Studies of mortality of atomic bomb survivors. Report 13: Solid cancer and noncancer disease mortality: 1950-1997

Radiation induced dynamic mutations and transgenerational effects

Many studies have confirmed that radiation can induce genomic instability in whole body systems. Although the molecular mechanisms underlying induced genomic instability are not known at present, this interesting phenomenon could be the manifestation of a cellular fail-safe system in which fidelity of repair and replication is down-regulated to tolerate DNA damage. Two features of genomic instability namely, delayed mutation and untargeted mutation, require two mechanisms of ;damage memory' and ;damage sensing, signal transduction and execution' to induce mutations at a non damaged-site. In this report, the phenomenon of transgenerational genomic instability and possible mechanisms are discussed using mouse data collected in our laboratory as the main bases.

Protracted radiation exposure and cancer mortality in the Techa River Cohort

In the 1950s many thousands of people living in rural villages on the Techa River received protracted internal and external exposures to ionizing radiation from the release of radioactive material from the Mayak plutonium production complex. The Extended Techa River Cohort includes 29,873 people born before 1950 who lived near the river sometime between 1950 and 1960. Vital status and cause of death are known for most cohort members. Individualized dose estimates have been computed using the Techa River Dosimetry System 2000. The analyses provide strong evidence of long-term carcinogenic effects of protracted low-dose-rate exposures; however, the risk estimates must be interpreted with caution because of uncertainties in the dose estimates. We provide preliminary radiation risk estimates for cancer mortality based on 1,842 solid cancer deaths (excluding bone cancer) and 61 deaths from leukemia. The excess relative risk per gray for solid cancer is 0.92 (95% CI 0.2; 1.7), while those for leukemia, including and excluding chronic lymphocytic leukemia, are 4.2 (CI 95% 1.2; 13) and 6.5 (CI 95% 1.8; 24), respectively. It is estimated that about 2.5% of the solid cancer deaths and 63% of the leukemia deaths are associated with the radiation exposure.

Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose-response relationships

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED(rad-ther)) in the irradiated organs. The OED(rad-ther) concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose-response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose-response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin's disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin's disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.

Age-at-exposure effects on risk estimates for non-cancer mortality in the Japanese atomic bomb survivors

Statistically significant increases in non-cancer disease mortality with radiation dose have been observed among survivors of the atomic bombings of Hiroshima and Nagasaki. The increasing trends arise particularly for diseases of the circulatory, digestive, and respiratory systems. Rates for survivors exposed to a dose of 1 Sv are elevated by about 10%, a smaller relative increase than that for cancer. The aetiology of this increased risk is not yet understood. Neither animal nor human studies have found clear evidence for excess non-cancer mortality at the lower range of doses received by A-bomb survivors. In this paper, we examine the age and time patterns of excess risks in the A-bomb survivors. The results suggest that the excess relative risk of non-cancer disease mortality might be highest for exposure at ages 30-49 years, and that those exposed at ages 0-29 years might have a very low excess relative risk compared with those exposed at older ages. The differences in excess relative risk for different age-at-exposure groups imply that the dose response relationships for non-cancer disease mortality need to be modelled with adjustment for age-at-exposure.

Radiation exposure due to local fallout from Soviet atmospheric nuclear weapons testing in Kazakhstan: solid cancer mortality in the Semipalatinsk historical cohort, 1960-1999

Little information is available on the health effects of exposures to fallout from Soviet nuclear weapons testing and on the combined external and internal environmental exposures that have resulted from these tests. This paper reports the first analysis of the Semipalatinsk historical cohort exposed in the vicinity of the Semipalatinsk nuclear test site, Kazakhstan. The cohort study, which includes 19,545 inhabitants of exposed and comparison villages of the Semipalatinsk region, was set up in the 1960s and comprises 582,750 person-years of follow-up between 1960 and 1999. Cumulative effective radiation dose estimates in this cohort range from 20 mSv to approximately 4 Sv. Rates of mortality and cancer mortality in the exposed group substantially exceeded those of the comparison group. Dose-response analyses within the exposed group confirmed a significant trend with dose for all solid cancers (P < 0.0001) and for digestive and respiratory cancers (P = 0.0255 and P < 0.0001), whereas no consistent dose-response trend was found for all causes of death (P = 0.4296). Regarding specific cancer sites, a significant trend with dose was observed for lung cancer (P = 0.0001), stomach cancer (P = 0.0050), and female breast cancer (P = 0.0040) as well as for esophagus cancer in women (P = 0.0030). The excess relative risk per sievert for all solid cancers combined was 1.77 (1.35; 2.27) based on the total cohort data, yet a selection bias regarding the comparison group could not be entirely ruled out. The excess relative risk per sievert based on the cohort's exposed group was 0.81 (0.46; 1.33) for all solid cancers combined and thus still exceeds current risk estimates from the Life Span Study. Future epidemiological assessments based on this cohort will benefit from extension of follow-up and ongoing validation of dosimetric data.

Biomarkers of space radiation risk

Radiation risk estimates are based on epidemiological data obtained on Earth for cohorts exposed predominantly to acute doses of gamma rays, and the extrapolation to the space environment is highly problematic and error-prone. The uncertainty can be reduced if risk estimates are compared directly to space radiation-induced biological alterations, i.e. by detecting biomarkers in astronauts. Chromosomal aberrations in peripheral blood lymphocytes are the only biomarker that can provide simultaneous information on dose, dose equivalent and risk, and they have been measured extensively in astronauts during the past 10 years. Individual relative risks calculated from chromosomal aberration measurements in crew members after single space missions in low-Earth orbit fall in the same range as the estimates derived from physical dosimetry, suggesting that the current system for radiogenic risk evaluation is essentially sound. However, the output of the biomarker test is dependent upon the sampling time. Recent results show a fast time-dependent decay of chromosomal aberrations in blood lymphocytes after space flight and a lack of correlation between translocations and cumulative dose in astronauts involved in two to five space missions. This "time factor" may reflect individual variability and time dependence in the risk produced by exposure to cosmic radiation during the flight. Biomarkers may be superior to dose in predicting space radiation risk, pending technical improvements in sensitivity, and validation by epidemiological studies.

The Techa River Cohort: Study Design and Follow-up Methods

Residents living on the banks of the Techa River in the Southern Urals region of Russia were exposed to radioactive contamination from the Mayak plutonium production and separation facility that discharged liquid radioactive waste into this river. This paper describes the methods used to establish and follow the Extended Techa River Cohort (ETRC), which includes almost 30,000 people living along the Techa River who were exposed to a complex mixture of radionuclides, largely 90Sr and 137Cs. The system of regular follow-up allows ascertainment of vital status, cause of death and cancer incidence. With over 50 years of follow-up and over 50% deceased, the ETRC now provides a valuable opportunity to study a wide range of health effects, both early and late, associated with protracted internal and external radiation exposures. The wide range of doses allows analysis of the nature of the dose-response relationship based on internal comparisons. Other features of the cohort are the high proportion (40%) exposed under age 20, and the inclusion of both sexes. The limitations of the study include loss to follow-up due to difficulties in tracing some cohort members and migration and incomplete ascertainment of cause of death.

