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.

Comparison of calculation methods used for the determination of anthelmintic resistance in sheep in a temperate continental climate.

This study compared results obtained with five different fecal egg count reduction (FECR) calculation methods for defining resistance to ivermectin, fenbendazole, and levamisole in gastrointestinal nematodes of sheep in a temperate continental climate: FECR1 and FECR2 used pre-and posttreatment fecal egg count (FEC) means from both treated and control animals, but FECR1 used arithmetic means, whereas FECR2 used geometric means; FECR3 used arithmetic means for pre- and posttreatment FECs from treated animals only; FECR4 was calculated using only arithmetic means for posttreatment FECs from treated and control animals; and FECR5 was calculated using mean FEC estimates from a general linear mixed model. The classification of farm anthelmintic resistance (AR) status varied, depending on which FECR calculation method was used and whether a bias correction term (BCT, i.e., half the minimum detection limit) was added to the zeroes or not. Overall, agreement between all methods was higher when a BCT was used, particularly when levels of resistance were low. FECR4 showed the highest agreement with all the other FECR methods. We therefore recommend that small ruminant clinicians use the FECR4 formula with a BCT for AR determination, as this would reduce the cost of the FECRT, while still minimizing bias and allowing for comparisons between different farms. For researchers, we recommend the use of FECR1 or FECR2, as the inclusion of both pre- and posttreatment FECs and use of randomly allocated animals in treatment and control groups makes these methods mathematically more likely to estimate the true anthelmintic efficacy.

Comparison of calculation methods used for the determination of anthelmintic resistance in sheep in a temperate continental climate.

This study compared results obtained with five different fecal egg count reduction (FECR) calculation methods for defining resistance to ivermectin, fenbendazole, and levamisole in gastrointestinal nematodes of sheep in a temperate continental climate: FECR1 and FECR2 used pre- and posttreatment fecal egg count (FEC) means from both treated and control animals, but FECR1 used arithmetic means, whereas FECR2 used geometric means; FECR3 used arithmetic means for pre- and posttreatment FECs from treated animals only; FECR4 was calculated using only arithmetic means for posttreatment FECs from treated and control animals; and FECR5 was calculated using mean FEC estimates from a general linear mixed model. The classification of farm anthelmintic resistance (AR) status varied, depending on which FECR calculation method was used and whether a bias correction term (BCT, i.e., half the minimum detection limit) was added to the zeroes or not. Overall, agreement between all methods was higher when a BCT was used, particularly when levels of resistance were low. FECR4 showed the highest agreement with all the other FECR methods. We therefore recommend that small ruminant clinicians use the FECR4 formula with a BCT for AR determination, as this would reduce the cost of the FECRT, while still minimizing bias and allowing for comparisons between different farms. For researchers, we recommend the use of FECR1 or FECR2, as the inclusion of both pre- and posttreatment FECs and use of randomly allocated animals in treatment and control groups makes these methods mathematically more likely to estimate the true anthelmintic efficacy.

Taenia ovis infection and its control: a Canadian perspective.

Distributed worldwide, Taenia ovis infection is responsible for the condemnation of sheep carcasses in many countries. This review highlights the programme used in New Zealand to successfully control T. ovis in sheep, and discusses how similar approaches may be modified for use in Canada, given what is currently known about the epidemiology of T. ovis. The lifecycle of the parasite is well known, involving dogs as the definitive host and sheep or goats as the intermediate host. An effective vaccine does exist, although it is not presently commercially available. In New Zealand an industry-based, non-regulatory programme was created to educate producers about T. ovis and necessary control strategies, including the need to treat farm dogs with cestocides regularly. This programme resulted in a substantial decrease in the prevalence of T. ovis infections between 1991 and 2012. Historically, T. ovis was not a concern for the Canadian sheep industry, but more recently the percentage of lamb condemnations due to T. ovis has increased from 1.5% in 2006 to 55% in 2012. It has been suggested that coyotes may be transmitting T. ovis, but this has not been confirmed. Recommendation are made for the Canadian sheep industry to adopt a control programme similar to that used in New Zealand in order to reduce the prevalence of T. ovis infection.

A longitudinal study on the effect of lambing season on the periparturient egg rise in Ontario sheep flocks.

