USE OF ANTHROPOMORPHIC HETEROGENEOUS PHYSICAL PHANTOMS FOR VALIDATION OF COMPUTATIONAL DOSIMETRY OF MEDICAL PERSONNEL AND PATIENTS

In the dosimetry of ionizing radiation, the phantoms of the human body, which are used as a replacement for thehuman body in physical measurements and calculations, play an important, but sometimes underestimated, role.There are physical phantoms used directly for measurements, and mathematical phantoms for computationaldosimetry. Their complexity varies from simple geometry applied for calibration purposes up to very complex, whichsimulates in detail the shapes of organs and tissues of the human body. The use of physical anthropomorphic phantoms makes it possible to effectively optimize radiation doses by adjusting the parameters of CT-scanning (computed tomography) in accordance with the characteristics of the patient without compromising image quality. The useof phantoms is an indispensable approach to estimate the actual doses to the organs or to determine the effectivedose of workers - values that are regulated, but cannot be directly measured.The article contains an overview of types, designs and the fields of application of anthropomorphic heterogeneousphysical phantoms of a human with special emphasis on their use for validation of models and methods of computational dosimetry.

THE REQUIREMENTS FOR PERSONAL MONITORING OF OCCUPATIONAL EXPOSURE: INTERNATIONAL EXPERIENCE AND UKRAINIAN REALITIES

The article includes analysis and generalizations about international and national experience as well as regulatory requirements for the organization and performance of occupational monitoring for radiation exposure (category A personnel), filling of the national dose registries. It is shown that for practical reasons it is justifiable to provide universal individual monitoring of category A personnel, regardless of the expected dose of radiation. The establish ment and functioning the national dose registry should not be limited to the mechanical collection and accumulation of data of non-guaranteed quality. Instead, both a quality management program and a scientific and methodological center should become components of the dose monitoring and registration system ensuring the quality and reliability of data on occupational exposure doses. Besides the dose records, the data sets should include information about methods used, work conditions, employees' health status. Information exchange infrastructure and data protection policies should be built in accordance with national approaches under the auspices of the State Agency for E-Governance in Ukraine.

RADIATION RISKS OF THYROID CANCER IN CHORNOBYL CLEAN-UP WORKERS USING THE ALTERNATIVE ESTIMATES OF DOSES OF EXTERNAL EXPOSURE

OBJECTIVE

The objective of this study was to estimate the thyroid cancer radiation risks - excess absolute risk(EAR), excess relative risk (ERR) and attributable fraction of risk (AR) in the cohort of 150,813 Ukrainian male clean-up workers during the 1986-2012 period (more than 25 years after the Chornobyl accident).

MATERIALS AND METHODS

The cohort under study of 150,813 Ukrainian men who participated emergency and clean-up work in 1986-1990 was formed based on the data of the Ukrainian State Register of persons affected due toChornobyl accident (SRU). The identification of thyroid cancer cases (216) was carried out by linking the SRU data-base with the National Cancer Registry of Ukraine (NCRU) data. Standardised incidence ratios (SIR) were estimatedcomparing thyroid cancer incidence in the cohort with the corresponding national indices. Excess absolute risk(EAR), excess relative risk (ERR) and attributable fraction of risk (AR) were calculated accounting for the alterna-tive dose estimates. The following sources of the average dose values for Ukrainian liquidators were used: officialtotal external dose records according to UNSCEAR 2008 report and results of external red bone marrow dose recon-struction by the RADRUE method for the cohort sample. For the radiation risk evaluation, these estimates were con-versed to the average external thyroid dose.

RESULTS

Results of the long term study (1986-2012) of thyroid cancer risks in a cohort of 150813 Chornobyl clean-up workers («liquidators») from Ukraine are presented. Two options for the average thyroid dose estimates were usedfor radiation risks evaluation. According to the SRU and NCRU 216 incident thyroid cancers were diagnosed in 1986-2012 within the studied cohort with an overall SIR of 3.35 (95 % confidence interval (CI) 2.51-3.80). The SIR esti-mates were elevated throughout the entire follow-up period. Investigation of a contribution of the external expo-sure (according to the alternative values) showed the elevated dose associated thyroid cancer rates in the studiedcohort. Alternatively estimated EAR/104 PY Gy were of 1.86 (95 % CI 0.47-3.24) and 2.07 (95 % CI 0.53-3.62);ERR/Gy - 2.38 (95 % CI 0.60-4.15) and 2.66 (95 % CI 0.68-4.64) and AR % (Gy) 70.4 % and 72.7 % Gy.

