Socio-economic variation in CT scanning in Northern England, 1990-2002.

BACKGROUND: Socio-economic status is known to influence health throughout life. In childhood, studies have shown increased injury rates in more deprived settings. Socio-economic status may therefore be related to rates of certain medical procedures, such as computed tomography (CT) scans. This study aimed to assess socio-economic variation among young people having CT scans in Northern England between 1990 and 2002 inclusive. METHODS: Electronic data were obtained from Radiology Information Systems of all nine National Health Service hospital Trusts in the region. CT scan data, including sex, date of scan, age at scan, number and type of scans were assessed in relation to quintiles of Townsend deprivation scores, obtained from linkage of postcodes with census data, using χ2 tests and Spearman rank correlations. RESULTS: During the study period, 39,676 scans were recorded on 21,089 patients, with 38,007 scans and 19,485 patients (11344 male and 8132 female) linkable to Townsend scores. The overall distributions of both scans and patients by quintile of Townsend deprivation scores were significantly different to the distributions of Townsend scores from the census wards included in the study (p < 0.0001). There was a significant association between type of scan and deprivation quintile (p < 0.0001), primarily due to the higher proportions of head scans in the three most deprived quintiles, and slightly higher proportions of chest scans and abdomen and pelvis scans in the least deprived groups. There was also a significant association (p < 0.0001) between the patient's age at the time of the CT scan and Townsend deprivation quintiles, with slightly increasing proportions of younger children with increasing deprivation. A similar association with age (p < 0.0001) was seen when restricting the data to include only the first scan of each patient. The number of scans per patient was also associated with Townsend deprivation quintiles (p = 0.014). CONCLUSIONS: Social inequalities exist in the numbers of young people undergoing CT scans with those from deprived areas more likely to do so. This may reflect the rates of injuries in these individuals and implies that certain groups within the population may receive higher radiation doses than others due to medical procedures.

Proportion of second cancers attributable to radiotherapy treatment in adults: a cohort study in the US SEER cancer registries.

BACKGROUND: Improvements in cancer survival have made the long-term risks from treatments more important, including the risk of developing a second cancer after radiotherapy. We aimed to estimate the proportion of second cancers attributable to radiotherapy in adults with data from the US Surveillance, Epidemiology and End Results (SEER) cancer registries. METHODS: We used nine of the SEER registries to systematically analyse 15 cancer sites that are routinely treated with radiotherapy (oral and pharynx, salivary gland, rectum, anus, larynx, lung, soft tissue, female breast, cervix, endometrial, prostate, testes, eye and orbit, brain and CNS, and thyroid). The cohort we studied was composed of patients aged 20 years or older who were diagnosed with a first primary invasive solid cancer reported in the SEER registries between Jan 1, 1973, and Dec 31, 2002. Relative risks (RRs) for second cancer in patients treated with radiotherapy versus patients not treated with radiotherapy were estimated with Poisson regression adjusted for age, stage, and other potential confounders. FINDINGS: 647,672 cancer patients who were 5-year survivors were followed up for a mean 12 years (SD 4.5, range 5-34); 60,271 (9%) developed a second solid cancer. For each of the first cancer sites the RR of developing a second cancer associated with radiotherapy exceeded 1, and varied from 1.08 (95% CI 0.79-1.46) after cancers of the eye and orbit to 1.43 (1.13-1.84) after cancer of the testes. In general, the RR was highest for organs that typically received greater than 5 Gy, decreased with increasing age at diagnosis, and increased with time since diagnosis. We estimated a total of 3266 (2862-3670) excess second solid cancers that could be related to radiotherapy, that is 8% (7-9) of the total in all radiotherapy patients (≥1 year survivors) and five excess cancers per 1000 patients treated with radiotherapy by 15 years after diagnosis. INTERPRETATION: A relatively small proportion of second cancers are related to radiotherapy in adults, suggesting that most are due to other factors, such as lifestyle or genetics. FUNDING: US National Cancer Institute.

Common genetic variants related to genomic integrity and risk of papillary thyroid cancer.

