Science-informed Policy Making for Protecting People and the Environment from Radiation.

ABSTRACT: The process to arrive at the radiation protection practices of today to protect workers, patients, and the public, including sensitive populations, has been a long and deliberative one. This paper presents an overview of the US Environmental Protection Agency's (US EPA) responsibility in protecting human health and the environment from unnecessary exposure to radiation. The origins of this responsibility can be traced back to early efforts, a century ago, to protect workers from x rays and radium. The system of radiation protection we employ today is robust and informed by the latest scientific consensus. It has helped reduce or eliminate unnecessary exposures to workers, patients, and the public while enabling the safe and beneficial uses of radiation and radioactive material in diverse areas such as energy, medicine, research, and space exploration. Periodic reviews and analyses of research on health effects of radiation by scientific bodies such as the National Academy of Sciences, National Council on Radiation Protection and Measurements, United Nations Scientific Committee on the Effects of Atomic Radiation, and the International Commission on Radiological Protection continue to inform radiation protection practices while new scientific information is gathered. As a public health agency, US EPA is keenly interested in research findings that can better elucidate the effects of exposure to low doses and low dose rates of radiation as applicable to protection of diverse populations from various sources of exposure. Professional organizations such as the Health Physics Society can provide radiation protection practitioners with continuing education programs on the state of the science and describe the key underpinnings of the system of radiological protection. Such efforts will help equip and prepare radiation protection professionals to more effectively communicate radiation health information with their stakeholders.

Occupational radiation dose trends in U.S. radiologic technologists assisting with fluoroscopically-guided interventional procedures, 1980-2020.

PURPOSE: To summarize dose trends from 1980-2020 for 19,651 U.S. radiologic technologists who reported assisting with fluoroscopically-guided interventional procedures (FGIP), overall and by work history characteristics. METHODS: We summarized 762,310 annual personal dose equivalents at a 10 mm-reference depth ("doses") during 1980-2020 for 43,823 participants of the U.S. Radiologic Technologists (USRT) cohort who responded to work history questionnaires administered during 2012-2014. This population included 19,651 technologists who reported assisting with FGIP (≥1 time per month for ≥12 consecutive months) at any time during the study period. We estimated doses corresponding to assistance with FGIP by proximity to patients, monthly procedure frequency, and procedure type. We used box plots and summary statistics (e.g., median, percentiles) to describe annual doses and dose trends. RESULTS: Median annual dose corresponding to assistance with FGIP was 0.65 mSv, [interquartile range (IQR)=0.60-1.40; 95th percentile=6.80]. Higher occupational doses with wider variability were associated with close proximity to patients during assistance with FGIP (median=1.20 mSv; IQR=0.60-4.18; 95th percentile=12.66), performing ≥20 FGIP per month (median=0.75 mSv; IQR=0.60, 2.40; 95th percentile=9.44), and assisting with high-dose FGIP (median=0.70; IQR=0.60, 1.90; 95th percentile=8.30). CONCLUSION: Occupational doses corresponding to assistance with FGIP were generally low but varied with exposure frequency, procedure type, and proximity to patients. These results highlight the need for vigilant dose monitoring, radiation safety training, and proper protective equipment.

Radiation exposure and leukaemia risk among cohorts of persons exposed to low and moderate doses of external ionising radiation in childhood.

BACKGROUND: Many high-dose groups demonstrate increased leukaemia risks, with risk greatest following childhood exposure; risks at low/moderate doses are less clear. METHODS: We conducted a pooled analysis of the major radiation-associated leukaemias (acute myeloid leukaemia (AML) with/without the inclusion of myelodysplastic syndrome (MDS), chronic myeloid leukaemia (CML), acute lymphoblastic leukaemia (ALL)) in ten childhood-exposed groups, including Japanese atomic bomb survivors, four therapeutically irradiated and five diagnostically exposed cohorts, a mixture of incidence and mortality data. Relative/absolute risk Poisson regression models were fitted. RESULTS: Of 365 cases/deaths of leukaemias excluding chronic lymphocytic leukaemia, there were 272 AML/CML/ALL among 310,905 persons (7,641,362 person-years), with mean active bone marrow (ABM) dose of 0.11 Gy (range 0-5.95). We estimated significant (P < 0.005) linear excess relative risks/Gy (ERR/Gy) for: AML (n = 140) = 1.48 (95% CI 0.59-2.85), CML (n = 61) = 1.77 (95% CI 0.38-4.50), and ALL (n = 71) = 6.65 (95% CI 2.79-14.83). There is upward curvature in the dose response for ALL and AML over the full dose range, although at lower doses (<0.5 Gy) curvature for ALL is downwards. DISCUSSION: We found increased ERR/Gy for all major types of radiation-associated leukaemia after childhood exposure to ABM doses that were predominantly (for 99%) <1 Gy, and consistent with our prior analysis focusing on <100 mGy.

