Managing children during a radiological or nuclear emergency--Canadian perspectives.

Children have a higher chance of being contaminated by radioactive materials during a radiological or nuclear (RN) emergency. They are more sensitive to radiation health effects and suffer more significant psychosocial impacts than adults during emergency response. This paper presents a summary of recommendations on effective management of children during an RN emergency. These recommendations intend to be additional considerations for existing RN response protocols and procedures implemented at local, state/provincial, or national level.

Counting 241Am in the BfS human skull phantom on contact-evaluation in the human monitoring laboratory.

Skull counting can be used to assess the activity of radionuclides internally deposited in the bone. The Human Monitoring Laboratory (HML) at Health Canada conducted the measurement of 241Am in the BfS (Bundesamt für Strahlenschuts) skull phantom on contact with the skull for various positions. By placing the detector in contact, the HML can improve the counting efficiency by over 20% compared to placing the detector 1 cm above the surface of the skull. Among all the positions tested, the forehead position is the preferred counting geometry due to the design of HML's counting facility and the comfort it would provide to the individual being counted, although this counting position did not offer the highest counting efficiency for the gamma rays (either the 59.5 keV or the 26.3 keV) emitted by 241Am.

Using tea as an artificial urine in a Canadian performance testing program for fission/activation products.

In recent years, the National Calibration Reference Centre for Bioassay and In Vivo Monitoring (NCRC) at the Radiation Protection Bureau (RPB), Health Canada, has been conducting investigations with black tea to develop a matrix that can be used to replace urine in each of the following performance testing programs (PTP): (1) tritium, (2) carbon-14, (3) the DUAL (i.e., 3H/14C), and (4) fission/activation products (F/AP). A 1% tea solution with thimerosal, which had worked successfully for tritium, carbon-14, and the DUAL, was selected and tested for the F/AP PTP because of its similarity to urine in color and UV-VIS spectra. However, application of this tea to samples of the F/AP program containing 133Ba, 137Cs, 57Co, and 60Co produced precipitates, which was an unexpected result. Further experiments showed that replacement of thimerosal with an alcohol at about 5% eliminated the precipitation problem. The alcohol can be ethanol, methanol, or isopropanol. In the experiments, the 1% tea, preserved with alcohol, remained clear and stable for at least 100 d. The duration of each PTP for the NCRC is limited to 90 d. Application of the CNSC S-106 regulatory standard to the tea produced acceptable accuracy and precision results. It was concluded that a suitable tea matrix for the F/AP program had been found.

Effect of respiratory motion on lung counting efficiency using a 4D NURBS-based cardio-torso (NCAT) phantom.

The Human Monitoring Laboratory (Canada) has looked at parameters (lung volume, lung deposition pattern, etc.) that can affect the counting efficiency of its lung counting system. The calibration of the system is performed using the Lawrence Livermore National Laboratory (LLNL) torso phantom; however, the effect of respiratory motion cannot be accounted for using these phantoms. When measuring an internal deposition in the lungs of a subject, respiration causes a change in the volume of the lungs and the thoracic cavity and introduces a variable distance between the lungs and the detectors. These changes may have an impact on the counting efficiency and may need to be considered during a measurement. In this study, the HML has simulated the respiration motion using a 4D non-uniform rational b-spline (NURBS)-based Cardiac-Torso (NCAT) phantom and determined the impact of that motion on the counting efficiency of their lung counting system during measurement. The respiratory motion was simulated by a 16 timeframe cycled 4D NURBS-based NCAT phantom developed at the Department of Biomedical Engineering and Radiology, University of North Carolina. The counting efficiency of the four germanium detectors comprising the HML lung counting system was obtained using MCNPX version 2.6E for photon energies between 17 and 1,000 keV. The amount of uncertainty due to the breathing motion was estimated by looking at the efficiency bias, which was highest at low photon energies as expected due to attenuation and geometry effects. Also, to reduce the influence of the detectors' positioning, an array was calculated by adding the individual detector tallies for a given energy and timeframe. For photon energies of 40 keV and higher, the array efficiency bias showed an underestimation of about 5%. If compared to other parameters already studied by the HML, this value demonstrates the insignificant impact of the breathing motion.

Modeling population screening process for maximizing throughputs.

