Personal dosimetry for positron emitters, and occupational exposures from clinical use of gallium-68.

The current status and issues regarding positron dosimetry in nuclear medicine are summarized. The suitability of the United Kingdom Health Security Agency extremity and eye beta-gamma personal thermoluminescence dosemeters are then considered. Monte Carlo modelling is performed to determine their responses and derive sets of calibration factors, along withHp(0.07) andHp(3) conversion coefficients, for carbon-11, nitrogen-13, oxygen-15, fluorine-18 and gallium-68 sources, which are commonly used in positron emission tomography (PET) computed tomography; data for these isotopes is assumed extrapolatable to other positron sources. It is found that the dosemeters are adequate for assessing exposures to PET radionuclides, even if their routine calibrations to caesium-137 were maintained. An idealized set of measurements representing gallium-68 exposure scenarios is then described, including reproducible mock-ups of individuals manipulating vials and syringes. Finally, a short case-study is presented that explores occupational doses during routine clinical use of gallium-68. The extremity dosemeter results demonstrated significant variations dependent upon the exposure conditions, with some seen to be comparatively large; whole-body and eye dose rates per activity were found to be lower. The importance of routine dose monitoring of workers is emphasized, with the need for a longer-termed follow-up study demonstrated.

Biomarker support for ADHD diagnosis based on Event Related Potentials and scores from an attention test.

ADHD is a heterogeneous neurodevelopmental disorder associated with dysfunctions in several brain systems. Objective markers of brain dysfunction for clinical assessment are lacking. Many studies applying electroencephalography (EEG) and neuropsychological tests find significant differences between ADHD and controls, but the effect sizes (ES) are often too small for diagnostic purposes. This study aimed to compute a diagnostic index for ADHD by combining behavioral test scores from a cued visual go/no-go task and Event Related Potentials (ERPs). Sixty-one children (age 9-12 years) diagnosed with ADHD and 69 age- and gender-matched typically developing children (TDC) underwent EEG-recording while tested on a go/no-go task. Based on comparisons of ERP group-means and task-performance, variables that differed significantly between the groups with at least moderate ES were converted to a five points percentile scale and multiplied by the ES of the variable. The sum-scores of the variables constituted the diagnostic index. The index discriminated significantly between patients and TDC with a large ES. This index was applied to an independent sample (20 ADHD, 21 TDC), distinguishing the groups with an even larger ES. The diagnostic index described has the potential to support assessment. Further research establishing diagnostic indexes for differential diagnoses is needed.

Virtual estimation of effective dose in neutron fields.

The PODIUM project aims to provide real-time assessments of occupationally exposed workers by tracking their motion and combining this with a simulation of the radiation field. The present work describes the approach that would be taken in mixed neutron-gamma fields, and details the methods for generating and applying an effective dose rate map; the required fluence to effective dose conversion coefficients at intercardinal angles are also presented. A proof-of-concept of the approach is demonstrated using a simple simulated workplace field within a calibration laboratory, with corroborative comparisons made against survey instrument measurements generally confirming good agreement. Simulated tracking of an individual within the facility was performed, recording a 1.25µSv total effective dose and accounting for dose rates as low as 0.5 nSv h-1, which is much lower than anything that could be accurately measured by physical neutron dosemeters in such a field.

12- and 18-month follow-up after residential treatment of methamphetamine dependence: Influence of treatment drop-out and different treatment concepts.

This study investigates the effects of two different residential treatments and of treatment drop-out in a German methamphetamine (MA) dependent sample. 108 subjects from two addiction treatment concepts were recruited at treatment begin and followed-up at 12 (T2) and 18 (T3) months after treatment. Based on follow-up samples (n = 38 at T2, n = 25 at T3), 77.1% at T2 and 68.0% at T3 were MA abstinent. Classifying everyone, who did not participate at follow-ups as having had a relapse, showed MA-abstinence rates of 25.0% (at T2) and 15.7% (at T3). There was no difference in MA-use between treatment conditions nor between treatment completers and drop-outs. Having injected any substance predicted MA-use at T2 (p = .03). The median time of relapse was 1.5 days after hospital release. Depression scores at T2 predicted MA-use at T3 (p = .02). T2 participants that dropped out of treatment had higher craving scores at T2, than T2 subjects who completed treatment (p = .03). The results show positive effects of current inpatient treatment programs without differences between different concepts. More research is needed to clarify the impact of treatment drop-out. Attention should be paid to a successful transition from residential to outpatient services and to a reduction of study attrition.

Effectiveness of methamphetamine abuse treatment: Predictors of treatment completion and comparison of two residential treatment programs.

