Cancer risk among staff at two radiotherapy departments in Denmark

Exposure to procedural ionizing radiation and cancer risk among physicians

BACKGROUND

Physicians in certain specialities are routinely exposed to procedural ionizing radiation. Their risk of cancer is unknown, including by cancer sub-types.

AIMS

To assess cancer risk among exposed physicians.

METHODS

This population-based case-control study was completed in Ontario, Canada, where healthcare is universal, using linkage of physician billing claims to a province-wide cancer registry. Up to five cancer-free physician controls were matched to each cancer-affected physician, by sex, and both age at and year of, entry into practice. Cumulative exposure to procedural ionizing radiation was captured by physician billing claims. Conditional logistic regression generated an odds ratio (OR) of cancer per 1000 procedures performed and as a binary exposure comparing physicians above the upper 95th percentile cumulative number of procedures (≥200) to those below this cut point.

RESULTS

Mean (standard deviation) age of the 1265 cases and 5772 non-cancer controls was 39.7 (10.7) and 37.7 (9.0) years, and 45% and 49% were female, respectively. After a median (interquartile ranges) of 13.0 (6.9-20.4) and 12.5 (6.5-20.1) years of lookback among cases and controls, the OR of cancer was 1.02 (95% confidence interval 0.99-1.05; P = NS) per 1000 additional procedures performed. Modelling the cumulative exposure to procedures nonlinearly did not change the observed association (P > 0.40 for each). Comparing physicians above versus below the upper 95th percentile cumulative number of procedures, the OR of cancer was 1.23 (95% confidence interval 0.75-2.01, P = NS).

CONCLUSIONS

Physician exposure to procedural ionizing radiation was not associated with a higher risk of cancer. Measures that minimize radiation exposure should continue.

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Occupational Skin Disease in Physicians: A Review of the Literature

OBJECTIVES

Occupational skin disease (OSD) arises from work-related activity. However, there is a paucity of literature on OSD in physicians. The aim of the this review was therefore to examine and summarize what types of symptomatic OSD physicians experience.

METHODS

We conducted a systematic literature search on Cochrane Library, Embase, and Pubmed.

RESULTS

Contact dermatitis from formaldehyde and glutaraldehyde were found in 11.5 and 13.5% of cases, respectively. In total 2.4-14.9% had latex allergy. The reported standardized incidence ratio of squamous cell carcinoma and melanoma was up to 2.15 [95% confidence interval (CI) 1.57-1.95] and 3.2 (95% CI 1.38-6.31). Transmission of human papilloma virus (HPV) particles during carbon dioxide laser wart ablation were found in 70% of samples collected from protective gloves and in 52% of samples from vapors.

CONCLUSIONS

The most frequently reported OSD in physicians is contact dermatitis from allergens in disinfectants and rubber gloves. There is also a risk of cutaneous reactions to latex. The incidence of skin cancer was higher in physicians than in the general population, and the reason for this remains unexplained and potentially biased. There are no reports of transmission of patient HPV to surgeons during wart ablation, possibly because of proper use of protective equipment.

Ferlins and TgDOC2 in Toxoplasma Microneme, Rhoptry and Dense Granule Secretion

The host cell invasion process of apicomplexan parasites like Toxoplasma gondii is facilitated by sequential exocytosis of the microneme, rhoptry and dense granule organelles. Exocytosis is facilitated by a double C2 domain (DOC2) protein family. This class of C2 domains is derived from an ancestral calcium (Ca2+) binding archetype, although this feature is optional in extant C2 domains. DOC2 domains provide combinatorial power to the C2 domain, which is further enhanced in ferlins that harbor 5-7 C2 domains. Ca2+ conditionally engages the C2 domain with lipids, membranes, and/or proteins to facilitating vesicular trafficking and membrane fusion. The widely conserved T. gondii ferlins 1 (FER1) and 2 (FER2) are responsible for microneme and rhoptry exocytosis, respectively, whereas an unconventional TgDOC2 is essential for microneme exocytosis. The general role of ferlins in endolysosmal pathways is consistent with the repurposed apicomplexan endosomal pathways in lineage specific secretory organelles. Ferlins can facilitate membrane fusion without SNAREs, again pertinent to the Apicomplexa. How temporal raises in Ca2+ combined with spatiotemporally available membrane lipids and post-translational modifications mesh to facilitate sequential exocytosis events is discussed. In addition, new data on cross-talk between secretion events together with the identification of a new microneme protein, MIC21, is presented.

