3D Printed Lung Phantom for Individual Monitoring.

ABSTRACT: The Human Monitoring Laboratory, Health Canada (HML), has used a 3D printer to re-engineer its Lawrence Livermore National Laboratory (LLNL) foam lung sets (manufactured by Radiology Support Devices, Inc., Long Beach, CA). The foam sets are currently the HML standard for calibrating and performance testing lung-counting systems in Canada. This paper describes the process of creating and validating new 3D-printed lung sets modeled from one of the HML's existing RSD foam sets. The existing sets were custom made, making them costly and difficult to obtain or replace. Also, after many years of use, the HML has found that they are prone to wear and tear. When used with planar inserts containing various isotopes, the blank sets can become contaminated and are difficult to clean. Using 3D printing, the HML has created new blank lung sets that are nearly identical copies of the originals and are inexpensive and easily manufactured. Measurements using natural uranium (Nat U), 241Am, and 152Eu planar lung inserts were performed to compare obtained efficiencies at a wide range of energies using the original RSD foam sets and the 3D-printed ones. Both the foam and the 3D-printed lung sets were counted using the LLNL chest phantom positioned in the same counting geometry in the lung counting system. Biases, all below 15%, were obtained between the foam and the 3D-printed sets for energies above 40 KeV. Based on these results, as well as cost benefits and ease of use, the HML has decided to replace its original RSD foam lung set with the 3D-printed version for its lung performance testing program.

Optimizing the Positioning of Detectors for Improved Counting Efficiencies Using Monte Carlo Simulations.

ABSTRACT: The Human Monitoring Laboratory (HML) at Health Canada updated its whole-body counter with four new electrically cooled HPGe detectors. To optimize the counting efficiency of the new system, Monte Carlo simulation was used to model the whole-body counter using a reference BOMAB male phantom. The resulting modeled counting efficiencies showed that the best position to install the four new detectors could be obtained without performing laborious real measurements, thereby reducing the cost of preparing the BOMAB phantoms and reconfiguring the detector arrays in multiple geometries, saving time and energy.

Monitoring and Dose Assessment for Children Following a Radiation Emergency-Part II: Calibration Factors for Thyroid Monitoring.

Past radiological and nuclear accidents have demonstrated that monitoring a large number of children following a radiological and nuclear emergency can be challenging, in accommodating their needs as well as adapting monitoring protocols and applying age-specific biokinetics to account for various ages and body sizes. This paper presents the derived calibration factors for thyroid monitoring of children of all ages recommended by the International Commission on Radiological Protection using four selected detectors at given times following a short-term (acute) intake of I by inhalation. These calibration factors were derived by Monte Carlo simulations using the models of various detectors and pediatric voxel phantoms. A collection of lookup tables is presented in this paper which may be directly used as a quick reference by emergency response personnel or technical experts performing thyroid monitoring and assessment without doing time-consuming calculations.

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.

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.

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%.

A Monte Carlo Simulation of the in vivo measurement of lung activity in the Lawrence Livermore National Laboratory torso phantom.

A torso phantom was developed by the Lawrence Livermore National Laboratory (LLNL) that serves as a standard for intercomparison and intercalibration of detector systems used to measure low-energy photons from radionuclides, such as americium deposited in the lungs. DICOM images of the second-generation Human Monitoring Laboratory-Lawrence Livermore National Laboratory (HML-LLNL) torso phantom were segmented and converted into three-dimensional (3D) voxel phantoms to simulate the response of high purity germanium (HPGe) detector systems, as found in the HML new lung counter using a Monte Carlo technique. The photon energies of interest in this study were 17.5, 26.4, 45.4, 59.5, 122, 244, and 344 keV. The detection efficiencies at these photon energies were predicted for different chest wall thicknesses (1.49 to 6.35 cm) and compared to measured values obtained with lungs containing (241)Am (34.8 kBq) and (152)Eu (10.4 kBq). It was observed that no statistically significant differences exist at the 95% confidence level between the mean values of simulated and measured detection efficiencies. Comparisons between the simulated and measured detection efficiencies reveal a variation of 20% at 17.5 keV and 1% at 59.5 keV. It was found that small changes in the formulation of the tissue substitute material caused no significant change in the outcome of Monte Carlo simulations.

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 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.

Assessment of the chest wall thickness of the lawrence livermore torso phantom using a voxel image.