Causes of cardiovascular and noncardiovascular death in the ISCHEMIA trial.

BACKGROUND: The International Study of Comparative Health Effectiveness with Medical and Invasive Approaches trial demonstrated no overall difference in the composite primary endpoint and the secondary endpoints of cardiovascular (CV) death/myocardial infarction or all-cause mortality between an initial invasive or conservative strategy among participants with chronic coronary disease and moderate or severe myocardial ischemia. Detailed cause-specific death analyses have not been reported. METHODS: We compared overall and cause-specific death rates by treatment group using Cox models with adjustment for pre-specified baseline covariates. Cause of death was adjudicated by an independent Clinical Events Committee as CV, non-CV, and undetermined. We evaluated the association of risk factors and treatment strategy with cause of death. RESULTS: Four-year cumulative incidence rates for CV death were similar between invasive and conservative strategies (2.6% vs 3.0%; hazard ratio [HR] 0.98; 95% CI [0.70-1.38]), but non-CV death rates were higher in the invasive strategy (3.3% vs 2.1%; HR 1.45 [1.00-2.09]). Overall, 13% of deaths were attributed to undetermined causes (38/289). Fewer undetermined deaths (0.6% vs 1.3%; HR 0.48 [0.24-0.95]) and more malignancy deaths (2.0% vs 0.8%; HR 2.11 [1.23-3.60]) occurred in the invasive strategy than in the conservative strategy. CONCLUSIONS: In International Study of Comparative Health Effectiveness with Medical and Invasive Approaches, all-cause and CV death rates were similar between treatment strategies. The observation of fewer undetermined deaths and more malignancy deaths in the invasive strategy remains unexplained. These findings should be interpreted with caution in the context of prior studies and the overall trial results.

Collar Badge Lens Dose Equivalent Values among United States Physicians Performing Fluoroscopically Guided Interventional Procedures.

PURPOSE: To describe the range of occupational badge dose readings and annualized dose records among physicians performing fluoroscopically guided interventional (FGI) procedures using job title information provided by the same 3 major medical institutions in 2009, 2012, and 2015. MATERIALS AND METHODS: The Radiation Safety Office of selected hospitals was contacted to request assistance with identifying physicians in a large commercial dosimetry database. All entries judged to be uninformative of occupational doses to FGI procedure staff were excluded. Monthly and annualized doses were described with univariate statistics and box-and-whisker plots. RESULTS: The dosimetry data set of interventional radiology staff contained 169 annual dose records from 77 different physicians and 698 annual dose records from 455 nonphysicians. The median annualized lens dose equivalent values among physicians (11.9 mSv; interquartile range [IQR], 6.9-20.0 mSv) was nearly 3-fold higher than those among nonphysician medical staff assisting with FGI procedures (4.0 mSv; IQR, 1.8-6.7 mSv) (P < .001). During the study period, without eye protection, 25% (23 of 93) of the physician annualized lens dose equivalent values may have exceeded 20 mSv; for nonphysician medical staff, this value may have been exceeded 3.5% (6 of 173) of the time. However, these values did not account for eye protection. CONCLUSIONS: The findings from this study highlight the importance of mitigating occupational dose to the eyes of medical staff, particularly physicians, performing or assisting with FGI procedures. Training on radiation protection principles, the use of personal protective equipment, and patient radiation dose management can all help ensure that the occupational radiation dose is adequately controlled.

Trends in Occupational Radiation Doses for U.S. Radiologic Technologists Performing General Radiologic and Nuclear Medicine Procedures, 1980-2015.