Following a large-scale radiation emergency, affected populations will need to be screened soon after for potential contamination (external or internal). Effective management of the available resources can help maximize the screening throughputs. This paper reports the modeling results for screening throughputs in a population screening center using a set resource, considering two major variables, the arrival rate (number of people arriving at the screening center per minute) and the contamination probability (the probability of finding a contaminated group). Both the full process (including all sub-processes in a population screening center) and the core process (including only the screening sub-processes: pre-screening, portal monitoring, and whole body counting) were simulated. As expected, for both processes, as the arrival rate increases, the screening center can get overwhelmed. Interestingly, the contamination probability becomes a significant factor for screening throughputs only when the arrival rate becomes high. The results show that following an emergency, when the arrival rate is high, much more resources will need to be deployed to the population screening center or multiple screening centers will need to be established.

Monte Carlo model of HPGe detectors used in routine lung counting.

An MCNP model of a pair of planar HPGe detectors (designated as: detector 3 and detector 4), that are used for routine lung counting at AECL, was developed. The model was benchmarked against experimental results, where a multi-line (152)Eu source was counted in several different geometrical arrangements. The best agreement for both detectors was achieved when side and back dead layers (of both detectors) were quadrupled, with respect to the ones quoted by their manufacturer (Canberra). In the case of detector 4, the agreement between simulated and measured spectra was within 4%, throughout the whole γ-spectrum, spanning 70-1600 keV. The same was true for detector 3 at the lower end of the γ-spectrum. However, at the high end of the γ-spectrum, the agreement was within 7% and 12% for (152)Eu γ-lines at 778.9 and 1408.01 keV.

Reevaluation of (241)Am content in the USTUR case 0102 leg phantom.

The (241)Am contents in the United States Transuranium and Uranium Registries' (USTUR) case 0102 leg phantom were previously estimated to be 1,243 ± 11 Bq. Recent analysis of the computed tomography images of the phantom revealed multiple bone structures missing from various regions of the phantom skeleton including: posterior ilium, anterior ilium, ischium, femur proximal end, femur middle shaft, femur distal end, patella, tibia distal shaft, fibula distal shaft, and fibula distal end. Additionally, the fifth metatarsal and all of the fifth-digit phalanges were found to be completely missing from the foot. A three-dimensional (3D) model of the leg phantom was created using 3D-Doctor software. Volumes of missing bone structures were outlined separately based on the anatomical assessment of those structures. Weights of the missing bone samples were calculated. Consequently, the value of total( 241)Am activity in the USTUR leg phantom is 1,218 ± 11 Bq. This activity is about 2.0% less than the previously published value of 1,243 ± 11 Bq. External gamma detector response was simulated considering both activity values (1,243 and 1,218 Bq) across the five different locations along the USTUR leg phantom: foot, middle leg, knee, middle thigh, and hip. Each counting position was chosen such that it was above the missing bone structure locations. The highest difference observed between the two counting efficiencies (each corresponding to the two different quantities of estimated activity) was 8.2% and 9.4% for locations above the foot and middle thigh, respectively. Other counting locations (middle leg, knee, and hip) showed efficiency variations of about 1%.

Effect of a Simulation of 241Am Deposition Pattern in the Leg Bones on the Detection Efficiency of a High Purity Germanium Detector.

A computational model using an MCNPX version 2.6.0 code and a leg voxel phantom was previously constructed and validated against the in vivo measurements of the United States Transuranium and Uranium Registries (USTUR) case 0846 leg. Using the MCNPX model, different simulation scenarios of Am distribution in the bones and tissue material of a leg were performed, and their effects on the detection efficiency and activity calculation were examined. The purpose of this work is to ensure and increase the simulation sensitivity of real contaminated human bones and reduce the simulated efficiency error associated with the distribution of Am activity within the leg bones when using a high purity germanium [HP(Ge)] detector. The results showed that the simulated detection efficiency obtained from the uniform distribution of Am in the leg bones was underestimated by a factor of up to 0.3 compared with the measured and simulated detection efficiency obtained from the non-uniform distribution of Am in different sections of the leg bones. The p-value of a one-way analysis of variance (ANOVA) F-test among the mean values of the simulated detection efficiencies was calculated and provided evidence of a significant difference. The uncertainty in the bone activity estimate could be quite large (25% to 30%) if calibration of detection efficiency is based on assuming a uniform distribution of Am in the phantom to estimate the USTUR case 0846 leg activity. It is therefore recommended that during calibration of detectors, a non-uniform distribution of Am in different sections of the bones should be used rather than a uniform distribution. Additionally, an assumption of a uniform distribution of Am will simulate Am activity deposited in the leg bones of a real contamination case inadequately.

The HML's new voxel phantoms: two human males, one human female, and two male canines.

