of Animal Teeth as Dosimeters.

The technique of electron paramagnetic resonance dosimetry using tooth enamel was established in the late 1960s, and considerable research has been conducted to learn more about the benefits of using human teeth as dosimeters for the purpose of retrospective dose reconstruction. Comparatively few studies have been done which have investigated animal teeth for the same purpose. The potential exists for utilizing animal teeth as dosimeters to reconstruct doses received by a species, as well as by humans. Animals investigated in electron paramagnetic resonance studies included cows, rats, mice, dogs, pigs, rhesus monkeys, goats, reindeer, walruses, bison, polar foxes, moose, and polar bears. Much has been determined regarding the characteristics of animal teeth, and overall the use of animal teeth for electron paramagnetic resonance dosimetry appears to be a viable means of estimating external dose. Although much has been learned from animal studies, there remain unanswered questions related to electron paramagnetic resonance dosimetry and the use of animal teeth as electron paramagnetic resonance dosimeters. This article summarizes the findings of animal electron paramagnetic resonance studies and outlines what is still unknown.

Suitability of Japanese wild boar tooth enamel for use as an Electron Spin Resonance dosimeter

The objective of this study was to determine the suitability of Japanese wild boar tooth enamel to evaluate lifetime radiation doses using Electron Spin Resonance Dosimetry (ESR). The opportunity to utilize tooth enamel of Japanese wild boar as a dosimeter is of particular interest due to their importance in the ecosystem within the Fukushima Exclusion Zone. Relevant characteristics were investigated which included the degree of linearity and variability in dose response of wild boar tooth enamel in the range of 1.2–12 Gy. The tooth enamel was found to have a linear dose response in this range. Teeth harvested from the same boar exhibited a variation in dose response ranging from 3.4 to 79.9%. Tooth enamel from deciduous teeth of young boar exhibited greater uniformity in radiation dose response than permanent tooth enamel taken from old boar. This finding suggests that the additive dose method would be more appropriate for performing precise dose reconstructions using tooth enamel of old boar. Preliminary results for retrospective doses varied between 0.2 and 1.4 Gy. Critical level and decision level doses were calculated for the samples used in this study, and values suggest that this methodology would be best utilized for wild boar with estimated absorbed doses exceeding 1 Gy. Information obtained during this study will be used with data collected in future studies to determine the suitability of wild boar tooth enamel for use with ESR dosimetry.

Study of new practical ESR dosimeter based on carbonated hydroxyapatite and its dosimetric properties.

The development of new dosimeters with good dosimetric properties is important for quality control in radiation applications. A new practical electron spin resonance (ESR) dosimeter based on carbonated hydroxyapatite that simulated the composition and structure of tooth enamel was specially synthesized. The synthesized material was investigated by transmission electron microscope, X-ray diffraction, fourier transform infrared spectroscopy and X-ray photo electron spectroscopy to confirm to the main composition of carbonated hydroxyapatite with CO32- successfully doped into the crystal lattice through optimizing the synthesis process of C/P molar ratio, pH value dynamical adjustment, annealing temperature and time. The dosimetric properties were systematically investigated by ESR spectroscopy. The results indicated that the radiation induced signal had a good dose response within a relatively wide dose range. The dose response was linear in the dose range of 0–400 Gy with a correlation coefficient of 0.9999 and had dose accumulative effect in the experimental dose range of 0–100 Gy. In a wider dose range up to 30 kGy, the dose response also presented linear feature in double-logarithmic coordinate system with a correlation coefficient of 0.9970. The dose detection limit was about 0.34Gy with a given probability of 95% confidence level depending upon a rigid calculation algorithm. The signal was extremely stable in the observation time of 360 days with a variation coefficient of 3.8%. The radiation sensitivity of the material showed no remarkable variation against photon energy from 662 KeV to 1.25 MeV and dose rate from 0.86 Gy/min to 12.17 Gy/min. The material showed more sensitive in lower photon energy range below 662 keV, which hint additional calibration may need when using in special photon energy condition. The preliminary results suggested that this newly developed dosimeter was potential to become a practical dosimeter that would expand the application fields of ESR dosimetry.

