Cancer among medical diagnostic x-ray workers in China

Effect of using different strips on reducing the most common error in panoramic imaging: A randomised controlled trial on palatoglossal air space shadow

INTRODUCTION

Panoramic radiography quality can be impaired by some errors such as positioning errors. Palatoglossal air space shadow error is one of the most common positioning errors and it is due to the tongue not sticking to the roof of the palate. Techniques used to deal with this error might help prevent unnecessary radiation to patients and save them time and money. The study aimed to investigate the effects of using celluloid matrix and edible tapes (fruit leather and chewing gum) on reducing the palatoglossal air space shadow error in panoramic imaging.

METHODS

In our study, 270 patients referred to the Department of Radiology were randomised into three groups: a control group, a celluloid matrix group and an edible tapes group. Before panoramic imaging, all patients were instructed to adhere their tongues to the roof of their mouths, with the distinction that for the celluloid matrix and edible tapes groups, patients were asked to place celluloid tapes, fruit leathers, or chewing gums on their tongues before doing so. The routine imaging process was then performed, and the results were compared across groups to evaluate the incidence of palatoglossal air space shadow error.

RESULTS

The number of error-free images in each fruit leather, chewing gum and celluloid tape group were significantly higher than the control group (all cases P < 0.05). The chances of error-free images in the fruit leather groups were the highest (9.57 times). The age (P = 0.136) and gender (P = 0.272) of patients had no significant effect on the results of interventions.

CONCLUSION

The application of fruit leathers, chewing gums and celluloid tapes reduced the palatoglossal air space shadow error of panoramic imaging.

Mortality among medical radiation workers in the United States, 1965-2016

BACKGROUND

Estimates of radiation risks following prolonged exposures at low doses and low-dose rates are uncertain. Medical radiation workers are a major component of the Million Person Study (MPS) of low-dose health effects. Annual personal dose equivalents, H_P(10), for individual workers are available to facilitate dose-response analyses for lung cancer, leukemia, ischemic heart disease (IHD) and other causes of death.

MATERIALS AND METHODS

The Landauer, Inc. dosimetry database identified 109,019 medical and associated radiation workers first monitored 1965-1994. Vital status and cause of death were determined through 2016. Mean absorbed doses to red bone marrow (RBM), lung, heart, and other organs were estimated by adjusting the recorded H_P(10) for each worker by scaling factors, accounting for exposure geometry, the energy of the incident photon radiation, sex of the worker and whether an apron was worn. There were 4 exposure scenarios: general radiology characterized by low-energy x-ray exposure with no lead apron use, interventional radiologists/cardiologists who wore aprons, nuclear medicine personnel and radiation oncologists exposed to high-energy photon radiation, and other workers. Standardized mortality ratio (SMR) analyses were performed. Cox proportional hazards models were used to estimate organ-specific radiation risks.

RESULTS

Overall, 11,433 deaths occurred (SMR 0.60; 95%CI 0.59,0.61), 126 from leukemia other than chronic lymphocytic leukemia (CLL), 850 from lung cancer, and 1654 from IHD. The mean duration of monitoring was 23.7 y. The excess relative rate (ERR) per 100 mGy was estimated as 0.10 (95% CI -0.34, 0.54) for leukemia other than CLL, 0.15 (0.02, 0.27) for lung cancer, and -0.10 (-0.27, 0.06) for IHD. The ERR for lung cancer was 0.16 (0.01, 0.32) among the 55,218 male workers and 0.09 (-0.19, 0.36) among the 53,801 female workers; a difference that was not statistically significant (p-value = 0.23).

CONCLUSIONS

Medical radiation workers were at increased risk for lung cancer that was higher among men than women, although this difference was not statistically significant. In contrast, the study of Japanese atomic bomb survivors exposed briefly to radiation in 1945 found females to be nearly 3 times the radiation risk of lung cancer compared with males on a relative scale. For medical workers, there were no statistically significant radiation associations with leukemia excluding CLL, IHD or other specific causes of death. Combining these data with other cohorts within the MPS, such as nuclear power plant workers and nuclear submariners, will enable more precise estimates of radiation risks at relatively low cumulative doses.

Occupational radiation exposure and cancer incidence in a cohort of diagnostic medical radiation workers in South Korea

Objectives

We investigated the association between protracted low-dose ionising radiation and the risk of cancer in medical radiation workers, the largest group of workers with occupational radiation exposures.

Methods

Data of all South Korean diagnostic medical radiation workers enrolled at the National Dose Registry during 1996–2011 were merged with the death and cancer incidence data until 31 December 2017. SIRs, relative risks and excess relative risks (ERRs) for cancer were calculated to quantify the radiation dose–response relationship using Poisson regression models.

