Extremity Dosemeters Research Articles

A New Extremity System and Performance at INEL

The TLD extremity dosimetry system described herein incorporates the components necessary for personnel extremity monitoring to meet current and proposed requirements. Single and dual element TLD dosemeters, ranging in thicknesses from 20 to 100 mg.cm -2 , and appropriate filtration comprise the extremity detectors which are uniquely identified by bar code labels. A dose algorithm used in conjunction with the dosemeters and TLD reader technology are capable of reporting shallow dose H p (0.07) from betas, low and high energy photons using any combination of these dosemeters. Performance tests and results were obtained by the Idaho National Engineering Laboratory (INEL) Operational Dosimetry Unit in the evaluation of a single extremity dosemeter capable of simultaneously monitoring beta and high energy gamma. Four TL materials and two filter types were tested in various combinations to 137 Cs photons, uranium slab, 90 Sr/ 90 Y, and 204 Tl beta, irradiations. An overview of the current INEL system dosemeter response, linearity, angular dependence, residual, and effects of physical damage to the dosemeter were tested. The results of these tests, presented here, lead to the preliminary conclusion that an extremity dosemeter can be constructed to monitor beta and high energy gamma radiation simultaneously.

Laser Heating of Thermoluminescent Films: Dose Mapping Applied to Beta Dosimetry

This work addresses radiation dose mapping based on scanning of laser heated thermoluminescent foils used for dose distribution analyses of beta radiation fields. Results are presented from dose homogeneity measurements, determination of depth-dose profile in tissue and studies of energy and angular responses of CaSO 4 :Dy-based TL foils for irradiation in air with beta rays ( 147 Pm, 204 Tl and 90 Sr/ 90 Y). Laser scanning results are compared with results from measurements using very thin graphite-mixed MgB 4 O 7 :Dy TL detectors. Results show that detectors based on CaSO 4 :Dy films will be suitable as extremity dosemeters for monitoring in beta radiation fields.

TSEE Response of BeO Thin Film Detectors Irradiated on ISO Rod Phantoms to Photons and Beta Radiation

Working Group 2 of the International Organisation for Standardisation (ISO) recommends a cylindrical PMMA (rod) phantom of 19 mm in diameter for the calibration of extremity dosemeters. Exoelectron emitting BeO thin film detectors on graphite substrates, covered with a polypyrrole foil of 6.7 mg.cm-2, were exposed on this rod phantom to photons and beta radiation for response assessment. Exposures to photons were carried out with heavily filtered X rays of various energies, 137Cs and 60Co, exposures to beta radiation with 90Sr/90Y, 204Tl and 147Pm. For perpendicular radiation incidence the results are related to measurements free-in-air, the angular dependence of the response to photons is compared with calculated data of Hp(0.07,a). For beta radiation the measured Hp(0.07,a) values are, within the margins of measurement uncertainty, comparable with the corresponding values achieved on the commonly used slab phantom. Certain discrepancies at larger angles of radiation incidence are caused by attenuation and scattering effects at the substrate side wall of 0.4 mm height around the TSEE sensitive plane.

Measurements of Beta Ray Spectra in CANDU Nuclear Generating Stations Using a Silicon Detector Coincidence Telescope

The measurement of beta ray spectra at various work locations inside nuclear generating stations operated by Ontario Hydro is described. The measurements were carried out using an advanced coincidence telescope spectrometer using silicon detectors only. The spectrometer is capable of measuring electron energies over the range 60 keV-2500 keV with close to 100% coincidence efficiency. Photon rejection is carried out by requiring a coincidence between either two or three silicon detectors. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermoluminescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm -2 ) results in a value of 2.73 ± 0.77 and for the extremity dosemeter (240 mg.cm -2 ) an average value of 4.42 ± 1.17 is obtained. These values are 57% and 120% greater, respectively, than the current values used by Ontario Hydro. In addition, beta correction factors for nine representative spectra were calculated for 40 mg.cm -2 and 20 mg.cm -2 chips and the results demonstrate the benefits of decreased dosemeter thickness. The average value of the beta correction factor, as well as the spread in the beta correction factor, decreases dramatically from 4.80 ± 2.1 (240mg.cm -2 ) to 1.29 ± 0.1 (20 mg.cm -2 ).