Monte Carlo simulation of energy absorbed in phenolic ESR dosimeters added with gadolinium exposed to thermal, epithermal and fast neutrons

Abstract In this work analyses of the energy released per unit mass in phenolic compound exposed to neutron beams were performed with the aim of predicting the increase in dose achievable by addition of gadolinium (Gd) inside the pellets. In particular, Monte Carlo (MC) simulations were carried out for IRGANOX® 1076 phenolic compound irradiated with neutron beams with different energy spectra at various depths inside a water phantom. The addition of gadolinium increases sensitivity of phenolic ESR (electron spin resonance) dosimeters to neutrons thanks to the high gadolinium cross section for neutron capture and to the large number of secondary particles (mainly Auger and internal conversion electrons) which are able to release energy inside the sensitive material layers. For small depths in water phantom and low energy neutron spectra the increase in dose due to gadolinium is large (more than a factor 50). The enhancement is smaller in case of epithermal neutron beam, whereas the increase in dose for fast neutrons is less than 50%. In order to have a comparison with other ESR dosimeters the energy released per unit mass in phenolic compound was compared with that calculated in alanine pellets. For thermal neutron beams the energy released in phenolic compound with gadolinium is comparable to that released in alanine for small depths in phantom, whereas it is larger than in alanine for large depths. In case of epithermal and fast neutron beams the energy released in phenolic compound is larger than in alanine samples because the elastic scattering with hydrogen nuclei is more probable for high neutron energies and this phenolic compound is characterized by an higher number of 1H nuclei than alanine. All results here found suggest that these phenolic pellets could be fruitfully used for dosimetric applications in Neutron Capture Therapy.

Radiation sensitivity and EPR dosimetric potential of gallic acid and its esters

� Radiation sensitivity of gallic acid and its esters were studied in intermediate and low radiation dose range using EPR. � While the irradiated samples of GA were presented complex EPR spectra the esters presented singlet ESR spectra. � Samples were compared to alanine in terms of the dosimetric point of view. � The radiation sensitivities of the investigated materials were very low at intermediate doses. � Lauryl ester of gallic acid was found to present a good sensitivity below 10 Gy. abstract In the preset work the radiation sensitivities of Gallic Acid anhydrous and monohydrate, Octyl, Lauryl, and Ethyl Gallate (GA, GAm, OG, LG, and EG) were investigated in the intermediate (0.5-20 kGy) and low radiation (o10 Gy) dose range using Electron Paramagnetic Resonance (EPR) spectroscopy. While OG, LG, and EG are presented a singlet EPR spectra, their radiation sensitivity found to be very different in the intermediate dose range. At low radiation dose range (o10 Gy) only LG is found to be present a signal that easily distinguished from the noise signals. The intermediate and low dose range radiation sensi- tivities are compared using well known EPR dosimeter alanine. The radiation yields (G) of the interested material were found to be 1.34 � 10 � 2 , 1.48 � 10 � 2 ,4 .14� 10 � 2 , and 6.03 � 10 � 2 , 9.44 � 10 � 2 for EG, GA, GAm, OG, and LG, respectively at the intermediate dose range. It is found that the simple EPR spectra and the noticeable EPR signal of LG make it a promising dosimetric material to be used below 10 Gy of radiation dose.

Strontium sulfate as an EPR dosimeter for radiation technology application

The dosimetric characteristics of γ-radiation induced defects in strontium sulfate rod dosimeter are investigated using electron paramagnetic resonance (EPR) technique focusing on the low dose range of 1–100Gy. Significant EPR signals of spectroscopic splitting factor (g) 2.01075, 2.04225, 2.03166, 2.00774 and 1.9219086 are observed in the rod upon γ-irradiation. The intensity of the signals increases linearly with increasing absorbed doses up to 100Gy. The EPR response of irradiated dosimeter exhibits good stability over three months of storage. In addition, the response during irradiation is independent on both relative humidity (from 0% to 65%) and temperature (from 10°C to 35°C). The prepared rods are nearly water equivalent in the range of 0.4–5MeV and the overall uncertainty (2σ) of dose monitoring is approximately 4.26%.

ESR investigation of sucrose radicals produced by 0.25−4.5 Gy doses of X-ray irradiation

We investigated stable radicals produced by 0.25−4.5 Gy doses of X-ray irradiation of sucrose. Electron spin resonance (ESR) is able to observe the signal from sucrose irradiated at 0.25 Gy. The ESR signal intensity of the radicals is related to the accumulated dose, and it increases linearly with increasing absorbed dose. In addition, we examined the effect of dose rate (0.50−1.5 Gy/min) on the signal intensity of the irradiated sucrose. The stable radical production did not exhibit dose rate dependence. In addition, the peak corresponding to the irradiated glucose was observed to increase more with increasing absorbed dose than the peak corresponding to irradiated fructose. Therefore, the present ESR results regarding the 0.25−4.5 Gy irradiation of sucrose provide new insights into a possible sucrose ESR dosimeter.