This paper describes the methodology of measuring the chest wall thickness using the voxel image of the Lawrence Livermore National Lab (LLNL) torso phantom. The LLNL phantom is used as a standard to calibrate a lung counter consisting of a 2 × 2 array of germanium detectors. In general, an average thickness estimated from four counting positions is used as the chest wall thickness for a given overlay plate. For a given overlay, the outer chest surface differs from that of inner one, and the chest wall thickness varies from one position to other. The LLNL phantom with chest plate and C4 overlay plate installed was scanned with a CT (computed tomography) scanner. The image data, collected in DICOM (Digital Imaging and Communication) format, were converted to the MCNP input file by using the Scan2Mcnp program. The MCNP file was visualized and analyzed with the Moritz visual editor. An analytic expression was formulated and solved to calculate the chest wall thickness by using the point detector responses (F 5 tally of MCNP). To map the chest thickness, the entire chest wall was meshed into virtual grids of 1 cm width. A source and detector pair was moved along the inner and outer surface of the chest wall from right to left at different heights from neck to abdomen. For each height (z(k)), (x(i), y(j)) coordinates for the detector source pair were calculated from the visual editor and were scaled on-screen. For each (x(i), y(j), z(k)) position, a mesh thickness was measured from on-screen measurement and by solving the detector responses. The chest wall thicknesses at different positions on the outer surface of the chest were compared and verified using two methods.

Comparison of two leg phantoms containing (241)Am in bone.

Three facilities (CIEMAT, HMGU and HML) have used their in vivo counters to compare two leg phantoms. One was commercially produced with (241)Am activity artificially added to the bone inserts. The other, the United States Transuranium and Uranium Registries' (USTUR) leg phantom, was manufactured from (241)Am-contaminated bones resulting from an intake. The comparison of the two types of leg phantoms showed that the two phantoms are not similar in their activity distributions. An error in a bone activity estimate could be quite large if the commercial leg phantom is used to estimate what is contained in the USTUR leg phantom and, consequently, a real person. As the latter phantom was created as a result of a real contamination, it is deemed to be the more representative of what would actually happen if a person were internally contaminated with (241)Am.

International workshop on emergency radiobioassay: considerations, gaps and recommendations.

An international workshop on emergency radiobioassay was held in Ottawa, Canada, 1-3 September 2010. Sixty-five scientists and public health officials from five countries attended the workshop and gave 36 presentations. During the workshop, many considerations were raised, gaps identified, and recommendations given for emergency radiobioassay for both preparedness and response in case of a radiological or nuclear incident. In short, some bioassay methods and protocols need to be developed, validated, and exercised; national and international radiobioassay laboratory networks should be established; and communications and collaborations among public health officials, monitoring experts, and medical staff are encouraged. All these activities are required to make us better prepared for an RN emergency.

Design and testing of a new stand for the BOMAB family of phantoms.

A new stand has been designed to support the Bottle Manikin Absorber Phantoms when the phantoms are counted in the vertical position in a whole-body counter. The stand previously used by the Human Monitoring Laboratory was constructed from metal and was heavy to transport and making height adjustments to accommodate different phantom sizes was very time consuming. The new stand is constructed from lightweight plastic materials and allows easy height adjustments to accommodate different phantom sizes while supporting the weight of the phantoms. The stand was evaluated inside a whole-body counter at a nuclear-generating station and met all operational requirements for accessibility and ease of use.

Error analysis for the in-vivo measurement of radionuclides in wounds: Monte Carlo study.

This paper describes calculation of error associated with the direct in-vivo measurements of radionuclides in a wound. A typical radiation injury to a hand with Am radionuclide is illustrated for error analysis. A Monte Carlo model was developed and the detector pulse spectrum studied with a custom-designed HPGe detector. A pinhole collimator was designed, and its performance with a wide area detector was studied. The results show that significant errors might propagate if the lowest energy peaks of Am are used during in vivo measurements of the wound. In comparison to that, less uncertainty was found for 26.3 and 59.5 keV gamma peaks, and those levels are recommended for estimation of wound depth and activity.

Tools for creating and manipulating voxel phantoms.

The National Internal Radiation Assessment Section's Human Monitoring Laboratory (HML) has purchased and developed a number of in-house tools to create and edit voxel phantoms. This paper describes the methodology developed in the HML using those tools to prepare input files for Monte Carlo simulations using voxel phantoms. Three examples are given. The in-house tools described in this paper, and the phantoms that have been created using them, are all publically available upon request from the corresponding author.