Estimation of cancer mortality associated with repetitive computed tomography scanning

RATIONALE

Low-dose radiation from computed tomography (CT) may increase the risk of certain cancers, especially in children.

OBJECTIVE

We sought to estimate the excess all-cause and cancer-specific mortality, which may be associated with repeated CT scanning of patients with cystic fibrosis (CF).

METHODS

The radiation dose was calculated for a published CF surveillance CT scanning protocol of biennial CT scans, and the risk per scan was estimated using atom-bomb survivor data. A computational model was developed to calculate the excess mortality in a CF cohort associated with radiation from the CT scan and to evaluate the effects of background survival, scanning interval, and level of CT radiation used. The model assumed that there would be no survival benefits associated with repeated surveillance CT scanning.

RESULTS

The average radiation dose for the published CT protocol was 1 mSv. Survival reduction associated with annual scans from age 2 yr until death was approximately 1 mo and 2 yr for CF cohorts, with a median survival of 26 and 50 yr, respectively. Corresponding cumulative cancer mortality was approximately 2 and 13% at age 40 and 65 yr, respectively. Biennial CT scanning reduced all-cause and cumulative cancer mortality by half.

CONCLUSION

Routine lifelong annual CT scans carry a low risk of radiation-induced mortality in CF. However, as the overall survival increases for patients with CF, the risk of radiation-induced mortality may modestly increase. These data indicate that radiation dose must be considered in routine CT imaging strategies for patients with CF, to ensure that benefits outweigh the risks.

Do glucose and lipid metabolism affect cancer development in Nagasaki atomic bomb survivors?

The relationship between lipid or glucose metabolism and cancer has not yet been elucidated. We conducted 75-g oral glucose tolerance tests (75-g OGTTs) and lipid measurements between 1983 and 1985 in 516 Nagasaki atomic bomb survivors. Excluding those who already had cancer at the baseline examinations and those who developed cancers or died of any cause within 5 yr after the baseline examinations, we determined incident cancer cases until 2000 in the remaining 451 subjects (214 males and 237 females) and evaluated, by means of the Cox proportional hazard model, whether glucose or lipid metabolism predicts cancer development. The age- and sex-adjusted relative risk (RR) for incident cancer was 0.903 (95% confidence interval, CI = 0.842-0.968), 1.740 (95% CI = 1.238-2.446), 1.653 (95% CI = 0.922-2.965), and 1.024 (95% CI = 0.996-1.053) for total cholesterol (10 mg/dl), radiation dose (1 Sv), smoking, and 1-h blood glucose (1-h BG; 10 mg/dl) in 75-g OGTTs, respectively. Multiple regression analysis of age, sex, smoking, body mass index, 1-h BG, triglycerides, total cholesterol, high-density lipoprotein cholesterol, and radiation dose also showed that total cholesterol was negatively (RR = 0.872; 95% CI = 0.793-0.958) and radiation dose positively (RR = 1.809; 95% CI = 1.252-2.613) related to incident cancer. Cholesterol could be negatively and radiation dose positively associated with cancer development independently.

Lung cancer in Mayak workers: interaction of smoking and plutonium exposure

Lung cancer mortality among 5,058 male workers of the Mayak Production Association has been analyzed with emphasis on the interaction of smoking and radiation exposure by using the two-step clonal expansion (TSCE) model of carcinogenesis. The cohort consists of all Mayak workers with known smoking status, who were employed in the period 1948-1972, and who either had the plutonium concentration in urine measured or who worked in the reactors, where plutonium exposure was negligible. Those who died during the first two years after the first urine sampling were excluded. The follow-up extended until the end of 1998. During this time, 2,176 workers died, including 244 lung cancer cases. Mayak workers were exposed to external (gamma and neutron) radiation, and in the radiochemical and plutonium plants to plutonium. In the preferred TSCE model, internal radiation and smoking act on the clonal expansion of pre-carcinogenic clones. Assuming a plutonium radiation weighting factor of 20, the excess relative risk per lung dose was estimated to be 0.11 (95% CI: 0.08; 0.17) Sv(-1). Most of the lung cancer deaths are found to be due to smoking. The second main factor is the interaction of smoking and internal radiation. The model is sub-multiplicative in relative risks due to smoking and radiation. In a multiplicative version of the TSCE model, internal radiation acts on initiation and transformation rates. This model version agrees with conventional epidemiological risk models, because it also suggests a higher risk estimate than the preferred TSCE model. However, it fits the data less well than the preferred model.

Second cancers among 40,576 testicular cancer patients: focus on long-term survivors

BACKGROUND

Although second primary cancers are a leading cause of death among men with testicular cancer, few studies have quantified risks among long-term survivors.

METHODS

Within 14 population-based tumor registries in Europe and North America (1943-2001), we identified 40,576 1-year survivors of testicular cancer and ascertained data on any new incident solid tumors among these patients. We used Poisson regression analysis to model relative risks (RRs) and excess absolute risks (EARs) of second solid cancers. All statistical tests were two-sided.

RESULTS

A total of 2,285 second solid cancers were reported in the cohort. The relative risk and EAR decreased with increasing age at testicular cancer diagnosis (P < .001); the EAR increased with attained age (P < .001) but the excess RR decreased. Among 10-year survivors diagnosed with testicular cancer at age 35 years, the risk of developing a second solid tumor was increased (RR = 1.9, 95% confidence interval [CI] = 1.8 to 2.1). Risk remained statistically significantly elevated for 35 years (RR = 1.7, 95% CI = 1.5 to 2.0; P < .001). We observed statistically significantly elevated risks, for the first time, for cancers of the pleura (malignant mesothelioma; RR = 3.4, 95% CI = 1.7 to 5.9) and esophagus (RR = 1.7, 95% CI = 1.0 to 2.6). Cancers of the lung (RR = 1.5, 95% CI = 1.2 to 1.7), colon (RR = 2.0, 95% CI = 1.7 to 2.5), bladder (RR = 2.7, 95% CI = 2.2 to 3.1), pancreas (RR = 3.6, 95% CI = 2.8 to 4.6), and stomach (RR = 4.0, 95% CI = 3.2 to 4.8) accounted for almost 60% of the total excess. Overall patterns were similar for seminoma and nonseminoma patients, with lower risks observed for nonseminoma patients treated after 1975. Statistically significantly increased risks of solid cancers were observed among patients treated with radiotherapy alone (RR = 2.0, 95% CI = 1.9 to 2.2), chemotherapy alone (RR = 1.8, 95% CI = 1.3 to 2.5), and both (RR = 2.9, 95% CI = 1.9 to 4.2). For patients diagnosed with seminomas or nonseminomatous tumors at age 35 years, cumulative risks of solid cancer 40 years later (i.e., to age 75 years) were 36% and 31%, respectively, compared with 23% for the general population.