Results

A total of 3392 first primary cancer cases were identified among 93 920 diagnostic medical radiation workers. The mean cumulative badge dose in the cohort was 7.20 mSv. The ERRs for solid cancer with a 5-year lag and haematopoietic cancers with a 2-year lag for all workers were 0.15 per 100 mGy (95% CI −0.20 to 0.51) and 0.09 per 100 mGy (95% CI −2.02 to 2.20), respectively. The ERRs for cancers did not significantly vary by job title, different lag years or after excluding thyroid and lung cancers. Sensitivity analyses restricted to workers employed for at least 1 year, or who were employed in or after 1996, or who had exposure to a cumulative badge dose of 1 mSv or more showed similar results.

Conclusions

Occupational radiation doses were not significantly associated with cancer incidence among South Korean diagnostic medical radiation workers. However, cautious interpretation of ERRs is needed due to the limitations of short follow-up and low cumulative radiation doses.

Dental X-Rays and the Risk of Thyroid Cancer and Meningioma: A Systematic Review and Meta-Analysis of Current Epidemiological Evidence

Background: Exposure to moderate-to-high doses of ionizing radiation is the only established environmental risk factor for thyroid cancer and brain and central nervous system tumors. Considering the high lifetime prevalence and frequency of exposure to dental X-rays, the most common source of diagnostic radiation exposure in the general population, even a small associated increase in cancer risk would be of considerable public health importance. With the objective to inform clinical practice and guidelines, we synthesized the current epidemiological evidence on the association between dental X-rays and the risk of thyroid cancer, meningioma, and other cancers of the head and neck region. Methods: The Medline, Embase, and Web of Science databases were searched to identify eligible studies. Summary odds ratio/relative risk estimates and confidence intervals were extracted, and pooled risk ratios (RRs) for each cancer were calculated using random effects meta-analysis. Results: The literature search identified 5537 publications; of these, 26 studies including 10,868 cancer patients were included in the synthesis. The random effects meta-analyses, based on seven studies of thyroid cancer (six case/control, one cohort) and eight studies of meningioma (all case/control), showed that multiple (or repeated) exposures to dental X-rays were significantly associated with an increased risk of thyroid cancer (pooled RR = 1.87 [95% confidence interval, CI 1.11-3.15]) and meningioma (pooled RR = 1.53 [CI 1.26-1.85]). There was no association with glioma, and there were too few studies of other cancers of the head and neck region to conduct a meaningful meta-analysis. Conclusions: Based on a meta-analysis of retrospective case/control studies, these findings provide some support to the hypothesis that multiple (or repeated) exposures to dental X-rays may be associated with an increased risk of thyroid cancer and meningioma. These studies did not include individual organ doses and ages at exposure, and are subject to recall bias and other limitations. Furthermore, the thyroid exposure has decreased dramatically over time from the use of thyroid shields and improved technology/equipment. Prospective studies, based on dental X-ray records and patient follow-up, are needed to test the hypothesis further and clarify the possible cancer risk associated with dental radiography, as although the risk at the individual level, particularly with improved technology/equipment, is likely to be very low, the proportion of the population exposed is high. Considering that about one-third of the general population in developed countries is routinely exposed to one or more dental X-rays per year, these findings manifest the need to reduce diagnostic radiation exposure as much as possible.

Assessing liver proteins and enzymes of medical workers exposed to ionizing radiation (IR)

The cross-sectional study was conducted to examine hepatic function via liver enzymes/proteins assessments, along with the estimation of an inflammatory response from C-reactive protein (CRP)-which is a liver-synthesized protein. The liver function tests with aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and bilirubin (BBN), and CRP test were conducted for radiation-exposed workers-REW (n = 32) and radiation-unexposed workers-RUW (n = 21). The annual average effective doses (AAED) were measured from thermoluminescent dosimeter. A t test and bivariate correlation analyses were applied. Only one worker had a high AST value (50 U/L), one worker had a negligible high ALT value (43 U/L) and only one worker had a negligible high bilirubin value (1.3 g/dL). There were normal levels of CRP (up to 6 mg/L) in all individuals. There existed a nonsignificant difference (p < 0.050) between the mean values of liver enzymes and proteins in all exposed and unexposed workers. Nonsignificant weak correlations are reported in liver enzymes/proteins parameters: AST, ALT, ALP, BBN, CRP with the AAED range (whole-body: 0.91-3.39 mSv) during 2011-2015. The normal values of liver enzymes/proteins' (AST, ALT, ALP, BBN, CRP) values may ensure a good hepatic health of radiation-exposed medical workers with AAED range mentioned. We found that low ionizing radiation doses did not alter the liver function test parameters and did not affect the concentration of an inflammatory response protein, i.e., CRP.

