Cancer risks attributable to low doses of ionizing radiation: assessing what we really know

The Chernobyl accident 20 years on: an assessment of the health consequences and the international response

Twenty years after the Chernobyl accident the WHO and the International Atomic Energy Authority issued a reassuring statement about the consequences. Our objectives in this study were to evaluate the health impact of the Chernobyl accident, assess the international response to the accident, and consider how to improve responses to future accidents. So far, radiation to the thyroid from radioisotopes of iodine has caused several thousand cases of thyroid cancer but very few deaths; exposed children were most susceptible. The focus on thyroid cancer has diverted attention from possible nonthyroid effects. The international response to the accident was inadequate and uncoordinated, and has been unjustifiably reassuring. Accurate assessment in future health effects is not currently possible in the light of dose uncertainties, current debates over radiation actions, and the lessons from the late consequences of atomic bomb exposure. Because of the uncertainties from and the consequences of the accident, it is essential that investigations of its effects should be broadened and supported for the long term. The United Nations should initiate an independent review of the actions and assignments of the agencies concerned, with recommendations for dealing with future international-scale accidents. These should involve independent scientists and ensure cooperation rather than rivalry.

Are passive smoking, air pollution and obesity a greater mortality risk than major radiation incidents?

BACKGROUND

Following a nuclear incident, the communication and perception of radiation risk becomes a (perhaps the) major public health issue. In response to such incidents it is therefore crucial to communicate radiation health risks in the context of other more common environmental and lifestyle risk factors. This study compares the risk of mortality from past radiation exposures (to people who survived the Hiroshima and Nagasaki atomic bombs and those exposed after the Chernobyl accident) with risks arising from air pollution, obesity and passive and active smoking.

METHODS

A comparative assessment of mortality risks from ionising radiation was carried out by estimating radiation risks for realistic exposure scenarios and assessing those risks in comparison with risks from air pollution, obesity and passive and active smoking.

RESULTS

The mortality risk to populations exposed to radiation from the Chernobyl accident may be no higher than that for other more common risk factors such as air pollution or passive smoking. Radiation exposures experienced by the most exposed group of survivors of Hiroshima and Nagasaki led to an average loss of life expectancy significantly lower than that caused by severe obesity or active smoking.

CONCLUSION

Population-averaged risks from exposures following major radiation incidents are clearly significant, but may be no greater than those from other much more common environmental and lifestyle factors. This comparative analysis, whilst highlighting inevitable uncertainties in risk quantification and comparison, helps place the potential consequences of radiation exposures in the context of other public health risks.

Review of radiation risks from computed tomography: essentials for the pediatric surgeon

BACKGROUND/PURPOSE

Over the past several years, increasing attention has been focused on the potential for radiation exposure from computed tomography (CT) for inducing the development of cancers. An understanding of these issues is important for the practice of pediatric surgery.

METHODS

Medline based clinical review of current medical literature of the risks for the induction of cancers by CT. Data includes estimates of cancer risk from computer models, epidemiologic data from survivors of atomic bomb radiation exposure, and consensus opinions from expert panels.

RESULTS

Review of scientific evidence demonstrates varied opinions, but consensus suggests there may be a potential for an increased risk of cancer from low level radiation exposure such as from CT. These calculations suggest that there may be as high as 1 fatal cancer for every 1000 CT scans performed in a young child.

CONCLUSIONS

Pediatric surgeons should be aware of the potential risks of CT. Minimizing the radiation risks of CT is a complex endeavor, and will require investments from pediatric surgeons as well as pediatric radiologists.

Cytogenetic effect of low dose gamma-radiation in Hordeum vulgare seedlings: non-linear dose-effect relationship

The induction of chromosome aberrations in Hordeum vulgare germinated seeds was studied after ionizing irradiation with doses in the range of 10-1,000 mGy. The relationship between the frequency of aberrant cells and the absorbed dose was found to be nonlinear. A dose-independent plateau in the dose range from about 50 to 500 mGy was observed, where the level of cytogenetic damage was significantly different from the spontaneous level. The comparison of the goodness of the experimental data fitting with mathematical models of different complexity, using the most common quantitative criteria, demonstrated the advantage of a piecewise linear model over linear and polynomial models in approximating the frequency of cytogenetical disturbances. The results of the study support the hypothesis of indirect mechanisms of mutagenesis induced by low doses. Fundamental and applied implications of these findings are discussed.

Low-dose irradiation of nontransformed cells stimulates the selective removal of precancerous cells via intercellular induction of apoptosis

An important stage in tumorigenesis is the ability of a precancerous cell to escape natural anticancer signals imposed on it by neighboring cells and its microenvironment. We have previously characterized a system of intercellular induction of apoptosis whereby nontransformed cells selectively remove transformed cells from coculture via cytokine and reactive oxygen/nitrogen species (ROS/RNS) signaling. We report that irradiation of nontransformed cells with low doses of either high linear energy transfer (LET) alpha-particles or low-LET gamma-rays leads to stimulation of intercellular induction of apoptosis. The use of scavengers and inhibitors confirms the involvement of ROS/RNS signaling and of the importance of transformed cell NADPH oxidase in the selectivity of the system. Doses as low as 2-mGy gamma-rays and 0.29-mGy alpha-particles were sufficient to produce an observable increase in transformed cell apoptosis. This radiation-stimulated effect saturates at very low doses (50 mGy for gamma-rays and 25 mGy for alpha-particles). The use of transforming growth factor-beta (TGF-beta) neutralizing antibody confirms a role for the cytokine in the radiation-induced signaling. The system may represent a natural anticancer mechanism stimulated by extremely low doses of ionizing radiation.

Diagnostic reference levels and effective dose in paediatric cardiac catheterization

European states within the EEC are required to establish and use diagnostic reference levels (DRLs) in X-ray examinations. However, up to now there have been no DRLs for cardiac catheterization in children, nor as a rule is the effective dose estimated. We have evaluated the dose-area products (DAPs) for three different types of angiocardiography systems over a time span of 8 years. For each system DAP increased in proportion to the body weight (BW) over two orders of magnitude. The proportionality constant decreased over the years. To reduce the broad distribution of DAP the doses for cine acquisition (DAPA) and fluoroscopy (DAPF) were indexed with respect to the total numbers of acquired images (AN) and the total times of fluoroscopy (FT). DAPA/AN is directly proportional to BW with a high correlation (r = 0.896, n = 1346). Likewise, DAPF/FT is proportional to BW from 0.1 kg to 100 kg (r = 0.84, n = 2138). Therefore, by normalizing DAP to BW the growth dependent variation of DAP can be eliminated. There are numerous short examinations with very small total DAPs, which were separated from the group of diagnostic examinations. The mean DAP/BW of this group is 0.41 Gycm2 kg(-1) (90th percentile: 0.81 Gycm2 kg(-1), n = 1106). For interventional procedures in congenital heart diseases DAP/BW is significantly higher (p<0.001) (mean: 0.56 Gycm2 kg(-1), 90th percentile: 1.16 Gycm2 kg(-1), n = 883). There are significant differences between different types of interventional procedures, the mean values being between 0.35 Gycm2 kg(-1) (occlusion of patent ductus botalli, n = 165) and 1.30 Gycm2 kg(-1) (occlusion of ventricular septal defect, n = 32). For patients who are catheterized several times over the years, the cumulative effective dose (E) may reach high values, being especially high for patients with hypoplastic left heart syndrome (typically 11 mSv). E is derived from DAP/BW by use of a constant DAP/BW to E conversion factor, independent of the age of the patient. DAP/BW is appropriate to describe paediatric DRLs and is recommended instead of using mean DAP values for age groups.

