Implications of recent epidemiologic studies for the linear nonthreshold model and radiation protection.

The recently published NCRP Commentary No. 27 evaluated the new information from epidemiologic studies as to their degree of support for applying the linear nonthreshold (LNT) model of carcinogenic effects for radiation protection purposes (NCRP 2018 Implications of Recent Epidemiologic Studies for the Linear Nonthreshold Model and Radiation Protection, Commentary No. 27 (Bethesda, MD: National Council on Radiation Protection and Measurements)). The aim was to determine whether recent epidemiologic studies of low-LET radiation, particularly those at low doses and/or low dose rates (LD/LDR), broadly support the LNT model of carcinogenic risk or, on the contrary, demonstrate sufficient evidence that the LNT model is inappropriate for the purposes of radiation protection. An updated review was needed because a considerable number of reports of radiation epidemiologic studies based on new or updated data have been published since other major reviews were conducted by national and international scientific committees. The Commentary provides a critical review of the LD/LDR studies that are most directly applicable to current occupational, environmental and medical radiation exposure circumstances. This Memorandum summarises several of the more important LD/LDR studies that incorporate radiation dose responses for solid cancer and leukemia that were reviewed in Commentary No. 27. In addition, an overview is provided of radiation studies of breast and thyroid cancers, and cancer after childhood exposures. Non-cancers are briefly touched upon such as ischemic heart disease, cataracts, and heritable genetic effects. To assess the applicability and utility of the LNT model for radiation protection, the Commentary evaluated 29 epidemiologic studies or groups of studies, primarily of total solid cancer, in terms of strengths and weaknesses in their epidemiologic methods, dosimetry approaches, and statistical modelling, and the degree to which they supported a LNT model for continued use in radiation protection. Recommendations for how to make epidemiologic radiation studies more informative are outlined. The NCRP Committee recognises that the risks from LD/LDR exposures are small and uncertain. The Committee judged that the available epidemiologic data were broadly supportive of the LNT model and that at this time no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes.

Estimating the lifetime risk of cancer associated with multiple CT scans.

Multiple CT scans are often done on the same patient resulting in an increased risk of cancer. Prior publications have estimated risks on a population basis and often using an effective dose. Simply adding up the risks from single scans does not correctly account for the survival function. A methodology for estimating personal radiation risks attributed to multiple CT imaging using organ doses is presented in this article. The estimated magnitude of the attributable risk fraction for the possible development of radiation-induced cancer indicates the necessity for strong clinical justification when ordering multiple CT scans.

Estimation of risk from medical radiation exposure based on effective and organ dose: how much difference is there?

The authors compare radiation risks of potential cancer following diagnostic radiation exposure evaluated with the use of organ and effective doses. Lifetime attributable risk values of CT scanning are estimated with the use of ICRP (Publication 103) risk models and Russian national medical statistics data. For populations under the age of 50, the risk evaluated using organ doses usually differs from that using effective doses by <30 %. In older populations, the difference can be up to a factor of 3. Calculated values of lifetime attributable cancer risk for particular organs are presented as well.

CT scanning: patterns of use and dose.

CT scanning is a relatively high-dose procedure. In spite of the use of magnetic resonance imaging, with faster CT scanners and helical techniques CT is becoming more common. There are few data from practice in the United States regarding the age and sex distribution of patients receiving CT scans, what type of scan and how many scans they receive, or how much radiation dose CT scans contribute. We reviewed over 33,700 consecutive CT examinations done at our institution in 1998 and 1999. Information on the types of scans as well as the age and sex distribution of the patients was determined. Between 1990 and 1999, CT examinations in our institution increased from 6.1% to 11.1% of all radiology procedures. Nineteen per cent of all patients seen in our department in the last year had at least one CT scan and more than half had multiple scans on the same day. Thirty-six per cent of all patients had a prior CT examination done on an earlier date. The male/female ratio of patients was 56/44. Studies of children age 0-15 years comprised 11.2% of scans. The highest percentage of scans was done in the 36-50-year-old age group. CT scanning accounted for 67% of the effective dose from diagnostic radiology. In most large hospitals in the United States CT scanning probably accounts for more than 10% of diagnostic radiology examinations and about two-thirds of the radiation dose. Most patients have multiple scan sequences. Studies done on children are probably more common than previously thought.

192IrCl acid skin burn: case report and review of the literature.