The Human Monitoring Laboratory (HML) has created five new voxel phantoms that can be used for Monte Carlo simulations. Three phantoms were created from computer tomography image sets that were obtained from facilities in Italy and the USA: a human male and the male canines. Two other phantoms were constructed from commercially available software that is used to demonstrate human anatomical features: a human male and a human female. All the voxel phantoms created by the HML that are described in this note are available at no cost to interested researchers.

Evaluation of tea as a matrix in a dual (3H/14C) performance testing program in Canada.

Urine is the most popular matrix used in performance testing programs (PTP) and inter-comparison programs (ICP) for bioassay. Because it comes from humans, there are concerns regarding its biosafety. For large programs, its collection can take several hours or days to complete. In addition, natural urine has an unpleasant smell, which tends to worsen with increasing storage time. In order to solve some of these problems, the Bioassay Section at the Radiation Protection Bureau in Health Canada has been investigating the use of tea in both PTP and ICP exercises. A method based on diluting tea steeps and scanning them in the UV-VIS range of the light spectrum to select appropriate concentrations as simulated urine for the programs has been published. So far, however, only single H and single C in tea have been studied. The results were found to be compatible and very successful under the S-106 standard of the Canadian Nuclear Safety Commission. This report is an extension of similar investigations and shows that tea samples spiked with both H and C (DUAL) are also compatible and produce excellent PTP results.

Improving global laboratory capabilities for emergency radionuclide bioassay.

During a radiological or nuclear emergency, first-responders and the general public may be internally contaminated with the radionuclide(s) involved. A timely radionuclide bioassay provides important information about contamination, for subsequent dose assessment and medical management. Both technical and operational gaps are discussed in this paper. As many people may need to be assessed in a short period of time, any single laboratory may find its capabilities insufficient. Laboratories from other regions or other countries may be called upon for assistance. This paper proposes a roadmap to improve global capabilities in emergency radionuclide bioassay, suggesting a phased approach for establishing a global laboratory network. Existing international collaboration platforms could provide the base on which to build such a network.

Evaluation of a commercial software package's ability to calibrate an in vivo counter for emergency response.

A commercial detector calibration package has been assessed for its use to calibrate the Human Monitoring Laboratory's Portable Whole Body Counter that is used for emergency response. The advantage of such a calibration software is that calibrations can be derived very quickly once the model has been designed. The commercial package's predictions were compared to experimental point source data and to predictions from Monte Carlo simulations. It was found that the software adequately predicted the counting efficiencies of a point source geometry to values derived from Monte Carlo simulations and experimental work. Both the standing and seated counting geometries agreed sufficiently well that the commercial package could be used in the field.

Voxel phantoms: the new ICRP computational phantoms: how do they compare?

Two new voxel phantoms, ICRP Adult Female (AF) and ICRP Adult Male (AM), have been compared with BOMAB (BOttle Mannikin ABsorber) phantoms and other voxel phantoms of similar size (NORMAN and VIP-Man) using Monte Carlo simulations to assess their counting efficiencies in a whole body counter. The results show that the ICRP phantoms, compared with NORMAN and VIP-Man, had counting efficiencies that ranged from 3% to 59% higher over the energy range 122 keV to 1,836 keV, a trend that is also exhibited by the comparable BOMAB phantoms. A comparison of all the voxel phantoms' results to those of the BOMAB phantom corresponding to reference man shows that the NORMAN and VIP-Man have mostly lower counting efficiencies, whereas the ICRP phantoms have higher counting efficiencies than the PM (Phantom Male) BOMAB phantom. This could be due to differences in the internal structure of each of the voxel phantoms. As expected, the ICRP AF (female voxel) had the highest efficiency due to being the smallest of all the phantoms.

Evaluation of Ludlum Corporation's portable portal monitor and comparison with the HML'S existing portal monitors.

Since the Human Monitoring Laboratory compared two types of portal monitors (the P3 and the MiniSentry) that could be field deployed in response to an emergency, two more brands have been added to the inventory. This paper summarizes a comparison of the capabilities of the previous portal monitors with the two additions: the Thermo Eberline TPM-903B and the Ludlum 52-1-1. The comparison shows that none of the portals greatly exceed the others in capability, but that each will have their place during emergency deployment; however, when beta radiation or low energy gamma radiation is suspected, then the best choice would be the Ludlum 52-1-1.

Linear dimensions and volumes of human lungs obtained from CT images.