Solid cancer incidence among Chinese medical diagnostic x-ray workers, 1950-1995: Estimation of radiation-related risks

The objective of this study was to estimate solid cancer risk attributable to long-term, fractionated occupational exposure to low doses of ionizing radiation. Based on cancer incidence for the period 1950-1995 in a cohort of 27,011 Chinese medical diagnostic X-ray workers and a comparison cohort of 25,782 Chinese physicians who did not use X-ray equipment in their work, we used Poisson regression to fit excess relative risk (ERR) and excess absolute risk (EAR) dose-response models for incidence of all solid cancers combined. Radiation dose reconstruction was based on a previously published method that relied on simulating measurements for multiple X-ray machines, workplaces and working conditions, information about protective measures, including use of lead aprons, and work histories. The resulting model was used to estimate calendar year-specific badge dose calibrated as personal dose equivalent (Sv). To obtain calendar year-specific colon doses (Gy), we applied a standard organ conversion factor. A total of 1,643 cases of solid cancer were identified in 1.45 million person-years of follow-up. In both ERR and EAR models, a statistically significant radiation dose-response relationship was observed for solid cancers as a group. Averaged over both sexes, and using colon dose as the dose metric, the estimated ERR/Gy was 0.87 (95% CI: 0.48, 1.45), and the EAR was 22 per 10(4)PY-Gy (95% CI: 14, 32) at age 50. We obtained estimates of the ERR and EAR of solid cancers per unit dose that are compatible with those derived from other populations chronically exposed to low dose-rate occupational or environmental radiation.

A national survey of occupational radiation exposure among diagnostic radiologic technologists in South Korea

The objective of this study was to investigate representative occupational characteristics and radiation exposure for South Korean radiologic technologists. The authors conducted a national survey by stratified sampling of South Korean administrative districts and types of medical facilities. A total of 585 technologists were surveyed, and survey data were linked with dosimetry data from the National Dose Registry. A total of 73 % of radiologic technologists sampled were male, 62 % were younger than age 40 and 86.5 % began employment after 1990. The most frequent practices among radiologic technologists were diagnostic routine X-ray followed by computed tomography (CT) and portable X-ray. Male workers were more frequently involved in CT, portable X-ray and interventional radiology whereas female workers carried out most mammography procedures. The average annual effective dose was 2.3 mSv for male and 1.3 mSv for female workers. The dose was significantly higher for workers in the provinces and those who had recently started work.

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.

Dental x-rays and the risk of thyroid cancer: a case-control study

The thyroid gland is highly susceptible to radiation carcinogenesis and exposure to high-dose ionising radiation is the only established cause of thyroid cancer. Dental radiography, a common source of low-dose diagnostic radiation exposure in the general population, is often overlooked as a radiation hazard to the gland and may be associated with the risk of thyroid cancer. An increased risk of thyroid cancer has been reported in dentists, dental assistants, and x-ray workers; and exposure to dental x-rays has been associated with an increased risk of meningiomas and salivary tumours.

METHODS

To examine whether exposure to dental x-rays was associated with the risk of thyroid cancer, we conducted a population-based case-control interview study among 313 patients with thyroid cancer and a similar number of individually matched (year of birth +/- three years, gender, nationality, district of residence) control subjects in Kuwait.

RESULTS

Conditional logistic regression analysis, adjusted for other upper-body x-rays, showed that exposure to dental x-rays was significantly associated with an increased risk of thyroid cancer (odds ratio = 2.1, 95% confidence interval: 1.4, 3.1) (p=0.001) with a dose-response pattern (p for trend <0.0001). The association did not vary appreciably by age, gender, nationality, level of education, or parity.

DISCUSSION

These findings, based on self-report by cases/controls, provide some support to the hypothesis that exposure to dental x-rays, particularly multiple exposures, may be associated with an increased risk of thyroid cancer; and warrant further study in settings where historical dental x-ray records may be available.

The non-Hodgkin lymphomas: a review of the epidemiologic literature

The non-Hodgkin lymphomas (NHL) are a heterogeneous group of B-cell and T-cell neoplasms that arise primarily in the lymph nodes. NHL incidence rates in the US doubled between about 1970 and 1990, and stabilized during the 1990s. NHL accounts for approximately 3.4% of cancer deaths in the US. Although some of the observed patterns in NHL have been related to HIV/AIDS, these conditions cannot fully explain the magnitude of the changes; neither do changes in classification systems nor improved diagnostic capabilities. Studies of occupational and environmental exposures (e.g., pesticides, solvents) have produced no consistent pattern of significant positive associations. Inverse associations with ultraviolet radiation exposure and alcohol and fish intake, and positive associations with meat and saturated fat intake have been reported in several studies; additional studies are needed to confirm or refute these associations. Family history of NHL or other hematolympho-proliferative cancers and personal history of several autoimmune disorders are associated with increased risk of NHL, but are not likely to account for a large proportion of cases. HIV and other infectious agents, such as human herpesvirus 8 and Epstein-Barr, appear to be associated with differing types of NHL, such as some B-cell lymphomas. Future epidemiologic studies should evaluate associations by NHL type, enhance exposure information collected, and elucidate factors that may identify susceptible (or resistant) subpopulations because of genetic, immunologic or other characteristics. The extent to which the etiology of NHL types may differ is important to resolve in ongoing and future studies.