Ionising radiation as a risk factor for lymphoma: a review

The ability of ionising radiation to induce lymphoma is unclear. Here, we present a narrative review of epidemiological evidence of the risk of lymphoma, including chronic lymphocytic leukaemia (CLL) and multiple myeloma (MM), among various exposed populations including atomic bombing survivors, industrial and medical radiation workers, and individuals exposed for medical purposes. Overall, there is a suggestion of a positive dose-dependent association between radiation exposure and lymphoma. The magnitude of this association is highly imprecise, however, with wide confidence intervals frequently including zero risk. External comparisons tend to show similar incidence and mortality rates to the general population. Currently, there is insufficient information on the impact of age at exposure, high versus low linear energy transfer radiation, external versus internal or acute versus chronic exposures. Associations are stronger for males than females, and stronger for non-Hodgkin lymphoma and MM than for Hodgkin lymphoma, while the risk of radiation-induced CLL may be non-existent. This broad grouping of diverse diseases could potentially obscure stronger associations for certain subtypes, each with a different cell of origin. Additionally, the classification of malignancies as leukaemia or lymphoma may result in similar diseases being analysed separately, while distinct diseases are analysed in the same category. Uncertainty in cell of origin means the appropriate organ for dose response analysis is unclear. Further uncertainties arise from potential confounding or bias due to infectious causes and immunosuppression. The potential interaction between radiation and other risk factors is unknown. Combined, these uncertainties make lymphoma perhaps the most challenging malignancy to study in radiation epidemiology.

Occupational low-dose irradiation and cancer risk among medical radiation workers

Background

Medical workers are the largest group of workers occupationally exposed to low doses of ionizing radiation (IR) worldwide.

Aims

This review presents all the cohorts of medical workers exposed in the world and summarizes cancer risks associated with radiation exposure in this population.

Methods

Epidemiological studies on health professionals exposed to IR published from 1975 to 2019 were reviewed. Strength of evidence was assessed according to the modified Royal College of General Practitioners three-star system.

Results

Among the 16 epidemiological studies focusing on cancers from 11 cohorts among medical staff exposed to radiation, higher risks of cancer were observed for pre-1950 exposure and for medical workers who performed fluoroscopically guided interventional procedures or radionuclides procedures compared to those who did not. However, strength of evidence supporting the associations remains moderate as several methodological limits including the lack of dosimetry data, lifestyle factors and recent updates may obscure the link between medical occupational exposure and cancer occurrence.

Conclusions

Excess risk of cancer is suspected for high and former exposures. The more highly exposed professions, i.e. interventional physicians and nuclear medicine workers, should be monitored carefully. Collaborative projects aiming to increase the quantity and quality of information of the studied populations would be a key point

Should future interventional neuroradiologists be screened for mutations that impair radiation-induced DNA repair?

In our current medical practice, an increasing number of specialists now have access to radiology technical platforms in order to perform imaging-guided procedures. Although knowledge about the current guidelines and radiation protection devices is a pre-requisite for the use of radiation, the preventive measures are often more or less strictly followed, leading to chronic daily exposure to significant doses of radiation and large accumulated lifetime exposures. Aortic intervention, electrophysiology, and neuro intervention in particular can result in large doses to the operators. Interventionalists might try to rationalize their dismissal of the exposure risks with various excuses: they don't know where they left their badges (even though, guiltily, they would readily admit it is good practice to always wear them), the estimated short duration of the procedure, significant muscular strain and spasm caused by the heaviness of lead aprons, decreased dexterity with lead gloves, or discomfort in wearing lead protective glasses. But their dismissive attitude is most likely due to the inherent inability to feel threatened by something they cannot see or feel, a commitment to the patient at all cost, and a culture of bravado that reinforces their behavior.