The epidemiology of the periparturient egg rise (PPER) of gastrointestinal nematodes (GINs) in sheep remains unclear, and may be influenced by the lambing season. This longitudinal study was performed to determine the effect of out-of-season lambing on the PPER in ewes in Ontario, and whether total plasma protein (TPP) and packed cell volume (PCV) were associated with the PPER. Six farms that practiced out-of-season lambing were enrolled, and sampled for three consecutive lambing seasons (winter, spring and autumn). For each lambing season, all farms were visited five times. On the first visit for each lambing season, 15-20 pregnant ewes and 15-20 non-pregnant/early gestation ewes were randomly selected. At each visit, fecal samples were collected from all selected animals and processed individually to measure GIN fecal egg counts (FECs). Blood samples were collected on three visits in each lambing period and processed to measure TPP and PCV. The ewes were classified into one of five production stages (maintenance [i.e. not pregnant], early or late gestation [<120 d and ≥ 120 d, respectively], and early or late lactation [<40 d and ≥ 40 d, respectively]) based on information collected during farm visits. Linear mixed models were developed for the TPP, PCV and logarithmic-transformed FEC (lnFEC). During the winter and spring lambing season, the FECs increased gradually over the gestation period and peaked during lactation, with these increases being larger in ewes with a low PCV (three-way interaction in the final model). In the autumn lambing season, the FECs started off higher in early gestation, and increased rapidly to peak in late gestation, particularly for animals with low PCV levels. In the TPP model, PCV and lnFEC were positively associated with TPP. During both autumn and winter lambing seasons, the TPP decreased from maintenance throughout gestation and early lactation, followed by an increase in late lactation, except for when there were high FECs. During the spring lambing season, TPP peaked at early gestation, and then decreased in late gestation, to increase more gradually over lactation. In the PCV model, PCV increased with TPP and decreased exponentially with increases in lnFEC. The PPER occurred during all three lambing seasons, and its magnitude and distribution varied with the lambing season, suggesting that the PPER in ewes depends on both environmental and animal physiological factors, an important consideration when implementing preventive parasite control strategies on sheep farms that practice out-of-season lambing.

Anthelmintic resistance in sheep flocks in Ontario, Canada.

Gastrointestinal nematodes (GIN) are a significant constraint to pasture-based sheep production worldwide. Anthelmintic resistance (AR) has been reported in most sheep-raising areas in the world, yet little is known about the AR status in Canada. This study was conducted to determine the frequency of AR in GIN in sheep flocks in Ontario, Canada. Forty-seven sheep flocks were enrolled in the study, and their level of parasitism was monitored monthly throughout a grazing season by analyzing owner-acquired fecal samples from 15 grazing lambs per flock. When the mean GIN fecal egg count (FEC) reached a threshold of 200 eggs per gram (epg), oral ivermectin was supplied to producers to check ivermectin efficacy; the reduction in mean FEC 14 days after ivermectin treatment was calculated. 'Drench failure' was defined as a reduction in mean FEC of <95%. In those flocks with apparent drench failure, researchers performed a Fecal Egg Count Reduction Test (FECRT), dividing sheep into 4 treatment groups (n=10-15): control (i.e. untreated), ivermectin, and, if sufficient numbers of animals - fenbendazole and levamisole. AR was defined as a reduction in mean FEC <95% and a lower 95% confidence interval <90%. Larval cultures were performed on pooled post-treatment FECRT samples. Larval Development Assays (LDAs) to detect the presence of resistance to thiabendazole and levamisole were performed prior to the ivermectin drench check on pooled owner-acquired fecal samples that reached the 200 epg threshold. Approximately 89% (42/47) of the farms reached the FEC threshold of 200 epg; 93% (39/42) of these farms performed an ivermectin drench check, and 88% (34/39) of these farms had drench failure. The FECRT was performed on 29 of the 34 farms. Resistance to ivermectin, fenbendazole and levamisole was demonstrated on 97% (28/29), 95% (19/20) and 6% (1/17) of the farms tested, respectively, with considerable variability in resistance levels among farms. Haemonchus sp. was the most commonly cultured parasite from post-treatment fecal samples. LDA results for 21 farms were available; of these, 14% (3/21) and 62% (13/21) had low and high levels of thiabendazole resistance, respectively, while none of the farms exhibited resistance to levamisole. Amongst these tested farms, resistance to both ivermectin and benzimidazoles was very common. These findings strongly suggest that AR, particularly in Haemonchus sp., is a serious problem in these sheep flocks. Thus, marked changes in GIN management need to be instituted immediately to mitigate a worsening situation.

