Comparing risk estimates following diagnostic CT radiation exposures employing different methodological approaches.

The current study has two aims: the first is to quantify the difference between radiation risks estimated with the use of organ or effective doses, particularly when planning pediatric and adult computed tomography (CT) examinations. The second aim is to determine the method of calculating organ doses and cancer risk using dose-length product (DLP) for typical routine CT examinations. In both cases, the radiation-induced cancer risks from medical CT examinations were evaluated as a function of gender and age. Lifetime attributable risk values from CT scanning were estimated with the use of ICRP (Publication 103) risk models and Russian national medical statistics data. For populations under the age of 50 y, the risk estimates based on organ doses usually are 30% higher than estimates based on effective doses. In older populations, the difference can be up to a factor of 2.5. The typical distributions of organ doses were defined for Chest Routine, Abdominal Routine, and Head Routine examinations. The distributions of organ doses were dependent on the anatomical region of scanning. The most exposed organs/tissues were thyroid, breast, esophagus, and lungs in cases of Chest Routine examination; liver, stomach, colon, ovaries, and bladder in cases of Abdominal Routine examination; and brain for Head Routine examinations. The conversion factors for calculation of typical organ doses or tissues at risk using DLP were determined. Lifetime attributable risk of cancer estimated with organ doses calculated from DLP was compared with the risk estimated on the basis of organ doses measured with the use of silicon photodiode dosimeters. The estimated difference in LAR is less than 29%.

Systematic review and meta-analysis of circulatory disease from exposure to low-level ionizing radiation and estimates of potential population mortality risks.

BACKGROUND: Although high doses of ionizing radiation have long been linked to circulatory disease, evidence for an association at lower exposures remains controversial. However, recent analyses suggest excess relative risks at occupational exposure levels. OBJECTIVES: We performed a systematic review and meta-analysis to summarize information on circulatory disease risks associated with moderate- and low-level whole-body ionizing radiation exposures. METHODS: We conducted PubMed/ISI Thomson searches of peer-reviewed papers published since 1990 using the terms "radiation" AND "heart" AND "disease," OR "radiation" AND "stroke," OR "radiation" AND "circulatory" AND "disease." Radiation exposures had to be whole-body, with a cumulative mean dose of < 0.5 Sv, or at a low dose rate (< 10 mSv/day). We estimated population risks of circulatory disease from low-level radiation exposure using excess relative risk estimates from this meta-analysis and current mortality rates for nine major developed countries. RESULTS: Estimated excess population risks for all circulatory diseases combined ranged from 2.5%/Sv [95% confidence interval (CI): 0.8, 4.2] for France to 8.5%/Sv (95% CI: 4.0, 13.0) for Russia. CONCLUSIONS: Our review supports an association between circulatory disease mortality and low and moderate doses of ionizing radiation. Our analysis was limited by heterogeneity among studies (particularly for noncardiac end points), the possibility of uncontrolled confounding in some occupational groups by lifestyle factors, and higher dose groups (> 0.5 Sv) generally driving the observed trends. If confirmed, our findings suggest that overall radiation-related mortality is about twice that currently estimated based on estimates for cancer end points alone (which range from 4.2% to 5.6%/Sv for these populations).

Estimation of individualized radiation risk from chronic occupational exposure in Russia.

Internationally, the upper limit of acceptable individualized risk from occupational exposure for nuclear industry workers is determined by the death probability 10(-3) y(-1). The same risk value of 10(-3) y(-1) is established by the radiation safety standards currently in force in Russia. The United Nations Scientific Committee on the Effects of Atomic Radiation has proposed the formulas for estimating individualized risk of developing cancer with allowance for radiation dose, age at exposure, attained age, and sex. This methodology is first applied to estimate individualized radiation risk for Russian nuclear industry workers (49,900 persons) who were monitored for radiation exposure through the use of personal dosimeters. The estimates show that in 2006 the threshold of 10(-3) y(-1) for individualized risk is exceeded for 755 persons, which is 1.6% of all workers covered by personal dose monitoring. The excess absolute risk (EAR) and attributable risk (AR) were estimated for all cancers, solid cancers, and leukemias.

Risk of thyroid cancer after exposure to 131I in childhood.

BACKGROUND: After the Chernobyl nuclear power plant accident in April 1986, a large increase in the incidence of childhood thyroid cancer was reported in contaminated areas. Most of the radiation exposure to the thyroid was from iodine isotopes, especially 131I. We carried out a population-based case-control study of thyroid cancer in Belarus and the Russian Federation to evaluate the risk of thyroid cancer after exposure to radioactive iodine in childhood and to investigate environmental and host factors that may modify this risk. METHODS: We studied 276 case patients with thyroid cancer through 1998 and 1300 matched control subjects, all aged younger than 15 years at the time of the accident. Individual doses were estimated for each subject based on their whereabouts and dietary habits at the time of the accident and in following days, weeks, and years; their likely stable iodine status at the time of the accident was also evaluated. Data were analyzed by conditional logistic regression using several different models. All statistical tests were two-sided. RESULTS: A strong dose-response relationship was observed between radiation dose to the thyroid received in childhood and thyroid cancer risk (P<.001). For a dose of 1 Gy, the estimated odds ratio of thyroid cancer varied from 5.5 (95% confidence interval [CI] = 3.1 to 9.5) to 8.4 (95% CI = 4.1 to 17.3), depending on the risk model. A linear dose-response relationship was observed up to 1.5-2 Gy. The risk of radiation-related thyroid cancer was three times higher in iodine-deficient areas (relative risk [RR]= 3.2, 95% CI = 1.9 to 5.5) than elsewhere. Administration of potassium iodide as a dietary supplement reduced this risk of radiation-related thyroid cancer by a factor of 3 (RR = 0.34, 95% CI = 0.1 to 0.9, for consumption of potassium iodide versus no consumption). CONCLUSION: Exposure to (131)I in childhood is associated with an increased risk of thyroid cancer. Both iodine deficiency and iodine supplementation appear to modify this risk. These results have important public health implications: stable iodine supplementation in iodine-deficient populations may substantially reduce the risk of thyroid cancer related to radioactive iodines in case of exposure to radioactive iodines in childhood that may occur after radiation accidents or during medical diagnostic and therapeutic procedures.

Non-cancer thyroid diseases among children in the Kaluga and Bryansk regions of the Russian Federation exposed to radiation following the Chernobyl accident.

This paper presents results of estimated radiation risks of non-cancer thyroid diseases in the people from Kaluga and Bryansk regions of the Russian Federation exposed in their childhood to radioiodine as a result of the Chernobyl accident. This work was carried out under the Joint Medical Research Project on non-cancer thyroid diseases conducted by Sasakawa Memorial Health Foundation and the Medical Radiological Research Center of the Russian Academy of Medical Sciences. The subjects were 2,457 people who underwent health examinations from 1997 to the end of 1999 who had individual radiometric thyroid data obtained between May and June 1986 and were aged 10 y or less at the time of exposure. The thyroid absorbed doses from incorporated 131I were estimated on the basis of measurements of exposure dose rate in the vicinity of the subject's thyroid and liver. A compartment model accounting for 131I metabolism in humans and cows was used. The estimated dose varied from 0 to 6 Gy, and its distribution was approximately lognormal with a mean of 0.132 Gy and standard deviation of 0.45 Gy. The prevalence of diffuse goiter in males showed a significant dose-response (p = 0.03) with an estimated odds ratio 1.36 at 1 Gy.