Measurements of Beta Ray Spectra Inside Nuclear Generating Stations Using a Silicon Detector Coincidence Telescope: Skin Dose Beta Correction Factors for TL Elements

The measurement of beta ray spectra at various work locations inside nuclear generating stations operated by Ontario Hydro is described. The measurements were carried out using an advanced coincidence telescope spectrometer using silicon detectors only. The spectrometer is capable of measuring electron energies over the range 70-2500 keV with close to 100% efficiency. Over 40 beta ray spectra were measured at various work locations in three nuclear generating stations. Photon rejection is carried out by requiring a coincidence between either two or three detectors. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermoluminescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm -2 ) results in a value of 2.73 ± 0.77 and for the extremity dosemeter (240 mg.cm -2 ) an average value of 4.42 ± 1.17 is obtained. These values are 57% and 120% greater, respectively, than the current values used by Ontario Hydro. In addition, beta correction factors for nine representative spectra were calculated for 40 mg.cm -2 and 20 mg cm -2 chips, and the results demonstrate the benefits of decreased dosemeter thickness. The average value of the beta correction factor, as well as the spread in the beta correction factor, decreases dramatically from 4.80 ± 2.1 (240 mg.cm -2 ) to 1.29 ± 0.1 (20 mg.cm -2 ).

Air Kerma to Dose Equivalent Conversion Coefficients for Cylindrical Phantoms Irradiated by Extended Plane-Parallel Photon Beams of Oblique Incidence Relative to the Cylinder Main Axis

For the purposes of type testing extremity dosemeters, the conversion coefficients between the receptor-free air collision kerma and the collision kerma for 4-element ICRU tissue have been calculated at a depth of 0.07 mm in two right-angled circular cylinder phantoms made of 4-element ICRU tissue and irradiated by extended plane-parallel photon beams of oblique incidence relative to the cylinder's main axis. The cylinders were 30 cm in length and 1.9 cm or 7.3 cm in diameter, representing a finger or the lower arm. The calculations were performed by Monte Carlo simulation of the energy transport of monoenergetic photons through the phantoms as a function of energy and of the angle of incidence. The angle was varied between 0 o and 90 o, the energy between 4 keV and 1.25 MeV. The results for monoenergetic photons have also been used to derive the corresponding conversion coefficients for a variety of X ray beam qualities frequently employed in the procedure for calibrating and type testing personal radiation protection dosemeters.

Angular Dependence Factors and Air Kerma to Dose Equivalent Conversion Coefficients for Cylindrical Phantoms Irradiated by Plane-Parallel Extended Monoenergetic Photon Beams

With the aid of the Monte Carlo method, conversion coefficients between the receptor-free air collision kerma and the collision kerma for 4-element ICRU tissue have been calculated at a depth of 0.007 g.cm −2 in circular cylinder phantoms irradiated by broad plane-parallel photon beams in a direction perpendicular to the cylinder main axis. The phantom material was ICRU tissue or PMMA; the phantom diameter 1.9 cm, 7.3 cm, or 30 cm; the phantom length 30 cm. The calculations were performed for monoenergetic photons in the energy range between 4 keV and 1.25 MeV. The conversion coefficients can be used in the field of extremity dosimetry to convert measured kerma or exposure values into personal dose equivalents: the results for the 7.3 cm diameter cylinder phantoms for the calibration of wrist or ankle dosemeters; those for the 1.9 cm diameter phantoms for the calibration of finger dosemeters. In addition to the conversion coefficients, their angular dependence factors in the middle plane of the phantoms perpendicular to the main axis were also studied. Such quantities for the ICRU tissue phantoms are necessary in the procedure for type testing extremity dosemeters on rod or pillar phantoms

Angular Dependence Factors and Air Kerma to Dose Equivalent Conversion Coefficients for 1.9 cm Rod and 7.3 cm Pillar Phantoms Irradiated by Extended Monodirectional X Ray Beams

Based on radiation simulations for the transport of monoenergetic photons through right-angled circular cylinder phantoms, the conversion coefficients between receptor-free air collision kerma and the collision kerma for 4-element ICRU tissue have been investigated for extended plane parallel X ray beams in two 1.9 cm rod phantoms and two 7.3 cm pillar phantoms 30 cm in length made of 4-element ICRU tissue or PMMA; the X ray beam direction was perpendicular to the phantoms' main axis. Two different types of quantities were calculated for each phantom, (i) the conversion coefficient at that point in the circular middle plane of the phantom perpendicular to its main axis which is localised at a depth of 0.007 g.cm-2 on the radius opposed to the beam direction and (ii) the angular dependence factor which describes the change of the conversion coefficient at the same point in the phantom after performing a rotation round the phantom's main axis. All these data, in particular those for the tissue phantoms, are of interest in the procedure for calibrating and type testing extremity dosemeters; the data on rod phantoms for finger dosemeters and those on pillar phantoms for wrist and ankle dosemeters.