Doses and risks from uranium are not increased significantly by interactions with natural background photon radiation.

The impact of depleted uranium (DU) on human health has been the subject of much conjecture. Both the chemical and radiological aspects of its behaviour in the human body have previously been investigated in detail, with the radiological impact being assumed to be linked to the alpha decay of uranium. More recently, it has been proposed that the accumulation in tissue of high-Z materials, such as DU, may give rise to enhanced local energy deposition in the presence of natural background photon radiation due to the high photoelectric interaction cross sections of high-Z atoms. It is speculated that, in addition to producing short-range photoelectrons, these events will be followed by intense Auger and Coster-Kronig electron emission, thereby causing levels of cell damage that are unaccounted for in conventional models of radiological risk. In this study, the physical and biological bases of these claims are investigated. The potential magnitudes of any effect are evaluated and discussed, and compared with the risks from other radiological or chemical hazards. Monte Carlo calculations are performed to estimate likely energy depositions due to the presence of uranium in human tissues in photon fields: whole body doses, organ doses in anthropomorphic phantoms and nano-/micro-dosimetric scenarios are each considered. The proposal is shown generally to be based on sound physics, but overall the impact on human health is expected to be negligible.

Determination of the level of benzo[a]pyrene in fatty foods and food supplements.

A routine method was developed for the quantification of benzo[a]pyrene (BaP) in edible oils and food supplements. BaP is often taken as an indicator of the presence of polycyclic aromatic hydrocarbons. The method consists of on-line liquid chromatography clean-up followed by injection to an HPLC system with fluorescence detection. The method has good performance characteristics and gave good results in proficiency tests. From 2002 to 2004, about 1350 samples of oils and food supplements were analysed using this method to test the level of BaP. About 20% of the edible oils contained more than 1.2 microg kg-1 BaP (which is the limit applied by the Dutch Food and Consumer Product Safety Authority until 1 April 2005, and includes measurement uncertainty). In the case of food supplements, more then 30% contained too high levels of BaP, ranging from 1.2 to 135 microg kg-1.

Glandularity and mean glandular dose determined for individual women at four regional breast cancer screening units in the Netherlands.

The nationwide breast cancer screening programme using mammography has been in full operation in The Netherlands since 1997. There is concern that the mean glandular doses due to mammography might be differing between different regions of the country due to differences in glandularity and compressed breast thickness. To investigate regional differences, glandularity, compressed breast thickness and mean glandular dose were determined for individual breasts during screening at mammography units at four locations in The Netherlands. Differences in glandularity were observed, which could be related qualitatively to differences in age of the participants at the different locations. Mean glandular dose depends on compressed breast thickness, glandularity and technical conditions of screening. The lowest average value of the mean glandular dose was found for the unit in Amsterdam. This is most likely due to the use of the Mo/Rh anode/filter combination at this unit, in addition to the Mo/Mo combination. At the other three units, almost exclusively the Mo/Mo anode/filter combination was used. Differences in mean glandular dose averaged per unit could be related mainly to differences in tube-current exposure-time product values. Consequently, it is concluded that differences in mean glandular dose at different units are marginal.

Method for determination of the mean fraction of glandular tissue in individual female breasts using mammography.

The nationwide breast cancer screening programme using mammography has been in full operation in the Netherlands since 1997. Quality control of the screening programme has been assigned to the National Expert and Training Centre for Breast Cancer Screening. Limits are set to the mean glandular dose and the centre monitors these for all facilities engaged in the screening programme. This procedure is restricted to the determination of the entrance dose on a 5 cm thick polymethylmethacrylate (PMMA) phantom. The mean glandular dose for a compressed breast is estimated from these data. Individual breasts may deviate largely from this 5 cm PMMA breast model. Not only may the compressed breast size vary from 2 to 10 cm, but breast composition varies also. The mean glandular dose is dependent on the fraction of glandular tissue (glandularity) of the breast. To estimate the risk related to individual mammograms requires the development of a method for determination of the glandularity of individual breasts. A method has been developed to derive the glandularity using the attenuation of mammography x-rays in the breast. The method was applied to a series of mammograms at a screening unit. The results, i.e., a glandularity of 93% within the range of 0 to 1, were comparable with data in the literature. The glandularity as a function of compressed breast thickness is similar to results from other investigators using differing methods.