CONCLUSIONS

Testicular cancer survivors are at statistically significantly increased risk of solid tumors for at least 35 years after treatment. Young patients may experience high levels of risk as they reach older ages. The statistically significantly increased risk of malignant mesothelioma in testicular cancer survivors has, to our knowledge, not been observed previously in a cohort of patients treated with radiotherapy.

Simulation of organ-specific patient effective dose due to secondary neutrons in proton radiation treatment

Cancer patients undergoing radiation treatment are exposed to high doses to the target (tumour), intermediate doses to adjacent tissues and low doses from scattered radiation to all parts of the body. In the case of proton therapy, secondary neutrons generated in the accelerator head and inside the patient reach many areas in the patient body. Due to the improved efficacy of management of cancer patients, the number of long term survivors post-radiation treatment is increasing substantially. This results in concern about the risk of radiation-induced cancer appearing at late post-treatment times. This paper presents a case study to determine the effective dose from secondary neutrons in patients undergoing proton treatment. A whole-body patient model, VIP-Man, was employed as the patient model. The geometry dataset generated from studies made on VIP-Man was implemented into the GEANT4 Monte Carlo code. Two proton treatment plans for tumours in the lung and paranasal sinus were simulated. The organ doses and ICRP-60 radiation and tissue weighting factors were used to calculate the effective dose. Results show whole body effective doses for the two proton plans of 0.162 Sv and 0.0266 Sv, respectively, to which the major contributor is due to neutrons from the proton treatment nozzle. There is a substantial difference among organs depending on the treatment site.

The Protective Role of Fruits and Vegetables against Radiation-Induced Cancer

The role of fruits and vegetables in protecting against radiation-induced cancer and the positive evidence from epidemiology and ancillary investigations are discussed in this review. The recently reported Hiroshima and Nagasaki atomic bomb survivor studies provide strong evidence for the protective role of fruits and vegetables against radiation-induced cancer. The anticarcinogenic substances contained in, and the anticarcinogenic mechanisms proposed for, fruits and vegetables are reviewed. The anticarcinogenic effectiveness of fruits and vegetables are compared with that of dietary supplements. The reasons for the observed superiority of fruits and vegetables are advanced.

Ionizing radiation alters myofilament calcium sensitivity in vascular smooth muscle: potential role of protein kinase C

Radiation exposure increases vascular responsiveness, and this change involves endothelial damage, as well as direct effects on vascular smooth muscle. In this study, we tested the hypothesis that myofilament Ca2+sensitivity in vascular smooth muscle is increased from single whole body gamma irradiation (6 Gy). We measured contractile responses from intact and permeabilized rat thoracic aortic rings combined with cytosolic Ca2+([Ca2+]i) measurements. The sensitivity to KCl and phenylephrine increased significantly in tissues from animals on the 9th and 30th days postirradiation compared with control. Irradiation also significantly increased Ca2+sensitivity in β-escin permeabilized smooth muscle on the 9th and 30th days postirradiation. Inhibitors of protein kinase C, chelerythrine, and staurosporine, had no effect on the pCa-tension curves in control permeabilized tissues but significantly decreased Ca2+sensitivity in permeabilized tissues on the 9th and 30th days postirradiation. Phorbol dibutyrate (PDBu, 10−7M) increased Ca2+sensitivity in control skinned smooth muscle but was without effect in irradiated vascular rings. Simultaneous measurement of contractile force and [Ca2+]ishowed that myofilament Ca2+sensitivity defined as the ratio of force change to [Ca2+]isignificantly increased following γ-irradiation. PDBu (10−6M) stimulation of intact aorta produced a sustained contraction, while the increase in [Ca2+]iwas transient. In irradiated tissues, PDBu-induced contractions were greater than those seen in control tissues but there was no elevation in [Ca2+]i. Taken together, these data strongly support the hypothesis that irradiation increases the sensitivity of vascular smooth muscle myofilaments to Ca2+and this effect is dependent on activation of protein kinase C.

Modeling Intercellular Interactions during Carcinogenesis

By modulating the microenvironment of malignant or premalignant cells, inhibitory or stimulatory signals from nearby cells can play a key role in carcinogenesis. However, current commonly used quantitative models for induction of cancers by ionizing radiation focus on single cells and their progeny. Intercellular interactions are neglected or assumed to be confined to unidirectional radiation bystander effect signals from cells of the same tissue type. We here formulate a parsimoniously parameterized two-stage logistic (TSL) carcinogenesis model that incorporates some effects of intercellular interactions during the growth of premalignant cells. We show that for baseline tumor rates, involving no radiation apart from background radiation, this TSL model gives acceptable fits to a number of data sets. Specifically, it gives the same baseline hazard function, using the same number of adjustable parameters, as does the commonly used two-stage clonal expansion (TSCE) model, so it is automatically applicable to the many data sets on baseline cancer that have been analyzed using the TSCE model. For perturbations of baseline rates due to radiation, the models differ. We argue from epidemiological and laboratory evidence, especially results for the atomic bomb survivors, that for radiation carcinogenesis the TSL model gives results at least as realistic as the TSCE or similar models, despite involving fewer adjustable parameters in many cases.

Long-term mortality from heart disease and lung cancer after radiotherapy for early breast cancer: prospective cohort study of about 300,000 women in US SEER cancer registries

BACKGROUND

Radiotherapy for early breast cancer can decrease breast cancer mortality but increase other mortality, mainly from heart disease and lung cancer. The mean cardiac dose from irradiation of a left-sided breast cancer can be two or three times that for a right-sided breast cancer. The mean ipsilateral (ie, on the same side as the breast cancer) lung dose can also be two or three times the mean contralateral lung dose. Particularly during the 1970s, when typical heart and lung exposures were greater than now, the laterality of an irradiated breast cancer could measurably affect cardiac mortality and mortality from cancer of the right or the left lung decades later. This study aimed to assess the hazards in the general US population from routine cancer-registry and death-certificate data.

METHODS

We analysed data for 308 861 US women with early breast cancer of known laterality (left-sided or right-sided) who were registered in the US Surveillance Epidemiology and End Results (SEER) cancer registries during 1973-2001 and followed prospectively for cause-specific mortality until Jan 1, 2002.