Nested Case-control Study of Occupational Radiation Exposure and Breast and Esophagus Cancer Risk among Medical Diagnostic X Ray Workers in Jiangsu of China

Medical diagnostic X-ray workers are one occupational group that expose to the long-term low-dose external radiation over their working lifetime, and they may under risk of different cancers. This study aims to determine the relationship between the occupational X-ray radiation exposure and cancer risk among these workers in Jiangsu, China. We conducted Nested case-control study to investigate the occupational X-ray radiation exposure and cancer risk. Data were collected through self-administered questionnaire, which includes but not limits to demographic data, personal behaviors and family history of cancer. Retrospective dose reconstruction was conducted to estimate the cumulative doses of the x-ray workers. Inferential statistics, t-test and 2 tests were used to compare the differences between each group. We used the logistic regression model to calculate the odds ratio (OR) and 95% confidence interval (CI) of cancer by adjusting the age, gender. All 34 breast cancer cases and 45 esophageal cancer cases that detected in a cohort conducted among health workers between 1950~2011 were included in this presented study, and 158 cancer-free controls were selected by frequency-matched (1:2). Our study found that the occupational radiation exposure was associated with a significantly increased cancer risk compared with the control, especially in breast cancer and esophageal cancer (adjusted OR=2.90, 95% CI: 1.19-7.04 for breast cancer; OR=4.19, 95% CI: 1.87-9.38 for esophageal cancer, and OR=3.43, 95% CI: 1.92-6.12 for total cancer, respectively). The occupational X-ray radiation exposure was associated with increasing cancer risk, which indicates that proper intervention and prevention strategies may be needed in order to bring down the occupational cancer risk.

Radiation-induced noncancer risks in interventional cardiology: optimisation of procedures and staff and patient dose reduction

Concerns about ionizing radiation during interventional cardiology have been increased in recent years as a result of rapid growth in interventional procedure volumes and the high radiation doses associated with some procedures. Noncancer radiation risks to cardiologists and medical staff in terms of radiation-induced cataracts and skin injuries for patients appear clear potential consequences of interventional cardiology procedures, while radiation-induced potential risk of developing cardiovascular effects remains less clear. This paper provides an overview of the evidence-based reviews of concerns about noncancer risks of radiation exposure in interventional cardiology. Strategies commonly undertaken to reduce radiation doses to both medical staff and patients during interventional cardiology procedures are discussed; optimisation of interventional cardiology procedures is highlighted.

Cancer and non-cancer brain and eye effects of chronic low-dose ionizing radiation exposure

BACKGROUND

According to a fundamental law of radiobiology ("Law of Bergonié and Tribondeau", 1906), the brain is a paradigm of a highly differentiated organ with low mitotic activity, and is thus radio-resistant. This assumption has been challenged by recent evidence discussed in the present review.

RESULTS

Ionizing radiation is an established environmental cause of brain cancer. Although direct evidence is lacking in contemporary fluoroscopy due to obvious sample size limitation, limited follow-up time and lack of focused research, anecdotal reports of clusters have appeared in the literature, raising the suspicion that brain cancer may be a professional disease of interventional cardiologists. In addition, although terminally differentiated neurons have reduced or mild proliferative capacity, and are therefore not regarded as critical radiation targets, adult neurogenesis occurs in the dentate gyrus of the hippocampus and the olfactory bulb, and is important for mood, learning/memory and normal olfactory function, whose impairment is a recognized early biomarker of neurodegenerative diseases. The head doses involved in radiotherapy are high, usually above 2 Sv, whereas the low-dose range of professional exposure typically involves lifetime cumulative whole-body exposure in the low-dose range of < 200 mSv, but with head exposure which may (in absence of protection) arrive at a head equivalent dose of 1 to 3 Sv after a professional lifetime (corresponding to a brain equivalent dose around 500 mSv).

CONCLUSIONS

At this point, a systematic assessment of brain (cancer and non-cancer) effects of chronic low-dose radiation exposure in interventional cardiologists and staff is needed.

Historical review of occupational exposures and cancer risks in medical radiation workers

Epidemiological studies of medical radiation workers have found excess risks of leukemia, skin and female breast cancer in those employed before 1950 but little consistent evidence of cancer risk increases subsequently. Occupational radiation-related dose-response data and recent and lifetime cancer risk data are limited for radiologists and radiologic technologists and lacking for physicians and technologists performing fluoroscopically guided procedures. Survey data demonstrate that occupational doses to radiologists and radiologic technologists have declined over time. Eighty mostly small studies of cardiologists and fewer studies of other physicians reveal that effective doses to physicians per interventional procedure vary by more than an order of magnitude. For medical radiation workers, there is an urgent need to expand the limited information on average annual, time-trend and organ doses from occupational radiation exposures and to assess lifetime cancer risks of these workers. For physicians and technologists performing interventional procedures, more information about occupational doses should be collected and long-term follow-up studies of cancer and other serious disease risks should be initiated. Such studies will help optimize standardized protocols for radiologic procedures, determine whether current radiation protection measures for medical radiation workers are adequate, provide guidance on cancer screening needs, and yield valuable insights on cancer risks associated with chronic radiation exposure.