The investigation of lithium formate hydrate, sodium dithionate and N-methyl taurine as clinical EPR dosimeters

IntroductionEPR-dosimetry using l-α-alanine is an established method for measuring high doses of ionizing radiation. However, since a minimum dose of approximately 4 Gy is required to achieve sufficient low uncertainties (1–2%) for clinical application, alternative dosimeter materials are being inquired. Lithium formate (LiFo) monohydrate has been studied by several groups and has revealed several promising properties in the low dose region (<4 Gy). The fading properties, however, are somewhat unpredictable, and depend on properties not yet fully uncovered. This paper reports the results from a study of lithium formate hydrate and N-methyl taurine as potential low dose EPR dosimeters. Methods and materialsPellet shaped dosimeters of lithium formate monohydrate, lithium formate hydrate, sodium dithionate and N-methyl taurine were produced using a manual Weber press, l-α-alanine was obtained from Harwell dosimeters and irradiated using 60 kV and 6 MV X-ray beams, and Co-60 gamma-rays to a dose of 30 Gy and dose ranges of 0.5–100 Gy and 2–20 Gy respectively. The dosimeters were measured using an Electron Paramagnetic Resonance (EPR)-spectrometer. The detector responses for 6 MV and Co-60 radiation beams, the fading behaviors and signal shape in time were investigated. ResultsLithium formate monohydrate and lithium formate hydrate are apparently associated with near identical EPR-spectra (mainly one broad line), and the same spectrum arises for all radiation energies investigated. The shape of the EPR resonance remains constant with time, but the intensities decreases, and the fading is more prominent for the monohydrate than for the hydrate. The EPR resonance associated with N-methyl taurine is more complex than the resonance associated with LiFo and it changes with time, implying radical transitions and growth. ConclusionsThe study showed that lithium formate hydrate is a strong candidate for EPR dosimetry with slightly better fading characteristics compared to lithium formate monohydrate.

Magnesium lactate mixed with EVA polymer/paraffin as an EPR dosimeter for radiation processing application

The dosimetric characteristics of γ-radiation-induced defects in magnesium lactate (ML) rods (3.5mm×10mm) formulated by mixing ML with molten mixtures of paraffin wax and EVA copolymer have been investigated using electron paramagnetic resonance (EPR). The EPR spectrum of irradiated ML rods was characterized by a quartet signal with the spectroscopic splitting g-factor of 2.0048±0.0003 at 0.4mT. The useful dose range of the rod dosimeter was 100Gy to 80kGy. The mass attenuation coefficient, μ/ρ, and the mass energy-absorption coefficient, μen/ρ, versus energy in the range of 10keV to 20MeV indicate that the prepared ML dosimeter is typically adipose tissue equivalent overall this energy range. The overall combined uncertainties (at 2σ) associated with routine dose monitoring in the dose range of 0.1–10kGy and 10–80kGy were found to be 6.14% and 6.36%, respectively.

Investigation of signal fading in lithium formate EPR dosimeters using a new sensitive method

The aim of this study was to investigate signal fading in lithium formate electron paramagnetic resonance (EPR) dosimeters used for clinical applications in radiotherapy. A new experimental method for determination of signal fading, designed to resolve small changes in signal from slowly decaying unstable radicals, was used. Possible signal fading in lithium formate due to different storage temperatures was also tested. Air humidity was kept at a constant level of 33% throughout the experiments. The conclusion drawn from the investigations was that the EPR signal from lithium formate is stable during at least 1 month after irradiation and is not sensitive to variations in storage temperature <40 °C when kept at a relative air humidity of 33%. This makes lithium formate a suitable dosimeter for transfer dosimetry in clinical audits.

Radical Formation in Lithium Formate EPR Dosimeters after Irradiation with Protons and Nitrogen Ions

Radical formation in polycrystalline lithium formate monohydrate after irradiation with gamma rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.7-3.9 and 110-164 keV/microm for gamma rays, protons and nitrogen ions, respectively. Doses between 5 and 20 Gy were given. The EPR reading (the area under the EPR absorption resonance) increased linearly with dose for all types of radiation. As the LET increased, the relative effectiveness (the EPR reading per dose relative to that for gamma rays) decreased, while the EPR line width increased. Track structure theory and modeling of detector effectiveness predicted the dosimeter response observed after proton and nitrogen-ion irradiation. A semi-empirical line broadening model including dipolar spin-spin interactions was developed that explained the dependence of the line width on LET. The findings indicate that the local radical density in lithium formate is increased after high-LET irradiation.