Multiple myeloma: A review of the epidemiologic literature

Multiple myeloma, a neoplasm of plasma cells, accounts for approximately approximately 15% of lymphatohematopoietic cancers (LHC) and 2% of all cancers in the US. Incidence rates increase with age, particularly after age 40, and are higher in men, particularly African American men. The etiology is unknown with no established lifestyle, occupational or environmental risk factors. Although several factors have been implicated as potentially etiologic, findings are inconsistent. We reviewed epidemiologic studies that evaluated lifestyle, dietary, occupational and environmental factors; immune function, family history and genetic factors; and the hypothesized precursor, monoclonal gammopathies of undetermined significance (MGUS). Because multiple myeloma is an uncommon disease, etiologic assessments can be difficult because of small numbers of cases in occupational cohort studies, and few subjects reporting exposure to specific agents in case-control studies. Elevated risks have been reported consistently among persons with a positive family history of LHC. A few studies have reported a relationship between obesity and multiple myeloma, and this may be a promising area of research. Factors underlying higher incidence rates of multiple myeloma in African Americans are not understood. The progression from MGUS to multiple myeloma has been reported in several studies; however, there are no established risk factors for MGUS. To improve our understanding of the causes of multiple myeloma, future research efforts should seek the causes of MGUS. More research is also needed on the genetic factors of multiple myeloma, given the strong familial clustering of the disease.

Epidemiology and outcomes research for MGUS, myeloma and amyloidosis

The epidemiology of plasma cell dyscrasias clearly links to a complicated multi-factorial pathogenic pathway that at the individual patient level gives no clear indication of why the malignant process has occurred but factors in the environment and within the genome give clues and are discussed. MGUS is a pre-malignant disorder characterised by monoclonal plasma cell proliferation in the bone marrow and no end-organ damage; the patients are asymptomatic. Primary amyloidosis is a rare disorder that is characterised by deposition of amyloid fibrils composed of immunoglobulin light chain fragments; symptoms relate to the affected organ. Multiple myeloma is a malignant disease of plasma cells and with improvements in treatment, patients can now expect a doubling of median survival to 5 years, a 20% chance of surviving >10 years and a 50% chance of complete remission (CR), morphological and biochemical. The challenge is now to determine exactly what this means to the individual myeloma patient in terms of benefit, and to society as a whole and this is the basis of 'outcomes research' which is discussed in this review.

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.

Occupation and thyroid cancer risk in Sweden

OBJECTIVE

The objective of this study was to identify occupations and industries with increased incidence of thyroid cancer in Swedish workers.

METHOD

Standardized incidence ratios were computed for each job and industry for the period 1971-1989 through record-linkage with the Swedish National Cancer and Death Registers. Age-, period-, geographically adjusted relative risks were calculated using Poisson models.

RESULTS

Increased risks were found for teachers, construction carpenters, policemen, and prison/reformatory officials in men, and medical technicians, shop managers, tailors, and shoecutters among women. Industries with risk excess are manufacture of agricultural machinery, manufacture of computing/accessories, and public administration/police among men; and manufacture of prefabricated wooden buildings, electric installation work, and wholesale of live animals/fertilizers/oilseed/grain among women.

CONCLUSIONS

Our results corroborate some previously reported increased risks. Further research is needed to assess the influence of specific chemical agents related with some of the highlighted work environments.

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.

Immunoglobulin A monoclonal gammopathy in two horses with multiple myeloma

The clinical findings in two horses with secretory multiple myeloma and secondary immunoglobulin A (IgA) monoclonal gammopathy were non-specific and included weight loss, pale mucous membranes, limb oedema and bacterial respiratory tract infection. Consistent laboratory abnormalities included hyperproteinaemia, hyperglobulinaemia, hypoalbuminaemia and hypercalcaemia. The diagnosis was based on the presence of IgA monoclonal gammopathy in serum and urine and bone marrow plasmacytosis (> 10 per cent). One horse was euthanased; it had neoplastic plasma cell infiltrates in its kidneys, spleen, liver, bone marrow, myocardium and adrenal glands. The other horse was treated for a bacterial pneumonia and was still alive six months after it was first examined.

Occupational cancer among women: where have we been and where are we going?