Cancer risks in a population with prolonged low dose-rate gamma-radiation exposure in radiocontaminated buildings, 1983-2002

PURPOSE

To assess cancer risks in a population that received prolonged low dose-rate gamma-irradiation for about 10 years as a result of occupying buildings containing 60Co-contaminated steel in Taiwan.

MATERIALS AND METHODS

The cancer risks were compared with those populations with the same temporal and geographic characteristics in Taiwan by standardized incidence ratios (SIR), adjusted for age and gender. The association of cancer risks with excess cumulative exposure was further evaluated for their relative risks by the Poisson multiple regression analysis.

RESULT

A total of 7271 people were registered as the exposed population, with 101,560 person-years at risk. The average excess cumulative exposure was approximately 47.8 mSv (range < 1 - 2,363 mSv). A total of 141 exposed subjects with various cancers were observed, while 95 developed leukemia or solid cancers after more than 2 or 10 years initial residence in contaminated buildings respectively. The SIR were significantly higher for all leukemia except chronic lymphocytic leukemia (n = 6, SIR = 3.6, 95% confidence interval [CI] 1.2 - 7.4) in men, and marginally significant for thyroid cancers (n = 6, SIR = 2.6, 95% CI 1.0 - 5.7) in women. On the other hand, all cancers combined, all solid cancers combined were shown to exhibit significant exposure-dependent increased risks in individuals with the initial exposure before the age of 30, but not beyond this age.

CONCLUSIONS

The results suggest that prolonged low dose-rate radiation exposure appeared to increase risks of developing certain cancers in specific subgroups of this population in Taiwan.

Secondary carcinogenesis in patients treated with radiation: a review of data on radiation-induced cancers in human, non-human primate, canine and rodent subjects

Concern for risk of radiation-induced cancer is growing with the increasing number of cancer patients surviving long term. This study examined data on radiation transformation of mammalian cells in vitro and on the risk of an increased cancer incidence after irradiation of mice, dogs, monkeys, atomic bomb survivors, occupationally exposed persons, and patients treated with radiation. Transformation of cells lines in vitro increased linearly with dose from approximately 1 to approximately 4-5 Gy. At <0.1 Gy, transformation was not increased in all studies. Dose-response relationships for cancer incidence varied with mouse strain, gender and tissue/organ. Risk of cancer in Macaca mulatta was not raised at 0.25-2.8 Gy. From the atomic bomb survivor study, risk is accepted as increasing linearly to 2 Sv for establishing exposure standards. In irradiated patients, risk of cancer increased significantly from 1 to 45 Gy (a low to a high dose level) for stomach and pancreas, but not for bladder and rectum (1-60 Gy) or kidney (1-15 Gy). Risk for several organs/tissues increased substantially at doses far above 2 Gy. There is great heterogeneity in risk of radiation-associated cancer between species, strains of a species, and organs within a species. At present, the heterogeneity between and within patient populations of virtually every parameter considered in risk estimation results in substantial uncertainty in quantification of a general risk factor. An implication of this review is that reduced risks of secondary cancer should be achieved by any technique that achieved a dose reduction down to approximately [corrected] 0.1 Gy, i.e. dose to tissues distant from the target. The proportionate gain should be greatest for dose decrement to less than 2 Gy.

Targeted and Nontargeted Effects of Low-Dose Ionizing Radiation on Delayed Genomic Instability in Human Cells

All humans receive some radiation exposure and the risk for radiation-induced cancer at low doses is based on the assumption that there is a linear non-threshold relationship between dose and subsequent effect. Consequently, risk is extrapolated linearly from high radiation doses to very low doses. However, adaptive responses, bystander effects, and death-inducing effect may influence health effects associated with low-dose radiation exposure. Adaptive response is the phenomenon by which cells irradiated with a sublethal radiation dose can become less susceptible to subsequent high-dose radiation exposure. Bystander effects are nontargeted effects observed in cells that were not irradiated but were either in contact with or received soluble signals from irradiated cells. These non-hit bystander cells can exhibit damage typically associated with direct radiation exposure. Death-inducing effect is a phenomenon whereby medium from human-hamster hybrid cells displaying radiation-induced chromosomal instability is toxic to unirradiated parental cells. In this study, we show that human RKO cells do not exhibit adaptive response, bystander effect, or death-inducing effect, as measured by cell killing, or delayed genomic instability in a stably transfected plasmid-based green fluorescent protein assay measuring homologous recombination and delayed mutation/deletion events. However, growth medium conditioned by some chromosomally unstable RKO derivatives induced genomic instability, indicating that these cells can secrete factor(s) that elicit responses in nonirradiated cells. Furthermore, low radiation doses suppressed the induction of delayed genomic instability by a subsequent high dose, indicative of an adaptive response for radiation-induced genomic instability. These results highlight the inherent variability in cellular responses to low-dose radiation exposure and add to the uncertainties associated with evaluating potential hazards at these low doses.

Novel applications of ultrasound in pediatric emergency medicine

A new field, termed emergency ultrasound (EUS), has recently been established. The past decade saw rapid development in the field of EUS in adult patients, especially as performed by emergency medicine physicians. Ultrasound imaging offers several advantages over traditional radiographic techniques, many of which are especially relevant to patients in the pediatric emergency department. Recent literature has documented increased use of EUS for pediatric patients. This review will examine basic principles of ultrasound relevant to pediatric emergency medicine physicians. Emphasis will be placed on understanding the instrument and its limitations. In addition, we will review recent developments in this field. It is our goal that the reader will gain an understanding of the strengths and limitations of this instrument and will therefore be in a position to plan their own program in EUS in pediatrics. Furthermore, it is hoped that this review will serve as an impetus for innovative research, to refine and extend the indications of this modality to benefit patients in the pediatric emergency department.

New advances in radiation biology

Current understanding of risk associated with low-dose radiation exposure has for many years been embedded in the linear-no-threshold (LNT) approach, based on simple extrapolation from the Japanese atomic bomb survivors. Radiation biology research has supported the LNT approach although much of this has been limited to relatively high-dose studies. Recently, with new advances for studying effects of low-dose exposure in experimental models and advances in molecular and cellular biology, a range of new effects of biological responses to radiation has been observed. These include genomic instability, adaptive responses and bystander effects. Most have one feature in common in that they are observed at low doses and suggest significant non-linear responses. These new observations pose a significant challenge to our understanding of low-dose exposure and require further study to elucidate mechanisms and determine their relevance.