CONCLUSIONS

Obtained results prove the dose dependent increase of thyroid cancer incidence among UkrainianChornobyl clean-up workers. These conclusions are consistent with those received for combined cohort of Belarus,Russia and Baltic States liquidators.

A genomic copy number signature predicts radiation exposure in post-Chernobyl breast cancer

Breast cancer is the second leading cause of cancer death among women worldwide and besides life style, age and genetic risk factors, exposure to ionizing radiation is known to increase the risk for breast cancer. Further, DNA copy number alterations (CNAs), which can result from radiation-induced double-strand breaks, are frequently occurring in breast cancer cells. We set out to identify a signature of CNAs discriminating breast cancers from radiation-exposed and non-exposed female patients. We analyzed resected breast cancer tissues from 68 exposed female Chernobyl clean-up workers and evacuees and 68 matched non-exposed control patients for CNAs by array comparative genomic hybridization analysis (aCGH). Using a stepwise forward-backward selection approach a non-complex CNA signature, that is, less than ten features, was identified in the training data set, which could be subsequently validated in the validation data set (p value < 0.05). The signature consisted of nine copy number regions located on chromosomal bands 7q11.22-11.23, 7q21.3, 16q24.3, 17q21.31, 20p11.23-11.21, 1p21.1, 2q35, 2q35, 6p22.2. The signature was independent of any clinical characteristics of the patients. In all, we identified a CNA signature that has the potential to allow identification of radiation-associated breast cancer at the individual level.

Genomic characterization of chronic lymphocytic leukemia (CLL) in radiation-exposed Chornobyl cleanup workers

BACKGROUND

Chronic lymphocytic leukemia (CLL) was the predominant leukemia in a recent study of Chornobyl cleanup workers from Ukraine exposed to radiation (UR-CLL). Radiation risks of CLL significantly increased with increasing bone marrow radiation doses. Current analysis aimed to clarify whether the increased risks were due to radiation or to genetic mutations in the Ukrainian population.

METHODS

A detailed characterization of the genomic landscape was performed in a unique sample of 16 UR-CLL patients and age- and sex-matched unexposed general population Ukrainian-CLL (UN-CLL) and Western-CLL (W-CLL) patients (n = 28 and 100, respectively).

RESULTS

Mutations in telomere-maintenance pathway genes POT1 and ATM were more frequent in UR-CLL compared to UN-CLL and W-CLL (both p < 0.05). No significant enrichment in copy-number abnormalities at del13q14, del11q, del17p or trisomy12 was identified in UR-CLL compared to other groups. Type of work performed in the Chornobyl zone, age at exposure and at diagnosis, calendar time, and Rai stage were significant predictors of total genetic lesions (all p < 0.05). Tumor telomere length was significantly longer in UR-CLL than in UN-CLL (p = 0.009) and was associated with the POT1 mutation and survival.

CONCLUSIONS

No significant enrichment in copy-number abnormalities at CLL-associated genes was identified in UR-CLL compared to other groups. The novel associations between radiation exposure, telomere maintenance and CLL prognosis identified in this unique case series provide suggestive, though limited data and merit further investigation.

