Review of dosimetry instrumentation in digital and interventional radiology

Some dosimetry instruments and products are reviewed, the main emphasis being on patient dosimetry, recommendations for accuracy in different measurement applications and the results of some intercomparisons. It seems to be a common problem that the users of the general purpose air kerma (Ka) meters, dose-area product (DAP) meters or products such as thermoluminescence (TL) dosemeters are not always able to select the correct ionisation chamber, the calibration factor of a DAP meter or the TL dosemeter material and type, respectively, for different radiation conditions. The combined DAP and Ka meters developed recently, as well as the exposure data acquisition systems designed for monitoring one or more quantities or for determining the effective dose of a complicated examination, are described briefly. The most advanced software of these systems is able to display the dose distributions for the most exposed areas of the skin, on-line.     

The use of passive environmental TLDs in the operation of the Spanish early warning network 'REVIRA'

As required by different international agreements, the regulatory body in Spain (Consejo de Seguridad Nuclear) implemented in 1992 a national automatic network (REVIRA) that continuously monitors radiation levels in order to give early warning of incidents having potential transboundary implications. The detector for environmental gamma-radiation dose rate is an active instrument based on a Geiger-Müller counter. However, the use of passive environmental dosemeters provides an additional low-cost dose estimate with an independent centralised calibration and even better basic features than active instruments. Since 1999, all 25 REVIRA stations have been monitored with passive TL environmental dosemeters based on LiF:Mg,Cu,P and operated according to the procedures established at Ciemat. This paper presents the obtained results and the further analysis considering differences in aspects such as photon energy response, inherent background or response to cosmic rays. The benefits of the use of passive environmental dosemeters in early warning networks are discussed.     

Individual monitoring based on magnesium borate

Valuable features of magnesium borate sintered solid thermoluminescence dosemeters (TLDs), such as near tissue- equivalence, high sensitivity, and good performances for X, gamma, beta and neutron dosimetry, were developed and produced by the Institute of Nuclear Sciences, Vinca. These features form the basis for using this type of TLDs successfully for legal personal dosimetry control in Serbia for the past 27 y. The dosimetric properties of this TL material are presented in this study.     

Energy response of different types of RADOS personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) TL detectors

The photon energy response of different RADOS (Mirion Technologies) personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) thermoluminescence (TL) detectors was investigated. Three types of badges were applied. The irradiation with reference photon radiation qualities N (the narrow spectrum series), and S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037 [International Organization for Standardization (ISO). X and gamma reference radiations for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy. ISO 4037. Part 1-4 (1999)], in the energy range of 16-1250 keV, were performed at the Dosimetry Laboratory Seibersdorf. The results demonstrated that a readout of a single MTS-N or MCP-N detector under the Al filter can be used to determine Hp(10) according to requirements of IEC 61066 [International Electrotechnical Commission (IEC). Thermoluminescence dosimetry systems for personal and environmental monitoring. International Standard IEC 61066 (2006)] for TL systems for personal dosimetry. The new RADOS badge with the experimental type of a holder (i.e. Cu/Al filters) is a very good tool for identifying the radiation quality (photon energy).     

The ENEA neutron personal dosimetry service

The ENEA Radiation Protection Institute has been operating the only neutron personal dosimetry service in Italy since the 1970s. Since the 1980s the service has been based on PADC (poly allyl diglycol carbonate) for fast neutron dosimetry, while thermal neutron dosimetry has been performed using thermoluminescence (TL) dosemeters. Since the service was started, a number of aspects have undergone evolution. The latest and most important changes are as follows: in 1998 a new PADC material was introduced in routine, since 2001 TL thermal dosimetry has been based on LiF(Mg,Cu,P) [GR-200] and (7)LiF(Mg,Cu,P) [GR-207] detectors and since 2003 a new image analysis reading system for the fast neutron dosemeters has been used. Herein an updated summary of how the service operates and performs today is presented. The approaches to calibration and traceability to estimate the quantity of H(p)(10) are mentioned. Results obtained at the performance test of dosimetric services in the EU member states and Switzerland sponsored by the European Commission and organised by Eurados in 1999 are reported. Last but not least, quality assurance (QA) procedures introduced in the routine operation to track the whole process of dose evaluation (i.e. plastic QA, acceptance test, test etching bath reproducibility and 'dummy customer' (blind test) for each issuing monitoring period) are presented and discussed.     