Elaboration of microbiological guidelines as an element of codes of hygienic practices for small and/or less developed businesses to verify compliance with hazard analysis critical control point.

Effective assurance of microbiological food safety practices in small and/or less developed businesses is not yet resolved. Although a start has been made by drafting hygiene codes, feasible methods for verifying manufacturing processes that rely on strict and meaningful criteria to be applied to process points are still lacking. This investigation is a model study with various types of ready-to-eat foods aimed at verifying adequate processing for safety and subsequent meticulous hygienic handling and safe storage of foods in small and/or less developed businesses by the use of quantitative methods for selected indicator organisms, as standardized by the International Organization for Standardization. The manufacture of the foods that were used in this study invariably included (i) a heat processing step that ensured a level of lethality of nonsporing organisms at least equivalent to the reduction of such organisms attained in the pasteurization of milk and (ii) effective means of prevention of postprocess recontamination and recolorization. The results of this study indicate that simple microbiological criteria used for this purpose, including aerobic mesophilic colony (standard plate) counts, Enterobacteriaceae counts, and, in some instances, enumeration of yeast propagules, allow adequate verification of good practices throughout. This verification through monitoring of samples taken during processing in small and/or less developed businesses was found to be an attractive alternative to the conventional examination of end products.

Calculation of absorbed dose around a facility for disposing of low activity natural radioactive waste (C3-dump).

A C3-dump is a facility for disposing of low activity natural radioactive waste containing the uranium series 238U, the thorium series 232Th and 40K. Only the external radiation owing to gamma rays, X-rays and annihilation photons is considered in this study. For two situations--the semi-infinite slab and the tourist geometry--the conversion coefficients from specific activity to air kerma rate at 1 m above the relevant level are calculated. In the first situation the waste material is in contact with the air but in the tourist geometry it is covered with a 1.35 m thick layer. For the calculations, the Monte Carlo radiation transport code MCNP is used. The yield and photon energy for each radionuclide are according to the database of Oak Ridge National Laboratory. For the tourist situation, the depth-dose distribution through the covering layer is calculated and extrapolated to determine the exit dose.

Quality control of equipment used in digital and interventional radiology.

Digital and interventional radiology are increasingly important areas of radiology. Quality control (QC) of such equipment is of particular importance to avoid unnecessary high doses and to help to achieve good image quality. Within the DIMOND III project, equipment requirements and specifications for digital and interventional radiology have been formulated. A protocol for QC tests has been drafted based on various national and international recommendations. Tests are included for various parts of the imaging chain, i.e. X-ray tube and generator, X-ray tube control system, laser printer and display station, and image quality and patient dose. Preliminary tolerance levels have been set for the various tests, after initial measurements. To check the suitability of QC tests and stated tolerance levels, measurements were made at the University Hospital Gasthuisberg in Leuven for equipment used for paediatric radiology and a unit used for chest examinations. The results of the various tests are reported.

Investigation of possible methods for equipment self-tests in digital radiology.

Quality control in digital radiology can be time-consuming. Equipment self-tests may significantly decrease staff workload. The two most essential parameters for radiology systems are image quality and patient dose. Concerning patient dose, information on the dose-area product (DAP) values generally forms the basis for assessment of patient dose. DAP-values can be measured using a transmission ionisation chamber or calculated from equipment settings. In the present study, various image quality parameters were derived using a contrast-detail (C-D) phantom. The investigation included a computer-aided assessment of C-D images, which produced various parameters, and also parameters based upon scoring by human observers. In addition, another parameter was calculated from modulation transfer function (MTF) measurements. The automatically calculated parameters showed good correlation with human readings, although the number of X-ray systems studied is still limited. We propose a combined evaluation of DAP and automatically calculated C-D or MTF parameters for equipment self-tests.

Assessment of a carcinogenic risk for treatment of Graves' ophthalmopathy in dependence on age and irradiation geometry.