DNA damage is an important mechanism in carcinogenesis, so genes related to maintaining genomic integrity may influence papillary thyroid cancer (PTC) risk. Candidate gene studies targeting some of these genes have identified only a few polymorphisms associated with risk of PTC. Here, we expanded the scope of previous candidate studies by increasing the number and coverage of genes related to maintenance of genomic integrity. We evaluated 5077 tag single-nucleotide polymorphisms (SNPs) from 340 candidate gene regions hypothesized to be involved in DNA repair, epigenetics, tumor suppression, apoptosis, telomere function and cell cycle control and signaling pathways in a case-control study of 344 PTC cases and 452 matched controls. We estimated odds ratios for associations of single SNPs with PTC risk and combined P values for SNPs in the same gene region or pathway to obtain gene region-specific or pathway-specific P values using adaptive rank-truncated product methods. Nine SNPs had P values <0.0005, three of which were in HDAC4 and were inversely related to PTC risk. After multiple comparisons adjustment, no SNPs remained associated with PTC risk. Seven gene regions were associated with PTC risk at P < 0.01, including HUS1, ALKBH3, HDAC4, BAK1, FAF1_CDKN2C, DACT3 and FZD6. Our results suggest a possible role of genes involved in maintenance of genomic integrity in relation to risk of PTC.

CT scans in young people in Northern England: trends and patterns 1993-2002.

BACKGROUND: Although CT can be greatly beneficial, its relatively high radiation doses have caused public health concerns. OBJECTIVE: To assess patterns in CT usage among patients aged less than 22 years in Northern England during the period 1993-2002. MATERIALS AND METHODS: Electronic data were obtained from radiology information systems of all nine National Health Service trusts in the region. RESULTS: A total of 38,681 scans had been performed in 20,483 patients aged less than 22 years. The number of CT examinations rose, with the steepest increase between 1997 and 2000. The number of patients scanned per year increased less dramatically, with 2.24/1,000 population aged less than 22 years having one scan or more in 1993 compared to 3.54/1,000 in 2002. This reflects an increase in the median number of scans per patient, which rose from 1 in 1993 to 2 by 1999. More than 70% of CT examinations were of the head, with the number of head examinations varying with time and patient age. CONCLUSION: The frequency of CT scans in this population more than doubled during the study period. This is partly, but not wholly, explained by an increase in the number of scans per patient.

Prospective study of body mass index, physical activity and thyroid cancer.

Increased body size and physical inactivity are positively related to risk of several cancers, but only few epidemiologic studies have investigated body-mass index (BMI) and physical activity in relation to thyroid cancer. We examined the relations of BMI and physical activity to thyroid cancer in a prospective cohort of 484,326 United States men and women, followed from 1995/1996 to 2003. During 3,490,300 person-years of follow-up, we documented 352 newly incident cases of thyroid cancer. The multivariate relative risks (RR) of thyroid cancer for BMI values of 18.5-24.9 (reference), 25.0-29.9 and >/=30 kg m(-2) were 1.0, 1.27 and 1.39 [95% confidence interval (CI) = 1.05-1.85]. Adiposity predicted papillary thyroid cancers (RR comparing extreme BMI categories = 1.47; 95% CI = 1.03-2.10) and, based on small numbers, suggestively predicted follicular thyroid cancers (RR = 1.49; 95% CI = 0.79-2.82) and anaplastic thyroid cancers (RR = 5.80; 95% CI = 0.99-34.19). No relation with BMI was noted for medullary thyroid cancers (RR = 0.97; 95% CI = 0.27-3.43). The positive relation of BMI to total thyroid cancer was evident for men but not for women. However, the test of interaction (p = 0.463) indicated no statistically significant gender difference. Physical activity was unassociated with thyroid cancer. The RRs of total thyroid cancer for low (reference), intermediate, and high level of physical activity were 1.0, 1.01 and 1.01 (95% CI = 0.76-1.34, p for trend = 0.931), respectively. Our results support an adverse effect of adiposity on risk for developing total and papillary, and possibly follicular thyroid cancers. Based on only 15 cases, adiposity was unrelated to medullary thyroid cancers. Physical activity was unrelated to total thyroid cancer.

Nonradiation risk factors for thyroid cancer in the US Radiologic Technologists Study.