FINDINGS

115 165 (37%) received radiotherapy. Among those who did not, tumour laterality was of little relevance to subsequent mortality. For women diagnosed during 1973-82 and irradiated, the cardiac mortality ratio (left versus right tumour laterality) was 1.20 (95% CI 1.04-1.38) less than 10 years afterwards, 1.42 (1.11-1.82) 10-14 years afterwards, and 1.58 (1.29-1.95) after 15 years or more (trend: 2p=0.03). For women diagnosed during 1983-92 and irradiated, the cardiac mortality ratio was 1.04 (0.91-1.18) less than 10 years afterwards and 1.27 (0.99-1.63) 10 or more years afterwards. For women diagnosed during 1993-2001 and irradiated the cardiac mortality ratio was 0.96 (0.82-1.12), with none yet followed for 10 years. Among women irradiated for breast cancer who subsequently developed an ipsilateral or contralateral lung cancer, the lung cancer mortality ratio (ipsilateral versus contralateral) for women diagnosed during 1973-82 and irradiated was 1.17 (0.62-2.19), 2.00 (1.00-4.00), and 2.71 (1.65-4.48), respectively, less than 10 years, 10-14 years, and 15 or more years afterwards (trend: 2p=0.04). For women irradiated after 1982 there is, as yet, little information on lung cancer risks more than 10 years afterwards.

INTERPRETATION

US breast cancer radiotherapy regimens of the 1970s and early 1980s appreciably increased mortality from heart disease and lung cancer 10-20 years afterwards with, as yet, little direct evidence on the hazards after more than 20 years. Since the early 1980s, improvements in radiotherapy planning should have reduced such risks, but the long-term hazards in the general populations of various countries still need to be monitored directly.

Unilateral multiple primary tumours in an atomic-bomb survivor

We report here a case of an atomic-bomb survivor with sequential, unilateral, multiple-organ primary tumours after exposure to direct external radiation. This 67-year-old woman was 8 years old when she was exposed to radiation from the atomic bomb. At the time of the explosion, she was in an open area, but hiding behind a tree, which shielded her left side. Therefore, the right side of her body was exposed to radiation directly and primarily. Since then, she has been diagnosed sequentially with breast cancer, ovarian tumour, thyroid tumour, head skin cancer and lung cancer. In each case, the tumour was on the right side of her body at the ages of 31, 38, 54, 58 and 64 years old, respectively. This case study indicates that the risk of multiple primary tumours should be considered in older atomic-bomb survivors.

Neoplastic transformation in vitro induced by low doses of 232 MeV protons

The aim was to define the dose--response curve for high-energy proton-induced neoplastic transformation in vitro. The HeLa x skin fibroblast human hybrid cell assay was used to determine the frequency of neoplastic transformation following doses of 232 MeV protons (mean linear energy transfer, LET=0.44 keV microm(-1)) in the range 5-600 mGy. Proton irradiations were carried out at the Loma Linda University Proton Treatment Facility, CA, USA. The data indicate no evidence for induction of transformation below a dose of 100 mGy. At doses of 5 and 50 mGy, there is evidence for a possible suppression of transformation frequencies below that for spontaneous transformation. The shape of the dose--response curve for high-energy proton-induced transformation of the human hybrid cell line CGL1 does not follow a linear no-threshold model and shows evidence for a threshold as well as for possible suppression of transformation at doses <100 mGy, similar to that seen for other low-LET radiations.

Age at exposure to ionising radiation and cancer mortality among Hanford workers: follow up through 1994

BACKGROUND

Studies of workers at the plutonium production factory in Hanford, WA have led to conflicting conclusions about the role of age at exposure as a modifier of associations between ionising radiation and cancer.

AIMS

To evaluate the influence of age at exposure on radiation risk estimates in an updated follow up of Hanford workers.

METHODS

A cohort of 26 389 workers hired between 1944 and 1978 was followed through 1994 to ascertain vital status and causes of death. External radiation dose estimates were derived from personal dosimeters. Poisson regression was used to estimate associations between mortality and cumulative external radiation dose at all ages, and in specific age ranges.

RESULTS

A total of 8153 deaths were identified, 2265 of which included cancer as an underlying or contributory cause. Estimates of the excess relative risk per Sievert (ERR/Sv) for cumulative radiation doses at all ages combined were negative for all cause and leukaemia and positive for all cancer and lung cancer. Cumulative doses accrued at ages below 35, 35-44, and 45-54 showed little association with mortality. For cumulative dose accrued at ages 55 and above (10 year lag), the estimated ERR/Sv for all cancers was 3.24 (90% CI: 0.80 to 6.17), primarily due to an association with lung cancer (ERR/Sv: 9.05, 90% CI: 2.96 to 17.92).

CONCLUSIONS

Associations between radiation and cancer mortality in this cohort are primarily a function of doses at older ages and deaths from lung cancer. The association of older age radiation exposures and cancer mortality is similar to observations from several other occupational studies.

Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries

OBJECTIVES

To provide direct estimates of risk of cancer after protracted low doses of ionising radiation and to strengthen the scientific basis of radiation protection standards for environmental, occupational, and medical diagnostic exposures.

DESIGN

Multinational retrospective cohort study of cancer mortality.

SETTING

Cohorts of workers in the nuclear industry in 15 countries.

PARTICIPANTS

407 391 workers individually monitored for external radiation with a total follow-up of 5.2 million person years.

MAIN OUTCOME MEASUREMENTS

Estimates of excess relative risks per sievert (Sv) of radiation dose for mortality from cancers other than leukaemia and from leukaemia excluding chronic lymphocytic leukaemia, the main causes of death considered by radiation protection authorities.

RESULTS

The excess relative risk for cancers other than leukaemia was 0.97 per Sv, 95% confidence interval 0.14 to 1.97. Analyses of causes of death related or unrelated to smoking indicate that, although confounding by smoking may be present, it is unlikely to explain all of this increased risk. The excess relative risk for leukaemia excluding chronic lymphocytic leukaemia was 1.93 per Sv (< 0 to 8.47). On the basis of these estimates, 1-2% of deaths from cancer among workers in this cohort may be attributable to radiation.

CONCLUSIONS

These estimates, from the largest study of nuclear workers ever conducted, are higher than, but statistically compatible with, the risk estimates used for current radiation protection standards. The results suggest that there is a small excess risk of cancer, even at the low doses and dose rates typically received by nuclear workers in this study.