Individual neutron monitoring in workplaces with mixed neutron/photon radiation

EVIDOS ('evaluation of individual dosimetry in mixed neutron and photon radiation fields') is an European Commission (EC)-sponsored project that aims at a significant improvement of radiation protection dosimetry in mixed neutron/photon fields via spectrometric and dosimetric investigations in representative workplaces of the nuclear industry. In particular, new spectrometry methods are developed that provide the energy and direction distribution of the neutron fluence from which the reference dosimetric quantities are derived and compared to the readings of dosemeters. The final results of the project will be a comprehensive set of spectrometric and dosimetric data for the workplaces and an analysis of the performance of dosemeters, including novel electronic dosemeters. This paper gives an overview of the project and focuses on the results from measurements performed in calibration fields with broad energy distributions (simulated workplace fields) and on the first results from workplaces in the nuclear industry, inside a boiling water reactor and around a spent fuel transport cask.     

Performance of different thermoluminescence dosimeters in 90SR+90Y radiation fields

The dosimetry of beta radiation is a difficult process especially because of the low penetration of beta particles in matter. The dosemeter utilised for this kind of procedure needs to approximate an ideal point-like detector: it should be as thin as possible, and its area should be small. The thermoluminescence dosemeters (TLDs) meet with these requirement properties. The aim of this work was to study the dosimetric characteristics of different TLDs to verify the possibility of their use for the calibration of 90Sr+90Y plane applicators. The response reproducibility, calibration curves, TL response as a function of the source-detector distance, the transmission factors and the linearity of the sample response were obtained for several types of dosimetric pellets.     

The use of computerised glow curve analysis will optimise personal thermoluminescence dosimetry measurements. Opposing the proposition

Referring to the proposition for this debate, it is necessary to consider what is meant by 'optimise personal thermoluminescence dosimetry measurements'. Much research has been performed on the thermoluminescence glow curves that can be used to determine absorbed dose, and much of the knowledge gained from this research has been put into practice. Thermoluminescence dosemeters are capable of measuring an extremely wide range of doses and dose rates. Nearly all types of radiation can be measured, and some TL dosemeters have been designed to function as elementary spectrometers. More recently, the microdosimetric properties of TL dosemeters have been investigated. TL dosemeters are worn by a large proportion of radiation workers worldwide. But, can we conclude that thermoluminescence dosimetry measurements are at an optimum level? Perhaps that is not a fair question because it may be impossible to say when anything is truly optimum. Although the techniques pointed out by our debaters may not yet be used by all large, personal dosimetry services, as with many recent innovations, implementation may be as near as the next computer chip upgrade.     

Thermoluminescence response of K2YF5:Tb3+ crystals to photon radiation fields

This investigation has been performed to test the feasibility of using K2YF5:Tb3+ crystals as thermoluminescence dosemeters (TLD). K2YF5 single crystals doped with 0.2, 10.0 and 50.0 at.% of trivalent optically active Tb3+ ions as well as K2TbF5 and undoped K2YF5 crystals have been synthesized under hydrothermal conditions. Polished crystal platelets with thickness of about 1 mm have been irradiated with X and gamma rays in order to study thermoluminescent (TL) sensitivity as well as dose and energy response in terms of the Tb3+ concentration in K2YF5. Within this concentration series, K2YF5 crystals doped with 10.0 at.% Tb3+ have been found to have maximum TL response due to a broad asymmetric TL glow peak at 269 degrees C with good linearity of dose response and reproducibility of dose measurements. After deconvolution, the main dosimetric peak has been revealed to be composed of two individual peaks, both with linear TL response behaviour, centered at 210 and 269 degrees C. As it has been proved, the linear TL signal coefficient for K2Y0.9Tb0.1F5 is almost 10 times greater than that for commercial TLD-100 (LiF:Mg,Ti), irradiated with a 137Cs gamma radiation source at the same conditions. The reported results indicate that K2YF5 crystals doped with Tb3+ have potential as promising materials for radiation dosemeters.     

Use of composites of topaz-glass as TSEE and TL dosemeters

The properties of the thermally stimulated exoelectron emission (TSEE) and thermoluminescent (TL) emission of topaz-glass composites were studied with the aim of using them as solid-state dosemeters. The TSEE response was studied as a function of radiation energy and as a function of absorbed dose. Topaz-glass composites presented a linear TL and TSEE response to dose within a range of 0.01-1 Gy. The topaz-glass composites presented higher TSEE peaks than topaz-Teflon pellets. In the dosimetry of radiotherapic fields normally the responses of the topaz-glass dosemeters are comparable to topaz-Teflon pellets. The results confirmed that these new dosemeters can be useful in monitoring the quality of the radiation sources. This dose mapping technique is particularly useful in investigating dose distribution throughout a planned target volume.     