BACKGROUND: There is an increasing demand of evidence-based treatment options for methamphetamine users, but research in this field is limited. This study therefore evaluates the efficacy of two residential treatment programs for methamphetamine users. METHOD: A total of 108 patients with a history of methamphetamine abuse from two inpatient rehabilitation centers were studied for psychiatric symptoms, craving, psychosocial resources, and cognitive functioning at the start and end of therapy. Patients from one center ("amphetamine type stimulant group") received conventional group therapy plus an additional 10 h of group therapy focusing on stimulant use. Patients from the other center ("treatment as usual") received conventional group therapy only. Predictors of drop-out were estimated. RESULTS: A drop-out rate of 40.7% was observed without a significant difference between both centers. Patients remained significantly longer in treatment as usual compared to amphetamine type stimulant treatment. Irrespective of treatment program, craving and psychiatric symptoms significantly decreased while psychosocial resources, processing speed, and cognitive flexibility improved over time. Other cognitive measures yielded mixed results. History of injection drug use was a significant predictor for treatment drop-out. CONCLUSIONS: Existing treatments are effective in reducing craving and psychiatric symptoms. Additional stimulant specific groups do not appear to influence treatment completion and secondary outcome measures. Institutions should therefore offer treatment for methamphetamine users, even if they do not provide a therapy content focusing on methamphetamine. History of injection drug use should receive attention in treatment to prevent drop-out. Changes in cognitive functioning need to be further explored.

The effects of a revised operational dose quantity on the response characteristics of neutron survey instruments.

The ICRU is considering revising the definition of ambient dose equivalent. This paper investigates the impacts of the proposed change on four designs of neutron survey instrument, the GNU, HSREM, LB6411 and Studsvik 2202D, in terms of their respective energy dependences of response and their performances in realistic workplace fields. In some circumstances the current designs of instrument still produce acceptable characteristics, but in general they may need to be re-optimized to better match the requirements of the new operational quantity; to that end, a simple retrofit solution for the GNU is demonstrated. The performance criteria against which instruments are judged may also need to be revised to reflect the proposed change.

THE RESPONSE OF THE PHE NEUTRON PERSONAL DOSEMETER IN TERMS OF THE PROPOSED ICRU PERSONAL DOSE EQUIVALENT.

The ICRU is considering amending the definition of the operational quantity for personnel monitoring. The present work investigates the impact of the proposed change on the PHE neutron personal dosemeter, which utilizes electrochemically etched PADC and is currently optimized in terms of Hp(10). The energy-dependent dose response characteristics of the dosemeter, and its performance in realistic workplace neutron fields, are calculated and compared for both the current and proposed dose quantities, for both frontal and rotationally isotropic fields. Adoption of the proposed quantity would make the dosemeter more sensitive to normally incident neutrons, but it would require some modification to ensure that it is able to meet the recommendations of the current ISO standard at all energies and its directional dependence of response would be poorer. The implications of this are discussed.

THE PHE FORTUITOUS DOSIMETRY CAPABILITY BASED ON OPTICALLY STIMULATED LUMINESCENCE OF MOBILE PHONES.

The Public Health England fortuitous dosimetry capability is reviewed, with particular attention focussed on the derivation of its energy and fading corrections, the Monte Carlo techniques used to generate the calibration factors between phone and body doses, and the procedures set in place to facilitate a reliable and effective service.

CALIBRATION OF THERMOLUMINESCENCE AND FILM DOSEMETERS FOR SKIN DOSES FROM HIGH-ACTIVITY MICROPARTICLES.

The use of EXT-RAD™ extremity TLDs and radiochromic film to measure doses from primarily beta-emitting microparticles is discussed. Specific calibration techniques have been developed, using both Monte Carlo modelling and experiments. Results for a (90)Sr/(90)Y microparticle are presented to illustrate the general techniques and to demonstrate reasonable agreement between the dosimetry methods.

Development of a retrospective/fortuitous accident dosimetry service based on OSL of mobile phones.

Work is presented on the development of a retrospective/fortuitous accident dosimetry service using optically stimulated luminescence of resistors found in mobile phones to determine the doses of radiation to members of the public following a radiological accident or terrorist incident. The system is described and discussed in terms of its likely accuracy in a real incident.

Measurements with the new PHE neutron survey instrument.

A novel design of survey instrument has been developed to accurately estimate ambient dose equivalent from neutrons with energies in the range from thermal to 20 MeV. The device features moderating and attenuating layers to ease measurement of fast and intermediate energy neutrons, combined with guides that channel low-energy neutrons to the single, central detector. A prototype of this device has been constructed and exposed to a set of calibration fields: the resulting measured responses are presented and discussed here, and compared against Monte Carlo data. A simple simulated workplace neutron field has also been developed to test the device.

Monte Carlo modelling of 90Sr/90Y and 85Kr beta fields for Hp(3) measurements.

In support of research aimed at developing a thermoluminescence dosemeter capable of accurately measuring ionising radiation doses to the lens of the eye, Monte Carlo modelling of a standard beta exposure set-up has been performed. It was found that electrons with an energy distribution corresponding to the beta emission spectrum from (85)Kr deposit negligible doses at a depth of 3 mm in tissue, but doses from (90)Sr/(90)Y are significant; free in air and fluence-to-Hp(3,θ°) and -Hp(0.07,θ°) conversion coefficient data were found for this field for exposures at 0°, 30° and 60° angles of incidence, and the response characteristics of the new eye dosemeter were evaluated. It was shown that the results were not affected greatly by the shape of the calibration phantom. However, it was demonstrated that the presence of intermediating air and beam flattening filters hardens the energy distribution of the field at the point of test, relative to a raw (90)Sr/(90)Y source, and this impacts dose depositions.