The incidence of thyroid cancer has been rapidly increasing in the United States, but few risk factors have been established. The authors prospectively examined the associations of self-reported medical history, anthropometric factors, and behavioral factors with thyroid cancer risk among 90,713 US radiologic technologists (69,506 women and 21,207 men) followed from 1983 through 2006. Incident thyroid cancers in 242 women and 40 men were reported. Elevated risks were observed for women with benign thyroid conditions (hazard ratio (HR) = 2.35, 95% confidence interval (CI): 1.73, 3.20), benign breast disease (HR = 1.56, 95% CI: 1.08, 2.26), asthma (HR = 1.68, 95% CI: 1.00, 2.83), and body mass index > or =35.0 versus 18.5-24.9 kg/m(2) (HR = 1.74, 95% CI: 1.03, 2.94; P-trend = 0.04). Current smoking was inversely associated with thyroid cancer risk (HR = 0.54). No clear associations emerged for reproductive factors, other medical conditions, alcohol intake, or physical activity. Despite few thyroid cancers in men, men with benign thyroid conditions had a significantly increased risk of thyroid cancer (HR = 4.65, 95% CI: 1.62, 13.34), and results for other risk factors were similar to those for women. Consistent with prior studies, obesity and benign thyroid conditions increased and current smoking decreased the risk of thyroid cancer. The novel findings for benign breast disease and asthma warrant further investigation.

Leukemia incidence among people exposed to chronic radiation from the contaminated Techa River, 1953-2005.

Beginning in 1950, people living on the banks of the Techa River received chronic low-dose-rate internal and external radiation exposures as a result of releases from the Mayak nuclear weapons plutonium production facility in the Southern Urals region of the Russian Federation. The Techa River cohort includes about 30,000 people who resided in riverside villages sometime between 1950 and 1960. Cumulative red bone marrow doses range up to 2 Gy with a mean of 0.3 Gy and a median of 0.2 Gy. Between 1953 and 2005, 93 first primary cases of leukemia, including 23 cases of chronic lymphatic leukemia (CLL), were ascertained among the cohort members. A significant linear dose-response relationship was seen for leukemias other than CLL (P < 0.001), but not for CLL. The estimated excess relative risk per Gy is 4.9 (95% confidence interval (CI): 1.6; 14.3) for leukemias other than CLL and less than 0 (95% upper bound 1.4) for CLL.

Diagnostic X-ray examinations and increased chromosome translocations: evidence from three studies.

Controversy regarding potential health risks from increased use of medical diagnostic radiologic examinations has come to public attention. We evaluated whether chromosome damage, specifically translocations, which are a potentially intermediate biomarker for cancer risk, was increased after exposure to diagnostic X-rays, with particular interest in the ionizing radiation dose-response below the level of approximately 50 mGy. Chromosome translocation frequency data from three separately conducted occupational studies of ionizing radiation were pooled together. Studies 1 and 2 included 79 and 150 medical radiologic technologists, respectively, and study 3 included 83 airline pilots and 50 university faculty members (total = 155 women and 207 men; mean age = 62 years, range 34-90). Information on personal history of radiographic examinations was collected from a detailed questionnaire. We computed a cumulative red bone marrow (RBM) dose score based on the numbers and types of X-ray examinations reported with 1 unit approximating 1 mGy. Poisson regression analyses were adjusted for age and laboratory method. Mean RBM dose scores were 49, 42, and 11 for Studies 1-3, respectively (overall mean = 33.5, range 0-303). Translocation frequencies significantly increased with increasing dose score (P < 0.001). Restricting the analysis to the lowest dose scores of under 50 did not materially change these results. We conclude that chromosome damage is associated with low levels of radiation exposure from diagnostic X-ray examinations, including dose scores of approximately 50 and lower, suggesting the possibility of long-term adverse health effects.

Rising thyroid cancer incidence in the United States by demographic and tumor characteristics, 1980-2005.