In view of the probable carcinogenic risk due to the irradiation of Graves' ophthalmopathy in young patients the effective dose was assessed for two geometries. Adjusting the field to the conical outline of the orbit resulted in appreciable reduction in dose to uninvolved areas such as brain and bone marrow. In Leiden and in Essen the initial target dose was 20 Gy in 10 fractions of 2 Gy. Since 1996 the target dose in Essen was lowered to 10 fractions of 1.6 Gy with equal positive results. The combined effect of field optimization and 20% reduction in target dose has lowered the effective dose from 65 to 34 mSv. The attributable lifetime risk for fatal malignancies of 0.3% as a population average will be considerably reduced when the exposure occurs at older age.

Recent EULEP dosimetry intercomparisons for whole body irradiation of mice. European Late Effects Project group.

PURPOSE: To foster quality assurance of dosimetry among the institutes involved in joint studies on late effects of ionizing radiation. MATERIALS AND METHODS: The participants in the dosimetry intercomparison received for each facility two mouse phantoms loaded with LiF thermoluminescent dosemeters (TLD) and a control badge. The participants were requested to irradiate the test phantoms in the actual arrangement used for whole body irradiation of mice, such that the dose in the centre of the test phantoms was 2 Gy and the dose distribution was uniform. The readout of the TLD and the dose evaluation were made at the organizing institute. RESULTS: Ten institutes operating 14 exposure facilities in four countries took part in the intercomparison. For one facility a dose deviation between 5 and 10% was found, whereas for two others the deviation exceeded 10%. The requirement for uniform dose distribution in a mouse phantom was not fulfilled by six exposure facilities. The causes for the dose discrepancies were found for two participants whereas for one participant the problems were only partly resolved. Non-uniform dose distributions are mainly related to unilateral irradiations. CONCLUSION: The seven EULEP dosimetry intercomparisons clearly show the need for quality assurance of dosimetry in radiobiology.

Calculated energy response correction factors for LiF thermoluminescent dosemeters employed in the seventh EULEP dosimetry intercomparison.

Several dosimetry intercomparisons for whole body irradiation of mice have been organized by the European Late Effects Project Group (EULEP). These studies were performed employing a mouse phantom loaded with LiF thermoluminescent dosemeters (TLDs). In-phantom, the energy response of the LiF TLDs differs from free-in-air, due to spectral differences caused by attenuation and scatter of x-rays. From previous studies, energy response correction factors in-phantom relative to free-in-air were available for full scatter conditions. In the more recent intercomparisons, however, full scatter conditions were not always employed by the participants. Therefore, Monte Carlo calculations of radiation transport were performed to verify the LiF TLD energy response correction factors in-phantom relative to free-in-air for full scatter conditions and to obtain energy response correction factors for geometries where full scatter conditions are not met. For incident x-rays with HVLs in the 1 to 3.5 mm Cu range, the energy response correction factor in-phantom deviates by 2 to 4 per cent from that measured free-in-air. This is in reasonable agreement with previously published results. The energy response correction factors obtained from the present study refer to a calibration in terms of muscle tissue dose in-phantom using 60Co gamma rays. For geometries where full scatter conditions are not fulfilled, the energy response correction factors are different by up to about 3 per cent at maximum from that at full scatter conditions. The dependence of the energy response correction factor as a function of the position in-phantom is small, i.e. about 1 per cent at maximum between central and top or bottom positions.

Assessment of lifetime gained as a result of mammographic breast cancer screening using a computer model.

A computer model for the simulation of breast cancer screening (MBS) is used to calculate the results of screening in terms of lifetime. To optimize breast cancer screening protocols, risk (lifetime lost due to radiation-induced tumours) versus benefit (lifetime gained due to early detection of breast cancer) analyses are performed for a simulated stable Swedish female population. The present study focuses on the results of different screening strategies employing single view mammography, including starting and finishing ages of screening, time interval between successive screening sessions as well as the influence of high detection screening and differences between different populations, based on lifetime lost or gained. To test the stability of the recommendations with respect to possible changes in the variables used in MBS, calculations are also performed for high risk factors for breast tumour induction using both the additive and multiplicative risk models, fast growing breast tumours, late incidence of breast tumours and age dependent survival. The results of the simulations expressed in terms of lifetime gained suggest that a theoretical benefit can be obtained employing starting and finishing ages of 35 and 75 years, respectively. In terms of number of fatal breast tumours, the favourable screening period is 40-80 years. It is concluded that the recommendations are stable for changes in the input variables of MBS. The benefits of higher detection screening are more marked for younger than for older women. A high screening frequency results in more lifetime gained, especially at relatively young ages, whereas for older ages the effect is only marginal.