Adaptive responses to low-dose/low-dose-rate gamma rays in normal human fibroblasts: the role of growth architecture and oxidative metabolism

To investigate low-dose/low-dose-rate effects of low-linear energy transfer (LET) ionizing radiation, we used gamma-irradiated cells adapted to grow in a three-dimensional architecture that mimics cell growth in vivo. We determined the cellular, molecular and biochemical changes in these cells. Quiescent normal human fibroblasts were irradiated with single acute or chronic doses (1-10 cGy) of (137)Cs gamma rays. Whereas exposure to an acute dose of 10 cGy increased micronucleus formation, protraction of the dose over 48 h reduced micronucleus frequency to a level similar to or lower than what occurs spontaneously. The protracted treatment also up-regulated the cellular content of the antioxidant glutathione. These changes correlated with modulation of phospho-TP53 (serine 15), a stress marker that was regulated by doses as low as 1 cGy. The DNA damage that occurred after exposure to an acute dose of 10 cGy was protected against in two ways: (1) up-regulation of cellular antioxidant enzyme activity by ectopic overexpression of MnSOD, catalase or glutathione peroxidase, and (2) inhibition of superoxide anion generation by flavin-containing oxidases. These results support a significant role for oxidative metabolism in mediating low-dose radiation effects and demonstrate that cell culture in three dimensions is ideal to investigate radiation-induced adaptive responses. Expression of connexin 43, a constitutive protein of gap junctions, and the G(1) checkpoint were more sensitive to regulation by gamma rays in cells maintained in a three-dimensional than in a two-dimensional configuration.

Leukocyte DNA Damage after Multi–Detector Row CT: A Quantitative Biomarker of Low-Level Radiation Exposure

PURPOSE

To prospectively determine if gammaH2AX (phosphorylated form of H2AX histone variant)-based visualization and quantification of DNA damage induced in peripheral blood mononuclear cells (PBMCs) can be used to estimate the radiation dose received by adult patients who undergo multidetector computed tomography (CT).

MATERIALS AND METHODS

After institutional review board approval and written informed patient consent were obtained, eight women and five men (mean age, 63.8 years) who would be undergoing chest-abdominal-pelvic CT or chest CT only were recruited. Venous blood samples obtained before scanning were exposed to different radiation doses in vitro and incubated for 5-30 minutes to obtain reference values of gammaH2AX focus yield. Additional blood samples were taken 5-30 minutes after CT. Leukocytes were isolated, fixed, and stained for gammaH2AX expression. The gammaH2AX focus yields were determined with fluorescence microscopy, and the radiation doses delivered during CT were estimated by comparing post-CT focus yields with in vitro pre-CT focus yields. These CT radiation doses were compared with doses calculated by using phantom dosimetry and Monte Carlo data sets. Data were analyzed by using linear regression, the dispersion index test, and the contaminated Poisson method.

RESULTS

Compared with the gammaH2AX focus yields in blood samples taken before CT (0.06 focus per cell+/-0.01 [mean+/-standard error of mean]), the yields in blood samples taken 5 minutes after chest-abdominal-pelvic CT (0.52 focus per cell+/-0.02) were 8-10-fold higher and corresponded to a mean radiation dose of 16.4 mGy (95% confidence interval: 15.1, 17.7). The mean yield of 0.24 focus per cell+/-0.04 in one patient after chest CT corresponded to a mean radiation dose of 6.3 mGy+/-1.4. In comparison, phantom dosimetry-calculated total blood doses were 13.85 mGy with whole-body CT and 5.16 mGy with chest CT.

CONCLUSION

gammaH2AX focus yield in blood cells may be a useful quantitative biomarker of human low-level radiation exposure.

Can low dose diagnostic dental radiation trigger Sjögren’s syndrome?

Sjögren's syndrome (SS), first described by Swedish ophthalmologist Henrik Sjögren in 1930, is a chronic inflammatory, autoimmune disorder characterized by diminished lacrimal and salivary glands secretion resulting in keratoconjunctivitis sicca and xerostomia. One factor instrumental in severe salivary gland damage and salivary flow decrement is radiation therapy. Apoptosis, implicated in autoimmune diseases, has been shown to be responsible for this damage. However, there are no studies investigating the effect of diagnostic radiation (low dose) on salivary glands. A safe level of radiation has not been established thus far. Diagnostic radiation has been used from 1896, but generally applied only from 1916. Dr. Sjögren identified SS in 1930. It is possible that the introduction of X-rays for diagnostic purposes is associated with SS onset. Available data show drastically reduced use of diagnostic dental radiation in developing countries and a concomitantly drastically reduced or lack of SS in these countries. In countries like India with a population of 1.1 billion (health care level II country), primary SS has been reported to be rare (total of 27 and 23 primary SS and secondary SS patients respectively reported thus far), while a health care level I country like USA, with a population of 300 million, there are about 2-4 million SS patients. Health care level IV countries do not have a single reported case of SS. There is also evidence for ultraviolet radiation inducing subcutaneous lupus erythematosus, an autoimmune disorder. We hypothesize that diagnostic dental radiation could be a factor for the development of SS as a result of either radiation induced apoptosis or through oxidative modification of proteins.

Coronary calcium scoring with MDCT: The radiation dose to the breast and the effectiveness of bismuth breast shield

OBJECTIVE

The purpose of our study was to determine the breast radiation dose during coronary calcium scoring with multidetector computerized tomography (MDCT). We also evaluated the degree of dose reduction by using a bismuth breast shield when performing coronary calcium scoring with MDCT.

MATERIALS AND METHODS

The dose reduction achievable by shielding the adult (35 years or older) female breasts was studied in 25 women who underwent coronary calcium scoring with MDCT. All examinations were performed with a 16-MDCT scanner. To compare the shielded versus unshielded breast dose, the examinations were performed with (right breast) and without (left breast) breast shielding in all patients. With this technique the superficial breast doses were calculated. To determine the average glandular breast radiation dose, we imaged an anthropomorphic dosimetric phantom into which calibrated dosimeters were placed to measure the dose to the breast. The phantom was imaged using the same protocol. Radiation doses to the breasts with and without the breast shielding were measured and compared using the Student's t-test.

RESULTS

The mean radiation doses with and without the breast shield were 5.71+/-1.1 mGy versus 9.08+/-1.5 mGy, respectively. The breast shield provided a 37.12% decrease in radiation dose to the breast with shielding. The difference between the dose received by the breasts with and without bismuth shielding was significant, with a p-value of less than 0.001.