Thyroid cancer incidence has been rising in the United States, and this trend has often been attributed to heightened medical surveillance and the use of improved diagnostics. Thyroid cancer incidence varies by sex and race/ethnicity, and these factors also influence access to and utilization of healthcare. We therefore examined thyroid cancer incidence rates by demographic and tumor characteristics based on 48,403 thyroid cancer patients diagnosed during 1980-2005 from the Surveillance, Epidemiology and End Results program of the National Cancer Institute. The rates varied by histologic type, sex, and race/ethnicity. Papillary carcinoma was the only histologic type for which incidence rates increased consistently among all racial/ethnic groups. Subsequent analyses focused on the 39,706 papillary thyroid cancers diagnosed during this period. Papillary carcinoma rates increased most rapidly among females. Between 1992-1995 and 2003-2005, they increased nearly 100% among White non-Hispanics and Black females but only 20% to 50% among White Hispanics, Asian/Pacific Islanders, and Black males. The increases were most rapid for localized stage and small tumors; however, rates also increased for large tumors and tumors of regional and distant stage. Since 1992-1995, half the overall increase in papillary carcinoma rates was due to increasing rates of very small (2 cm. Among White females, the rate of increase for cancers>5 cm almost equaled that for the smallest cancers. Medical surveillance and more sensitive diagnostic procedures cannot completely explain the observed increases in papillary thyroid cancer rates. Thus, other possible explanations should be explored.

Thyroid nodules, polymorphic variants in DNA repair and RET-related genes, and interaction with ionizing radiation exposure from nuclear tests in Kazakhstan.

Risk factors for thyroid cancer remain largely unknown except for ionizing radiation exposure during childhood and a history of benign thyroid nodules. Because thyroid nodules are more common than thyroid cancers and are associated with thyroid cancer risk, we evaluated several polymorphisms potentially relevant to thyroid tumors and assessed interaction with ionizing radiation exposure to the thyroid gland. Thyroid nodules were detected in 1998 by ultrasound screening of 2997 persons who lived near the Semipalatinsk nuclear test site in Kazakhstan when they were children (1949-1962). Cases with thyroid nodules (n = 907) were frequency matched (1:1) to those without nodules by ethnicity (Kazakh or Russian), gender and age at screening. Thyroid gland radiation doses were estimated from fallout deposition patterns, residence history and diet. We analyzed 23 polymorphisms in 13 genes and assessed interaction with ionizing radiation exposure using likelihood ratio tests (LRT). Elevated thyroid nodule risks were associated with the minor alleles of RET S836S (rs1800862, P = 0.03) and GFRA1 -193C>G (rs not assigned, P = 0.05) and decreased risk with XRCC1 R194W (rs1799782, P trend = 0.03) and TGFB1 T263I (rs1800472, P = 0.009). Similar patterns of association were observed for a small number of papillary thyroid cancers (n = 25). Ionizing radiation exposure to the thyroid gland was associated with significantly increased risk of thyroid nodules (age and gender adjusted excess odds ratio/Gy = 0.30, 95% CI 0.05-0.56), with evidence for interaction by genotype found for XRCC1 R194W (LRT P value = 0.02). Polymorphisms in RET signaling, DNA repair and proliferation genes may be related to risk of thyroid nodules, consistent with some previous reports on thyroid cancer. Borderline support for gene-radiation interaction was found for a variant in XRCC1, a key base excision repair protein. Other pathways such as genes in double-strand break repair, apoptosis and genes related to proliferation should also be pursued.

Radiation risks from pediatric computed tomography scanning.

Although radiological exams are not frequently used to diagnose unsuspected endocrine disease, computed tomography (CT) plays a significant role in today's endocrinology. Despite the known association between radiation exposure during childhood and cancer, the use of pediatric CT, which delivers non-negligible radiation doses to some organs and tissues, continues to rise sharply. The purpose of this review is to describe the current use of pediatric CT, explain basic concepts in ionizing radiation physics and dosimetry, and discuss potential risks from pediatric CT scans. Finally, we will summarize two recent programs for reducing and controlling exposure to ionizing radiation from pediatric CT: the As Low As Reasonably Achievable (ALARA) concept and the Image Gently initiative. Promoting public awareness and particularly educating referring physicians, including endocrinologists, about the potential radiation-associated risks from CT scans, is essential for reducing unnecessary radiation exposure from CT in children.