Lung cancer risk among US radiologic technologists, 1983-1998

While exposure to moderate to high-dose ionizing radiation is an established risk factor for lung cancer, the relationship between lung cancer and chronic low dose radiation remains uncertain. We examined lung cancer risk among 71,894 US radiologic technologists who were certified during 1926-1982, responded to a baseline questionnaire (1983-1989), and were free of cancer other than non-melanoma skin cancer at baseline. Study participants were followed until completion of a second questionnaire (1994-1998), death, or August 31, 1998. We identified 287 lung cancer cases: 66 incident cases and 221 decedents. Exposure to radiation was inferred based on work history information provided in the baseline questionnaire. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazard models adjusted for age, race/ethnicity and smoking. Smoking-adjusted lung cancer risk was not related to working as a radiologic technologist in early years when radiation exposures were likely highest (RR = 0.9; 95% CI, 0.5-1.8 for year first worked before 1940 compared to year first worked >or=1960), nor was risk related to the year first worked after 1940 or the number of years worked in any decade. While lung cancer risk was increased in radiologic technologists who held patients for X-rays, or who allowed others to take numerous practice X-rays on them, the trend was not statistically significant in either case. Although we adjusted for smoking, the possibility of residual confounding exists. Overall, we find very limited evidence that chronic low-to-moderate dose occupational exposure increased lung cancer risk in the US Radiologic Technologist cohort.

Interventional radiography and mortality risks in U.S. radiologic technologists

With the exponential increase in minimally invasive fluoroscopically guided interventional radiologic procedures, concern has increased about the health effects on staff and patients of radiation exposure from these procedures. There has been no systematic epidemiologic investigation to quantify serious disease risks or mortality. To quantify all-cause, circulatory system disease and cancer mortality risks in U.S. radiologic technologists who work with interventional radiographic procedures, we evaluated mortality risks in a nationwide cohort of 88,766 U.S. radiologic technologists (77% female) who completed a self-administered questionnaire during 1994-1998 and were followed through 31 December 2003. We obtained information on work experience, types of procedures (including fluoroscopically guided interventional procedures), and protective measures plus medical, family cancer history, lifestyle, and reproductive information. Cox proportional hazards regression models were used to compute relative risks (RRs) with 95% confidence intervals (CIs). Between completion of the questionnaire and the end of follow-up, there were 3,581 deaths, including 1,209 from malignancies and 979 from circulatory system diseases. Compared to radiologic technologists who never or rarely performed or assisted with fluoroscopically guided interventional procedures, all-cause mortality risks were not increased among those working on such procedures daily. Similarly, there was no increased risk of mortality resulting from all circulatory system diseases combined, all cancers combined, or female breast cancer among technologists who daily performed or assisted with fluoroscopically guided interventional procedures. Based on small numbers of deaths (n=151), there were non-significant excesses (40%-70%) in mortality from cerebrovascular disease among technologists ever working with these procedures. The absence of significantly elevated mortality risks in radiologic technologists reporting the highest frequency of interventional radiography procedures must be interpreted cautiously in light of the small number of deaths during the relatively short follow-up. The present study cannot rule out increased risks of cerebrovascular disease, specific cancers, and diseases with low case-fatality rates or a long latency period preceding death.

Case report: Hydroquinone and/or glutaraldehyde induced acute myeloid leukaemia?

BACKGROUND

Exposures to high doses of irradiation, to chemotherapy, benzene, petroleum products, paints, embalming fluids, ethylene oxide, herbicides, pesticides, and smoking have been associated with an increased risk of acute myelogenous leukemia (AML). Although there in no epidemiological evidence of relation between X-ray developer, fixer and replenisher liquids and AML, these included glutaraldehyde which has weakly associated with lymphocytic leukemia in rats and hydroquinone has been increasingly implicated in producing leukemia, causing DNA and chromosomal damage, inhibits topo-isomerase II, alter hematopoiesis and inhibit apoptosis of neoplastic cells.