This work provides the results of a collaboration between the Human Monitoring Laboratory (HML) and the Centre Hospitalier de l'Université de Montréal (CHUM) in which CHUM provided CT lung image sets from 166 patients for the analysis of linear dimensions and lung volume. This work has shown that a large amount of data exists in the medical community that can be of value to the health physics community. The intent of this study was to determine the range of linear dimensional parameters that could be used for torso phantom development for males and females; understand and characterize the variability of linear lung dimensions for males and females; replace the brief table in ICRP 23 with more modern data for males and females; identify an empirical formula that would predict linear dimensions of human lungs from age, height and/or weight for males and females; characterize the left, right, and total lung volumes of males and females in this data set; and compare the lung volumes of males and females to published equations for determining lung volumes. It was found that linear dimensions of lungs are essentially independent of age, height, and weight, so predictive equations cannot be formulated; however, the ranges of those parameters have now been established for the population studied herein. The data presented here are more modern than the brief table that appeared in ICRP 23, and the average values could be used as future guidelines. Whole lung volumes have been determined from the voxel lung phantoms, and empirical formulae have been developed for males and females in this data set; these compare favorably with the published values in ICRP 66.

Preparation and application of steeps of tea as new simulations of urine for the performance testing programme of 14C.

(14)C is one of the radionuclides for which the Canadian Nuclear Safety Commission has developed performance testing programmes (PTPs). During the PTP exercises, clients receive samples of natural urine containing spiked radionuclides, for testing. In these programmes, urine has disadvantages. These include (1) slow collection times from donors, (2) unpleasant smell and (3) potential to transmit diseases. To assist in solving some of these problems, the Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring has conducted research with tea solutions, to find simpler, safer and more readily available alternatives to urine. This paper provides a new technique by which steeps of black tea have been successfully prepared for the (14)C PTP. The results of tea solutions compared well with those of urine. It was concluded that tea steeps, of which the spectroscopic and colour quenching properties have been adjusted, do provide appropriate urine simulations, suitable for use in PTPs.

Lung counting: comparison of detector performance with a four detector array that has either metal or carbon fibre end caps, and the effect on mda calculation.

This study described the performance of an array of high-purity Germanium detectors, designed with two different end cap materials-steel and carbon fibre. The advantages and disadvantages of using this detector type in the estimation of the minimum detectable activity (MDA) for different energy peaks of isotope (152)Eu were illustrated. A Monte Carlo model was developed to study the detection efficiency for the detector array. A voxelised Lawrence Livermore torso phantom, equipped with lung, chest plates and overlay plates, was used to mimic a typical lung counting protocol with the array of detectors. The lung of the phantom simulated the volumetric source organ. A significantly low MDA was estimated for energy peaks at 40 keV and at a chest wall thickness of 6.64 cm.

Revised requirements for radiation emergency bioassay techniques for the public and first responders.

This technical note reports the required sensitivities for bioassay techniques derived from a 0.1 Sv effective dose incurred in the first year following an emergency (recommended by ICRP) and those derived from a 0.25 Sv committed effective dose (recommended by NCRP) as dose thresholds for possible medical attention. During a large-scale radiological or nuclear emergency, the dose threshold chosen for medical attention may be raised, as available resources may be insufficient for conducting a sensitive contamination assessment and medical treatment of a large population exposed to radioactive contamination.

An emergency radiobioassay method for 226Ra in human urine samples.

A new radioanalytical method was developed for rapid determination of (226)Ra in human urine samples. The method is based on organic removal and decolourisation of a urine sample by a polymeric (acrylic ester) solid phase sorbent material followed by extraction and preconcentration of (226)Ra in an organic solvent using a dispersive liquid-liquid microextraction technique. Radiometric measurement of (226)Ra was carried out using a liquid scintillation counting instrument. The minimum detectable activity for the method (0.15 Bq l(-1)) is lower than the required sensitivity of 0.2 Bq l(-1) for (226)Ra in human urine samples as defined in the requirements for radiation emergency bioassay techniques for the public and first responders based on the dose threshold for possible medical attention recommended by the International Commission on Radiological Protection (ICRP). The accuracy (expressed as relative bias, B(r)) and repeatability of the method (expressed as relative precision, S(B)) evaluated at the reference level (2 Bq l(-1)) were found to be -4.5 and 2.6 %, respectively. The sample turnaround time was <5 h for a single urine sample and <20 h for a batch of six urine samples. With the fast sample turnaround time combined with the potential to carry out the analysis in a field deployable mobile laboratory, the newly developed method can be used for emergency radiobioassay of (226)Ra in human urine samples following a radiological or nuclear accident.