Lung, liver and bone cancer mortality in Mayak workers.

Workers at the Mayak nuclear facility in the Russian Federation offer the only adequate human data for evaluating cancer risks from exposure to plutonium. Risks of mortality from cancers of the lung, liver and bone, the organs receiving the largest doses from plutonium, were evaluated in a cohort of 17,740 workers initially hired 1948-1972 using, for the first time, recently improved individual organ dose estimates. Excess relative risk (ERR) models were used to evaluate risks as functions of internal (plutonium) dose, external (primarily gamma) dose, gender, attained age and smoking. By December 31, 2003, 681 lung cancer deaths, 75 liver cancer deaths and 30 bone cancer deaths had occurred. Of these 786 deaths, 239 (30%) were attributed to plutonium exposure. Significant plutonium dose-response relationships (p < 0.001) were observed for all 3 endpoints, with lung and liver cancer risks reasonably described by linear functions. At attained age 60, the ERRs per Gy for lung cancer were 7.1 for males and 15 for females; the averaged-attained age ERRs for liver cancer were 2.6 and 29 for males and females, respectively; those for bone cancer were 0.76 and 3.4. This study is the first to present and compare dose-response analyses for cancers of all 3 organs. The unique Mayak cohort with its high exposures and well characterized doses has allowed quantification of the plutonium dose-response for lung, liver and bone cancer risks based on direct human data. These results will play an important role in plutonium risk assessment.

A cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: dose-response analysis of thyroid follicular adenomas detected during first screening in Ukraine (1998-2000).

The Chornobyl (Chernobyl) accident in 1986 exposed many individuals to radioactive iodines, chiefly (131)I, the effects of which on benign thyroid diseases are largely unknown. To investigate the risk of follicular adenoma in relation to radiation dose after Chornobyl, the authors analyzed the baseline data from a prospective screening cohort study of those exposed as children or adolescents. A stratified random sample was selected from all individuals who were younger than 18 years, had thyroid radioactivity measurements taken within 2 months after the accident, and resided in the three heavily contaminated areas in Ukraine. This analysis is based on the 23 cases diagnosed in 12,504 subjects for whom personal history of thyroid diseases was known. The dose-response relation was linear with an excess relative risk of 2.07 per gray (95% confidence interval: 0.28, 10.31). The risk was significantly higher in women compared with men, with no clear modifying effects of age at exposure. In conclusion, persons exposed to radioactive iodines as children and adolescents have an increased risk of follicular adenoma, though it is smaller than the risk of thyroid cancer in the same cohort. Compared with results from other studies, this estimate is somewhat smaller, but confidence intervals overlap, suggesting compatibility.

Acoustic neuromas following childhood radiation treatment for benign conditions of the head and neck.

Childhood radiation exposure has been associated with an increased risk for developing several neoplasms, particularly benign and malignant thyroid tumors, but little is known about the risk of developing acoustic neuromas. The aim of this study was to confirm whether there is a risk for acoustic neuromas and, if so, to determine its magnitude and duration. We investigated the time trend and dose-response relationships for acoustic neuroma incidence in a cohort of 3,112 individuals who were irradiated as children between 1939 and 1962. Most of the patients were treated to reduce the size of their tonsils and adenoids and received substantial radiation exposure to the cerebellopontine angle, the site of acoustic neuromas. Forty-three patients developed benign acoustic neuromas, forty of them surgically resected, far in excess of what might be expected from data derived from brain tumor registries. The mean dose (+/-SD) to the cerebellopontine angle was 4.6 +/- 1.9 Gy. The relative risk per Gy was 1.14 (95% confidence interval 1.0-1.3). The earliest case occurred 20.4 years after exposure and the latest 55 years after exposure (mean 38.3 +/- 10.1 years). Our study provides support for an association between acoustic neuromas and childhood radiation exposure. Although acoustic neuromas are usually benign and often asymptomatic, many cause significant morbidity. Following childhood radiation exposure, they appear after a long latency and continue to occur many decades afterward. Any symptoms of an acoustic neuroma in a patient with a history of radiation to the head and neck area should be investigated carefully, and the threshold for employing imaging should be lowered.