A worker was contaminated following a chemical explosion that splashed an HNO3 radioactive solution containing approximately 180 MBq (5 mCi) 192Ir onto the left side of his face. Initial efforts reduced the contamination at least fivefold. Removal of a patch of contaminated hair was necessary. Most of the contamination was fixed to the skin; only a small amount of contamination was absorbed.

Performance of radiologic and nuclear medicine examinations in the 6 months before death.

PURPOSE: To determine the rate of use and type of radiologic and nuclear medicine examinations performed prior to the death of an individual. MATERIALS AND METHODS: Radiologic and nuclear medicine examination data from the University of New Mexico Hospital were analyzed and correlated with death records from the New Mexico Department of Vital Statistics. The study cohort included 558 patients who were treated between July 1992 and June 1993 and died within 6 months. The records for the 558 patients were analyzed according to the type and number of examinations performed within 30 days and 6 months prior to death. RESULTS: Of 26,067 patients examined during the year, 558 (2%) underwent a radiographic or nuclear medicine examination in the 6 months prior to death. That group of patients underwent a total of 6,196 radiographic or nuclear medicine examinations (4.6%) out of a total of 134,892 examinations that were performed in that year. The rate of use was highest in those patients who were younger than 1 year at death. CONCLUSION: Approximately 5% or fewer radiologic and nuclear medicine examinations were performed during the final 6 months of an illness.

Benefits versus risks from mammography: a critical reassessment.

BACKGROUND: The use of mammography has increased rapidly over the last decade. The justification for mammographic examinations is the potential benefit they provide in detecting breast cancer at an early stage and reducing mortality. However, this benefit must be balanced against the associated potential risk of radiation carcinogenesis, economic costs, and a number of other factors. Most publications to date have used radiation risk factors and data from studies that were published over a decade ago, which now have been superseded by the results of more recent epidemiological studies. METHODS: This report examines the current literature regarding the benefits of cancer detection and the risk of radiation carcinogenesis, and calculates the ratio of benefit and risk for women who begin annual mammography screening at different ages. We have used current data to calculate the expected individual benefits and radiation risks associated with annual mammographic screening. RESULTS: It now appears that there is little risk of breast cancer associated with radiation exposure from annual mammography in women over the age of 35, although there is some indication that exposure of younger women may pose a risk for those women in a genetically sensitive subgroup. CONCLUSIONS: New data document that for a woman beginning annual mammographic screening at age 50 and continuing until age 75, the benefit exceeds the radiation risk by a factor of almost 100. Even for a woman who begins annual screening at age 35 and continues until age 75, the benefit of reduced mortality is projected to exceed the radiation risk by factor of more than 25.

Radiation dose and image quality of double-loaded cassettes.

Some U.S. hospitals double-load x-ray cassettes for certain procedures. Loading two films in the same cassette for portable emergency room (ER), intensive care unit (ICU), or operating room radiographs provides both the referring clinicians and the radiologists with immediate images. Our study demonstrates a cost increase of 15%, an increase in air kerma for a chest x ray from 0.12 to 0.35 mGy (12-35 mrad), slight differences in optical density, image contrast, and spatial resolution under double-loading conditions. Our study shows that double loading cassettes may improve patient care by economically expediting the communication of radiographic findings. The decision to double load portable ICU or ER cassettes must be based on a balance of factors.

Breast mammographic pattern: a concatenation of confounding and breast cancer risk factors.

A mammographic pattern of > 25% radiodensity is associated with increased risk for breast cancer. Mammographic pattern is influenced by age, body weight, reproductive factors, and race/ethnicity. The interaction among these factors in predicting breast radiographic pattern, and their association with the presence of histologic markers of increased risk of breast cancer, is poorly defined. To elucidate the relations among epidemiologic, radiographic, and histologic markers of breast cancer risk, the authors studied these factors in an unselected forensic autopsy series, accumulated between 1978 and 1983, of 486 women aged 15-98 years at death. Older age and/or postmenopausal status was the strongest predictor of radiolucent breast pattern. Obesity, defined as a Quetelet index (weight(kg)/height(m)2) of > 25, and large breast size were also highly significant predictors of breast radiolucency. Factors related to parity were not significant predictors of breast parenchymal pattern. Native American race was an independent predictor of breast radiolucency in this population. A dense parenchymal pattern was associated with increased prevalence of marked cystic change and the presence of duct epithelial hyperplasia in women under age 35. The results support the association of breast radiodensity with ethnic/racial, reproductive, and histologic factors predictive of cancer risk. However, this association is overshadowed by the effects of obesity and aging or menopause.