Present status and self-reported diseases of the Korean atomic bomb survivors: a mail questionnaire survey

Many Koreans were forced to move to Japan while Korea was occupied by Japan. Consequently, when the atomic bombs were dropped on Hiroshima and Nagasaki an estimated 40,000 Koreans died and 30,000 survived. In 2004, 2,235 Koreans were registered as A-bomb survivors in South Korea. A mail questionnaire survey to evaluate the present status and self-reported diseases of the Korean survivors was conducted. In total, 1,256 questionnaires were returned and analysed. The most frequent chronic diseases reported by Korean survivors were hypertension (40.1 per cent), peptic ulcer disease (25.7 per cent), anaemia (23.3 per cent) and cataracts (23.1 per cent). The most frequent malignant diseases were stomach cancer (1.9 per cent), colon cancer (0.5 per cent) and leukaemia/multiple myeloma (0.4 per cent). This study suggests that further investigations are needed into the health concerns of the survivors and into health protection measures.

Mass screening with CT colonography: should the radiation exposure be of concern?

BACKGROUND & AIMS

Computed tomography colonography (CTC), particularly using noncathartic techniques, has the clear potential to increase compliance for colorectal cancer screening. Because the geometry for CTC is highly advantageous, it can be performed with lower radiation doses than almost any other CT examination. If CTC were to become a standard screening tool for the population age 50 years and older, the potential market in the United States would soon be over 100 million people. Therefore, it is pertinent to consider the radiation exposure and any potential radiation risk to the population from such a mass CTC screening program.

METHODS

Organ doses from CTC examinations can be estimated with standard techniques. These doses can be applied to organ- and dose-specific radiation cancer risk estimates to estimate the excess cancer risk resulting from the radiation from a paired (supine and prone) CTC examination.

RESULTS

The cancer risks associated with the radiation exposure from CTC are unlikely to be zero, but they are small. A best estimate for the absolute lifetime cancer risk associated with the radiation exposure using typical current scanner techniques is about 0.14% for paired CTC scans for a 50-year-old, and about half that for a 70-year-old. These values probably could be reduced by factors of 5 or 10 with optimized CTC protocols.

CONCLUSIONS

In terms of the radiation exposure, the benefit-risk ratio potentially is large for CTC.

[Introduction of a mammography screening program in Germany. Consideration of benefits and risks]

For women between 50 and 70 years of age, X-ray mammography presently represents the most effective method for early breast cancer detection. It is commonly accepted that quality assured mammography examinations conducted at regular intervals can reduce mortality from breast cancer. In the year 2002, the German Bundestag agreed to the implementation of a mammography screening program for Germany based on the European guidelines. The effectiveness of a mammography screening program is controversially discussed and two of the most commonly cited hazards are the occurrence of false-positive results and the so-called overdiagnosis. Another issue of criticism is the radiation risk due to the mammography examinations. However, in women aged 50-70 years the radiation risk has no substantial importance. In contrast to the present situation in Germany in which opportunistic screening is widespread, standardized quality assured screening will guarantee that false-positive rates are kept as low as possible and that further assessment diagnostics are effective and minimally invasive.

Patient doses in multi-slice CT and the importance of optimisation

Substantive surveys of patient doses arising from CT examinations have been conducted in our Hospital. In the first instance doses were measured on a single-slice Siemens Plus 4 scanner. A similar survey was conducted initially following commissioning of a Siemens multi-slice Sensation scanner and subsequently after some effort was made to optimise scanning protocols. Doses are reported in terms of dose-length products (DLPs) and as effective doses. The optimisation process on the multi-slice scanner resulted in a reduction in DLP values by between 14% and 58%. With two exceptions, significantly lower or comparable DLP values were obtained when meaningful comparisons were made with results previously obtained with the single-slice scanner. Specific results for the multi-slice scanner in terms of the median DLP in mGy.cm (and median effective dose in mSv) are: routine brain, 660 (1.5); routine chest, 195 (4.0); chest with portal liver phase, 370 (7.2); routine chest with high resolution component, 250 (5.1); chest/abdomen/pelvis with contrast, 560 (11.0); routine abdomen without contrast, 145 (2.4); routine abdomen with contrast 215 (3.6); routine abdomen/pelvis without contrast, 230 (4.4); routine abdomen/pelvis with contrast, 345 (6.3); abdomen/pelvis triple phase, 715 (13.3); renal scan, 260 (4.6); lumbar spine, 445 (7.2); cerebral angiography, 240 (0.58); pulmonary angiography, 165 (3.4); aortic angiography, 305 (5.7). Based on the survey findings possible values for CT examination local diagnostic reference levels (LDRLs) are suggested.

Risk of Thyroid Cancer After Exposure to 131 I 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.

Radiation as a Nervous System Toxin

Neurotoxicity from radiation can range widely and produce effects that may include (1) small absolute increases in cancer risks, (2) subtle effects on higher level functioning in some individuals, (3) severe cognitive impairment in some individuals, (4) severe focal injury tat may include necrosis or irreversible loss of function, and (5) overwhelming and rapidly fatal diffuse injury associated with high-dose, whole-body exposures. An understanding of the implications of nervous system exposure to radiation can guide efforts in radiation protection and aid in the optimization of the medical uses of radiation.

Male Breast Cancer Incidence Among Atomic Bomb Survivors

To learn more about the role of ionizing radiation in the development of male breast cancer, we evaluated male breast cancer incidence among 45 880 male members of the Life Span Study cohort of Japanese atomic bomb survivors. Male breast cancers, diagnosed between January 1, 1958, and December 31, 1998, were identified through the Hiroshima and Nagasaki Tumor Registries. Nine male breast cancers were diagnosed among exposed Life Span Study members (crude rate = 1.8 per 100,000 person-years), and three were diagnosed among nonexposed cohort members (crude rate = 0.5 per 100,000 person-years). A statistically significant dose-response relation was observed (excess relative risk per sievert = 8, 95% confidence interval = 0.8 to 48; P = .01). Our finding of a statistically significant association between ionizing radiation and male breast cancer incidence adds to the very limited information that shows an association between radiation exposure and an increased risk of male breast cancer.

Low doses of ionizing radiation and circulatory diseases: a systematic review of the published epidemiological evidence

Recent analyses of mortality among atomic bomb survivors have suggested a linear dose-response relationship between ionizing radiation and diseases of the circulatory system for exposures in the range 0-4 Sv. If confirmed, this has substantial implications. We have therefore reviewed the published literature to see if other epidemiological data support this finding. Other studies allowing a comparison of the rates of circulatory disease in individuals drawn from the same population but exposed to ionizing radiation at different levels within the range 0-5 Gy or 0-5 Sv were identified through systematic literature searches. Twenty-six studies were identified. In some, disease rates among those exposed at different levels may have differed for reasons unrelated to radiation exposure, while many had low power to detect effects of the relevant magnitude. Among the remainder, one study found appreciable evidence that exposure to low-dose radiation was associated with circulatory diseases, but five others, all with appreciable power, did not. We conclude that the other epidemiological data do not at present provide clear evidence of a risk of circulatory diseases at doses of ionizing radiation in the range 0-4 Sv, as suggested by the atomic bomb survivors. Further evidence is needed to characterize the possible risk.