Studies of occupational exposures have been a fruitful area of research for identifying carcinogens. Some of the early observations, such as increased risk of breast cancer among nuns and bone cancer among radium dial workers, were made among women. Recent research on cancer among women has shown increased risks of cancer in many industries and occupations. Estimates that 1% of cancer among women is attributable to occupation are based on research conducted mainly in the 1970s among men in developed countries. These studies do not reflect the dramatic changes in the participation of women in the workplace or the patterns of employment of women in developing countries. The proportion of women in the paid workforce, the amounts and types of unpaid labor, the distribution of women by economy sector, the scale of the workplaces, the allowable exposure levels in the workplace, and implementation of controls have changed over time and vary internationally. Occupational cancer researchers need to expand their focus on women, increase activities in developing countries, include newly created industries, use sophisticated exposure assessment methods, and, where appropriate, incorporate molecular epidemiologic techniques to discover new occupational carcinogens and to identify where better control measures are needed.

Lack of association between occupational radiation exposure and thyroid nodules in healthcare personnel

OBJECTIVES

To investigate whether healthcare workers routinely exposed to low-level ionizing radiation have a higher prevalence of thyroid nodularity.

METHODS

Presence of thyroid nodularity, as assessed by 10-MHz neck ultrasonography, was compared with accumulated radiation doses of 579 exposed university hospital workers (M:F 350:229) obliged to wear a personal dosimeter.

RESULTS

Nodules were detected in 141/579 (24.3%) subjects. Mean accumulated dose was not different among subjects with and without nodules (14.19+/-28.00 mSv vs 17.71+/-32.89 mSv; P=0.12). Duration of occupational exposure (<10 years vs 10-19 years vs >or=20 years) did not affect prevalence of nodularity. At multivariate analysis, only female gender and age were significant risk factors.

CONCLUSIONS

Mildly exposed health workers do not appear to incur any excess risk of thyroid nodularity.

Myeloma aetiology and epidemiology

Recently there have been substantial improvements in our understanding of the biology of myeloma. These findings have important implications for aetiological studies aimed at defining the causative factors for myeloma. Myeloma is closely related to monoclonal gammopathy of unknown significance (MGUS), which is now recognized to be very common in the older population. The epidemiology of these conditions is presented and discussed in the context of the genetic factors governing both the risk of developing MGUS or of transformation to myeloma. Biological studies support a role for aberrant class switch recombination early in the natural history of myeloma suggesting that factors in the environment may interact with this mechanism to increase myeloma risk. Case-control and cohort studies have identified several known and suspected environmental exposures. These exposures include high doses of ionizing radiation, and occupational exposure in the farming and petrochemical industries. The data supporting these associations are presented and discussed in the context of the molecular mechanisms underlying these exposures. In particular DNA damage occurring as a consequence could readily interact with the class switch recombination process to increase the risk of chromosomal translocations, oncogene deregulation and malignant transformation. A further hypothesis, which has been extensively investigated, is the role of chronic immune/antigenic stimulation and the risk of myeloma. This concept is difficult to explain in the context of our current immunological concepts. The data supporting the association and how molecular epidemiological studies using genetic variants in cytokine genes are allowing us to revisit this concept are discussed in detail.

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.

Is occupation a risk factor for thyroid cancer? Canadian Cancer Registries Epidemiology Research Group

A Canadian case-control study explored the etiology of thyroid cancer, including occupational exposure. Analysis of job history from 1272 thyroid cancer patients and 2666 controls revealed statistically significant risks among the following occupations: Wood Processing, Pulp and Papermaking (odds ratio [OR] = 2.54, 95% confidence interval [CI] = 1.11-5.83); Sales and Service (OR = 1.26, 95% CI = 1.05-1.52); and Clerical (OR = 0.81, 95% CI = 0.67-0.97). ORs were adjusted for age, sex, province, cigarette smoking, education, self-reported exposure to radiation at work, and duration of employment. Exposure to ionizing radiation or electromagnetic fields at work (inferred from job histories) did not affect risk, nor did socioeconomic status, measured by education, income, or occupational prestige. Possible explanations for the results and further investigations are discussed.

Occupational cancer among women: research status and methodologic considerations

Occupational causes of cancer have not been well-evaluated among women. An increase in the number of women in the work force in jobs with potentially hazardous exposures during the past few decades raises the question as to whether there is a need to enhance our efforts in this area. The inability to evaluate occupational causes of female gynecologic tumors in studies of men, plus the potential for variation in outcome responses between men and women because of gender-based exposure and susceptibility differences, underscore the need for investigations specifically focused on women. Investigations of occupational exposures and cancer risk among women may require design considerations that differ somewhat from studies of men. Issues to consider include the impact of studying outcomes with high survival (e.g., breast cancer), gender-specific exposure patterns and toxicokinetic processing of some chemicals, special limitations in the use of the general population as the referent, and the need to control for established risk factors for gynecologic tumors.