Use of radiology in U.S. general short-term hospitals: 1980-1990.

PURPOSE: To determine changes in usage of radiologic services between 1980 and 1990. MATERIALS AND METHODS: Complete data were obtained from 107 (42%) hospitals and incomplete data from eight (3%) (total survey response rate, 45%). Information was requested about the number of general radiologic examinations; specific modalities of computed tomography (CT), magnetic resonance (MR) imaging, nuclear medicine, and ultrasonography (US); and numbers of CT, MR imaging, and US machines. RESULTS: The number of general radiologic examinations in hospitals increased from approximately 126 million to 179 million (> 42%); for CT, from 3.6 million to 13.3 million; nuclear medicine, from 6.4 million to 7.4 million; and US, from 4.3 million to 11.8 million. MR imaging examinations performed during 1990 were estimated at 1.8 million. CONCLUSION: The number of radiologic examinations performed in U.S. hospitals increased by 30%-60% between 1980 and 1990, mainly due to increased usage of CT, MR imaging, and US.

Thyroid nodules in the population living around Chernobyl.

OBJECTIVE: To determine the baseline incidence, prevalence, and characteristics of thyroid nodules in the population living around the Chernobyl nuclear power plant and to compare the findings with unexposed populations. DESIGN: Prevalence study. Population samples from seven highly contaminated villages were compared with six nearby control villages of the same size and type. The data were obtained as part of the International Chernobyl Project conducted in 1990. SETTING: The study was conducted 4.5 years after the Chernobyl reactor accident that released large quantities of radionuclides, including radioiodine. PATIENTS OR OTHER PARTICIPANTS: Population samples of approximately 100 persons residing in both highly contaminated villages and control villages since the accident were compared. Individuals were selected on the basis of birth date as being 5, 10, 40, or 60 years old at the time of the study. All persons selected underwent a thyroid examination. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Two main outcome measures were used, both for thyroid nodularity: clinical palpation and high-resolution ultrasonography. RESULTS: There was no significant difference in thyroid nodularity between the study groups. Nodules were palpated in 0.7% of children and 2.9% of adults. Discrete nodules were found by ultrasonography in 0.5% of children and 14.9% of adults. Multinodular goiter was found in 3% of adults. Nodules were more common in females. CONCLUSIONS: Four and a half years after the Chernobyl accident, the incidence, prevalence, and characteristics of thyroid nodules were the same in population samples from both highly contaminated and control settlements and similar to results reported for unexposed populations in other countries.

The two-view radionuclide ventriculogram. Advantages of the LPO view.

This report is a prospective study of 33 male patients who underwent both contrast ventriculography (CVG) and radionuclide ventriculography (RVG) within a 24-hour period. Expert, blinded observers graded the left ventricle's regional wall motion (RWM) in the left anterior descending (LAD), left circumflex (LCx), and posterior descending arterial (PDA) distributions on right anterior oblique (RAO), and left anterior oblique (LAO) CVGs, and on anterior (ANT), LAO, 70 degrees left anterior oblique (LAO70), and left posterior oblique (LPO) RVGs. When statistically compared with CVG RWM standard data, RVG studies composed of LAO and LPO views were equal to the RVG studies composed of ANT, LAO, and LAO70 views in assessment of the LAD and LCx distributions. The RVG with LAO and LPO views was superior to the RVG with ANT, LAO, LAO70 in the detection of the posterior descending artery RWM. The authors conclude that accurate assessment of RWM is efficiently performed with the RVG composed of LAO and LPO views.

Comparison of CT, low-field-strength MR imaging, and high-field-strength MR imaging. Work in progress.

To assess objectively the sensitivity and specificity of low-field-strength (0.064 T) magnetic resonance (MR) imaging, a prospective blind study of 280 examinations was performed to compare low-field-strength MR imaging with computed tomography (CT) and with high-field-strength (1.5-T) MR imaging of the cranium. The sensitivity (defined as the true-positive rate) with high-field MR imaging was superior to that with low-field MR imaging and CT in helping detect overall abnormalities. Sensitivities were generally similar over a broad range of specific cranial central nervous system diseases. Low-field and high-field MR imaging were equivalent in the blind diagnoses of neoplasms and white matter disease, whereas low-field MR and CT were equivalent in the blind diagnoses of contusion, subdural and epidural hematoma, sinus disease, normality, and abnormality. The specificities with low-field MR imaging and CT were substantially better than those with high-field MR imaging.