Background Occupational doses to most medical radiation workers have declined substantially since the 1950s because of improvements in radiation protection practices. However, different patterns may have emerged for radiologic technologists working with nuclear medicine because of the higher per-procedure doses and increasing workloads. Purpose To summarize annual occupational doses during a 36-year period for a large cohort of U.S. radiologic technologists and to compare dose between general radiologic technologists and those specializing in nuclear medicine procedures. Materials and Methods Annual personal dose equivalents (referred to as doses) from 1980 to 2015 were summarized for 58 434 (62%) participants in the U.S. Radiologic Technologists (USRT) cohort who responded to the most recent mailed work history survey (years 2012-2014) and reported never regularly performing interventional procedures. Doses were partitioned according to the performance of nuclear medicine (yes or no, frequency, procedure type) by calendar year. Annual dose records were described by using summary statistics (eg, median and 25th and 75th percentiles). Results Median annual doses related to performance of general radiologic procedures decreased from 0.60 mSv (interquartile range [IQR], 0.10-1.9 mSv) in 1980 to levels below the limits of detection by 2015, whereas annual doses related to performance of nuclear medicine procedures remained relatively high during this period (median, 1.2 mSv; IQR, 0.12-3.0 mSv). Higher median annual doses were associated with more frequent (above vs below the median) performance of diagnostic nuclear medicine procedures (≥35 vs <35 times per week; 1.6 mSv [IQR, 0.30-3.3 mSv] and 0.9 mSv [IQR, 0.10-2.6 mSv]). Higher and more variable annual doses were associated with more frequent performance of cardiac nuclear medicine (≥10 times per week) and PET (nine or more times per week) examinations (median, 1.6 mSv [IQR, 0.30-2.2 mSv] and 2.2 mSv [IQR, 0.10-4.6 mSv], respectively). Conclusion Annual doses to U.S. radiologic technologists performing general radiologic procedures declined during a 36-year period. However, consistently higher and more variable doses were associated with the performance of nuclear medicine procedures, particularly cardiac nuclear medicine and PET procedures. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Mettler and Guiberteau in this issue.

Lymphoma and multiple myeloma in cohorts of persons exposed to ionising radiation at a young age.

There is limited evidence that non-leukaemic lymphoid malignancies are radiogenic. As radiation-related cancer risks are generally higher after childhood exposure, we analysed pooled lymphoid neoplasm data in nine cohorts first exposed to external radiation aged <21 years using active bone marrow (ABM) and, where available, lymphoid system doses, and harmonised outcome classification. Relative and absolute risk models were fitted. Years of entry spanned 1916-1981. At the end of follow-up (mean 42.1 years) there were 593 lymphoma (422 non-Hodgkin (NHL), 107 Hodgkin (HL), 64 uncertain subtype), 66 chronic lymphocytic leukaemia (CLL) and 122 multiple myeloma (MM) deaths and incident cases among 143,136 persons, with mean ABM dose 0.14 Gy (range 0-5.95 Gy) and mean age at first exposure 6.93 years. Excess relative risk (ERR) was not significantly increased for lymphoma (ERR/Gy = -0.001; 95% CI: -0.255, 0.279), HL (ERR/Gy = -0.113; 95% CI: -0.669, 0.709), NHL + CLL (ERR/Gy = 0.099; 95% CI: -0.149, 0.433), NHL (ERR/Gy = 0.068; 95% CI: -0.253, 0.421), CLL (ERR/Gy = 0.320; 95% CI: -0.678, 1.712), or MM (ERR/Gy = 0.149; 95% CI: -0.513, 1.063) (all p-trend > 0.4). In six cohorts with estimates of lymphatic tissue dose, borderline significant increased risks (p-trend = 0.02-0.07) were observed for NHL + CLL, NHL, and CLL. Further pooled epidemiological studies are needed with longer follow-up, central outcome review by expert hematopathologists, and assessment of radiation doses to lymphoid tissues.

Fluoroscopy X-Ray Organ-Specific Dosimetry System (FLUXOR) for Estimation of Organ Doses and Their Uncertainties in the Canadian Fluoroscopy Cohort Study.