CASE PRESENTATION

Two white females (A and B) hired in 1985 as medical radiation technologists in a primary care center, in Greece. In July 2001, woman A, 38-years-old, was diagnosed as having acute monocytic leukaemia (FAB M5). The patient did not respond to therapy and died three weeks later. In August 2001, woman B, 35-year-old, was diagnosed with acute promyelocytic leukaemia (FAB M3). Since discharge, she is in continuous complete remission. Both women were non smokers without any medical history. Shortly after these incidents official inspectors and experts inspected workplace, examined equipment, archives of repairs, notes, interviewed and monitored employees. They concluded that shielding was inadequate for balcony's door but personal monitoring did not show any exceeding of TLV of 20 mSv yearly and cytogenetics analysis did not reveal findings considered to be characteristics of ionizing exposure. Equipment for developing photos had a long list of repairs, mainly leakages of liquids and increases of temperature. On several occasions the floor has been flooded especially during 1987-1993 and 1997-2001. Inspection confirmed a complete lack of ventilation and many spoiled medical x-ray films. Employees reported that an "osmic" level was continuously evident and frequently developed symptoms of respiratory irritation and dizziness.

CONCLUSION

The findings support the hypothesis that the specific AML cases might have originated from exposure to chemicals, especially hydroquinone and/or glutaraldehyde. The report also emphasises the crucial role of inspection of facilities and enforcement of compliance with regulations in order to prevent similar incidents.

Breast cancer incidence in U.S. radiologic technologists

BACKGROUND

Studies of atomic bomb survivors and medically exposed populations have demonstrated an increased risk of breast cancer associated with acute or protracted, intermediate-dose or high-dose, ionizing radiation; however, the risks associated with low-dose and low-dose-rate (protracted) exposures are less certain.

METHODS

The authors evaluated incident breast cancer risks from 1983 to 1998 according to employment characteristics and a 4-level proxy index for cumulative radiation exposure based on 2 mail surveys among 56,436 U.S. female radiologic technologists who were certified from 1925 to 1980, adjusting for established breast cancer risk factors.

RESULTS

During follow-up, 1050 new breast cancer diagnoses were ascertained. Compared with radiologic technologists who began working in 1970 or later, adjusted breast cancer risks for those who first worked in the 1960s, 1950s, 1940s, from 1935 to 1939, and before 1935 were 1.0 (95% confidence interval [CI], 0.8-1.2), 1.2 (95% CI, 0.9-1.6), 1.0 (95% CI, 0.7-1.5), 1.8 (95% CI, 1.0-3.2), and 2.9 (95% CI, 1.3-6.2), respectively. The risk rose with the number of years worked before 1940 (P value for trend = .002) and was elevated significantly among those who began working before age 17 years (relative risk, 2.6; 95% CI, 1.3-5.1; 10 women) but was not related to the total years worked in the 1940s or later. Compared with technologists who had a Level 1 (minimal) proxy index for cumulative radiation exposure, breast cancer risks were 1.0 (95% CI, 0.9-1.2), 1.0 (95% CI, 0.7-1.3), and 1.5 (95% CI, 1.0-2.2), respectively, for technologists who had Level 2, Level 3, and Level 4 (highest) exposure.

CONCLUSIONS

Breast cancer risk was elevated significantly in female radiologic technologists who experienced daily low-dose radiation exposures over several years that potentially resulted in appreciable cumulative exposure. The increased risk for total years worked before 1940, but not later, was consistent with decreasing occupational radiation exposures, improvements in radiation technology, and more stringent radiation protection standards over time.

Estimating Historical Radiation Doses to a Cohort of U.S. Radiologic Technologists

Data have been collected and physical and statistical models have been constructed to estimate unknown occupational radiation doses among 90,000 members of the U.S. Radiologic Technologists cohort who responded to a baseline questionnaire during the mid-1980s. Since the availability of radiation dose data differed by calendar period, different models were developed and applied for years worked before 1960, 1960- 1976 and 1977-1984. The dose estimation used available film-badge measurements (approximately 350,000) for individual cohort members, information provided by the technologists on their work history and protection practices, and measurement and other data derived from the literature. The dosimetry model estimates annual and cumulative occupational badge doses (personal dose equivalent) for each technologist for each year worked from 1916 through 1984 as well as absorbed doses to organs and tissues including bone marrow, female breast, thyroid, ovary, testes, lung and skin. Assumptions have been made about critical variables including average energy of X rays, use of protective aprons, position of film badges, and minimum detectable doses. Uncertainty of badge and organ doses was characterized for each year of each technologist's working career. Monte Carlo methods were used to generate estimates of cumulative organ doses for preliminary cancer risk analyses. The models and predictions presented here, while continuing to be modified and improved, represent one of the most comprehensive dose reconstructions undertaken to date for a large cohort of medical radiation workers.