CONCLUSION

The high radiation during MDCT greatly exceeds the recommended doses and should not be underestimated. Bismuth in plane shielding for coronary calcium scoring with MDCT decreased the radiation dose to the breast. We recommend routine use of breast shields in female patients undergoing calcium scoring with MDCT.

Female Breast Radiation Exposure During Thorax Multidetector Computed Tomography and the Effectiveness of Bismuth Breast Shield to Reduce Breast Radiation Dose

OBJECTIVE

The purpose of our study was to determine the breast radiation dose when performing routine thoracic multidetector computed tomography (MDCT). We also evaluated dose reduction and the effect on image quality of using a bismuth breast shield when performing thoracic MDCT.

MATERIAL AND METHODS

The dose reduction achievable by shielding the adult (18 years or older) female breasts was studied in 50 women who underwent routine thoracic MDCT. All examinations were performed with a 16-MDCT scanner (Sensation Cardiac 16; Siemens Medical Solutions). To compare the shielded/unshielded breast dose, the examination was performed with (right breast) and without (left breast) breast shielding in all patients. With this technique, the superficial breast doses were calculated. To determine the average glandular breast radiation dose, we imaged an anthropomorphic dosimetric phantom into which calibrated dosimeters were placed to measure the dose to breast. The phantom was imaged using the same protocol. Radiation doses to the breasts with and without the breast shielding were measured and compared using the Student t test.

RESULTS

In the qualitative evaluation of the MDCT scans, all were considered to be of diagnostic quality. We did not see any differences in quality between the shielded and unshielded lung. The mean radiation doses to the breasts with the shield and to those without the shield were 8.6 +/- 2.33 versus 14.46 +/- 3.94 mGy, respectively. The breast shield enabled a 40.53% decrease in radiation dose to the breast. The difference between the dose received by the breasts with and that received by the breasts without bismuth shielding was significant, with a P value of less than 0.001.

CONCLUSIONS

Bismuth in-plane shielding for routine thoracic MDCT decreased radiation dose to the breast without qualitative changes in image quality. The other radiosensitive superficial organs (eg, testes and thyroid gland) specifically must be protected with shielding.

Augmentation of innate immunity by low-dose irradiation

The effect of low-dose irradiation on the immune system was investigated in mice. When a 0.2 Gy dose of X-ray irradiation was administered every other day for a total of four times, the number of lymphocytes yielded by the liver, spleen and thymus decreased at the initial stage (around day 10). At this stage, NK cells, extrathymic T cells and NKT cells were found to be radioresistant. In other words, conventional lymphocytes were radiosensitive, even in the case of low-dose irradiation. However, the number of lymphocytes in all tested immune organs increased beyond the control level at the recovery stage (around day 28). Enumeration of the absolute number of lymphocyte subsets showed that the most prominently expanding populations were NK cells, extrathymic T cells and NKT cells, especially in the liver where primordial lymphocytes are primarily present. Functional and phenotypic activation of these populations also occurred at the recovery stage. It raised a possibility that an initial activation of macrophages by low-dose irradiation then mediated the present phenomenon. These results suggest that low-dose irradiation eventually has the potential to induce a hormesis effect on the immune system.

DOE program--developing a scientific basis for responses to low-dose exposures: impact on dose-response relationships

The DOE Low Dose Radiation Research Program focuses on biological mechanisms involved in response to low doses of both low and high-LET radiation (< 0.1Gy). This research program represents a merging of new technologies with cutting edge biological techniques associated with genomics. This merger enables observation of radiation-induced cellular and molecular changes previously undetectable. These low-dose responses define mechanisms of interaction of radiation with living systems, and characterize the shape of dose-response. The research from this program suggests radiation paradigms regarding the involvement of radiation in the carcinogenic process. New biological phenomena observed at low doses include initial radiation-induced DNA damage and repair, changes in gene expression, adaptive responses and bystander effects. However, information from this cellular-molecular level cannot be directly extrapolated to risks in human populations. Links must be carefully developed between dose-response relationships at the cell and tissue levels and risk to human populations. The challenge and the ultimate goal of the Program is to determine if basic scientific data can be combined with more traditional epidemiological methods to improve the estimation of radiation risk from low level radiation exposures.

Radiation exposure of patients in comprehensive computed tomography of the head in acute stroke

BACKGROUND AND PURPOSE

To assess patient radiation exposure in comprehensive stroke imaging using multidetector row CT (MDCT) combining standard CT of the head, cerebral perfusion (CTP), and CT angiography (CTA) studies.

METHODS

Examination protocols for CT and CTA of cerebral and cervical vessels, as well as CTP were simulated using a Somatom Sensation Cardiac 64. Effective doses were derived from measurements with the use of lithium-fluoride thermoluminescent dosimeters (LiF-TLD) at several organ sites using an Alderson-Rando phantom.

RESULTS

LiF-TLD measurements resulted in effective doses of 1.7 mSv for CT, 1.9 mSv for CTA of intracranial vessels, and 2.8 mSv for CTA of cervical vessels, respectively. Depending on examination parameters, effective doses varied between 1.1 and 5.0 mSv for cerebral CTP. For CTP, local doses in the area of the primary beam ranged between 114 and 444 mGy.

CONCLUSIONS

Comprehensive stroke imaging may result in up to 9.5 mSv with possible local doses of 490 mGy. Although critical doses for organ damage (eg, cataract formation or hair loss) are not reached, physicians need to be aware of possible radiation induced sequelae particularly in repetitive examinations.

Lung cancer attributable to indoor radon exposure in france: impact of the risk models and uncertainty analysis

OBJECTIVE

The inhalation of radon, a well-established human carcinogen, is the principal-and omnipresent-source of radioactivity exposure for the general population of most countries. Scientists have thus sought to assess the lung cancer risk associated with indoor radon. Our aim here is to assess this risk in France, using all available epidemiologic results and performing an uncertainty analysis.

METHODS

We examined the exposure-response relations derived from cohorts of miners and from joint analyses of residential case-control studies and considered the interaction between radon and tobacco. The exposure data come from measurement campaigns conducted since the beginning of the 1980s by the Institute for Radiation Protection and Nuclear Safety and the Directorate-General of Health in France. We quantified the uncertainties associated with risk coefficients and exposures and calculated their impact on risk estimates.

RESULTS

The estimated number of lung cancer deaths attributable to indoor radon exposure ranges from 543 [90% uncertainty interval (UI) , 75-1,097] to 3,108 (90% UI, 2,996-3,221) , depending on the model considered. This calculation suggests that from 2.2% (90% UI, 0.3-4.4) to 12.4% (90% UI, 11.9-12.8) of these deaths in France may be attributable to indoor radon.

DISCUSSION

In this original work we used different exposure-response relations from several epidemiologic studies and found that regardless of the relation chosen, the number of lung cancer deaths attributable to indoor radon appears relatively stable. Smokers can reduce their risk not only by reducing their indoor radon concentration but also by giving up smoking.