Doses of Ukrainian female clean-up workers with diagnosed breast cancer

The Chernobyl reactor accident in 1986 has caused significant exposure to ionizing radiation of the Ukrainian population, in particular clean-up workers and evacuees from the exclusion zones. A study aiming at the discovery of radiation markers of the breast cancer was conducted from 2008 to 2015 within a collaborative project by HZM, LMU, and NRCRM. In this study, post-Chernobyl breast cancer cases both in radiation-exposed female patients diagnosed at age less than 60 from 1992 to 2014 and in non-exposed controls matched for residency, tumor type, age at diagnosis, TNM classification as well as tumor grading were investigated for molecular changes with special emphasis to copy number alterations and miRNA profiles. Cancer registry and clinical archive data were used to identify 435 breast cancer patients among female clean-up workers and 14 among evacuees from highly contaminated territories as candidates for the study. Of these, 129 breast cancer patients fit study inclusion criteria and were traced for individual reconstruction of the target organ (breast) doses. The doses were estimated for 71 exposed cases (clean-up workers and evacuees from which biomaterial was available for molecular studies and who agreed to participate in a dosimetric interview) by the use of the well-established RADRUE method, which was adjusted specifically for the assessment of breast doses. The results of 58 female clean-up workers showed a large inter-individual variability of doses in a range of about five orders of magnitude: from 0.03 to 929 mGy, with median of 5.8 mGy. The study provides the first quantitative estimate of exposures received by female clean-up workers, which represent a limited but very important group of population affected by the Chernobyl accident. The doses of 13 women evacuated after the accident who did not take part in the clean-up activities (from 4 to 45 mGy with median of 19 mGy) are in line with the previous estimates for the evacuees from Pripyat and the 30-km zone.

The characteristics of antibodies of mice immunized by human unconventional myosin 1c

Specific antibodies produced against a protein of interest are invaluable tools for monitoring the protein structure, intracellular location and biological activity. Inoculation of murine lymphoma cells into the peritoneal cavity of immunized mice provides generation of ascitic fluid containing a significant amount of antibody with desired antigen specificity. Here we demonstrated that the intraperitoneal administration of murine lymphoma NK/Ly cells in mice immunized with 48 kDa isoform of human blood serum unconventional myosin 1c leads to generation of ascitic fluid that contained specific IgG-antibodies. These antibodies were capable of binding of the unconventional myosin 1c isolated from blood serum of patients with multiple sclerosis, rheumatoid arthritis and systemic lupus erythematosis, and could be used for diagnostics of several autoimmune diseases, the multiple sclerosis in particular.

Expression of miRNA-26b-5p and its target TRPS1 is associated with radiation exposure in post-Chernobyl breast cancer

Ionizing radiation is a well-recognized risk factor for the development of breast cancer. However, it is unknown whether radiation-specific molecular oncogenic mechanisms exist. We investigated post-Chernobyl breast cancers from radiation-exposed female clean-up workers and nonexposed controls for molecular changes. Radiation-associated alterations identified in the discovery cohort (n = 38) were subsequently validated in a second cohort (n = 39). Increased expression of hsa-miR-26b-5p was associated with radiation exposure in both of the cohorts. Moreover, downregulation of the TRPS1 protein, which is a transcriptional target of hsa-miR-26b-5p, was associated with radiation exposure. As TRPS1 overexpression is common in sporadic breast cancer, its observed downregulation in radiation-associated breast cancer warrants clarification of the specific functional role of TRPS1 in the radiation context. For this purpose, the impact of TRPS1 on the transcriptome was characterized in two radiation-transformed breast cell culture models after siRNA-knockdown. Deregulated genes upon TRPS1 knockdown were associated with DNA-repair, cell cycle, mitosis, cell migration, angiogenesis and EMT pathways. Furthermore, we identified the interaction partners of TRPS1 from the transcriptomic correlation networks derived from gene expression data on radiation-transformed breast cell culture models and sporadic breast cancer tissues provided by the TCGA database. The genes correlating with TRPS1 in the radiation-transformed breast cell lines were primarily linked to DNA damage response and chromosome segregation, while the transcriptional interaction partners in the sporadic breast cancers were mostly associated with apoptosis. Thus, upregulation of hsa-miR-26b-5p and downregulation of TRPS1 in radiation-associated breast cancer tissue samples suggests these molecules representing radiation markers in breast cancer.

Clinical characteristics of chronic lymphocytic leukemia occurring in chornobyl cleanup workers