Incidence of haematopoietic malignancies in US radiologic technologists

BACKGROUND

There are limited data on risks of haematopoietic malignancies associated with protracted low-to-moderate dose radiation.

AIMS

To contribute the first incidence risk estimates for haematopoietic malignancies in relation to work history, procedures, practices, and protective measures in a large population of mostly female medical radiation workers.

METHODS

The investigators followed up 71,894 (77.9% female) US radiologic technologists, first certified during 1926-80, from completion of a baseline questionnaire (1983-89) to return of a second questionnaire (1994-98), diagnosis of a first cancer, death, or 31 August 1998 (731,306 person-years), whichever occurred first. Cox proportional hazards regression was used to compute risks.

RESULTS

Relative risks (RR) for leukaemias other than chronic lymphocytic leukaemia (non-CLL, 41 cases) were increased among technologists working five or more years before 1950 (RR = 6.6, 95% CI 1.0 to 41.9, based on seven cases) or holding patients 50 or more times for x ray examination (RR = 2.6, 95% CI 1.3 to 5.4). Risks of non-CLL leukaemias were not significantly related to the number of years subjects worked in more recent periods, the year or age first worked, the total years worked, specific procedures or equipment used, or personal radiotherapy. Working as a radiologic technologist was not significantly linked with risk of multiple myeloma (28 cases), non-Hodgkin's lymphoma (118 cases), Hodgkin's lymphoma (31 cases), or chronic lymphocytic leukaemia (23 cases).

CONCLUSION

Similar to results for single acute dose and fractionated high dose radiation exposures, there was increased risk for non-CLL leukaemias decades after initial protracted radiation exposure that likely cumulated to low-to-moderate doses.

Cancer Risks among Radiologists and Radiologic Technologists: Review of Epidemiologic Studies

Radiologists and radiologic technologists were among the earliest occupational groups exposed to ionizing radiation and represent a large segment of the working population exposed to radiation from human-made sources. The authors reviewed epidemiologic data on cancer risks from eight cohorts of over 270,000 radiologists and technologists in various countries. The most consistent finding was increased mortality due to leukemia among early workers employed before 1950, when radiation exposures were high. This, together with an increasing risk of leukemia with increasing duration of work in the early years, provided evidence of an excess risk of leukemia associated with occupational radiation exposure in that period. While findings on several types of solid cancers were less consistent, several studies provided evidence of a radiation effect for breast cancer and skin cancer. To date, there is no clear evidence of an increased cancer risk in medical radiation workers exposed to current levels of radiation doses. However, given a relatively short period of time for which the most recent workers have been followed up and in view of the increasing uses of radiation in modern medical practices, it is important to continue to monitor the health status of medical radiation workers.

Cancer incidence in the US radiologic technologists health study, 1983-1998

BACKGROUND

Workers exposed to low doses of radiation can provide information regarding cancer risks that are of public concern. However, characterizing risk at low doses requires large populations and ideally should include a large proportion of women, both of which rarely are available.

METHODS

Among 90305 radiologic technologists in the U.S. (77% women) who were followed during 1983-1998, data concerning incident cancer occurrence was obtained from mailed questionnaires and from death records. Standardized incidence ratios (SIRs) were computed using age-specific, gender-specific, race-specific, and calendar year-specific cancer rates from the Surveillance, Epidemiology, and End Results Program.

RESULTS

The SIR for all cancers in both genders combined was 1.04 (95% confidence interval [95% CI], 1.00-1.07; n = 3292 technologists). Female technologists had an elevated risk for all solid tumors combined (SIR = 1.06; 95% CI, 1.02-1.10; n = 2168 women) and for breast cancers (SIR = 1.16; 95% CI, 1.09-1.23; n = 970 women), melanoma (SIR = 1.66; 95% CI, 1.43-1.89; n = 181 women), and thyroid cancers (SIR = 1.54; 95% CI, 1.24-1.83; n = 107 women). Male technologists experienced a decreased risk for solid tumors (SIR = 0.92; 95% CI, 0.85-0.98; n = 755 men); however, melanoma (SIR = 1.39; 95% CI, 1.00-1.79; n = 56 men) and thyroid cancers (SIR = 2.23; 95% CI, 1.29-3.59; n = 17 men) were increased. Among both genders, the risks were decreased for buccal cavity/pharyngeal cancers (SIR = 0.73; 95% CI, 0.55-0.90; n = 54 technologists), rectal cancers (SIR = 0.62; 95% CI 0.48-0.76; n = 53 technologists), and lung cancers (SIR = 0.77, 95% CI, 0.70-0.85; n = 307 technologists).