The debate on the use of linear no threshold for assessing the effects of low doses

From December 2004 to July 2005, three reports on the effects of low doses of ionising radiation were released: ICRP (2004), the joint report of the French Academies of Science and Medicine (Tubiana et al 2005), and a report from the American Academy of Sciences (BEIR VII 2005). These reports quote the same recent articles on the biological effects of low doses, yet their conclusions diverge. The French report concludes that recent biological data show that the efficacy of defense mechanisms is modulated by dose and dose rate and that linear no threshold (LNT) is no longer plausible. The ICRP and the BEIR VII reports recognise that there are biologic arguments against LNT but feel that there are not sufficient biological proofs against it to change risk assessment methodology and subsequent regulatory policy based on LNT. They point out the remaining uncertainties and the lack of mechanistic explanations of phenomena such as low dose hyperlethality or the adaptive response. In this context, a critical analysis of the available data is necessary. The epidemiological data and the experimental data challenge the validity of the LNT hypothesis for assessing the carcinogenic effect of low doses, but do not allow its exclusion. Therefore, the main criteria for selecting the most reliable dose-effect relationship from a scientific point of view should be based on biological data. Their analysis should help one to understand the current controversy.

The chernobyl accident 20 years on: an assessment of the health consequences and the international response

BACKGROUND

The Chernobyl accident in 1986 caused widespread radioactive contamination and enormous concern. Twenty years later, the World Health Organization and the International Atomic Energy Authority issued a generally reassuring statement about the consequences. Accurate assessment of the consequences is important to the current debate on nuclear power.

OBJECTIVES

Our objectives in this study were to evaluate the health impact of the Chernobyl accident, assess the international response to the accident, and consider how to improve responses to future accidents.

DISCUSSION

So far, radiation to the thyroid from radioisotopes of iodine has caused several thousand cases of thyroid cancer but very few deaths ; exposed children were most susceptible. The focus on thyroid cancer has diverted attention from possible nonthyroid effects, such as mini-satellite instability, which is potentially important. The international response to the accident was inadequate and uncoordinated, and has been unjustifiably reassuring. Accurate assessment of Chernobyl's future health effects is not currently possible in the light of dose uncertainties, current debates over radiation actions, and the lessons from the late consequences of atomic bomb exposure.

CONCLUSIONS

Because of the uncertainties over the dose from and the consequences of the Chernobyl accident, it is essential that investigations of its effects should be broadened and supported for the long term. Because of the problems with the international response to Chernobyl, the United Nations should initiate an independent review of the actions and assignments of the agencies concerned, with recommendations for dealing with future international-scale accidents. These should involve independent scientists and ensure cooperation rather than rivalry.

Angiographic guidewire with measuring markers: design and clinical experience

PURPOSE

We have developed an angiographic guidewire with measuring markers to determine accurately how far a guidewire is inserted within a catheter. We investigated whether use of this guidewire reduces the risk of vascular injury and the fluoroscopic time during guidewire manipulations.

METHODS

Four markers were put on the surface of the guidewire at 80, 100, 110, and 120 cm from the tip. The actual lengths of 54 catheters from seven manufacturers were measured and compared with the nominal lengths. Sixty consecutive patients who underwent angiography were randomized into two groups: in one group guidewires with surface markers were used (marker group) and in the other group, conventional guidewires (control group). For each guidewire insertion, the fluoroscopic time before the guidewire was pushed forward into the vessel lumen was recorded. The number of occasions on which unintentionally the guidewire had already been pushed out of the catheter at the start of fluoroscopy was also evaluated.

RESULTS

The actual lengths of all catheters were greater than the nominal lengths by 1.0-11.0 cm. Mean fluoroscopic time for each guidewire insertion was 3.3 sec in the marker group and 5.7 sec in the control group (p < 0.05). Guidewires were unintentionally pushed out of the catheters without fluoroscopy three times (3.6%), in each case in the control group.

CONCLUSION

The guidewire with measuring markers is effective for enhancing safety and in reducing fluoroscopic radiation during angiographic procedures. It is recommended that operators be aware that actual lengths of catheters may vary significantly from the nominal lengths listed; they should be aware of this with any guidewire, but particularly with the angiographic measuring guidewire.

Array-CGH analyses of murine malignant lymphomas: genomic clues to understanding the effects of chronic exposure to low-dose-rate gamma rays on lymphomagenesis

We previously reported that mice chronically irradiated with low-dose-rate gamma rays had significantly shorter mean life spans than nonirradiated controls. This life shortening appeared to be due primarily to earlier death due to malignant lymphomas in the irradiated groups (Tanaka et al., Radiat. Res. 160, 376-379, 2003). To elucidate the molecular pathogenesis of murine lymphomas after low-dose-rate irradiation, chromosomal aberrations in 82 malignant lymphomas from mice irradiated at a dose rate of 21 mGy/day and from nonirradiated mice were compared precisely by microarray-based comparative genomic hybridization (array-CGH) analysis. The array carried 667 BAC clones densely selected for the genomic regions not only of lymphoma-related loci but also of surface antigen receptors, enabling immunogenotyping. Frequent detection of the apparent loss of the Igh region on chromosome 12 suggested that most lymphomas in both groups were of B-cell origin. Array-CGH profiles showed a frequent gain of whole chromosome 15 in lymphomas predominantly from the irradiated group. The profiles also demonstrated copy-number imbalances of partial chromosomal regions. Partial gains on chromosomes 12, 14 and X were found in tumors from nonirradiated mice, whereas losses on chromosomes 4 and 14 were significantly associated with the irradiated group. These findings suggest that lymphomagenesis under the effects of continuous low-dose-rate irradiation is accelerated by a mechanism different from spontaneous lymphomagenesis that is characterized by the unique spectrum of chromosomal aberrations.

Diagnostic CT Scans: Institutional Informed Consent Guidelines and Practices at Academic Medical Centers

OBJECTIVE

The purpose of this article is to characterize current informed consent practices for diagnostic CT scans at U.S. academic medical centers.

MATERIALS AND METHODS

We surveyed 113 radiology chairpersons associated with U.S. academic medical centers using a survey approved by our institutional review board. The need for informed consent for this study was waived. Chairpersons were asked if their institutions have guidelines for nonemergent CT scans (by whom; oral and/or written), if patients are informed of the purpose of their scans (by whom), what specific risks are outlined (allergic reaction, radiation risk and dose, others; by whom), and if patients are informed of alternatives to CT.

RESULTS

The study response rate was 81% (91/113). Of the respondents, two thirds (60/90) currently have guidelines for informed consent regarding CT scans. Radiology technologists were most likely to inform patients about CT (38/60, 63%) and possible risks (52/91, 57%), whereas ordering physicians were most likely to inform patients about CT's purpose (37/66, 56%). Fifty-two percent (30/58) of sites provided verbal information and 5% (3/58) provided information in written form. Possible allergic reaction to dye was explained at 84% (76/91) of sites, and possible radiation risk was explained at 15% (14/91) of sites. Nine percent (8/88) of sites informed patients of alternatives to CT.