Technical performance of the Luxel Al(2)O(3):C optically stimulated luminescence dosemeter element at radiation oncology and nuclear accident dose levels

The dose ranges typical for radiation oncology and nuclear accident dosimetry are on the order of 2-70 Gy and 0.1-5 Gy, respectively. In terms of solid-state passive dosimetry, thermoluminescent (TL) materials historically have been used extensively for these two applications, with silver-halide, leuco-dye and BaFBr:Eu-based films being used on a more limited basis than TL for radiation oncology. This present work provides results on the performance of a film based on an aluminum oxide, Al(2)O(3):C, for these dosimetry applications, using the optically stimulated luminescence (OSL) readout method. There have been few investigations of Al(2)O(3):C performance at radiation oncology and nuclear accident dose levels, and these have included minimal dosimetric and environmental effects information. Based on investigations already published, the authors of this present study determined that overall improvements over film and TLDs for this Al(2)O(3):C OSL technology at radiation oncology and nuclear accident dose levels may include (1) a more tissue-equivalent response to photons compared to X-ray film, (2) higher sensitivity, (3) ability to reread dosemeters and (4) diagnostic capability using small-area imaging. The results of the present investigation indicate that additional favourable performance characteristics for the Al(2)O(3):C dosemeter are a wide dynamic range (0.001-100 Gy), a response insensitive to temperature and moisture over a wide range, negligible dose rate dependence, and minimal change in post-irradiation response. As a radiation detection medium, this OSL phosphor offers an assortment of dosimetry properties that will permit it to compete with current radiation detection technologies such as silver-halide, leuco-dye and photostimulable-phosphor-based films, as well as TLDs.     

Intercomparison of passive dosimetry technology at EDF facilities in France

Since the spring of 1999, new French radiation protection legislation has allowed the use of passive dosemeters, other than the silver emulsion film badge, for the measurement of H(p)(10). Faced with the eventual obsolescence of its dosimetry system, Electricité de France (EDF, the French electricity provider) initiated a comparative study of passive dosemeters, based on different technologies, that had received accreditation by national laboratories and regulatory bodies, namely: TLD, RPL and OSL. An extended field study in nuclear power stations and medical X-ray departments has shown that all technologies provide compatible dosimetric estimates. It also showed that the selected dosemeters based on RPL and OSL technologies gave better results due to their energy responses and to a lower detection threshold compliant with the new regulation. A final suggestion to implement a new OSL based dosimetric system is made due to its overall performance and to its lower cost of implementation.     

Blue light stimulated luminescence in calcium fluoride, its characteristics and implications in radiation dosimetry

Strong optically stimulated luminescence (OSL), stimulated by blue light, has been observed, for the first time, in natural calcium fluoride (CaF(2)) phosphor, used as thermoluminescence dosemeters. Traps responsible for all three thermoluminescence (TL) peaks appearing upto 300 degrees C, i.e. 126, 196 and 264 degrees C, were observed to contribute to the blue light stimulated luminescence (BLSL) in CaF(2). When the areas under the respective curves (BLSL and TL) were measured, the BLSL measured at room temperature was found to be approximately 1.8 times the TL output of the dosimetry peak that appeared at approximately 264 degrees C. However, when measured after thermally annealing the first two TL peaks, the BLSL signal was found to be 0.26 times the TL output of the dosimetry peak at 264 degrees C. This paper describes the characteristics of the BLSL signal using linearly modulated OSL after subjecting the phosphor to different annealing treatments. Feasibility studies to assess the usefulness of BLSL in CaF(2) for environmental radiation monitoring are also discussed.     

Combined TL and 10B-alanine ESR dosimetry for BNCT

The dosimetric technique described in this paper is based on electron spin resonance (ESR) detectors using an alanine-boric compound acid enriched with (10)B, and beryllium oxide thermoluminescent (TL) detectors; with this combined dosimetry, it is possible to discriminate the doses due to thermal neutrons and gamma radiation in a mixed field. Irradiations were carried out inside the thermal column of a TRIGA MARK II water-pool-type research nuclear reactor, also used for Boron Neutron Capture therapy (BNCT) applications, with thermal neutron fluence from 10(9) to 10(14) nth cm(-2). The ESR dosemeters using the alanine-boron compound indicated ESR signals about 30-fold stronger than those using only alanine. Moreover, a negligible correction for the gamma contribution, measured with TL detectors, almost insensitive to thermal neutrons, was necessary. Therefore, a simultaneous analysis of our TL and ESR detectors allows discrimination between thermal neutron and gamma doses, as required in BNCT.     

