A mathematical approach to optimal selection of dose values in the additive dose method of EPR dosimetry

doi:10.1016/S1350-4487(96)00117-5

Radiation Measurements

Volume 27, Issue 2, April 1997, Pages 315-323

https://doi.org/10.1016/S1350-4487(96)00117-5 Get rights and content

Abstract

Additive dose methods commonly used in electron paramagnetic resonance (EPR) dosimetry are time consuming and labor intensive. We have developed a mathematical approach for determining optimal spacing of applied doses and the number of spectra which should be taken at each dose level. Expected uncertainties in the data points are assumed to be normally distributed with a fixed standard deviation and the linearity of the dose response is also assumed. The optimum spacing and number of points necessary for minimal error can be estimated as can the likely error in the resulting dose estimate. When low doses are being estimated for enamel samples, the optimal spacing is shown to be a concentration of points near the zero dose value with fewer spectra taken at a single high dose value within the range of known linearity. Optimization of the analytical process results in increased accuracy and sample throughput.

References (24)

M. Barabas et al.
Dose-response and thermal behavior of the ESR signal at g = 2.0006 in carbonates
Quaternary Science Reviews
(1992)
B.G. Dalgarno et al.
Evaluation of ESR as a radiation accident dosimetry technique
Applied Radiation and Isotopes
(1989)
R. Grun
Present status of ESR-dating
Applied Radiation and Isotopes
(1989)
R. Grun
Errors in dose assessment introduced by the use of the linear part of a saturation dose-response curve
Radiation Measurements
(1996)
E. Haskell et al.
An EPR intercomparison using teeth irradiated prior to crushing
Radiation Measurements
(1997)
E. Haskell et al.
Improved accuracy of EPR dosimetry using a constant rotation goniometer
Radiation Measurements
(1997)
C. Jacobs et al.
ESR study of gamma ray irradiated synthetic calcium carbonates
Applied Radiation and Isotopes
(1989)
A.D. Oduwole et al.
Transient ESR signals induced by γ-irradiation in tooth enamel and bone
Quaternary Science Reviews
(1994)
A.D. Oduwole et al.
Some ESR observations on bone, tooth enamel and eggshell
Applied Radiation and Isotopes
(1993)
V. Polyakov et al.
Effect of mechanically induced background signal on EPR dosimetry of tooth enamel
Radiation Measurements
(1995)

S. Toyoda et al.

ESR dating of quartz with stable component of impurity centers

Quaternary Science Reviews

(1994)

R. Walther et al.

ESR studies on flint with a difference spectrum method

Quaternary Science Reviews

(1994)

Cited by (24)