As part of ongoing efforts to assess lifespan disease mortality and incidence in 63,715 patients from the Canadian Fluoroscopy Cohort Study (CFCS) who were treated for tuberculosis between 1930 and 1969, we developed a new FLUoroscopy X-ray ORgan-specific dosimetry system (FLUXOR) to estimate radiation doses to various organs and tissues. Approximately 45% of patients received medical procedures accompanied by fluoroscopy, including artificial pneumothorax (air in pleural cavity to collapse of lungs), pneumoperitoneum (air in peritoneal cavity), aspiration of fluid from pleural cavity and gastrointestinal series. In addition, patients received chest radiographs for purposes of diagnosis and monitoring of disease status. FLUXOR utilizes age-, sex- and body size-dependent dose coefficients for fluoroscopy and radiography exams, estimated using radiation transport simulations in up-to-date computational hybrid anthropomorphic phantoms. The phantoms include an updated heart model, and were adjusted to match the estimated mean height and body mass of tuberculosis patients in Canada during the relevant time period. Patient-specific data (machine settings, exposure duration, patient orientation) used during individual fluoroscopy or radiography exams were not recorded. Doses to patients were based on parameter values inferred from interviews with 91 physicians practicing at the time, historical literature, and estimated number of procedures from patient records. FLUXOR uses probability distributions to represent the uncertainty in the unknown true, average value of each dosimetry parameter. Uncertainties were shared across all patients within specific subgroups of the cohort, defined by age at treatment, sex, type of procedure, time period of exams and region (Nova Scotia or other provinces). Monte Carlo techniques were used to propagate uncertainties, by sampling alternative average values for each parameter. Alternative average doses per exam were estimated for patients in each subgroup, with the total average dose per individual determined by the number of exams received. This process was repeated to produce alternative cohort vectors of average organ doses per patient. This article presents estimates of doses to lungs, female breast, active bone marrow and heart wall. Means and 95% confidence intervals (CI) of average organ doses across all 63,715 patients were 320 (160, 560) mGy to lungs, 250 (120, 450) mGy to female breast, 190 (100, 340) mGy to heart wall and 92 (47, 160) mGy to active bone marrow. Approximately 60% of all patients had average doses to the four studied organs of less than 10 mGy, 10% received between 10 and 100 mGy, 25% between 100 and 1,000 mGy, and 5% above 1,000 mGy. Pneumothorax was the medical procedure that accounted for the largest contribution to cohort average doses. The major contributors to uncertainty in estimated doses per procedure for the four organs of interest are the uncertainties in exposure duration, tube voltage, tube output, and patient orientation relative to the X-ray tube, with the uncertainty in exposure duration being most often the dominant source. Uncertainty in patient orientation was important for doses to female breast, and, to a lesser degree, for doses to heart wall. The uncertainty in number of exams was an important contributor to uncertainty for ∼30% of patients. The estimated organ doses and their uncertainties will be used for analyses of incidence and mortality of cancer and non-cancer diseases. The CFCS cohort is an important addition to existing radio-epidemiological cohorts, given the moderate-to-high doses received fractionated over several years, the type of irradiation (external irradiation only), radiation type (X rays only), a balanced combination of both genders and inclusion of people of all ages.

The HARMONIC project: study design for the assessment of radiation doses and associated cancer risks following cardiac fluoroscopy in childhood.

The HARMONIC project (Health Effects of Cardiac Fluoroscopy and Modern Radiotherapy in Paediatrics) is a European study aiming to improve our understanding of the long-term health risks from radiation exposures in childhood and early adulthood. Here, we present the study design for the cardiac fluoroscopy component of HARMONIC. A pooled cohort of approximately 100 000 patients who underwent cardiac fluoroscopy procedures in Belgium, France, Germany, Italy, Norway, Spain or the UK, while aged under 22 years, will be established from hospital records and/or insurance claims data. Doses to individual organs will be estimated from dose indicators recorded at the time of examination, using a lookup-table-based dosimetry system produced using Monte Carlo radiation transport simulations and anatomically realistic computational phantom models. Information on beam geometry and x-ray energy spectra will be obtained from a representative sample of radiation dose structured reports. Uncertainties in dose estimates will be modelled using 2D Monte Carlo methods. The cohort will be followed up using national registries and insurance records to determine vital status and cancer incidence. Information on organ transplantation (a major risk factor for cancer development in this patient group) and/or other conditions predisposing to cancer will be obtained from national or local registries and health insurance data, depending on country. The relationship between estimated radiation dose and cancer risk will be investigated using regression modelling. Results will improve information for patients and parents and aid clinicians in managing and implementing changes to reduce radiation risks without compromising medical benefits.

Organ Doses from Chest Radiographs in Tuberculosis Patients in Canada and Their Uncertainties in Periods from 1930 to 1969.

This paper describes a study to estimate absorbed doses to various organs from film-based chest radiographs and their uncertainties in the periods 1930 to 1948, 1949 to 1955, and 1956 to 1969. Estimated organ doses will be used in new analyses of risks of cancer and other diseases in tuberculosis patients in Canada who had chest fluoroscopic and radiographic examinations in those periods. In this paper, doses to lungs, female breast, active bone marrow, and heart from a single chest radiograph in adults and children of ages 1, 5, 10, and 15 y in the Canadian cohort and their uncertainties are estimated using (1) data on the tube voltage (kV), total filtration (mm Al), tube-current exposure-time product (mA s), and tube output (mR [mA s]) in each period; (2) assumptions about patient orientation, distance from the source to the skin of a patient, and film size; and (3) new calculations of sex- and age-specific organ dose conversion coefficients (organ doses per dose in air at skin entrance). Variations in estimated doses to each organ across the three periods are less than 20% in adults and up to about 30% at younger ages. Uncertainties in estimated organ doses are about a factor of 2 to 3 in adults and up to a factor of 4 at younger ages and are due mainly to uncertainties in the tube voltage and tube-current exposure-time product.