Micronucleus frequency in Gomel (Belarus) children affected and not affected by thyroid cancer

Cytogenetic monitoring was carried out on a group of children from Gomel (Belarus), one of the areas most severely affected by radioactive contamination following the accident at the Chernobyl nuclear power plant, in 1986. We performed the micronucleus test (MN) in binucleated lymphocytes of 42 children (mean age: 11+/-2.34 years), 16 of whom were affected by thyroid gland tumor. Thirty healthy children living in Pisa (mean age: 14.96+/-2.17 years) were enrolled in the study as controls. Thyroid tumor affected children living in Gomel showed a statistically significant increase in the frequency of micronucleated cells as compared with the healthy children from Pisa. Moreover, a significant correlation was found between MN frequency and both the presence of tumor and higher 137Cs contamination. In addition, higher 137Cs contamination was more frequently observed in tumor affected children. These results suggest that the increased MN frequency is attributable more to 137Cs contamination rather than to the presence of the tumor itself.

Occupational and Environmental Determinants for Benign Thyroid Disease and Follicular Thyroid Cancer

Occupational and environmental determinants of benign thyroid disease and follicular thyroid cancer were evaluated in a series of cases in 1977-1987. Of the cases initially diagnosed as follicular thyroid cancer, only 31 remained after a reclassification, whereas 44 were found to be benign thyroid disease. Both series were compared with 387 randomly selected population controls. Occupational solvent exposure was strongly associated with benign thyroid disease (odds ratio, OR, 2.8; 95% confidence interval, 95% CI, 0.9-9.0 for women and OR 18.9; 95% CI 2.2-161 for men). Eight of the nine men found to have benign disease had been exposed to solvents, and six of them to trichloroethylene. For both types of cases, a private well at the birth address increased the risk, OR 2.0; 95% CI 0.9-4.0 and OR 3.0; 95% CI 1.2-7.2, respectively, whereas the risk was lower for those living in coastal areas. Less fish and shellfish in the diet increased the risk for malignant thyroid disease only. Although based on small numbers, the study indicates etiologic roles of occupational and environmental factors for both conditions studied. The influences of occupation and diet differ, however, for the two outcomes.

Occupational risk factors for female breast cancer: a review

OBJECTIVES

Although progress has been made in identifying personal risk factors and in improving treatment for female breast cancer, incidence rates continue to increase. With women now occupying a sizable fraction of the workforce, it is worth inquiring whether there are occupational risk factors for breast cancer. This is a review of occupational studies on female breast cancer.

METHODS

Suitable reports and published articles with associations of female breast cancer and occupation were identified from technical reports, by searching the MEDLINE bibliographic data base, and by reviewing each paper on cancer that was published in 20 major journals during the period from about 1971-94.

RESULTS

A total of 115 studies were identified; 19 studies relied exclusively on data collected for administrative purposes, and there were four incident case-control studies and 92 cohort studies. Although data for individual industries, occupations, and exposures were sparse, there was limited evidence of an association with employment in the pharmaceutical industry and among cosmetologists and beauticians. Associations were also found for chemists and occupations with possible exposure to extremely low frequency electromagnetic fields, but potential methodological weaknesses preclude drawing any definite conclusions. There was little support for increased risks among textiles workers, dry cleaning workers, and nuclear industry workers.

CONCLUSIONS

Few high quality occupational studies directed specifically toward women have been carried out to allow the unambiguous identification of occupational risk factors for breast cancer. It is suggested that investigations that account for non-occupational risk factors and that assess exposure in a more detailed way be carried out. One strategy already suggested is to conduct population based, case-control studies in which subjects are interviewed about their occupational histories and exposure to chemical and physical agents which are then attributed from the job descriptions by a team of experts. These studies can then be supplemented when necessary with cohort studies of specific populations.

External radiation and thyroid neoplasia

Radiation remains the only factor that has been shown unequivocally to cause (nonmedullary) thyroid cancer. Recent advances include the analysis of the dose-response relationship using data pooled from multiple studies. This analysis confirms that radiation-induced thyroid cancers continue to occur, with a maximum risk at approximately 30 years after exposure. Physicians asked to evaluate patients with a history of radiation exposure should attempt to estimate the dose from the history and should be familiar with the other risk factors. For some individuals, screening should include thyroid imaging, but the results of such imaging, especially with thyroid ultrasound, should be interpreted with caution. The treatment of radiation-induced thyroid cancers is based on the observation that they appear to be no more aggressive than thyroid cancers not associated with radiation. In the future, more information should emerge about the role of cancer genes and susceptibility factors in radiation-induced thyroid cancer.

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.