CONCLUSION

Radiology technologists are more likely to inform patients about CT and associated risks than their physician counterparts. Although most academic medical centers currently have guidelines for informed consent regarding CT, only a minority of institutions inform patients about possible radiation risks and alternatives to CT.

Qualitative and quantitative analysis of phosphorylated ATM foci induced by low-dose ionizing radiation

We examined the formation of phosphorylated ataxia telangiectasia mutated (ATM) foci in exponentially growing normal human diploid cells exposed to low doses of X rays. Phosphorylated ATM foci were detected immediately after irradiation, and the number of foci decreased as the time after irradiation increased. The kinetics of phosphorylated ATM foci was comparable to that of phosphorylated histone H2AX. We found that there were fewer spontaneous phosphorylated ATM foci than that phosphorylated histone H2AX foci. Notably, significant numbers of phosphorylated histone H2AX foci, but not phosphorylated ATM foci, were detected in the S-phase cells. The induction of foci showed a linear dose-response relationship with doses ranging for 10 mGy to 1 Gy, and the average number of phosphorylated ATM foci per gray was approximately 50. The average size of the foci was comparable for the cells irradiated with 20 mGy and 1 Gy, and there was no significant difference in the kinetics of disappearance of foci, indicating that DNA double-strand breaks are similarly recognized by DNA damage checkpoints and are repaired irrespective of the dose.

Human skin responses to UV radiation: pigment in the upper epidermis protects against DNA damage in the lower epidermis and facilitates apoptosis

Melanin plays an important role in protecting the skin against UV radiation, and melanomas and basal/squamous cell carcinomas occur more frequently in individuals with fair/light skin. We previously reported that levels of melanin correlate inversely with amounts of DNA damage induced by UV in normal human skin of different racial/ethnic groups. We have now separately examined DNA damage in the upper and lower epidermal layers in various types of skin before and after exposure to UV and have measured subsequent apoptosis and phosphorylation of p53. The results show that two major mechanisms underlie the increased photocarcinogenesis in fair/light skin. First, UV-induced DNA damage in the lower epidermis (including keratinocyte stem cells and melanocytes) is more effectively prevented in darker skin, suggesting that the pigmented epidermis is an efficient UV filter. Second, UV-induced apoptosis is significantly greater in darker skin, which suggests that UV-damaged cells may be removed more efficiently in pigmented epidermis. The combination of decreased DNA damage and more efficient removal of UV-damaged cells may play a critical role in the decreased photocarcinogenesis seen in individuals with darker skin.

The CHEK2*1100delC allelic variant and risk of breast cancer: screening results from the Breast Cancer Family Registry

CHEK2, a serine-threonine kinase, is activated in response to agents, such as ionizing radiation, which induce DNA double-strand breaks. Activation of CHEK2 can result in cell cycle checkpoint arrest or apoptosis. One specific variant, CHEK2*1100delC, has been associated with an increased risk of breast cancer. In this population-based study, we screened 2,311 female breast cancer cases and 496 general population controls enrolled in the Ontario and Northern California Breast Cancer Family Registries for this variant (all controls were Canadian). Overall, 30 cases and one control carried the 1100delC allele. In Ontario, the weighted mutation carrier frequency among cases and controls was 1.34% and 0.20%, respectively [odds ratio (OR), 6.65; 95% confidence interval (95% CI), 2.37-18.68]. In California, the weighted population mutation carrier frequency in cases was 0.40%. Across all cases, 1 of 524 non-Caucasians (0.19%) and 29 of 1,775 Caucasians (1.63%) were mutation carriers (OR, 0.12; 95% CI, 0.02-0.89). Among Caucasian cases >45 years age at diagnosis, carrier status was associated with history of benign breast disease (OR, 3.18; 95% CI, 1.30-7.80) and exposure to diagnostic ionizing radiation (excluding mammography; OR, 3.21; 95% CI, 1.13-9.14); compared with women without exposure to ionizing radiation, the association was strongest among women exposed >15 years before diagnosis (OR, 4.28; 95% CI, 1.50-12.20) and among those who received two or more chest X-rays (OR, 3.63; 95% CI, 1.25-10.52). These data supporting the biological relevance of CHEK2 in breast carcinogenesis suggest that further studies examining the joint roles of CHEK2*1100delC carrier status and radiation exposure may be warranted.

What are the risks from medical X-rays and other low dose radiation?

The magnitude of the risks from low doses of radiation is one of the central questions in radiological protection. It is particularly relevant when discussing the justification and optimization of diagnostic medical exposures. Medical X-rays can undoubtedly confer substantial benefits in the healthcare of patients, but not without exposing them to effective doses ranging from a few microsieverts to a few tens of millisieverts. Do we have any evidence that these levels of exposure result in significant health risks to patients? The current consensus held by national and international radiological protection organizations is that, for these comparatively low doses, the most appropriate risk model is one in which the risk of radiation-induced cancer and hereditary disease is assumed to increase linearly with increasing radiation dose, with no threshold (the so-called linear no threshold (LNT) model). However, the LNT hypothesis has been challenged both by those who believe that low doses of radiation are more damaging than the hypothesis predicts and by those who believe that they are less harmful, and possibly even beneficial (often referred to as hormesis). This article reviews the evidence for and against both the LNT hypothesis and hormesis, and explains why the general scientific consensus is currently in favour of the LNT model as the most appropriate dose-response relationship for radiation protection purposes at low doses. Finally, the impact of the LNT model on the assessment of the risks from medical X-rays and how this affects the justification and optimization of such exposures is discussed.

Cancer risk from exposure to galactic cosmic rays: implications for space exploration by human beings

Space programmes are shifting toward planetary exploration, and in particular towards missions by human beings to the moon and Mars. However, exposure to space radiation is an important barrier to exploration of the solar system by human beings because of the biological effects of high-energy heavy ions. These ions have a high charge and energy, are the main contributors to radiation risk in deep space, and their biological effects are understood poorly. Predictions of the nature and magnitude of risks posed by exposure to radiation in space are subject to many uncertainties. In recent years, worldwide efforts have focussed on an increased understanding of the oncogenic potential of galactic cosmic rays. A review of the new results in this specialty will be presented here.