Similar prevalence of founder BRCA1 and BRCA2 mutations among Ashkenazi and non-Ashkenazi men with breast cancer: evidence from 261 cases in Israel, 1976-1999.

To evaluate the potential contribution of mutations in the BRCA1 and BRCA2 genes to male breast cancer (MBC), we expanded a previous study to screen a total of 261 Israeli men diagnosed with breast carcinoma. A total of 21 BRCA2 6174delT and 8 BRCA1 185delAG mutations were found. Similar frequencies of BRCA1 and BRCA2 mutation carriers were found among Ashkenazi (12.8%) and non-Ashkenazi Jews (9.1%). The combined prevalence of BRCA1/BRCA2 founder mutations among Ashkenazi Jewish men is slightly higher than for women, due to a higher frequency of BRCA2 mutations.

Increased frequency of chromosome translocations associated with diagnostic x-ray examinations.

Informative studies of cancer risks associated with medical radiation are difficult to conduct owing to low radiation doses, poor recall of diagnostic X rays, and long intervals before cancers occur. Chromosome aberrations have been associated with increased cancer risk and translocations are a known radiation biomarker. Seventy-nine U.S. radiologic technologists were selected for blood collection, and translocations were enumerated by whole chromosome painting. We developed a dose score to the red bone marrow for medical radiation exposure from X-ray examinations reported by the technologists that they received as patients. Using Poisson regression, we analyzed translocations in relation to the dose scores. Each dose score unit approximated 1 mGy. The estimated mean cumulative red bone marrow radiation dose score was 42 (range 1-265). After adjustment for age, occupational radiation, and radiotherapy for benign conditions, translocation frequencies significantly increased with increasing red bone marrow dose score with an estimate of 0.007 translocations per 100 CEs per score unit (95% CI, 0.002 to 0.013; P = 0.01). Chromosome damage has been linked with elevated cancer risk, and we found that cumulative radiation exposure from medical X-ray examinations was associated with increased numbers of chromosome translocations.

The Ukrainian-American study of leukemia and related disorders among Chornobyl cleanup workers from Ukraine: III. Radiation risks.

Leukemia is one of the cancers most susceptible to induction by ionizing radiation, but the effects of lower doses delivered over time have not been quantified adequately. After the Chornobyl (Chernobyl) accident in Ukraine in April 1986, several hundred thousand workers who were involved in cleaning up the site and its surroundings received fractionated exposure, primarily from external gamma radiation. To increase our understanding of the role of protracted low-dose radiation exposure in the etiology of leukemia, we conducted a nested case-control study of leukemia in a cohort of cleanup workers identified from the Chornobyl State Registry of Ukraine. The analysis is based on 71 cases of histologically confirmed leukemia diagnosed in 1986-2000 and 501 age- and residence-matched controls selected from the same cohort. Study subjects or their proxies were interviewed about their cleanup activities and other relevant factors. Individual bone marrow radiation doses were estimated by the RADRUE dose reconstruction method (mean dose = 76.4 mGy, SD = 213.4). We used conditional logistic regression to estimate leukemia risks. The excess relative risk (ERR) of total leukemia was 3.44 per Gy [95% confidence interval (CI) 0.47-9.78, P < 0.01]. The dose response was linear and did not differ significantly by calendar period of first work in the 30-km Chornobyl zone, duration or type of work. We found a similar dose-response relationship for chronic and non-chronic lymphocytic leukemia [ERR = 4.09 per Gy (95% CI < 0-14.41) and 2.73 per Gy (95% CI < 0-13.50), respectively]. To further clarify these issues, we are extending the case-control study to ascertain cases for another 6 years (2001-2006).

Excess lifetime cancer mortality risk attributable to radiation exposure from computed tomography examinations in children.