Extremity Dosimetry in Nuclear Medicine Services using Thermoluminescent Detectors

Abstract The Radiation Protection and Safety Centre in Algiers provides two types of dosemeters, one for monitoring doses to the whole body and skin and the other one for monitoring doses to the extremities of the body. In nuclear medicine services and radiopharmaceutical laboratories, hands and arms are often closer to a given radiation source than the main part of the body and therefore receive greater doses. In this context, extremity doses have been measured by a ring dosemeter and by a fingertip ultra-thin dosemeter. The ring dosemeter consists of a metallic ring with a circular indentation to hold a LiF chip which is covered with a 10 mg.cm-2 shrinkable black polyamide layer. The ultra-thin dosemeter contains a 5 mg.cm-2 LiF element for measuring doses at a depth of 7 mg.cm-2. These extremity dosemeters have been characterised before their use in the field. They have also been tested using radioisotopes of various energies. The doses received by the monitored workers were correlated with the amount of the handled activity. The doses obtained using the fingertip and the ring dosemeters are presented and discussed from a radiological point of view.

Extremity Dosimetry in Nuclear Medicine Services using Thermoluminescent Detectors

The Radiation Protection and Safety Centre in Algiers provides two types of dosemeters, one for monitoring doses to the whole body and skin and the other one for monitoring doses to the extremities of the body. In nuclear medicine services and radiopharmaceutical laboratories, hands and arms are often closer to a given radiation source than the main part of the body and therefore receive greater doses. In this context, extremity doses have been measured by a ring dosemeter and by a fingertip ultra-thin dosemeter. The ring dosemeter consists of a metallic ring with a circular indentation to hold a LiF chip which is covered with a 10 mg.cm-2 shrinkable black polyamide layer. The ultra-thin dosemeter contains a 5 mg.cm-2 LiF element for measuring doses at a depth of 7 mg.cm-2. These extremity dosemeters have been characterised before their use in the field. They have also been tested using radioisotopes of various energies. The doses received by the monitored workers were correlated with the amount of the handled activity. The doses obtained using the fingertip and the ring dosemeters are presented and discussed from a radiological point of view.

Study of GR200F LiF:Mg,Cu,P Detectors for Extremity Dosimetry

Abstract The dosimetric properties of GR200F LiF;Mg,Cu,P detectors with 5 mg.cm-2 sensitive layers have been studied for applications in extremity dosimetry. These properties included batch homogeneity, minimum detectable dose, reproducibility, residual signals, fading characteristics, linearity of response, effect of light exposure, photon energy and angular response, and beta energy and angular response. It was found that they are acceptable for extremity dosimetry. In particular, if used in conjunction with an extremity dosemeter holder with a window thickness of approximately 4 mg.cm-2, this detector can measure accurately the tissue dose at 7 mg.cm-2 delivered by low energy beta emitters such as 147Pm.

A New Extremity Dosemeter System Based on Thermoluminescence Dosimetry

A new extremity dosemeter system has been developed at GSF serving equally as a partial body dosemeter. It consists of (1) a TL detector sealed in a heat resistant plastic capsule as part of a thin and flexible plastic strip which can also be formed into a ring and closed with a re-usable closing mechanism, (2) automatic PC controlled readout equipment. The advantages of the detector device are: sterilisable even at autoclave temperatures if unirradiated, high resistance against chemical solvents, permanent identification number, mechanical stability, suitable for wearing in a number of places and easy readout. The readout equipment provides automatic dosemeter evaluation including magazine transport, code detection and heating control. The TL signal is detected by a PMT via a flexible fluid light pipe using a digitally operated photon counting system. The system provides a dose range according to DIN 6816 for extremity dosimetry, and passed the annual quality control by PTB. The prototype system was studied in a field test for six months at different radiological institutions with about 240 users each month.

Calculation of Neutron Fluence-to-Dose Conversion Factors for Extremities

The Pacific Northwest Laboratory is developing a standard for the performance testing of personnel extremity dosimeters for the US Department of Energy. Part of this effort requires the calculation of neutron fluence-to-dose conversion factors for finger and wrist extremities. This study focuses on conversion factors for two types of extremity models: namely the polymethyl methacrylate (PMMA) phantom (as specified in the draft standard for performance testing of extremity dosimeters) and more realistic extremity models composed of tissue-and-bone. Calculations for each type of model are based on both bare and D{sub 2}O-moderated {sup 252}Cf sources. The results are then tabulated and compared with whole-body conversion factors. More appropriate energy-averaged quality factors for the extremity models have also been computed from the neutron fluence in 50 equally spaced energy bins with energies from 2.53 {times} 10{sup {minus}8} to 15 MeV. Tabulated results show that conversion factors for both types of extremity phantom are 15 to 30% lower than the corresponcung whole-body phantom conversion factors for {sup 252}Cf neutron sources. This difference in extremity and whole-body conversion factors is attributable to the proportionally smaller amount of back-scattering that occurs in the extremity phantoms compared with whole-body phantoms.