Dose-response relationship for life-shortening and carcinogenesis in mice irradiated at day 7 postnatal age with dose range below 1 Gy of gamma rays

This study was designed to elucidate the dose-response relationships for life-shortening and tumorigenic effect in the dose range below 1 Gy of gamma rays delivered during the infant period. Female B6C3F1 mice were irradiated with 0.10, 0.48 or 0.95 Gy at 7 days of age. All irradiated mice were allowed to live out their entire life span together with a simultaneously ongoing control group under a specific pathogen-free condition. Shortening of the mean life span was 1.58% in mice irradiated with 0.10 Gy, which was statistically significant . The coefficient of the linear dose-response relationship for life-shortening was 11.21% Gy(-1). The attributable death fraction for all causes of death in 0.10 Gy group reached 0.092. The excess relative risk for death rate from all causes was 0.102 in the group irradiated with 0.10 Gy. The coefficient of the linear dose-response relationship of the excess relative risk for death rate from all causes was 1.30 Gy(-1). The mean number of types of solid tumors at the time of death in mice irradiated with 0.10 Gy was distinctly larger than that in the control group. The excess relative risk for death rate from solid tumors was 0.45 in mice irradiated with 0.10 Gy. The coefficient of the linear dose-response relationship of excess relative risk for death rate from solid tumors was 4.52 Gy(-1). Increase in incidences of the pituitary, ovarian and adrenal tumors was observed in mice irradiated with 0.10 Gy. The results of the present study showed that infant mice are susceptible to solid tumor induction, especially of the endocrine organs.

Peripheral doses in CyberKnife radiosurgery

The purpose of this work is to measure the dose outside the treatment field for conformal CyberKnife treatments, to compare the results to those obtained for similar treatments delivered with gamma knife or intensity-modulated radiation therapy (IMRT), and to investigate the sources of peripheral dose in CyberKnife radiosurgery. CyberKnife treatment plans were developed for two hypothetical lesions in an anthropomorphic phantom, one in the thorax and another in the brain, and measurements were made with LiF thermoluminescent dosimeters (TLD-100 capsules) placed within the phantom at various depths and distances from the irradiated volume. For the brain lesion, gamma knife and 6-MV IMRT treatment plans were also developed, and peripheral doses were measured at the same locations as for the CyberKnife plan. The relative contribution to the CyberKnife peripheral dose from inferior- or superior-oblique beams entering or exiting through the body, internally scattered radiation, and leakage radiation was assessed through additional experiments using the single-isocenter option of the CyberKnife treatment-planning program with different size collimators. CyberKnife peripheral doses (in cGy) ranged from 0.16 to 0.041% (+/- 0.003%) of the delivered number of monitor units (MU) at distances between 18 and 71 cm from the field edge. These values are two to five times larger than those measured for the comparable gamma knife brain treatment, and up to a factor of four times larger those measured in the IMRT experiment. Our results indicate that the CyberKnife peripheral dose is due largely to leakage radiation, however at distances less than 40 cm from the field edge, entrance, or exit dose from inferior- or superior-oblique beams can also contribute significantly. For distances larger than 40 cm from the field edge, the CyberKnife peripheral dose is directly related to the number of MU delivered, since leakage radiation is the dominant component.

Low-LET-induced radioprotective mechanisms within a stochastic two-stage cancer model

A stochastic two-stage cancer model with clonal expansion was used to investigate the potential impact on human lung cancer incidence of some aspects of the hormesis mechanisms suggested by Feinendegen (Health Phys. 52 663-669, 1987). The model was applied to low doses of low-LET radiation delivered at low dose rates. Non-linear responses arise in the model because radiologically induced adaptations in radical scavenging and DNA repair may reduce the biological consequences of DNA damage formed by endogenous processes and ionizing radiation. Sensitivity studies were conducted to identify critical model inputs and to help define the changes in cellular defense mechanisms necessary to produce a lifetime probability for lung cancer that deviates from a linear no-threshold (LNT) type of response. Our studies suggest that lung cancer risk predictions may be very sensitive to the induction of DNA damage by endogenous processes. For doses comparable to background radiation levels, endogenous DNA damage may account for as much as 50 to 80% of the predicted lung cancers. For an additional lifetime dose of 1 Gy from low-LET radiation, endogenous processes may still account for as much as 20% of the predicted cancers (Fig. 2). When both repair and scavengers are considered as inducible, radiation must enhance DNA repair and radical scavenging in excess of 30 to 40% of the baseline values to produce lifetime probabilities for lung cancer outside the range expected for endogenous processes and background radiation.

Accurate quantification of visceral adipose tissue (VAT) using water-saturation MRI and computer segmentation: Preliminary results

PURPOSE

To describe and evaluate the accuracy of water-saturation MRI and a computer segmentation program for quantification of visceral adipose tissue (VAT).

MATERIALS AND METHODS

MRI was performed on five patients with whole-volume coverage of the abdomen using two different sequences: 1) a T1-weighted spoiled gradient-echo breath-hold sequence (non-water-saturation) and 2) a T1-weighted spoiled gradient-echo water-saturation breath-hold sequence (water-saturation). The computer segmentation program analyzed the data and calculated VAT volumes (cm3) from both sequences. The data from one patient were additionally processed with the use of a manual technique. The intrastudy reproducibility of the proposed method using the water-saturation MRI sequence and the computer segmentation technique was tested by repeated measures of the automated system analysis (x 10) on MRI data from a single subject to calculate variability.

RESULTS

VAT volumes measured by the water-saturation MRI sequences were consistently greater than those measured by the non-water-saturation sequences. Comparison of VAT volumes derived from the water-saturation images and measured by the computer segmentation technique vs. the manual technique showed good correlation (K = 0.8), with a significant time-saving benefit associated with the automated method (5 minutes vs. 1 hour). There was poor correlation between VAT volume measurement calculated by the manual technique and the computer segmentation technique using non-water-saturation images. The reproducibility of the computer segmentation technique using data derived from water-saturation images was high, with a low variability (+/- 5%).

CONCLUSION

The results obtained demonstrate that the proposed method may be able to provide accurate quantification of VAT in a highly reproducible and efficient manner.

Computed tomographic angiography for the evaluation of aneurysmal subarachnoid hemorrhage

OBJECTIVES

Computed tomography (CT) followed by lumbar puncture (LP) is currently the criterion standard for diagnosing subarachnoid hemorrhage (SAH) in the emergency department (ED); however, this is based on studies involving a limited number of patients. The authors sought to assess the ability of CT angiography (CTA), a new diagnostic modality, in conjunction with CT/LP to detect SAH.

METHODS

Consecutive patients presenting to the ED with symptoms concerning for SAH were approached. All patients had an intravenous catheter placed and underwent a noncontrast head CT followed by CTA. Patients whose CT did not reveal evidence of SAH or other pathology underwent LP in the ED. CTAs were read within 24 hours by a neuroradiologist blinded to the patient's history.

RESULTS

A total of 131 patients were approached, 116 were enrolled, and 106 completed the study. In six of 116 patients (5.1%), aneurysm was found on CTA with normal CT and positive findings on LP; three had a positive CTA with normal CT and LP findings (one of which had a negative cerebral angiogram), and there was one false-positive CTA. Follow-up of all 131 patients showed no previously undiagnosed intracranial pathology. In this patient population, 4.3% (5/116) were ultimately found to have an SAH and/or aneurysm.

CONCLUSIONS

In this pilot study, CTA was found to be useful in the detection of cerebral aneurysms and may be useful in the diagnosis of aneurysmal SAH. A larger multicenter study would be useful to confirm these results.