A Scalable Database of Organ Doses for Common Diagnostic Fluoroscopy Procedures of Children: Procedures of Historical Practice for Use in Radiation Epidemiology Studies.

Assessment of health effects from low-dose radiation exposures in patients undergoing diagnostic imaging is an active area of research. High-quality dosimetry information pertaining to these medical exposures is generally not readily available to clinicians or epidemiologists studying radiation-related health risks. The purpose of this study was to provide methods for organ dose estimation in pediatric patients undergoing four common diagnostic fluoroscopy procedures: the upper gastrointestinal (UGI) series, the lower gastrointestinal (LGI) series, the voiding cystourethrogram (VCUG) and the modified barium swallow (MBS). Abstracted X-ray film data and physician interviews were combined to generate procedure outlines detailing X-ray beam projections, imaged anatomy, length of X-ray exposure, and presence and amount of contrast within imaged anatomy. Monte Carlo radiation transport simulations were completed for each of the four diagnostic fluoroscopy procedures across the 162-member (87 males and 75 females) University of Florida/National Cancer Institute pediatric phantom library, which covers variations in both subject height and weight. Absorbed doses to 28 organs, including the active marrow and bone endosteum, were assigned for all 162 phantoms by procedure. Additionally, we provide dose coefficients (DCs) in a series of supplementary tables. The DCs give organ doses normalized to procedure-specific dose metrics, including: air kerma-area product (µGy/mGy · cm2), air kerma at the reference point (µGy/µGy), number of spot films (SF) (µGy/number of SFs) and total fluoroscopy time (µGy/s). Organs accumulating the highest absorbed doses per procedure were as follows: kidneys between 0.9-25.4 mGy, 1.1-16.6 mGy and 1.1-9.7 mGy for the UGI, LGI and VCUG procedures, respectively, and salivary glands between 0.2-3.7 mGy for the MBS procedure. Average values of detriment-weighted dose, a phantom-specific surrogate for the effective dose based on ICRP Publication 103 tissue-weighting factors, were 0.98 mSv, 1.16 mSv, 0.83 mSv and 0.15 mSv for the UGI, LGI, VCUG and MBS procedures, respectively. Scalable database of organ dose coefficients by patient sex, height and weight, and by procedure exposure time, reference point air kerma, kerma-area product or number of spot films, allows clinicians and researchers to compute organ absorbed doses based on their institution-specific and patient-specific dose metrics. In addition to informing on patient dosimetry, this work has the potential to facilitate exposure assessments in epidemiological studies designed to investigate radiation-related risks.

A scalable database of organ doses for common diagnostic fluoroscopy examinations of children: procedures of current practice at the University of Florida.

Of all the medical imaging modalities that utilize ionizing radiation, fluoroscopy proves to be the most difficult to assess values of patient organ dose owing to the dynamic and patient-specific nature of the irradiation geometry and its associated x-ray beam characteristics. With the introduction of the radiation dose structured report (RDSR) in the mid-2000s, however, computational tools have been developed to extract patient and procedure-specific data for each irradiation event of the study, and when coupled to a computational phantom of the patient, values of skin and internal organ dose may be assessed. Unfortunately, many legacy and even current diagnostic fluoroscopy units do not have RDSR reporting capabilities, thus limiting these dosimetry reporting advances. Nevertheless, knowledge of patient organ doses for patient care, as well as for radiation epidemiology studies, remains a research and regulatory priority. In this study, we created procedural outlines which document all radiation exposure information required for organ dose assessment, akin to a reference RDSR, for six common diagnostic fluoroscopy procedures performed at the University of Florida (UF) Shands Pediatric Hospital. These procedures include the voiding cystourethrogram, the gastrostomy-tube placement, the lower gastrointestinal study, the rehabilitation swallow, the upper gastrointestinal study, and the upper gastrointestinal study with follow through. These procedural outlines were used to develop an extensive database of organ doses for the 162-member UF/NCI (National Cancer Institute) library of pediatric hybrid phantoms, with each member varying combinations of sex, height, and weight. The organ dose assessment accounts for the varying x-ray fields, fluoroscopy time, relative concentration of x-ray contrast in the organs, and changes in the fluoroscope output due to patient size. Furthermore, we are also reporting organ doses normalized to total fluoroscopy time, reference point air kerma, and kerma-area product, effectively providing procedure dose coefficients. The extensive organ dose library produced in this study may be used prospectively for patient organ dose reporting or retrospectively in epidemiological studies of radiation-associated health risks.

Cataract risk in US radiologic technologists assisting with fluoroscopically guided interventional procedures: a retrospective cohort study.