Determination of photon conversion factors relating exposure and dose for several extremity phantom designs.

Dosimetric measurements were performed to determine the exposure-to-dose conversion factors (Cx) for simple extremity phantoms suitable for extremity dosimeter performance testing. The phantoms studied represented the forearm or lower leg and the finger. Measurements were performed for solid plastic phantoms and for phantoms containing simulated bone material to determine the effect of backscattered radiations from the simulated bone to the phantom surface. Photon beam energies used for the measurements ranged from 16 keV to 1.25 MeV (average). The Cx factors for the finger phantoms did not vary significantly with phantom composition. The Cx factors in the arm/leg phantoms with the bone simulant material differed significantly from those for the solid plastic phantom over the energy range of 40-100 keV. This effect was attributed to the preferential absorption of the lower energy backscattered photons by the higher atomic number material that was contained in the bone-simulant insert. The position of the bone-simulating material below the surface of the phantom was more important than its size or level of bone equivalency. For calibrations and dosimeter testing, Al was found adequate as a bone-simulating material.

Methods of Measurement and Calibration in Personnel Dosimetry for External Irradiation: Presentation of the Concept and the Results of a Test Programme in Switzerland

In 1986 the Swiss working group on personnel dosimetry issued a recommendation on methods of calibration and measurement in personnel dosimetry for external radiation, based on ICRU report 39. The aim of the report was to give detailed and pragmatic guidance to the dosimetry services and the calibration labs. In the recommendation a definition is given for primary and secondary limited quantities, for calibration quantities and operational quantities as well as for their interrelationships. The second part of the report is a manual for the calibration and evaluation procedures for whole-body and extremity dosemeters for photon and electron radiation. Based on that recommendation an extended test programme has been performed for all dosimetry services in Switzerland. The results show that the legal introduction of the recommended concept has no severe consequences for the dosimetry services although a number of minor modifications are needed.

Re-Assessment of Dose from the Vinten Extremity Dosemeter

Re-Assessment of Dose from the Vinten Extremity Dosemeter

A small, multi-element fingertip dosimeter for beta radiation.

Many occupations involve potential exposures, directly or indirectly, to sources of beta radiation. The region of highest exposure, in many cases, will be the extremities and in particular the fingertips of people handling beta sources. Because current extremity dosimeters can significantly underestimate beta doses to the fingertips, an improved fingertip beta dosimeter was developed. The dosimeter employs a multi-element, multi-filter concept by stacking four or five thin (0.13 mm) LiF-Teflon TLDs to form the beta detector element. The entire dosimeter is approximately 1 mm thick, flexible and rugged enough for field use without interference of the user's manual dexterity. The fingertip dosimeter provides data for determining the beta energy of each exposure. The beta energy can be used to determine the TLD correction factor for converting the TLD output to beta dose. The data can be used to reconstruct the beta depth dose curve and the depth dose curve can be used to calculate the beta dose in tissue at 7 mg cm-2, for legal reporting purposes, or at any other desired depth within the range of the beta radiation. Relationships between the effective mass absorption coefficient and beta energy and between the beta correction factor and beta energy were determined for use in this study. Beta sources were fabricated for these studies, and an extrapolation chamber was used to determine reference beta doses. Tests of the fingertip dosimeter were performed by exposing it to single beta sources and to multiple beta sources. The dosimeter should be useful for monitoring exposures to beta energies ranging from 0.29-2.5 MeV.

The Energy and Angle Dependence of Response of the Vinten Extremity Dosemeter to Beta Radiation

The Energy and Angle Dependence of Response of the Vinten Extremity Dosemeter to Beta Radiation

Extremity Dosemeter Monitoring Service

Abstract The Vinten extremity dosemeter has already been shown to be an accurate and useful operational dosemeter. An instrument has been developed, and is described, for batch processing of such dosemeters for a routine extremity dosemeter service.

Energy and Angular Response of TL Dosemeters for Beta Ray Dosimetry

Abstract Measured data are presented showing the influence of detector thickness, filter thickness, and detector/filter geometry on the energy and angular response of a beta dosemeter. The investigation comprises different types of thermoluminescent detectors with Mylar filters of thicknesses ranging from 0 - 49 mg.cm-2. 147Pm, 204Tl and 90Y sources were used for the irradiations. The measurements were made by placing the detectors in depressions in a 1 cm thick Perspex phantom that was turned to obtain different irradiation angles. Comparative measurements were made with an extrapolation chamber. The results showed that thin TL detectors, e.g. graphite-mixed sintered MgB4O7:Dy pellets and the Vinten extremity dosemeter satisfy the requirement to measure Hs(0.07) with sufficient accuracy for use for personal monitoring for beta ray maximum energies above 0.2 MeV.