Health Phys. Abstracts，Volume 120,Number 2

Microbial Contamination Risk and Disinfection of Radiation Protective Garments

Stephen Balter1, Michelle A. Rodriguez2, Janett A. Pike3, Norman J. Kleiman4

(1. Departments of Radiology and Medicine, College of Physicians and Surgeons Columbia University, New York, NY 10032;

2. City University of New York (CUNY) Graduate School of Public Health and Health Policy New York, NY 10027;

3. Department of Environmental Health Sciences Mailman School of Public Health Columbia University, New York, NY 10032;

4. Infection Prevention & Control New York-Presbyterian Hospital New York, NY 10032)

Abstract:Healthcare-associated infections are a major public health concern for both patients and medical personnel. This has taken on greater urgency during the current COVID-19 pandemic. Radiation Personal Protective Equipment (RPPE) may contribute to risks of microbial contamination. This possibility was tested in 61 personal or shared-use lead aprons and thyroid collars at Columbia Presbyterian Irving Medical Center. Fifty percent tested positive for either bacterial or fungal contamination, mostly around the neckline of lead vests and thyroid collars. Repeated testing of garments some weeks to months later confirmed continued presence of microbial contamination. The possibility that hospital-approved disinfection agents could degrade the radio-protective features of these garments was also examined. Samples of identical construction to garments in regular use were subjected to either daily or weekly wipes with hypochlorite or alcohol-based hospital-approved cleaning agents for 6 mo. A third group of samples was maintained in contact with the cleaning agents for 6 mo. All samples were fluoroscoped four times during the study. None demonstrated any degradation in radioprotection. All samples were photographed monthly. Physical degradation of the outer plastic covering by concentrated hypochlorite and limited mechanical damage around stitched seams of the samples cleaned daily with alcohol was noted. Based on the high prevalence of microbial contamination, regular cleaning and disinfection protocols should be implemented. Regular cleaning with medical-facility-approved cleaning and disinfecting agents is likely to be effective at reducing the microbial load and unlikely to result in significant reduction in radioprotective properties of these garments.

Keywords: fluoroscopy; occupational safety; radiation, medical; radiation risk

Health Phys. 120(2):123-130; 2021

Encapsulated Gamma Source Contact Dose Conversion Factors:Updating NCRP-40 Guidance

Edward Waller1, Eric Heritage2

(1. Energy Systems and Nuclear Science, Health Physics and Environmental Safety, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1G 0C5;

2. Ontario Tech University, 2000 Simcoe Street North, Oshawa, Ontario, L1G 0C5)

Abstract:Secondary electron generation on the surface of encapsulated gamma sources can play a large role in the dose measured near the surface of the encapsulation. The National Council on Radiation Protection and Measurements Report No. 40 contains contact dose rate conversion factors for encapsulated gamma sources, along with recommended secondary electron correction factors. However, secondary electron correction factors were based on experiments performed in the 1930s and 1940s with encapsulated radium sources, and the correction factors for the other sources listed in the report were estimated based on these radium source measurements. Monte Carlo simulations were performed using the Particle and Heavy Ion Transport code System (PHITS) to calculate the contact dose rate conversion factors for each encapsulated gamma source presented in NCRP-40, taking into account the dose from both gamma rays and secondary electrons. These simulations showed that the contact dose rate conversion factors are much lower than those presented in NCRP-40, and the secondary electron contribution was much greater than the values proposed by NCRP-40. The original research used results from encapsulated226Ra experiments to determine the secondary electron correction factors for NCRP-40. To support the current Monte Carlo calculations, experiments were conducted using an encapsulated137Cs source, rare earth magnet, and ion chamber detector to show that the secondary electron correction factors presented in NCRP-40 were not applicable to the geometry of tissue in direct contact with the encapsulation. In this work, contact dose conversion factors for common encapsulated radionuclide sources are presented.