CONCLUSIONS

The elevated risk for breast cancer may have been related to occupational radiation exposure. The observed excesses of melanoma and thyroid cancers may reflect, at least in part, earlier detection among medical workers with easy access to health care.

Risk of melanoma among radiologic technologists in the United States

Our study examines the risk of melanoma among medical radiation workers in the U.S. Radiologic Technologists (USRT) study. We evaluated 68,588 white radiologic technologists (78.8% female), certified during 1926-1982, who responded to a baseline questionnaire (1983-1989) and were free of cancer other than nonmelanoma skin at that time. Participants were followed through completion of a second questionnaire (1994-1998). We identified 207 cases, 193 subjects who reported first primary melanoma and 14 decedents with melanoma listed as an underlying or contributory cause of death. We examined risks of occupational radiation exposures using work history information on practices, procedures, and protective measures reported on the baseline questionnaire. Based on Cox proportional hazards regression, melanoma was significantly associated with established risk factors, including constitutional characteristics (skin tone, eye and hair color), personal history of nonmelanoma skin cancer, family history of melanoma and indicators of residential sunlight exposure. Melanoma risk was increased among those who first worked before 1950 (RR = 1.8, 95% CI = 0.6-5.5), particularly among those who worked 5 or more years before 1950 (RR = 2.4; 0.7-8.7; p (trend) for years worked before 1950 = 0.03), when radiation exposures were likely highest. Risk was also modestly elevated among technologists who did not customarily use a lead apron or shield when they first began working (RR = 1.4; 0.8-2.5). Clarifying the possible role of exposure to chronic ionizing radiation in melanoma is likely to require nested case-control studies within occupational cohorts, such as this one, which will assess individual radiation doses, and detailed information about sun exposure, sunburn history and skin susceptibility characteristics.

Cancer and other causes of mortality among radiologic technologists in the United States

Data are limited on the role of chronic exposure to low-dose ionizing radiation in the etiology of cancer. In a nationwide cohort of 146,022 U.S. radiologic technologists (73% female), we evaluated mortality risks in relation to work characteristics. Standardized mortality ratios (SMRs) were computed to compare mortality in the total cohort vs. the general population of the United States. Mortality risks were low for all causes (SMR = 0.76) and for all cancers (SMR = 0.82) among the radiologic technologists. We also calculated relative risks (RR) for the 90,305 technologists who responded to a baseline mailed questionnaire, using Poisson regression models, adjusted for known risk factors. Risks were higher for all cancers (RR = 1.28, 95% confidence interval [CI] = 0.93-1.69) and breast cancer (RR = 2.92, 95% CI = 1.22-7.00) among radiologic technologists first employed prior to 1940 compared to those first employed in 1960 or later, and risks declined with more recent calendar year of first employment (p-trend = 0.04 and 0.002, respectively), irrespective of employment duration. Risk for the combined category of acute lymphocytic, acute myeloid and chronic myeloid leukemias was increased among those first employed prior to 1950 (RR = 1.64, 95% CI = 0.42-6.31) compared to those first employed in 1950 or later. Risks rose for breast cancer (p-trend = 0.018) and for acute lymphocytic, acute myeloid and chronic myeloid leukemias (p-trend = 0.05) with increasing duration of employment as a radiologic technologist prior to 1950. The elevated mortality risks for breast cancer and for the combined group of acute lymphocytic, acute myeloid and chronic myeloid leukemias are consistent with a radiation etiology given greater occupational exposures to ionizing radiation prior to 1950 than in more recent times.