OBJECTIVES: To assess radiation exposure-related work history and risk of cataract and cataract surgery among radiologic technologists assisting with fluoroscopically guided interventional procedures (FGIP). METHODS: This retrospective study included 35 751 radiologic technologists who reported being cataract-free at baseline (1994-1998) and completed a follow-up questionnaire (2013-2014). Frequencies of assisting with 21 types of FGIP and use of radiation protection equipment during five time periods (before 1970, 1970-1979, 1980-1989, 1990-1999, 2000-2009) were derived from an additional self-administered questionnaire in 2013-2014. Multivariable-adjusted relative risks (RRs) for self-reported cataract diagnosis and cataract surgery were estimated according to FGIP work history. RESULTS: During follow-up, 9372 technologists reported incident physician-diagnosed cataract; 4278 of incident cases reported undergoing cataract surgery. Technologists who ever assisted with FGIP had increased risk for cataract compared with those who never assisted with FGIP (RR: 1.18, 95% CI 1.11 to 1.25). Risk increased with increasing cumulative number of FGIP; the RR for technologists who assisted with >5000 FGIP compared with those who never assisted was 1.38 (95% CI 1.24 to 1.53; p trend <0.001). These associations were more pronounced for FGIP when technologists were located ≤3 feet (≤0.9 m) from the patient compared with >3 feet (>0.9 m) (RRs for >5000 at ≤3 feet vs never FGIP were 1.48, 95% CI 1.27 to 1.74 and 1.15, 95% CI 0.98 to 1.35, respectively; pdifference=0.04). Similar risks, although not statistically significant, were observed for cataract surgery. CONCLUSION: Technologists who reported assisting with FGIP, particularly high-volume FGIP within 3 feet of the patient, had increased risk of incident cataract. Additional investigation should evaluate estimated dose response and medically validated cataract type.

Body-weight dependent dose coefficients for adults exposed to idealised external photon fields.

In epidemiological investigations of cancer risk from occupational exposure, it is important to obtain an organ-specific dose for each cohort member for accurate risk analysis. To date, dose conversion coefficients, which convert physical dose measurement to organ dose, are only available for individuals with reference body size, which can differentially bias the estimated organ dose depending on the body mass index of cohort members. In the current study, we calculated the organ dose coefficients applicable to adult males and females with various body weights by using the Monte Carlo radiation transport technique combined with a library of body size-dependent hybrid computational phantoms exposed in six idealised irradiation geometries. We adapted the eight adult male phantoms, 175 cm tall with weights of 60, 70, 80, 90, 100, 110, 120 and 130 kg, and the nine adult female phantoms, 165 cm tall with weights of 50, 60, 70, 80, 90, 100, 110, 120 and 130 kg. The radiation transport was simulated using MCNPX 2.7 Monte Carlo code. Phantoms were irradiated by external photon fields in anterior posterior (AP), posterior-anterior, right and left lateral, rotational, and isotropic geometries. The results showed that the 60 kg adult male phantom shows 1.33-, 1.43-, 1.44- and 1.52-fold greater dose coefficients for the lungs, heart, stomach, and liver, respectively, than the 120 kg adult male phantom at 0.1 MeV in AP geometry. We derived exponential correlation between organ dose coefficients and body weight to facilitate calculation of organ dose coefficients for a given weight. The comprehensive organ dose coefficients and exponential regression model can be used to estimate more accurate organ dose for individuals of the two genders with various body weights exposed to external photon radiation.

Occupational radiation exposure and risk of cataract incidence in a cohort of US radiologic technologists.

It has long been known that relatively high-dose ionising radiation exposure (> 1 Gy) can induce cataract, but there has been no evidence that this occurs at low doses (< 100 mGy). To assess low-dose risk, participants from the US Radiologic Technologists Study, a large, prospective cohort, were followed from date of mailed questionnaire survey completed during 1994-1998 to the earliest of self-reported diagnosis of cataract/cataract surgery, cancer other than non-melanoma skin, or date of last survey (up to end 2014). Cox proportional hazards models with age as timescale were used, adjusted for a priori selected cataract risk factors (diabetes, body mass index, smoking history, race, sex, birth year, cumulative UVB radiant exposure). 12,336 out of 67,246 eligible technologists reported a history of diagnosis of cataract during 832,479 person years of follow-up, and 5509 from 67,709 eligible technologists reported undergoing cataract surgery with 888,420 person years of follow-up. The mean cumulative estimated 5-year lagged eye-lens absorbed dose from occupational radiation exposures was 55.7 mGy (interquartile range 23.6-69.0 mGy). Five-year lagged occupational radiation exposure was strongly associated with self-reported cataract, with an excess hazard ratio/mGy of 0.69 × 10-3 (95% CI 0.27 × 10-3 to 1.16 × 10-3, p < 0.001). Cataract risk remained statistically significant (p = 0.030) when analysis was restricted to < 100 mGy cumulative occupational radiation exposure to the eye lens. A non-significantly increased excess hazard ratio/mGy of 0.34 × 10-3 (95% CI - 0.19 × 10-3 to 0.97 × 10-3, p = 0.221) was observed for cataract surgery. Our results suggest that there is excess risk for cataract associated with radiation exposure from low-dose and low dose-rate occupational exposures.