Keywords: accident analysis; dose, skin; exposure, radiation; modeling, dose assessment

Health Phys. 120(2):131-144; 2021

Effective Dose Coefficients for Intakes of Uranium Via Contaminated Wounds for Reference Adults

Bin Zhang, Wei Sheng, Tian-Cheng Feng, Ming Xu, Jie-Ying Lei, Xin-Zhao He, Guo-Hui Yin1

(1. Northwest Institute of Nuclear Technology, Xi’an, China)

Abstract:Effective dose coefficients for intakes of uranium radionuclides via contaminated wounds have been calculated for reference adults following the procedures in the ICRP 103 series. The number of transformations in each source region for all members of the radioactive series from time of intake to 50 y post intake are calculated by coupling the NCRP 156 wound model to the ICRP 137 systemic models and ICRP 100 human alimentary tract model. Together with the ICRP 107 nuclear decay data for dosimetric calculations, the ICRP 133 specific absorbed fractions are implemented to calculate the radiation-weighted S coefficient deposited in each target organ or tissue from each transformation in each source region. Effective dose coefficients for different categories of intake materials via contaminated wounds are calculated for the three major uranium isotopes-238U,235U, and234U. Originating from the combined effects of the new absorbed fractions, biokinetic and dosimetric models, the new coefficients are generally reduced by a percentage of 23%-28% as compared to the old ones. The new dose coefficients benefit the assessment of internal exposures for intakes of uranium via contaminated wounds in actual applications.

Keywords: accidents, handling; dosimetry, internal; effective dose; uranium

Health Phys. 120(2):145-151; 2021

Dependence of Radiation-induced Signals on Geometry of Tooth Enamel Using a 1.15 GHz Electron Paramagnetic Resonance Spectrometer:Improvement of Dosimetric Accuracy

Jong In Park1,2, Kwon Choi1,2, Chang Uk Koo1,2, Jeonghun Oh1, Hiroshi Hirata3, Harold M. Swartz4, Sung-Joon Ye1,2,5

(1. Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826, Republic of Korea;

2. Biomedical Research Institute, Seoul National University Hospital, Seoul, 03080, Republic of Korea;

3. Division of Bioengineering and Bioinformatics, Graduate School of Information Science and Technology, Hokkaido University, Sapporo, 060-0814, Japan;

4. Geisel School of Medicine, HB 7785 Dartmouth College, Hanover, NH 03755;

5. Advanced Institutes of Convergence Technology, Seoul National University, 16229, Suwon, Republic of Korea)

Abstract:We aim to improve the accuracy of electron paramagnetic resonance (EPR)-based in vivo tooth dosimetry using the relationship between tooth geometry and radiation-induced signals (RIS). A homebuilt EPR spectrometer at L-band frequency of 1.15 GHz originally designed for non-invasive and in vivo measurements of intact teeth was used to measure the RIS of extracted human teeth. Twenty human central incisors were scanned by microCT and irradiated by 220 kVp X-rays. The RISs of the samples were measured by the EPR spectrometer as well as simulated by using the finite element analysis of the electromagnetic field. A linear relationship between simulated RISs and tooth geometric dimensions, such as enamel area, enamel volume, and labial enamel volume, was confirmed. The dose sensitivity was quantified as a slope of the calibration curve (i.e., RIS vs. dose) for each tooth sample. The linear regression of these dose sensitivities was established for each of three tooth geometric dimensions. Based on these findings, a method for the geometry correction was developed by use of expected dose sensitivity of a certain tooth for one of the tooth geometric dimensions. Using upper incisors, the mean absolute deviation (MAD) without correction was 1.48 Gy from an estimated dose of 10 Gy; however, the MAD corrected by enamel area, volume, and labial volume was reduced to 1.04 Gy, 0.77 Gy, and 0.83 Gy, respectively. In general, the method corrected by enamel volume showed the best accuracy in this study. This homebuilt EPR spectrometer for the purpose of non-invasive and in vivo tooth dosimetry was successfully tested for achieving measurements in situ. We demonstrated that the developed correction method could reduce dosimetric uncertainties resulting from the variations in tooth geometric dimensions.