Age-related differences in susceptibility to carcinogenesis. II. Approaches for application and uncertainty analyses for individual genetically acting carcinogens

In an earlier report we developed a quantitative likelihood-based analysis of the differences in sensitivity of rodents to mutagenic carcinogens across three life stages (fetal, birth to weaning, and weaning to 60 days) relative to exposures in adult life. Here we draw implications for assessing human risks for full lifetime exposures, taking into account three types of uncertainties in making projections from the rodent data: uncertainty in the central estimates of the life-stage-specific sensitivity factors estimated earlier, uncertainty from chemical-to-chemical differences in life-stage-specific sensitivities for carcinogenesis, and uncertainty in the mapping of rodent life stages to human ages/exposure periods. Among the uncertainties analyzed, the mapping of rodent life stages to human ages/exposure periods is most important quantitatively (a range of several-fold in estimates of the duration of the human equivalent of the highest sensitivity "birth to weaning" period in rodents). The combined effects of these uncertainties are estimated with Monte Carlo analyses. Overall, the estimated population arithmetic mean risk from lifetime exposures at a constant milligrams per kilogram body weight level to a generic mutagenic carcinogen is about 2.8-fold larger than expected from adult-only exposure with 5-95% confidence limits of 1.5- to 6-fold. The mean estimates for the 0- to 2-year and 2- to 15-year periods are about 35-55% larger than the 10- and 3-fold sensitivity factor adjustments recently proposed by the U.S. Environmental Protection Agency. The present results are based on data for only nine chemicals, including five mutagens. Risk inferences will be altered as data become available for other chemicals.

Somatic DNA damage in interventional cardiologists: a case-control study

Interventional cardiologists who work in cardiac catheterization laboratories are exposed to low doses of ionizing radiation that could pose a health hazard. DNA damage is considered to be the main initiating event by which radiation damage to cells results in development of cancer and hereditary disease. The aim of the present study was to assess the effects of chronic low-dose X-ray radiation exposure on somatic DNA damage of interventional cardiologists working in high-volume cardiac catheterization laboratories. For this analysis, we used peripheral lymphocytes and the assay for micronuclei (MNs), which is considered to be a reliable biological dosimeter for radiation exposure. We obtained peripheral blood from 62 physicians (mean age+/-se = 40.6+/-1.5 years): 31 interventional cardiologists (group I, exposed) and 31 age- and sex-matched clinical cardiologists (group II, nonexposed). Interventional cardiologists showed higher MN values (group I=20.5+/-1.6 vs. group II=12.8+/-1.3, P=0.001), although some overlap was apparent in the individual subject analysis. A correlation between years of professional activity and MN frequency value was detectable for interventional cardiologists (r=0.428, P=0.02) but not for clinical cardiologists (r=0.253, P=0.17). The results indicated that, overall, interventional cardiologists working in a high-volume catheterization laboratory have higher levels of somatic DNA damage when compared with clinical cardiologists working outside the catheterization laboratory. The amount of this damage varies and is only weakly related to the duration of professional exposure, which suggests that a dominant modulation of the underlying genetic substrate by environmental factors has a role in determining the harm in individual physicians.

Priority list of research areas for radiological nuclear threat countermeasures

To help the nation prepare for the possibility of a terrorist attack using radiological and nuclear devices, the Office of Science and Technology Policy and the Homeland Security Council established an interagency working group. The working group deliberated on the research needs for radiological/ nuclear threat countermeasures and identified and prioritized 18 areas for further attention. The highest priorities were given to research on (1) radioprotectors for use prior to exposure; (2) therapeutic agents for postexposure treatment; (3) antimicrobial therapy for infections associated with radiation exposure; (4) cytokines and growth factors; (5) mechanisms of radiation injury at the molecular, cellular, tissue and organism levels; and (6) automation of biodosimetric assays. High priority was given to (1) developing biomarkers for biodosimetry; (2) enhancing training in the radiation sciences; (3) exploring the consequences of combined injury; (4) establishing a repository of information regarding investigational countermeasures; and (5) following the health of an exposed population to better prepare for subsequent events. The research areas that the committee felt required the attention of the radiation research community are described in this report in an effort to inform this community about the needs of the nation and to encourage researchers to address these critical issues.

A Hypothesis: Radiation-Related Leukemia is Mainly Attributable to the Small Number of People who Carry Pre-existing Clonally Expanded Preleukemic Cells

Human leukemia frequently involves recurrent translocations. Since radiation is a well-known inducer of both leukemia and chromosomal translocations, it has long been suspected that radiation might cause leukemia by inducing specific translocations. However, recent studies clearly indicate that spontaneous translocations specific to acute lymphocytic leukemia (ALL) actually occur much more frequently than do leukemia cases with the same translocations. Moreover, the ALL-associated translocation-bearing cells are often found to have clonally expanded in individuals who do not develop ALL. Since radiation-induced DNA damage is generated essentially randomly in the genome, it does not seem likely that radiation could ever be responsible for the induction of identical translocations of relevance to ALL in multiple cells of an individual and hence be the primary cause of radiation-related leukemia. An alternative hypothesis described here is that the radiation-related ALL risk for a population is almost entirely attributable to a small number of predisposed individuals in whom relatively large numbers of translocation-carrying pre-ALL cells have accumulated. This preleukemic clone hypothesis explains various known characteristics of radiation-related ALL and implies that people who do not have substantial numbers of preleukemic cells (i.e. the great majority) are likely at low risk of developing leukemia. The hypothesis can also be applied to chronic myelogenous leukemia and to young-at-exposure cases of acute myelogenous leukemia.