Leukaemia and myeloid malignancy among people exposed to low doses (<100 mSv) of ionising radiation during childhood: a pooled analysis of nine historical cohort studies.

BACKGROUND: Substantial evidence links exposure to moderate or high doses of ionising radiation, particularly in childhood, with increased risk of leukaemia. The association of leukaemia with exposure to low-dose (<100 mSv) radiation is less certain, although this is the dose range most relevant to the general population. We aimed to estimate the risk of leukaemia associated with low-dose radiation exposure in childhood (age <21 years). METHODS: In this analysis of historical cohort studies, we pooled eligible cohorts reported up to June 30, 2014. We evaluated leukaemia and myeloid malignancy outcomes in these cohorts with the relevant International Classification of Diseases and International Classification of Diseases for Oncology definitions. The cohorts included had not been treated for malignant disease, had reported at least five cases of the relevant haematopoietic neoplasms, and estimated individual active bone marrow (ABM) doses. We restricted analysis to individuals who were younger than 21 years at first irradiation who had mean cumulative ABM doses of less than 100 mSv. Dose-response models were fitted by use of Poisson regression. The data were received in fully anonymised form by the statistical analyst. FINDINGS: We identified nine eligible cohorts from Canada, France, Japan, Sweden, the UK, and the USA, including 262 573 people who had been exposed to less than 100 mSv enrolled between June 4, 1915, and Dec 31, 2004. Mean follow-up was 19·63 years (SD 17·75) and mean cumulative ABM dose was 19·6 mSv (SD 22·7). 154 myeloid malignancies were identified (which included 79 acute myeloid leukaemias, eight myelodysplastic syndromes, and 36 chronic myeloid leukaemias, in addition to other unspecified myeloid malignancies) and 40 acute lymphoblastic leukaemias, with 221 leukaemias (including otherwise unclassified leukaemias but excluding chronic lymphocytic leukaemia) identified overall. The fitted relative risks at 100 mSv were 3·09 (95% CI 1·41-5·92; ptrend=0·008) for acute myeloid leukaemia and myelodysplastic syndromes combined, 2·56 (1·09-5·06; ptrend=0·033) for acute myeloid leukaemia, and 5·66 (1·35-19·71; ptrend=0·023) for acute lymphoblastic leukaemia. There was no clear dose-response for chronic myeloid leukaemia, which had a relative risk at 100 mSv of 0·36 (0·00-2·36; ptrend=0·394). There were few indications of between-cohort heterogeneity or departure from linearity. For acute myeloid leukaemia and myelodysplastic syndromes combined and for acute lymphoblastic leukaemia, the dose-responses remained significant for doses of less than 50 mSv. Excess absolute risks at 100 mSv were in the range of 0·1-0·4 cases or deaths per 10 000 person-years. INTERPRETATION: The risks of acute myeloid leukaemia and acute lymphoblastic leukaemia were significantly increased after cumulative doses of ionising radiation of less than 100 mSv in childhood or adolescence, with an excess risk also apparent for cumulative radiation doses of less than 50 mSv for some endpoints. These findings support an increased risk of leukaemia associated with low-dose exposure to radiation and imply that the current system of radiological protection is prudent and not overly protective. FUNDING: National Cancer Institute Intramural Research Program, National Cancer Institute, and US National Institutes for Health.

Occupational radiation exposure and glaucoma and macular degeneration in the US radiologic technologists.

There are well-documented associations of glaucoma with high-dose radiation exposure, but only a single study suggesting risk of glaucoma, and less conclusively macular degeneration, associated with moderate-dose exposure. We assessed risk of glaucoma and macular degeneration associated with occupational eye-lens radiation dose, using participants from the US Radiologic Technologists Study, followed from the date of surveys in 1994-1998, 2003-2005 to the earliest of diagnosis of glaucoma or macular degeneration, cancer other than non-melanoma skin cancer, or date of last survey (2012-2014). We excluded those with baseline disease or previous radiotherapy history. Cox proportional hazards models with age as timescale were used. There were 1631 cases of newly self-reported doctor-diagnosed cases of glaucoma and 1331 of macular degeneration among 69,568 and 69,969 eligible subjects, respectively. Estimated mean cumulative eye-lens absorbed dose from occupational radiation exposures was 0.058 Gy. The excess relative risk/Gy for glaucoma was -0.57 (95% CI -1.46, 0.60, p = 0.304) and for macular degeneration was 0.32 (95% CI -0.32, 1.27, p = 0.381), suggesting that there is no appreciable risk for either endpoint associated with low-dose and low dose-rate radiation exposure. Since this is the first examination of glaucoma and macular degeneration associated with low-dose radiation exposure, this result needs to be replicated in other low-dose studies.