The first KREDOS-EPR intercomparison exercise using alanine pellet dosimeter in South Korea
2020, Nuclear Engineering and Technology
Citation Excerpt :
The additive dose method generally estimates the initial dose in the process of obtaining a specific response curve for the same incrementally irradiated sample. Optimal spacing of the applied dose and the number of spectra were decided by referring to related literature [23,24]. The estimated initial dose was far from the center of the calibration range, so this method increased the confidence interval.
This paper presents the results of the first intercomparison exercise performed by the Korea retrospective dosimetry (KREDOS) working group using electron paramagnetic resonance (EPR) spectroscopy. The intercomparison employed the alanine dosimeter, which is commonly used as the standard dosimeter in EPR methods. Four laboratories participated in the dose assessment of blind samples, and one laboratory carried out irradiation of blind samples. Two types of alanine dosimeters (Bruker and Magnettech) with different geometries were used. Both dosimeters were blindly irradiated at three dose levels (0.60, 2.70, and 8.00 Gy) and four samples per dose were distributed to the participating laboratories. Assessments of blind doses by the laboratories were performed using their own measurement protocols. One laboratory did not participate in the measurements of Magnettech alanine dosimeter samples. Intercomparison results were analyzed by calculating the relative bias, E_n value, and z-score. The results reported by participating laboratories were overall satisfactory for doses of 2.70 and 8.00 Gy but were considerably overestimated with a relative bias range of 10–95% for 0.60 Gy, which is lower than the minimum detectable dose (MDD) of the alanine dosimeter. After the first intercomparison, participating laboratories are working to improve their alanine-EPR dosimetry systems through continuous meetings and are preparing a second intercomparison exercise for other materials.
Verification of radiotherapy doses by EPR dosimetry in patients’ teeth
2016, Radiation Measurements
The aim of this work was to verify applicability of electron paramagnetic resonance (EPR) ex vivo dosimetry in teeth enamel for determination of doses absorbed by patients during radiotherapy with radiation fields covering head regions and to examine with what accuracy the doses predicted by radiotherapy treatment plan (RTP) can be confirmed by doses measured ex post by the EPR method. The doses were determined in 22 enamel samples obtained from 11 patients who, after their radiotherapy treatment underwent extraction of teeth due to medical reasons. The delivered doses were determined by measuring EPR signals in enamel samples from the extracted teeth; magnitude of these signals is proportional to concentration of stable free radicals induced by radiation in the hydroxyapatite content of enamel. The measured doses were compared with doses planned in the teeth locations by RTP systems. The relation between the measured (D_m) and the planned (D_p) doses can be described as a linear function: D_m = s·D_p + b, with the slope s = 0.93 ± 0.03 and the intercept b = 0.67 ± 1.26. The deviations between the measured and calculated doses were in the (−12.6%, +1.9%) range with the average deviation of – 4.6%. It is concluded, than more accurate measurements, achievable when using a higher calibration dose than in the present study, are necessary to confirm or to deny the observed bias between the measured and planned doses.
EPR dosimetry with tooth enamel: A review
2010, Applied Radiation and Isotopes
Citation Excerpt :
The uncertainty arising from the calibration curve can be determined by the propagation of uncertainties in its intercept and its slope (the former is a constant term and the latter is a relative one). The mathematics needed for this calculation can be found elsewhere (Draper and Smith, 1998; Hayes et al., 1997). It should be also noted that the slope and the intercept are correlated (for implications of this see Appendix C and ISO, 1995, pp. 20–22).
When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.
Comparison of γ- And UV-light-induced EPR spectra of enamel from deciduous molar teeth
2005, Applied Radiation and Isotopes
From previous work, it is known that CO₂⁻ radicals in tooth enamel are induced by gamma as well as by UV-light exposure. The parameters of the EPR signal of the CO⁻₂ radical were found to be independent of the source of exposure. However, it would be desirable for retrospective dosimetry to identify other characteristic features of the EPR spectrum of tooth enamel, which would allow differentiation between the two sources of exposure. In the present work, enamel of deciduous molars was exposed to γ-radiation from a ⁶⁰Co-source and 254 nm UV-light from a low-pressure mercury lamp. The resulting EPR spectra were deconvoluted, and the native spectrum simulated from spectra of the CO⁻₂ radical, and two further EPR lines. Both EPR signals of the native spectrum were located at g=2.0046, but were different in line shape and width. One was a 1 mT wide isotropic signal of Gaussian line shape while the other was a 0.7 mT wide axial signal of Lorentzian line shape. A comparable study of the amplitudes of the native and CO₂⁻ signals was done before and after γ- and UV-light exposure. While the native signals were found to be only slightly sensitive to γ-radiation, their amplitude increased significantly on UV-light exposure. Feasibilities are discussed to distinguish different radiation sources by exposure-induced alterations of the native EPR spectrum.
Parameters affecting EPR dose reconstruction in teeth
2005, Applied Radiation and Isotopes
The aim of this paper is to analyze the lower limit of detection (LLD), linearity of dose response, variation of radiation sensitivity between different tooth enamel samples, and time/temperature stability of EPR biodosimetry in tooth enamel. The theoretical LLD is shown to be 0.46 mGy, which is far lower than the measured value of about 30 mGy. The main issues to lowering LLD are the differentiation of the radiation-induced component against the total EPR spectrum and the complex nature of the dose dependence of the EPR signal. The following questions are also discussed in detail: need for exfoliated or extracted teeth from persons of interest, accounting for background radiation contribution; conversion of tooth enamel absorbed dose to effective dose; accounting for internal exposure specifically from bone-seeking radionuclides. Conclusions on future development of EPR retrospective biodosimetry are made.
A critical discussion of the 2nd intercomparison on electron paramagnetic resonance dosimetry with tooth enamel
2001, Radiation Measurements
Recently, we have participated in ‘The 2nd International Intercomparison on EPR Tooth Dosimetry’ wherein 18 laboratories had to evaluate low-radiation doses (100–1000 mGy) in intact teeth (Wieser et al., Radiat. Meas., 32 (2000a) 549). The results of this international intercomparison seem to indicate a promising picture of EPR tooth dosimetry. In this paper, the two Belgian EPR participants present a more detailed and critical study of their contribution to this intercomparison. The methods used were maximum likelihood common factor analysis (MLCFA) and spectrum subtraction. Special attention is paid to potential problems with sample preparation, intrinsic dose evaluation, linearity of the dose response, and determination of dose uncertainties.

View all citing articles on Scopus

View full text

A mathematical approach to optimal selection of dose values in the additive dose method of EPR dosimetry

Abstract

Quaternary Science Reviews

Applied Radiation and Isotopes

Applied Radiation and Isotopes

Radiation Measurements

Radiation Measurements

Radiation Measurements

Applied Radiation and Isotopes

Quaternary Science Reviews

Applied Radiation and Isotopes

Radiation Measurements

Quaternary Science Reviews

Quaternary Science Reviews