Keywords: dose assessment; dosimetry; magnetic resonance imaging; radiation dose

Health Phys. 120(2):152-162; 2021

Temporal Attenuation of Gamma Dose Rate in Air Due to Radiocesium Downward Mobility in Soil

Hugo Velasco1

(1.Instituto de Matemática Aplicada San Luis, Universidad Nacional de San Luis/CONICET, Ejército de los Andes 950, San Luis, Argentina)

Abstract:The Chernobyl and Fukushima Dai-ichi Nuclear Power Plant accidents have demonstrated that radiocesium deposited on the ground was one of most important pathway contributions to the air dose rate. Cesium-134 contributes more significantly in the first period of 2-3 y. However,137Cs external exposure may remain relevant for decades. The contribution to the air dose rate attributable to these radionuclides is maximum at the deposition time and then usually decreases over time. The dose rate temporal reduction is a consequence of both the radionuclide physical decay and the radionuclide downward mobility in soil. In this investigation, this decreasing behavior of the air dose rate is approached using an empirical attenuation function, and its coefficients are computed in terms of the effective diffusion coefficient and downward migration rates of radiocesium in soil. The methodology is tested for different hypothetical scenarios and in real situations, including areas affected by the two major accidents at nuclear power plants.

Keywords: cesium; Chernobyl; dose assessment; fallout

Health Phys. 120(2):163-170; 2021

Design and Implementation of Matryoshka-type Neutron Spectrometer

Ning Lv, Jinxu Lv, Mingyan Sun, Wenhui Lv, Qizhan Xiao1

(1. Xi’an Research Institute of Hi-Tec, Xi’an 710025, China)

Abstract:Aiming at portability and mobility, the design and implementation of a portable neutron spectrometer, namely the Matryoshka-type Neutron Spectrometer, was completed while considering the idea of a Bonner Sphere Spectrometer. The Matryoshka-type Neutron Spectrometer used a spherical3He proportional counter as a thermal neutron detector. A number of cylindrical acrylic cups with diameters from 4 cm to 40 cm were made as containers for water as a moderator. The Monte Carlo method was adopted in order to obtain the energy response matrix of the Matryoshka-type Neutron Spectrometer. During the measurement, each acrylic cup contained water as a moderator, and the3He proportional counter was set to the geometric center to perform neutron counting. With the energy response matrix obtained above, the neutron spectrum was resolved by a classical inversion algorithm. After the measurement, water was drained and the acrylic cups were placed one inside the other, like a Matryoshka doll. The design of a Matryoshka-type Neutron Spectrometer has reduced the mass and volume of the Bonner Sphere Spectrometer and was not difficult to carry around. Comparison tests acquiring background and Am-Be source neutron spectra between the Matryoshka-type Neutron Spectrometer and Bonner Sphere Spectrometer proved the effectiveness of the Matryoshka-type Neutron Spectrometer.

Keywords: detector, radiation; neutron detection; radioactivity, natural; spectrometry, neutron

Health Phys. 120(2):171-176; 2021

Study of Alpha and Beta Radioactivity of Clay Originating from Radionuclides Belonging to the238U and232Th Families:Doses to the Skin of Potters

M. A. Misdaq, A. Talbi, A. Chaouqi1

(1.Nuclear Physics and Techniques Laboratory, Faculty of Sciences Semlalia, BP.2390, University of Cadi Ayyad, Marrakech, Morocco (URAC-15 Research Unit Associated to the CNRST, Rabat, Morocco))

Abstract:Pottery objects are presently more and more used for decoration in homes and hotels. To assess radiological hazards to potters,238U,232Th,222Rn, and220Rn radionuclides were analyzed in different clay body samples used for pottery production by means of CR-39 and LR-115 II track detectors. Data obtained were compared to those gotten by means of isotope dilution mass spectrometry. Annual equivalent doses to the skin of potters resulting from the energy loss of alpha-particles emitted by the radionuclides of the238U and232Th radioactive families were evaluated. Estimates of the annual equivalent doses to the skin of potters due to the emitted alpha-particles ranged between 6.45 mSy y-1cm-2and 17.50 mSy y-1cm-2and between 1.87 mSy y-1cm-2and 5.33 mSy y-1cm-2, respectively. Annual equivalent doses received by the skin of potters due to beta-particles (β-) emitted by the radionuclides of the238U and232Th series inside the studied clay body samples were determined. Alpha equivalent doses to the skin of potters resulting from the diffusion of222Rn and220Rn gases present in the studied clay body samples were calculated. A total maximum annual equivalent dose of 23.0 mSv y-1cm-2, resulting from the energy loss of alpha and beta minus particles emitted by the radionuclides of the238U and232Th series, was found for potters working 8 h d-1(6 d wk-1, 49.28 wk y-1).