Evaluation of the UF/NCI hybrid computational phantoms for use in organ dosimetry of pediatric patients undergoing fluoroscopically guided cardiac procedures.

Epidemiologic data demonstrate that pediatric patients face a higher relative risk of radiation induced cancers than their adult counterparts at equivalent exposures. Infants and children with congenital heart defects are a critical patient population exposed to ionizing radiation during life-saving procedures. These patients will likely incur numerous procedures throughout their lifespan, each time increasing their cumulative radiation absorbed dose. As continued improvements in long-term prognosis of congenital heart defect patients is achieved, a better understanding of organ radiation dose following treatment becomes increasingly vital. Dosimetry of these patients can be accomplished using Monte Carlo radiation transport simulations, coupled with modern anatomical patient models. The aim of this study was to evaluate the performance of the University of Florida/National Cancer Institute (UF/NCI) pediatric hybrid computational phantom library for organ dose assessment of patients that have undergone fluoroscopically guided cardiac catheterizations. In this study, two types of simulations were modeled. A dose assessment was performed on 29 patient-specific voxel phantoms (taken as representing the patient's true anatomy), height/weight-matched hybrid library phantoms, and age-matched reference phantoms. Two exposure studies were conducted for each phantom type. First, a parametric study was constructed by the attending pediatric interventional cardiologist at the University of Florida to model the range of parameters seen clinically. Second, four clinical cardiac procedures were simulated based upon internal logfiles captured by a Toshiba Infinix-i Cardiac Bi-Plane fluoroscopic unit. Performance of the phantom library was quantified by computing both the percent difference in individual organ doses, as well as the organ dose root mean square values for overall phantom assessment between the matched phantoms (UF/NCI library or reference) and the patient-specific phantoms. The UF/NCI hybrid phantoms performed at percent differences of between 15% and 30% for the parametric set of irradiation events. Among internal logfile reconstructed procedures, the UF/NCI hybrid phantoms performed with RMS organ dose values between 7% and 29%. Percent improvement in organ dosimetry via the use of hybrid library phantoms over the reference phantoms ranged from 6.6% to 93%. The use of a hybrid phantom library, Monte Carlo radiation transport methods, and clinical information on irradiation events provide a means for tracking organ dose in these radiosensitive patients undergoing fluoroscopically guided cardiac procedures.

Comparison of methods for individualized astronaut organ dosimetry: Morphometry-based phantom library versus body contour autoscaling of a reference phantom.

One of the hazards faced by space crew members in low-Earth orbit or in deep space is exposure to ionizing radiation. It has been shown previously that while differences in organ-specific and whole-body risk estimates due to body size variations are small for highly-penetrating galactic cosmic rays, large differences in these quantities can result from exposure to shorter-range trapped proton or solar particle event radiations. For this reason, it is desirable to use morphometrically accurate computational phantoms representing each astronaut for a risk analysis, especially in the case of a solar particle event. An algorithm was developed to automatically sculpt and scale the UF adult male and adult female hybrid reference phantom to the individual outer body contour of a given astronaut. This process begins with the creation of a laser-measured polygon mesh model of the astronaut's body contour. Using the auto-scaling program and selecting several anatomical landmarks, the UF adult male or female phantom is adjusted to match the laser-measured outer body contour of the astronaut. A dosimetry comparison study was conducted to compare the organ dose accuracy of both the autoscaled phantom and that based upon a height-weight matched phantom from the UF/NCI Computational Phantom Library. Monte Carlo methods were used to simulate the environment of the August 1972 and February 1956 solar particle events. Using a series of individual-specific voxel phantoms as a local benchmark standard, autoscaled phantom organ dose estimates were shown to provide a 1% and 10% improvement in organ dose accuracy for a population of females and males, respectively, as compared to organ doses derived from height-weight matched phantoms from the UF/NCI Computational Phantom Library. In addition, this slight improvement in organ dose accuracy from the autoscaled phantoms is accompanied by reduced computer storage requirements and a more rapid method for individualized phantom generation when compared to the UF/NCI Computational Phantom Library.