Temporal variation of excess mortality rate from solid tumors in mice irradiated at various ages with gamma rays

The influence of age at the time of irradiation on the lifetime risk for excess mortality from solid tumors, and on the temporal pattern of variation in the excess mortality rate, was analyzed using data obtained from a study of female B6C3F1 mice, which was conducted at the National Institute of Radiological Sciences, Chiba, Japan. Mice were irradiated with 1.9-Gy gamma rays at day 17 in intra-uterine age, or day 0, 7, 35, 105 or 365 in postnatal age. Control and irradiated mice were allowed to live out their entire life span under a specific pathogen-free condition. The primary cause of death for each mouse was determined by macroscopic and microscopic examination. The lifetime excess mortality from solid tumors was apparently higher in the mice irradiated during the neonatal to puberty period than in the mice irradiated during the intra-uterine or adult period. The median of time for manifestation of lifetime excess mortality since irradiation was shortest among mice exposed at 365 days of age and longest among mice exposed at 17 days of intra-uterine age. The excess mortality rate at any attained age was not independent of the age at irradiation. The excess mortality rate increased with increasing age, and the excess relative risk decreased with increasing age. The temporal variations of the excess mortality rate and background mortality rate were analyzed using the additive multi-stage model, which includes the assumptions that radiation-related carcinogenesis superimposes on background carcinogenesis, and that both radiation-related and background carcinogenesis involve multiple stages. The results of the analysis strongly suggested that the number of stages for manifestation of radiation-related carcinogenesis was less than that in background carcinogenesis for various types of solid tumors, and that the majority of stages were common in both radiation-related and background carcinogenesis. The additive multi-stage model well described the observed findings on the length of the latent period and temporal variations of the excess mortality rate and excess relative risk. It should be stressed that the magnitude of the lifetime risk was not only determined by a decrease in the number of hits for carcinogenesis but was also determined by another parameter which decides the initial value of excess mortality rate. Furthermore, we estimated the rate of decrease in the number of remaining hits for carcinogenesis, and it was found that the rate of decrease in the number of remaining hits was higher in several irradiated groups than that in the background carcinogenesis. However, radiation-induced genomic instability and/or delayed mutation may be of secondary importance when radiation was delivered promptly, because the present analysis revealed that the major action of radiation took place soon after irradiation, as one or more hits for transitions of stages for carcinogenesis.

Lung cancer in Mayak workers

The cohort of nuclear workers at the Mayak Production Association, located in the Russian Federation, is a unique resource for providing information on the health effects of exposure to plutonium as well as the effects of protracted external dose. Lung cancer mortality risks were evaluated in 21,790 Mayak workers, a much larger group than included in previous evaluations of lung cancer risks in this cohort. These analyses, which included 655 lung cancer deaths occurring in the period 1955-2000, were the first to evaluate both excess relative risk (ERR) and excess absolute risk (EAR) models and to give detailed attention to the modifying effects of gender, attained age and age at hire. Lung cancer risks were found to be significantly related to both internal dose to the lung from plutonium and external dose, and risks were described adequately by linear functions. For internal dose, the ERR per gray for females was about four times higher than that for males, whereas the EAR for females was less than half that for males; the ERR showed a strong decline with attained age, whereas the EAR increased with attained age until about age 65 and then decreased. Parallel analyses of lung cancer mortality risks in Mayak workers and Japanese A-bomb survivors were also conducted. Efforts currently under way to improve both internal and external dose estimates, and to develop data on smoking, should result in more accurate risk estimates in the future.

Patient exposure in medical X-ray imaging in Europe

Patients are exposed to X rays when undergoing medical examinations in diagnostic radiology. Exposure data acquired and assessed in Germany for the year 1997 resulted in a mean annual effective dose of 2 +/- 0.5 mSv per head of the population, thereby reaching or exceeding the average level of environmental radiation in many cases. The underlying frequency of medical X-ray examinations was approximately 136 million, i.e. approximately 1.7 examinations annually per head of the population. For comparison, corresponding data of other countries were extracted from the UNSCEAR 2000 report or originate from the literature. Data analysis shows significant differences in national radiological practices and a very uneven distribution of patient doses amongst the world population. The mean annual effective dose per head of the population varies by up to a factor of 60 between health care level I and IV countries, and still by a factor of approximately 6 within health care level I countries. While projection radiography has succeeded in reducing dose consumption, computed tomography and radiological interventions have given rise to a significant growth of patient exposure, and interventional radiology can even exceed thresholds for deterministic radiation effects. Patient exposure is further shown to result from misadministration and retakes of X-ray examinations, usually not registered, as well as from technical failures of X-ray facilities, which can cause significantly enhanced exposure times. Corresponding data are presented and comments are made on the international situation of non-harmonised data collection on patient exposure as well as of parameters affecting the assessment of exposure and risk.

Nonlinear response for neoplastic transformation following low doses of low let radiation

There are now several independent studies that indicate that the dose-response for the endpoint of radiation-induced neoplastic transformation in vitro is non-linear for low linear energy transfer (LET) radiation. At low doses (<10 cGy) the transformation frequency drops below that seen spontaneously. Importantly, this observation has been made using fluoroscopic energy x-rays, a commonly used modality in diagnostic radiology, the practice of which is responsible for the majority of radiation exposure to the general public. Since the transformation frequency is reduced over a large dose range (0.1 to 10cGy) it is likely that multiple mechanisms are involved and that the relative contribution of these may vary with dose. These include the killing of a subpopulation of cells prone to spontaneous transformation at the lowest doses, and the induction of DNA repair at somewhat higher doses. Protective effects of low doses of low LET radiation on other cancer-relevant endpoints in vitro and in vivo have also been observed by several independent laboratories. These observations strongly suggest that the linear-nonthreshold dose-response model is unlikely to apply to the induction of cancer by low doses of low LET radiation in humans.

Relationship of hepatocellular carcinoma to soya food consumption: A cohort-based, case-control study in Japan

To determine if the risk of hepatocellular carcinoma (HCC) is reduced by consumption of soya foods, we conducted a case-control study within a cohort of Japanese A-bomb survivors. We compared the prediagnosis consumption of isoflavone-rich miso soup and tofu to HCC risk, adjusting for hepatitis B (HBV) and C (HCV) viral infections, the major HCC risk factors in this population. The study included 176 pathologist-confirmed cases of HCC diagnosed in 1964-1988 and 560 controls who died of diseases other than liver cancer. We examined dietary information collected at least 2 years before diagnosis or death and tissue-based measures of viral hepatitis. Using logistic regression, crude ORs were 0.5 (95% CI 0.29-0.95) and 0.5 (95% CI 0.20-0.99) for high vs. low miso soup and tofu intake, respectively. Adjusting for year of birth, sex, HBV, HCV and other factors, the OR for miso soup was unchanged at 0.5 (95% CI 0.14-1.55), and miso results were similar when ORs were recalculated separately for earlier and later birth cohorts to assess consistency of results. The adjusted OR for tofu was 0.9 (95% CI 0.20-3.51). We also found a statistically significant (p < 0.0001) interaction between sex and HCV, with risk of HCC being substantially higher for women. We conclude that consumption of miso soup and other soya foods may reduce HCC risk.

Radiation exposure and cause specific mortality among nuclear workers in Belgium (1969-1994)

Cause specific mortality was studied in nuclear workers from five nuclear facilities in Belgium and compared to the general population. For the 1969-1994 period, mortality in male nuclear workers is significantly lower for all causes of death and for all cancer deaths. The same conclusions are reached if one assumes a latency period of 20 y between the first irradiation and cancer induction. In female workers, mortality due to all causes and all cancer deaths is not different from that of the general population. Analysis of cause specific mortality was performed for male and female workers for three endpoints: specific cancer sites, cardiovascular and respiratory diseases. No significant increase in mortality was observed. In male workers, the influence of cumulative dose was also investigated using four dose levels: no significant correlation was found. Smoking habits may be a confounding factor in smoking related health conditions.