Keywords: dose assessment; health effects; radiation protection; radioactivity, natural

Health Phys. 120(2):177-190; 2021

Influence of Neutralization Accelerated by the Soak Method on the Radon Exhalation of Cement-based Materials

Rong Yang1,2,3, Xiaowen Zhang1, Shengyang Feng1, Xiangyang Li2,3

(1. School of Resource Environment and Safety Engineering, University of South China, Hengyang 421001, China;

2. Hunan Province Engineering Research Center of Radioactive Control Technology in Uranium Mining and Metallurgy, University of South China, Hengyang 421001, China;

3. Hunan Province Engineering Technology Research Center of Uranium Tailings Treatment Technology, University of South China, Hengyang 421001, China)

Abstract:Radon is considered a significant contaminant that affects indoor air quality. Neutralization is one of the most important environmental factors in changing pore structure of cement-based materials that may release radon. Therefore, it is necessary to study the radon exhalation of cement-based materials impacted by neutralization, which is extremely lacking. Some concrete blocks were accelerated to neutralization by soaking in sodium bicarbonate solution, and the radon activity concentrations over the blocks were measured to investigate the effect of neutralization on radon exhalation. Controlled experiments were conducted with blocks in the initial dry state and soaked in pure water. The results show that the radon activity concentration exhaled from block is promoted by neutralization, and the promoting role of water is quite limited. The radon surface exhalation rate increases by increasing the sodium bicarbonate solution concentration from 0.5% to saturation.

Keywords: cement-based materials; sodium bicarbonate; neutralization; radon activity concentration

Health Phys. 120(2):191-200; 2020

Database of Families of Workers Chronically Exposed to Radiation:Data and Biospecimen Resources

Tamara Azizova1, Evgeniya Grigoryeva1, Galina Zhuntova1, Evgeniya Kirillova1, Christopher Loffredo2

(1. Federal State Unitary Enterprise “Southern Urals Biophysics Institute” at the Federal Medical Biological Agency of the Russian Federation;

2. Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC)

Abstract:Animal experiment findings suggest that high doses of ionizing radiation exposure (>1.0 Gy) may cause genetic and epigenetic effects in offspring. However, epidemiological studies of offspring of radiation-exposed parents did not find increased risks of any health effects. Findings of cellular/experimental investigations and studies of human health effects are contradicting, and further investigations are needed to help resolve ambiguities using updated and/or improved data. This paper provides a detailed description of a database of families of workers of the first Russian nuclear facility, Mayak Production Association, located in the Southern Urals in the Chelyabinsk region close to Ozyorsk city, which started its operation in 1948 and today consists of reactors, radiochemical and plutonium production plants, and auxiliary facilities. The Mayak worker cohort includes 22,377 individuals (25% females) who were hired at one of the main Mayak PA facilities between 1948 and 1982 and were externally or internally exposed to ionizing radiation over prolonged periods. Advantages of the cohort include its large size, extensive follow-up period (70 y), individually measured doses from external and internal exposure and the wide range of these doses, heterogeneity by gender/age/ethnicity/initial health status, complete data on vital status and causes of death, available medical information on morbidity and reproduction, available data on non-radiation factors, and stored biological specimens donated by more than one-third of the cohort members. Based on medical and dosimetry database “Clinics” containing raw data on workers of the study cohort, the Mayak workers’ family and offspring database was created. To date, it comprises 12,195 family couples (a husband and a wife) and 16,585 offspring. Biological specimens are available for more than 1,000 family triads (a husband, a wife, and their child). Stages of assembling the database and its descriptive characteristics are presented in this paper. Examples of potential applications of the database for investigations of non-targeted and transgenerational radiation effects in offspring of exposed parents are discussed.