Cancer incidence and risk estimation among medical x-ray workers in China, 1950-1995

Cancer incidence (1950-1995) among 27,011 medical diagnostic x-ray workers was compared by means of O/E system with that of 25,782 other medical specialists employed between 1950 and 1980 to provide evidence of human malignant tumors produced by protracted and fractionated exposure to ionizing radiation and to assess resultant cancer risk. Significant cancer risk was seen among diagnostic x-ray workers (RR = 1.2, 95% CI: 1.1-1.3). Significantly elevated risks were found for leukemia and cancers of skin, female breast, lung, liver, bladder, and esophagus; the RRs were 2.2, 4.1, 1.3, 1.2, 1.2, 1.8, and 2.7, respectively. The patterns of risk associated with years since beginning x-ray work and with age and calendar year of initial employment suggest that the excesses of leukemia, skin cancer, and female breast cancer-and possibly thyroid cancer-were related to occupational exposure to x rays. Because of a lack of individual dosimetry for Chinese medical x-ray workers (CMXW) before 1985, the dose was reconstructed by physical and biological retrospective dosimetry methods. The cancer risk of CMXW was estimated based on the reconstructed dose. The average cumulative dose for the earlier cohort (employed before 1970) was 551 mGy, and for the later cohort (employed from 1970 to 1980) it was 82 mGy. The RRs of leukemia and solid cancer were significantly high for the earlier cohort: 2.4 for leukemia, 1.2 for solid cancer. But no significant increase of RR was evident for the later cohort. The RR of leukemia was 1.7 and 1.1 for solid cancer. This means a significant cancer risk can be induced by long term fractionated exposure to ionizing radiation when the cumulative dose reaches a certain level.

First analysis of cancer incidence and occupational radiation exposure based on the National Dose Registry of Canada

A cohort study was conducted to investigate the relation between cancer incidence and occupational exposure to ionizing radiation. Records containing dose information from 1951 to 1988 for 191,333 persons were extracted from the National Dose Registry of Canada. The records were linked to the Canadian Cancer Data Base, with incidence data from 1969 to 1988. Standardized incidence ratios were calculated using Canadian cancer incidence rates stratified by age, sex, and calendar year. Excess relative risks were obtained from internally based dose-response analyses. The following significant results were found for males and females combined: a deficit in the standardized incidence ratio for all cancers combined; elevated standardized incidence ratios for thyroid cancer and melanoma; and elevated excess relative risks for rectum, leukemia, lung, all cancers combined, all except lung, and all except leukemia. For males, cancers of the colon, pancreas, and testis also showed significantly elevated excess relative risks. The specific cancer types listed above have been implicated in previous studies on occupational exposure to ionizing radiation, except for testis, colon, and melanoma, while the findings on thyroid cancer from previous studies are inconclusive. The thyroid standardized incidence ratios in this study are highly significant, but further investigation is needed to assess the possibility of association with occupational radiation exposure.

Is occupationally induced exposure to radiation a risk factor of thyroid nodule formation?

The prevalence of thyroid nodules was studied with ultrasonography in a group of male hospital workers (n = 44) who had been exposed occupationally to x-rays. This group was compared with a group of nonexposed workers (n = 88) who were age- and sex-matched with the exposed workers. Thyroid nodules were detected in 18 (41%) of the exposed workers, compared with 11 (13%) of the nonexposed controls. Both groups were subdivided with respect to age (i.e., 30-39 y, 40-49 y, 50-59 y), and there was a higher and significant relative risk for thyroid nodule formation in the exposed group. We also divided the groups into subgroups according to levels of exposure (i.e., nonexposed, exposed for < 20 y, and exposed for > 20 y), and a significant result was obtained with the linear-trend chi-square test. The preliminary results of our study suggest that occupationally induced exposure to radiation may be a risk factor for thyroid nodule formation.

Risk of thyroid nodules in subjects occupationally exposed to radiation: a cross sectional study

OBJECTIVES

To examine, by ultrasonography the prevalence of thyroid nodules in a cross sectional study of male medical workers occupationally exposed to chi radiation at the Pisa hospital, in comparison with controls matched for age and sex.

METHODS

50 male medical workers exposed to radiation were randomly matched for age (+/- 2 years) with 100 male workers not occupationally exposed to ionising radiation who lived in a slightly iodine deficient area of Tuscany (Lunigiana) (control group 1), and with 100 male workers not exposed to radiation who lived in the same area (Pisa) (control group 2).

RESULTS

Of the occupationally exposed subjects, thyroid nodules were detected in 19/50 (38.0%). Among controls, thyroid nodules were detected in 19/100 subjects of control group 1 and in 13/100 of control group 2. Comparison of exposed and control groups, stratified into 30-39, 40-49, and 50-59 year old age subgroups, showed a higher significant relative risk for thyroid nodules in the exposed subjects.

CONCLUSION

The results suggest that occupational exposure to radiation may be a risk factor for thyroid nodules.