Genotoxicity in the eyes of bystander cells

The controversial use of a linear, no threshold extrapolation model for low dose risk assessment has become even more so in light of the recent reports on the bystander phenomenon. The answer to the question as to which of the two phenomena, bystander versus adaptive response, is more important has practical implication in terms of low dose radiation risk assessment. In this review, genotoxicity is used as an endpoint to introduce the two phenomena, provide some insight into the mechanisms of bystander effect and to bridge the two low dose phenomena which operate in opposite directions: the bystander effect tends to exaggerate the effect at low doses, by communicating damage from hit to non-hit cells whereas the adaptive response confers resistance to a subsequent challenging dose by an initial low priming dose.

Cancer risk estimates for gamma-rays with regard to organ-specific doses Part II: site-specific solid cancers

Part I of this study presented an analysis of the solid cancer mortality data for 1950-1997 from the Japanese life-span study of the A-bomb survivors to assess the cancer risk for gamma-rays in terms of the organ-specific dose for all solid cancers combined. Compared to earlier analyses, considerably more curvature in the dose-effect relation is indicated by these computations, which now suggests a dose and dose-rate effectiveness factor of about 2. The computations are extended here in order to explore the site-specific solid cancer risks for various organs. A computational method has been developed whereby the site-specific cancer risks are all simultaneously computed with global age and gender effect modifiers. This provides a more parsimonious representation with fewer parameters and avoids the large relative standard errors which would otherwise result. The sensitivity of site-specific risks to the choices of the neutron RBE is examined. The site-specific risk estimates are quite sensitive to the neutron RBE for the least shielded organs such as the breast, bladder and oesophagus. For the deeper lying organs, such as the gallbladder, pancreas and uterus, the impact of the neutrons is much lower. With an assumed neutron RBE of 35, which is in line with results on low neutron doses in major past studies on rodents and which corresponds approximately to the current ICRP radiation weighting factor for neutrons, the neutrons appear to contribute about 40% of the observed excess cancer risk in the breast, i.e. the organ that is closest to the body surface. However, this neutron contribution fraction is only about 10% for deeper lying organs, such as the colon.

Flexible dose-response models for Japanese atomic bomb survivor data: Bayesian estimation and prediction of cancer risk

Generalised absolute risk models were fitted to the latest Japanese atomic bomb survivor cancer incidence data using Bayesian Markov Chain Monte Carlo methods, taking account of random errors in the DS86 dose estimates. The resulting uncertainty distributions in the relative risk model parameters were used to derive uncertainties in population cancer risks for a current UK population. Because of evidence for irregularities in the low-dose dose response, flexible dose-response models were used, consisting of a linear-quadratic-exponential model, used to model the high-dose part of the dose response, together with piecewise-linear adjustments for the two lowest dose groups. Following an assumed administered dose of 0.001 Sv, lifetime leukaemia radiation-induced incidence risks were estimated to be 1.11 x 10(-2) Sv(-1) (95% Bayesian CI -0.61, 2.38) using this model. Following an assumed administered dose of 0.001 Sv, lifetime solid cancer radiation-induced incidence risks were calculated to be 7.28 x 10(-2) Sv(-1) (95% Bayesian CI -10.63, 22.10) using this model. Overall, cancer incidence risks predicted by Bayesian Markov Chain Monte Carlo methods are similar to those derived by classical likelihood-based methods and which form the basis of established estimates of radiation-induced cancer risk.

Neoplastic TransformationIn Vitroafter Exposure to Low Doses of Mammographic-Energy X Rays: Quantitative and Mechanistic Aspects

The induction of neoplastic transformation in vitro after exposure of HeLa x skin fibroblast hybrid cells to low doses of mammography-energy (28 kVp) X rays has been studied. The data indicate no evidence of an increase in transformation frequency over the range 0.05 to 22 cGy, and doses in the range 0.05 to 1.1 cGy may result in suppression of transformation frequencies to levels below that seen spontaneously. This finding is not consistent with a linear, no-threshold dose- response curve. The dose range at which possible suppression is evident includes doses typically experienced in mammographic examination of the human breast. Experiments are described that attempt to elucidate any possible role of bystander effects in modulating this low-dose radiation response. Not unexpectedly, inhibition of gap junction intercellular communication (GJIC) with the inhibitor lindane did not result in any significant alteration of transformation frequencies seen at doses of 0.27 or 5.4 cGy in these subconfluent cultures. Furthermore, no evidence of a bystander effect associated with factors secreted into the extracellular medium was seen in medium transfer experiments. Thus, in this system and under the experimental conditions used, bystander effects would not appear to be playing a major role in modulating the shape of the dose-response curve.

The biological effects of diagnostic cardiac imaging on chronically exposed physicians: the importance of being non-ionizing

Ultrasounds and ionizing radiation are extensively used for diagnostic applications in the cardiology clinical practice. This paper reviewed the available information on occupational risk of the cardiologists who perform, every day, cardiac imaging procedures. At the moment, there are no consistent evidence that exposure to medical ultrasound is capable of inducing genetic effects, and representing a serious health hazard for clinical staff. In contrast, exposure to ionizing radiation may result in adverse health effect on clinical cardiologists. Although the current risk estimates are clouded by approximations and extrapolations, most data from cytogenetic studies have reported a detrimental effect on somatic DNA of professionally exposed personnel to chronic low doses of ionizing radiation. Since interventional cardiologists and electro-physiologists have the highest radiation exposure among health professionals, a major awareness is crucial for improving occupational protection. Furthermore, the use of a biological dosimeter could be a reliable tool for the risk quantification on an individual basis.

No evidence of radiation effect on mutation rates at hypervariable minisatellite loci in the germ cells of atomic bomb survivors

Human minisatellites consist of tandem arrays of short repeat sequences, and some are highly polymorphic in numbers of repeats among individuals. Since these loci mutate much more frequently than coding sequences, they make attractive markers for screening populations for genetic effects of mutagenic agents. Here we report the results of our analysis of mutations at eight hypervariable minisatellite loci in the offspring (61 from exposed families in 60 of which only one parent was exposed, and 58 from unexposed parents) of atomic bomb survivors with mean doses of >1 Sv. We found 44 mutations in paternal alleles and eight mutations in maternal alleles with no indication that the high doses of acutely applied radiation had caused significant genetic effects. Our finding contrasts with those of some other studies in which much lower radiation doses, applied chronically, caused significantly increased mutation rates. Possible reasons for this discrepancy are discussed.