Keywords: ionizing radiation exposure, prenatal; radiation-induced genetic effects; health effects

Health Phys. 120(2):201-211; 2021

Evaluation of Radiation Doses in Pediatric Patients Undergoing Conventional Chest X-ray Examination

Adnan Lahham, Ahlam Issa1

(1.Center for Radiation Science and Technology, Al-Quds University, P.O. Box 20002, East Jerusalem, Palestine)

Abstract:This work deals with the evaluation of radiation doses from chest x rays for 240 male and female pediatric patients selected randomly from four Palestinian hospitals. The patient population was divided into five age groups: Newborn, 1, 5, 10, and 15 y old. Doses were theoretically calculated by using Monte Carlo based codes: CALDOSE-X5 and PCXMC-2.0. Patients’ data and type of radiographic systems used as well as exposure factors were provided by the administrations of the selected hospitals. Absorbed organ doses from AP and PA projections were evaluated for 76 pediatric patients selected from one hospital in East Jerusalem. The highest mean organ dose for these patients was 0.085 mGy to the breast in AP projection. Effective doses were estimated for the five age groups for all patients. The highest average effective dose was found for patients in the age group of 10 y and was about 0.13 mSv, while the lowest average effective dose was found for the 5 y age group, about 0.06 mSv. The mean effective dose for all investigated patients in the five age categories was about 0.08 mSv. Variations in effective doses for the same age group and X-ray examination among involved hospitals are remarkable.

Keywords: dose, equivalent; dose, organ; exposure, radiation; x rays

Health Phys. 120(2):212-216; 2021

Economic Considerations for Radiation Protection in Medical Settings—Is It Time for a New Paradigm?

Sandor J. Demeter1

(1. Faculty of Health Sciences, College of Medicine, Department of Radiology, University of Manitoba, Winnipeg, Manitoba)

Abstract:The full ALARA principle includes “as low as reasonably achievable”takingsocialandeconomicfactorsintoconsideration. The International Commission on Radiological Protection advises a conventional cost benefit approach (e.g., cost per monetized averted stochastic effects or years of life saved) to considereconomicfactors. Given small incremental radiation dose reductions to patients, workers, or the public that may be realized in medical settings and the correspondingly small changes to theoretical stochastic effects, a conventional cost benefit approach is less than ideal. This is illustrated in the case studies presented in this paper. Alternate approaches, such as cost per unit of radiation dose averted (e.g., $/μSv averted), cancer induction/fatality probabilistic thresholds, or thresholds relative to natural background radiation may be alternate options. However, the decision regarding what is a “safe” level of radiation and what are reasonable costs to make it “safer” are driven by societal values and may vary from jurisdiction to jurisdiction.

Keywords: analysis, cost benefit; linear hypothesis; radiation protection; radiation, medical

Health Phys. 120(2):217-223; 2021

Analysis of Long-Term Quality Control Data for a137Cs Dosimetry Calibration Source

Jordan D. Noey, Robert M. Golduber, Kimberlee J. Kearfott1

(1.Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2104)

Abstract:Strict quality assurance programs are required for many radiological applications, but these seldom exist for verifying dosimetry calibration sources. After initial characterization of a dosimetry calibration facility, quality control procedures are recommended to ensure the early detection of any changes or malfunctions. These also result in refined knowledge about average dose rate and experimental variations in dose delivery. This paper describes the implementation of a phase I quality control protocol for a137Cs dosimetry calibration source and includes an analysis of the resulting data collected over a 24-mo period. During this time, substantial data was collected to establish trial control limits. Air kerma rate measurements were obtained using an ion chamber and were adjusted for decay, corrected for ambient temperature, pressure and humidity, and then analyzed using quality control charts. Three variations of rational subgrouping methods were used in order to find assignable causes of error, and Nelson’s Rules were followed to detect any non-random statistical variations. Measurements were subgrouped according to same-day measurements in order to detect positional errors as well as atmospheric correction errors. Additionally, measurements were subgrouped according to analogous experimental setups in order to detect failure in equipment or incorrect settings. Both were analyzed using the X-bar and R chart method. Similarly, individuals and moving ranges charts were used to carefully examine each position in order to observe any situational errors that may occur which include timing, positional, or interference errors. Each method was successful in identifying unique out-of-control data points that occurred during the phase I application of forming control limits. Over the 24-mo period, enough data points were deemed in-control to establish reliable trial limits. Future experiments will include the phase II application of gaining more reliable measurements in order to fine-tune the limits, as well as performing a designed experiment, where variables are purposefully changed in order to test the variation of the data.

Keywords: operational topics;137Cs; calibration; dosimetry, personnel

Health Phys. 120(2):227-242; 2021