BACKGROUND: The use of computed tomography in Israel has been growing rapidly during recent decades. The major drawback of this important technology is the exposure to ionizing radiation, especially among children who have increased organ radiosensitivity and a long lifetime to potentially develop radiation-related cancer. OBJECTIVE: To estimate the number of excess lifetime cancer deaths related to annual CT scans performed in children in Israel. METHODS: We used CT scan utilization data from 1999 to 2003 obtained from the second largest health management organization in the country to project age and gender-specific CT scan use nationwide. Based on published organ doses for common CT examinations and radiation-related cancer mortality risk estimates from studies in survivors of the atomic bomb, we estimated the excess lifetime risks for cancer mortality attributed to use of CT in children and adolescents (up to 18 years old) in Israel. RESULTS: We estimated that 17,686 pediatric scans were conducted annually in Israel during 1999-2003. We project that 9.5 lifetime deaths would be associated with 1 year of pediatric CT scanning. This number represents an excess of 0.29% over the total number of patients who are eventually estimated to die from cancer in their lifetime. CONCLUSIONS: Pediatric CT scans in Israel may result in a small but not negligible increased lifetime risk for cancer mortality. Because of the uncertainty regarding radiation effects at low doses, our estimates of CT-related cancer mortality should be considered with caution. Nevertheless, physicians, CT technologists, and health authorities should work together to minimize the radiation dose for children to as low as reasonably achievable and encourage responsible use of this essential diagnostic tool.

Thyroid cancer incidence among people living in areas contaminated by radiation from the Chernobyl accident.

As a result of the Chernobyl nuclear power plant accident, massive amounts of radioactive materials were released into the environment and large numbers of individuals living in Belarus, Russia, and Ukraine were exposed to radioactive iodines, primarily 131I. Iodine-131 concentrated in the thyroid gland of residents of the contaminated areas, with children and adolescents being particularly affected. In the decade after the accident, a substantial increase in thyroid cancer incidence was observed among exposed children in the three affected countries, and compelling evidence of an association between pediatric thyroid cancer incidence and radiation exposure to the thyroid gland accumulated. The data currently available suggest that both the magnitude and patterns of thyroid cancer risk are generally consistent with those reported following external exposure. Based on data from case-control studies, iodine deficiency appeared to enhance the risk of developing thyroid cancer following exposure from Chernobyl. Results from a recent large cohort study, however, did not support these findings. Data on adult exposure are limited and not entirely consistent. Similarly, information on thyroid cancer risks associated with in utero exposure is insufficient to draw conclusions. The lack of information on these two population groups indicates an important gap that needs to be filled. Twenty years after the accident, excess thyroid cancers are still occurring among persons exposed as children or adolescents, and, if external radiation can be used as a guide, we can expect an excess of radiation-associated thyroid cancers for several more decades. Since considerable uncertainties about the long-term health effects from Chernobyl remain, continued follow-up of the exposed populations should provide valuable information.

Proliferative activity of human thyroid cells in various age groups and its correlation with the risk of thyroid cancer after radiation exposure.

CONTEXT: The thyroid gland is vulnerable to the carcinogenic effects of ionizing radiation, and there is a well-documented inverse correlation between thyroid cancer and age at exposure, particularly for ages less than 20 yr. One of the factors responsible for this phenomenon may be more rapid cell proliferation in children. OBJECTIVE: The objective of this study was to determine the proliferative rate of normal human thyroid cells in different age groups. DESIGN: We used immunohistochemical analysis to determine the Ki-67 proliferative index in 117 thyroid glands obtained at autopsy, including 25 fetal thyroids (11-40 wk gestation), 55 childhood thyroids (0-19 yr), and 37 adult thyroids (20-60 yr). RESULTS: The rate of Ki-67 labeling in the three groups was 7.4 +/- 6.10, 0.23 +/- 0.15, and 0.08 +/- 0.04% respectively, demonstrating an overall trend for diminishing proliferative activity of thyroid cells with increasing age. However, a lack of correlation was noted between the slopes of cancer risk calculated from previous studies of irradiated populations and proliferative rate in the pediatric age intervals of 0-4 and 5-9 yr, suggesting that other factors are likely to be responsible for the particularly high sensitivity to radiation-induced thyroid cancer among the youngest children. CONCLUSIONS: Our findings of a general decrease in proliferative activity of thyroid cells with age may explain, at least in part, the higher risks of radiation-related thyroid cancer in children compared with adults. However, the variation in the rate of cell proliferation is unlikely to be responsible entirely for this phenomenon and other factors may also be involved.