Risk of cancer in children with the diagnosis immaturity at birth

Cancer risk in children born before term has been assessed in a large number of case-control studies but very rarely in cohort studies. We carried out a cohort study of 35 178 children with the diagnosis immaturity at birth in the Hospital Discharge Register during 1977-89. The children were followed for cancer in the Danish Cancer Registry until 1994 and comparisons were made with incidence rates for all children in Denmark. The 64 observed cases of childhood cancer in the cohort corresponded closely to the expected number {standardised incidence ratio (SIR) = 1.03; [95% confidence interval (CI) 0.80, 1.32]}. The only cancer site with an observed number that deviated significantly from the expected number was central nervous system (CNS) tumours (26 cases observed; SIR = 1.57; [95% CI 1.02, 2.30]) in particular medulloblastoma (9 cases observed; SIR = 3.1; [95% CI 1.4, 5.9]). In a nested case-control study of the CNS tumours, we found that more cases than controls had been exposed to diagnostic X-rays, but the result was not significant. Surprisingly, for those born before term, the risk of CNS tumours increased with increasing gestational age in the nested case-control data. Our results are in line with previous evidence that children born before term are not at increased risk for childhood cancer in general. An explanation behind the excess of CNS tumours could not be identified, but the effect of diagnostic X-rays in newborns may deserve further attention.

Surgeon's radiation exposure during percutaneous vertebroplasty

OBJECT

In this study the authors evaluated levels of radiation exposure to surgeons' protected and unprotected hands during fluoroscopically assisted vertebroplasty.

METHODS

The amount of radiation administered to 30 patients during 41 procedures in a controlled prospective trial over 6 months was assessed, comparing radiation exposure to the right and left hands in two neurosurgeons. Effective skin doses were evaluated using thermoluminescent finger dosimeters (ring dosimeters). The ratios of finger dosimeter exposure were compared between the glove-protected and unprotected left hands of two surgeons and both unprotected right hands. In addition, dose-area product (DAP) and fluoroscopy times were recorded in all patients. The mean treatment-effective dose to the surgeons' hands was 0.49 +/- 0.4 mSv in the glove-protected left hand and 1.81 +/- 1.31 mSv in the unprotected left hand (p < 0.05). The mean effective hand doses were 0.59 +/- 0.55 mSv in the unprotected right hand of the glove-protected surgeon and 0.62 +/- 0.55 mSv in the unprotected right hand of the control surgeon. The total corresponding fluoroscopy time was 38.55 minutes for the protected surgeon and 41.23 minutes for the unprotected one (p > 0.05). Lead glove shielding resulted in a radiation dose reduction of 75%. The total DAP for all procedures was 256,496 mGy/cm2 and 221,408 mGy/cm2 (p > 0.05) for the protected and unprotected surgeons, respectively.

CONCLUSIONS

This study emphasizes the importance of surgeons wearing lead glove protection on their leading hands during percutaneous vertebroplasty procedures and demonstrates a 75% reduction rate of exposure to radiation.

Infection, immune responses and the aetiology of childhood leukaemia

Childhood leukaemia is the principal subtype of paediatric cancer and, despite success in treatment, its causes remain enigmatic. A plethora of candidate environmental exposures have been proposed, but most lack a biological rationale or consistent epidemiological evidence. Although there might not be a single or exclusive cause, an abnormal immune response to common infection(s) has emerged as a plausible aetiological mechanism.

Estimating radiation-induced cancer risks at very low doses: rationale for using a linear no-threshold approach

The possible cancer risks caused by ionizing radiation doses of ~1 mSv or less are too small to be estimated directly from epidemiological data. The linear no-threshold (LNT) approach to estimating such risks involves using epidemiological data at higher (but still low) doses to establish an "anchor point", and then extrapolating the excess cancer risk linearly down from this point to the low dose of interest. The study in this issue by Professor Tubiana and colleagues, summarizing a French Academy of Sciences report, argues that such LNT extrapolations systematically give substantial overestimates of the excess cancer risk at very low doses. We suggest that, to the contrary, even if there are significant deviations from linearity in the relevant dose range, potentially caused by the effects of inter-cellular interactions or immune surveillance, we know almost nothing quantitatively about these effects. Consequently, we do not know the magnitude, nor even the direction of any such deviations from linearity-the risks could indeed be lower than those predicted by a linear extrapolation, but they could well be higher.

Recent reports on the effect of low doses of ionizing radiation and its dose-effect relationship

Recently, the risk associated with low doses of ionizing radiation has gained new interest. Here, we analyze and discuss the major differences between two reports recently published on this issue; the report of the French Academy of Sciences and of the French Academy of Medicine published in March 2005, and the BEIR VII-Phase 2 Report of the American National Academy of Sciences published as a preliminary version in July 2005. The conclusion of the French Report is that the linear no-threshold relationship (LNT) may greatly overestimate the carcinogenic effect of low doses (<100 mSv) and even more that of very low doses (<10 mSv), such as those delivered during X-ray examinations. Conversely, the conclusion of the BEIR VII report is that LNT should be used for assessing the detrimental effects of these low and very low doses. The causes of these diverging conclusions should be carefully examined. They seem to be mostly associated with the interpretation of recent biological data. The point of view of the French Report is that these recent data are incompatible with the postulate on which LNT is implicitly based, namely the constancy of the carcinogenic effect per unit dose, irrespective of dose and dose rate.

Extremely low dose ionizing radiation up-regulates CXC chemokines in normal human fibroblasts

Although the public today could be exposed to X-rays as high as 1 cGy due to diagnostic procedures, the biological effects of this low-dose range have not been well established. We searched through >23,000 transcripts in normal human fibroblasts, HFLIII, using a novel comprehensive expression analysis method. More than 200 genes were up-regulated transiently by 1 cGy of X-rays during the 1-hour period after irradiation. We determined the nucleotide sequence of 10 up-regulated transcripts with the greatest rate of increase in the irradiated HFLIII cells. Three of the 10 transcripts encoded CXC chemokines (CXCL1, CXCL2, and CXCL6). The rest included the transcripts of other secretory products (secretogranin II, thrombospondin type I domain containing 2, amphiregulin, and interleukin-6) and unknown genes. To test the involvement of CXC chemokines in cells irradiated with low doses, we irradiated HFLIII cells with 1 to 20 cGy X-rays and transferred the media from HFLIII culture to two melanoma cell lines characteristic of excessive numbers of the CXC chemokine-specific receptors. The growth of these melanoma lines were significantly stimulated by the medium from HFLIII irradiated at 1 to 5 cGy. Our results indicate that human cells respond to doses of radiation as low as 1 cGy, and mechanisms alternative to those involved in moderate/high-dose studies have to be considered in understanding the biological effects of diagnostic level radiation. In addition, our comprehensive approach using a novel expression profiling method is a powerful strategy to explore biological functions associated with very low levels of toxic agents.