Ionizing radiation and breast cancer in men (United States)

The purposes of this study were to determine whether exposure of the vestigial male breast to ionizing radiation is associated with an increase in risk of breast cancer and, if so, to determine whether the apparent effects on risk in men are similar to those reported for women. A population-based case-control study of breast cancer in men was conducted in 10 geographic areas of the United States. Information on possible prior exposure to ionizing radiation, and on other potential risk factors for breast cancer, was obtained from personal interviews of 227 cases and 300 controls who were recruited from October 1983 to September 1986. Evidence from this study that ionizing radiation can cause breast cancer in men includes: a modest trend of increasing risk with frequency of chest X-rays; an increase in risk in men with three or more radiographic examinations, especially if received prior to 1963; and an increase in risk in men who received X-ray treatments to the chest and adjacent body areas. Risk was increased only from 20 to 35 years after initial exposure from either radiographic examinations or X-ray treatments, and declined after three to four decades since last exposure, suggesting a wave of increased risk of finite duration following exposure. The doses of radiation received could not be estimated precisely, but those from diagnostic procedures were likely similar to those received by prepubertal females in prior studies, and the results of those and the present investigation are compatible. The carcinogenic effects of ionizing radiation may be similar in the male and prepubertal female breast.

A health survey of radiologic technologists

A health survey of more than 143,000 radiologic technologists is described. The population was identified from the 1982 computerized files of the American Registry of Radiologic Technologists, which was established in 1926. Inactive members were traced to obtain current addresses or death notifications. More than 6000 technologists were reported to have died. For all registrants who were alive when located, a detailed 16-page questionnaire was sent, covering occupational histories, medical conditions, and other personal and lifestyle characteristics. Nonrespondents were contacted by telephone to complete an abbreviated questionnaire. More than 104,000 responses were obtained. The overall response rate was 79%. Most technologists were female (76%), white (93%), and employed for an average of 12 years; 37% attended college, and approximately 50% never smoked cigarettes. Radiation exposure information was sought from employer records and commercial dosimetry companies. Technologists employed for the longest times had the highest estimated cumulative exposures, with approximately 9% with exposures greater than 5 cGy. There was a high correlation between cumulative occupational exposure and personal exposure to medical radiographs, related, in part, to the association of both factors with attained age. It is interesting that 10% of all technologists allowed others to practice taking radiographs on them during their training. Nearly 4% of the respondents reported having some type of cancer, mainly of the skin (1517), breast (665), and cervix (726). Prospective surveys will monitor cancer mortality rates through use of the National Death Index and cancer incidence through periodic mailings of questionnaires. This is the only occupational study of radiation employees who are primarily women and should provide new information on the possible risks associated with relatively low levels of exposure.

Cancer risk among staff at two radiotherapy departments in Denmark

In comparison with the general Danish population, the relative risk (RR) for cancer among staff members employed in two radiotherapy departments in Denmark during 1954-1982 and alive on 1 April 1968 was assessed by linkage to the Danish Cancer Registry. All staff had been monitored with film dosimeters for exposure to radiation. The study cohort consisted of 4151 persons, accruing 49553 person-years at risk. The collective radiation dose was 76.54 manSv and the mean dose 18.4 mSv. A total of 163 cancer cases were observed with 152.3 expected. The risks for cancers usually considered to be radiogenic were not elevated. A significant excess of prostatic cancer was observed (five cases, relative risk, 6.02; 95% confidence interval, 1.94-14.06); this is likely to be a chance finding. No relation was observed between radiation dose or years of exposure and cancer risk, but a weak non-significant increase in risk with time since first exposure was seen.

Cancer incidence among medical diagnostic X-ray workers in China, 1950 to 1985

A second follow-up of 27,011 diagnostic X-ray workers in China revealed a 21% greater incidence of cancer than expected based on the experience of 25,782 physicians who did not routinely use X-rays (RR = 1.21; 95% Cl: 1.08 to 1.35). This risk is lower than the 50% excess reported previously and reflects, in part, the reduced risk among workers first employed after 1965, when hospital exposures to radiation probably were lower than in earlier years. The X-ray workers were employed between 1950 and 1985 and followed for an average of 16.1 years. Significantly elevated risks were seen for leukemia (RR = 2.4, n = 34 cases), and cancers of the esophagus (RR = 5.2, n = 19), liver (RR = 1.8, n = 65), and skin (RR = 2.8, n = 9). Cancers of the breast (RR = 1.5, n = 20), thyroid (RR = 1.7, n = 8), and bone (RR = 7.6, n = 4) also occurred more often than expected. Non-significant deficits were observed for cancers of the oral cavity and pharynx (RR = 0.6, n = 16), colon and rectum (RR = 0.8, n = 20), stomach (RR = 0.8, n = 36), and lung (RR = 0.9, n = 45). Excess risks for leukemia and esophageal cancer were seen among men but not among women. The RR for leukemia was higher for X-ray workers who began employment before 1970 than for those who started more recently and also for those who were young when employment began. The patterns of risk associated with duration of work, and with age and calendar time of initial employment, suggest that the excesses of leukemia and skin cancer, and, possibly, cancers of the breast and thyroid, were due to occupational exposure to X-rays. However, there was little evidence that radiation contributed to the increased occurrences of liver or esophageal cancers.