A comparison of the response of PADC neutron dosemeters in high-energy neutron fields.

Within the framework of the EURADOS Working Group 11, a comparison of passive neutron dosemeters in high-energy neutron fields was organised in 2011. The aim of the exercise was to evaluate the response of poly-allyl-glycol-carbonate neutron dosemeters from various European dosimetry laboratories to high-energy neutron fields. Irradiations were performed at the iThemba LABS facility in South Africa with neutrons having energies up to 66 and 100 MeV.

Type testing of a head band dosemeter for measuring eye lens dose in terms of H(P)(3).

A new head band dosemeter, for the measurement of eye lens dose in terms of Hp(3), has been type tested by Public Health England's Centre for Radiation, Environmental and Chemical Hazards [formerly part of the UK Health Protection Agency (HPA)]. The type tests were based on the International Standard ISO 12794, drawing also upon earlier work at HPA. The results show that, unlike many existing dosemeters, the new head band dosemeter correctly measures Hp(3) for beta radiations as well as photons.

Individual monitoring for external radiation at accelerator facilities.

Individual monitoring at accelerator facilities is discussed, within the framework set out by the International Commission on Radiological Protection and with reference to the implementation of the recommendations of that body within the European Basic Safety Standards. Legislation in other parts of the world may differ, but a worldwide perspective on this subject would be too exhaustive. The fields at accelerator facilities are contrasted in terms of particle type and energy with those encountered at more conventional sites within the nuclear fuel cycle, medical applications and general industry. The implications for individual monitoring are discussed in relation to the dose quantities for these accelerator fields and also with respect to the personal dosemeters options.

The MCNP-4C2 design of a two element photon/electron dosemeter that uses magnesium/copper/phosphorus doped lithium fluoride.

The Health Protection Agency is changing from using detectors made from 7LiF:Mg,Ti in its photon/electron personal dosemeters, to 7LiF:Mg,Cu,P. Specifically, the Harshaw TLD-700H card is to be adopted. As a consequence of this change, the dosemeter holder is also being modified not only to accommodate the shape of the new card, but also to optimize the photon and electron response characteristics of the device. This redesign process was achieved using MCNP-4C2 and the kerma approximation, electron range/energy tables with additional electron transport calculations, and experimental validation, with different potential filters compared; the optimum filter studied was a polytetrafluoroethylene disc of diameter 18 mm and thickness 4.3 mm. Calculated relative response characteristics at different angles of incidence and energies between 16 and 6174 keV are presented for this new dosemeter configuration and compared with measured type-test results. A new estimate for the energy-dependent relative light conversion efficiency appropriate to the 7LiF:Mg,Cu,P was also derived for determining the correct dosemeter response.

Neutron area survey instrument measurements in the EVIDOS project.

Neutron survey instruments have been exposed at all the measurement locations used in the EVIDOS project. These results have an important impact in the interpretation of the results from the project, since operationally the survey instrument will be used for an initial assessment of and routine monitoring of the ambient dose equivalent dose rate. Additionally, since the response of these instruments is in some cases very well characterised, their systematic deviations from the reference quantities provide an important verification of the determination of those quantities.

Improved characterisation of the HPA PADC neutron personal dosemeter.

The fast neutron energy dependence of response of the HPA PADC neutron personal dosemeter has been measured from 144 keV to 19 MeV using monoenergetic neutron fields. Below 144 keV the relative energy and angle dependence of response have been determined using MCNP-4C2. New data from the SIGMA field at Cadarache, France, have been used to determine the appropriate scaling factor for the calculated response to thermal and intermediate energy neutrons. These newly determined response characteristics of the dosemeter are discussed with respect to its performance in the EVIDOS workplace field irradiations.

Modelling of neutron survey instrument performance and experimental validation of those calculated response data.

Three moderator-type neutron survey instruments have been modelled for energy and angle dependence of the response, in greater detail than before. These response data have been verified by comparison with published experimental measurements and measurements made specifically for this project. Influences on the instrument response have also been investigated. These have included its mode-of-use and perturbations caused by variations in the instrument manufacture. The implications of these new response data have been assessed by an extensive programme of folding the responses with workplace energy distributions.

Angle dependence of response characteristics of neutron survey instruments.

Neutron area survey instruments are designed to have an approximately isotropic response. In practice, the response cannot be perfectly isotropic for instruments that do not have spherical symmetry, and for all instruments it is modified by the inclusion of batteries, electronics, handles, etc. This affects the ability of the survey instrument to measure accurately an isotropic dose equivalent quantity. Measurements of the angle dependence of response for four of the most commonly used designs of survey instrument (Harwell 0949, Mark 7 NRM, NM2 and Studsvik 2202D) have been performed in a low-scatter room using radionuclide and monoenergetic neutron sources. The Monte Carlo code MCNP has been used to model the responses and to investigate their sensitivity to the polyethylene density, counting gas pressure and other manufacturing tolerances. Preliminary modelling results are presented here.