Thermoluminescent detectors applied in individual monitoring of radiation workers in Europe--a review based on the EURADOS questionnaire

Among the activities of EURADOS Working Group 2 formed by experts from several European countries is the harmonisation of individual monitoring as part of radiation protection of occupationally exposed persons. Here, we provide information about thermoluminescent detectors (TLDs) applied by the European dosimetric services and the dosimetric characteristics of dosemeters in which these detectors are applied. Among 91 services from 29 countries which responded to the EURADOS questionnaire, 61 apply dosemeters with TLDs for the determination of personal dose equivalent H(p)(10) for photons and beta radiation, and 16 services use TLDs for neutron albedo dosemeters. Those most frequently used are standard lithium fluoride TLDs (mainly TLD-100, TLD-700, Polish MTS-N and MTS-7, Russian DTG-4), high-sensitive lithium fluoride (GR-200, MCP-N) and lithium borate TLDs. Some services use calcium sulphate and calcium fluoride detectors. For neutron dosimetry, most services apply pairs of LiF:Mg,Ti TLDs with (6)Li and (7)Li. The characteristics (energy response) of individual dosemeters are mainly related to the energy response of the detectors and filters applied. The construction of filters in dosemeters applied for measurements of H(p)(10) and their energy response are also reviewed.     

The right choice: extremity dosemeter for different radiation fields

Measurements of weakly penetrating radiation in personal dosimetry present problems in the design of suitable detectors and in the interpretation of their readings. For the measurement of the individual beta radiation dose, personal dosemeters for the fingers/tips are required. LiF:Mg,Cu,P is a promising thermoluminescent (TL) material which allows the production of thin detectors with sufficient sensitivity. Dosimetric properties of two different types of extremity dosemeters, designed to measure the personal dose equivalent Hp(0.07), have been compared: LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD700H). A type test for energy response for photon and beta radiation according to ISO 4037-3 and ISO-6980 was carried out and the results for both dosemeters were compared. Simultaneous measurements with both types of dosemeters were performed at workplaces, where radiopharmaceuticals containing different radioisotopes are prepared and applied. Practices in these fields are characterized by handling of high activities at very small distances between source and skin. The results from the comparison of the two-dosemeter types are presented and analysed with respect to different radiation fields. Experiments showed a satisfactory sensitivity for the thinner dosemeter (TLD 700H) for detecting beta radiation at protection levels and a good energy response.     

Evaluation of individual monitoring in mixed neutron/photon fields: mid-term results from the EVIDOS project

EVIDOS is an EC sponsored project that aims at an evaluation and improvement of radiation protection dosimetry in mixed neutron/photon fields. This is performed through spectrometric and dosimetric investigations during different measurement campaigns in representative workplaces of the nuclear industry. The performance of routine and, in particular, novel personal dosemeters and survey instruments is tested in selected workplace fields. Reference values for the dose equivalent quantities, H(*)(10) and H(p)(10) and the effective dose E, are determined using different spectrometers that provide the energy distribution of the neutron fluence and using newly developed devices that determine the energy and directional distribution of the neutron fluence. The EVIDOS project has passed the mid-term, and three measurement campaigns have been performed. This paper will give an overview and some new results from the third campaign that was held in Mol (Belgium), around the research reactor VENUS and in the MOX producing plant of Belgonucléaire.     

Preliminary dosimetric characterisation of thermoluminescent materials for beta radiation monitoring at nuclear medicine services

Beta emitters are widely used in nuclear medicine for diagnostic and therapeutic purposes. The critical groups exposed to a radioactive patient include the staff, other patients and members of the public accompanying the patient. The aim of this work is to characterise thermoluminescent (TL) materials for the staff monitoring of nuclear medicine services that manipulate beta radiation solutions of (153)Sm. This study was performed using CaSO(4):Dy + Teflon pellets, produced at IPEN, with different dimensions. For the dosimetric characterisation, these TL dosemeters were exposed to gamma source ((60)Co) and to beta sealed sources ((90)Sr + (90)Y, (204)Tl and (147)Pm) and to a non-sealed source ((153)Sm). Results were obtained related to reproducibility, lower detection limits, calibration curves, angle and energy dependence of response. All tested materials show usefulness for monitoring of workers exposed to beta radiation.     

Study of the photon radiation performance of electronic personal dosemeters

Following the specifications and test methods given by international standards IEC-61526 and ISO 4037, the dosimetry department of the IPSN studied the photon radiation performance of seven recent electronic personal dosemeters: The personal dosimetric performance of each piece of equipment was tested with X and gamma radiation between 12 keV and 1.25 MeV.     

EURADOS self-sustained programme of intercomparisons for individual monitoring services

Within EURADOS working group 2, a system for self-sustained intercomparisons for individual monitoring services for external radiation was developed. With the intercomparison results, the participants can show compliance within their quality management system, compare their results with those from other participants and develop plans for improvement of their system. The costs of the exercises are covered by the participants fees. In this programme, the first intercomparison exercise for whole-body dosemeters has been executed in 2008 with 62 participating dosimetry systems from participants across Europe. In general, film systems show the largest deviations, although the results of some participants indicate that it is possible to achieve results with a film system with similar quality as for thermoluminescence dosimetry (TLD) systems. A second intercomparison has been organised for extremity dosemeters in 2009. For 2010 it is planned to organise a second intercomparison for whole-body dosemeters.