Overview of radiation-induced skin cancer in humans

There are about a dozen studies of the incidence of skin cancer among irradiated populations with known skin doses that are available for estimating the risk of radiation-induced skin cancer. It is of note that they provide no evidence for a dose threshold and are compatible with a linear dose-response relationship, at least for ultraviolet radiation exposed skin. The studies also provide varying amounts of evidence concerning a number of other important issues in assessing skin cancer risk: types of skin cancer induced by ionizing radiation, the appropriateness of relative risk vs absolute risk models, combined effects of ionizing and UV radiations, and variations in sensitivity to skin cancer induction among demographic and genetic subgroups. Little epidemiological information is available on several factors, such as the RBE for high-LET radiation, the effects of dose protraction or fractionation, or variations in risk by age at irradiation. A reasonable estimate of skin cancer lethality was 0.2 per cent when weighted for the relative proportions of squamous cell and basal cell skin cancers. Average risk estimates of radiation-induced skin cancer incidence were: absolute risk (AR) of 8.5 X 10(-4) person-year-Sv and excess relative risk (RR) of 52 per cent/Sv. Lifetime skin cancer risk was calculated by life-table methods for males from exposures spread out over ages 20-60 years. The estimates for excess skin cancer incidence were 2 per cent and 11 per cent per Sv under the AR and RR models, respectively, while the corresponding mortality risks were 4 X 10(-5) and 2 X 10(-4) per Sv.

The risk of breast cancer after irradiation of the thymus in infancy

It is well established that exposure to ionizing radiation during or after puberty increases a woman's risk for breast cancer, but it is less clear whether exposure to ionizing radiation very early in life is also carcinogenic. We studied the incidence of breast cancer prospectively in a cohort of 1201 women who received x-ray treatment in infancy for an enlarged thymus gland and in their 2469 nonirradiated sisters. After an average of 36 years of follow-up, there were 22 breast cancers in the irradiated group and 12 among their sisters, yielding an adjusted rate ratio of 3.6 (95 percent confidence interval, 1.8 to 7.3). The estimated mean absorbed dose of radiation to the breast was 0.69 Gy. The first breast cancer was diagnosed 28 years after irradiation. The dose-response relation was linear (P less than 0.0001), with a relative risk of 3.48 for 1 Gy of radiation (95 percent confidence interval, 2.1 to 6.2) and an additive excess risk of 5.7 per 10(4) person-years per gray (95 percent confidence interval, 2.9 to 9.5). We conclude that exposure of the female breast to ionizing radiation in infancy increases the risk of breast cancer later in life.

Radiation dose and breast cancer risk in patients treated for cancer of the cervix

The relationship between breast cancer and radiation treatment for cervical cancer was evaluated in an international study of 953 women who subsequently developed breast cancer and 1,806 matched controls. Radiation doses to the breast (average 0.31 Gy) and ovaries (average 32 Gy) were reconstructed for exposed subjects on the basis of their original radiotherapy records. Overall, 88% of the breast cancer cases and 89% of the controls received radiation treatment [relative risk (RR) = 0.88; 95% confidence interval (CI) = 0.7-1.2]. Among women with intact ovaries (561 cases, 1,037 controls), radiotherapy was linked to a significant 35% reduction in breast cancer risk, attributable in all likelihood to the cessation of ovarian function. Ovarian doses of 6 Gy were sufficient to reduce breast cancer risk but larger doses did not reduce risk further. This saturation-type response is probably due to the killing of a critical number of ovarian cells. Cervical cancer patients without ovaries (145 cases, 284 controls) were analyzed separately because such women are at especially low natural risk for breast cancer development. In theory, any effect of low-dose breast exposure, received incidentally during treatment for cervical cancer, should be more readily detectable. Among women without ovaries, there was a slight increase in breast cancer risk (RR = 1.07; 95% CI = 0.6-2.0), and a suggestion of a dose response with the RR being 1.0, 0.7, 1.5 and 3.1 for breast doses of 0, 0.01-0.24, 0.25-0.49 and 0.50+ Gy, respectively. However, this trend of increasing RR was not statistically significant. If low-dose radiation increases the risk of breast cancer among women over age 40 years, it appears that the risk is much lower than would be predicted from studies of younger women exposed to higher doses.