The recently demonstrated radiation-induction of chronic lymphocytic leukemia (CLL) raises the question as to whether the amount of radiation exposure influences any of the clinical characteristics of the disease. We evaluated the relationship between bone marrow radiation doses and clinical characteristics and survival of 79 CLL cases diagnosed during 1986-2006 in a cohort of 110 645 male workers who participated in the cleanup work of the Chornobyl nuclear accident in Ukraine in 1986. All diagnoses were confirmed by an independent International Hematology Panel. Patients were followed up to the date of death or end of follow-up on 31 October 2010. The median age at diagnosis was 57 years. Median bone marrow dose was 22.6 milligray (mGy) and was not associated with time between exposure and clinical diagnosis of CLL (latent period), age, peripheral blood lymphocyte count or clinical stage of disease in univariate and multivariate analyses. Latent period was significantly shorter among those older at first exposure, smokers and those with higher frequency of visits to the doctor prior to diagnosis. A significant increase in the risk of death with increasing radiation dose was observed (p = 0.03, hazard ratio = 2.38, 95% confidence interval: 1.11,5.08 comparing those with doses ≥22 mGy to doses <22 mGy). After adjustment for radiation dose, survival of CLL cases was significantly shorter among those with younger age at first exposure, higher peripheral blood lymphocyte count, more advanced clinical stage of disease and older age at diagnosis (all p < 0.05). This is the first study to examine association between bone marrow radiation doses from the Chornobyl accident and clinical manifestations of the CLL in Chornobyl cleanup workers. The current study provides new evidence on the association of radiation dose and younger age at first radiation exposure at Chornobyl with shorter survival after diagnosis. Future studies are necessary with more cases in order to improve the statistical power of these analyses and to determine their significance. Copyright © 2016 John Wiley & Sons, Ltd.

Study of antineoplastic action of novel isomeric derivatives of 4-thiazolidinone

Pyrazole- and aryl-substituted derivatives of 4-thiazolidinone belong to a perspective group of compounds with potential antitumor action. Earlier, we have demonstrated high toxicity in vitro of several 4-thiazolidinones derivatives towards tumor cell lines. To further enhance the antitumor activity of novel 4-thiazolidinones, their chemical scaffold was optimized, and new pyrazole-thiazolidinones were synthesized. That allowed us to combine in one molecule the potential pharmacophore centres of previously tested compounds. As a result, "hybrid" 4-thiazolidinones exhibit higher toxicity in vitro toward tumor cells of various origin. The molecular mechanisms of antineoplastic activity of these compounds and intensity of induction of apoptosis strongly depended on the position of the substituent in the thiazolidinone cycle. In particular, Les-3661 compound, containing pyrazoline fragment in the 4th position of thiazolidinone core, exhibits 14 times higher cytotoxic activity towards tumor cells (LC50 = 3 μM) in comparison to its 2-substituted isomer Les-3713 (LC50 = 42 μM). It is demonstrated that in terms of underlying molecular mechanisms for cytotoxic effect the Les-3661 compound induced caspase-8 and caspase-9 dependent mixed-type of apoptosis, while Les-3713 induced apoptosis mediated only by the caspase-8.

Testing and validation of methods for dose measuring in anisotropic fields under occupational exposure in interventional cardiology

STUDY OBJECTIVE

Experimental testing of the practical application of methodology developed for the individual effective doses assay in an NPP staff by means of 4 dosimeters in case of non-uniform external γ-exposure with known angular characteristics of the radiation field.

MATERIALS AND METHODS

Two series of experimental phantom measurements were held at the workplaces of interventional cardiologists during a procedures in an X-ray operating room.

RESULTS AND CONCLUSIONS

Dose fields in a body of healthcare professional are characterized by the high gradients and readings of individual dosimeters depending on location can differ from 1.5 to 10 times. Thus a single dosimeter is not a source of sufficient information for accurate estimation of an effective dose. Studies have confirmed the possibility of NPP technique application at the workplace of interventional cardiologist. The essential need for a strict control of the eye lens doses is demonstrated.

Radiation and the risk of chronic lymphocytic and other leukemias among chornobyl cleanup workers

BACKGROUND

Risks of most types of leukemia from exposure to acute high doses of ionizing radiation are well known, but risks associated with protracted exposures, as well as associations between radiation and chronic lymphocytic leukemia (CLL), are not clear.

OBJECTIVES

We estimated relative risks of CLL and non-CLL from protracted exposures to low-dose ionizing radiation.

METHODS

A nested case-control study was conducted in a cohort of 110,645 Ukrainian cleanup workers of the 1986 Chornobyl nuclear power plant accident. Cases of incident leukemia diagnosed in 1986-2006 were confirmed by a panel of expert hematologists/hematopathologists. Controls were matched to cases on place of residence and year of birth. We estimated individual bone marrow radiation doses by the Realistic Analytical Dose Reconstruction with Uncertainty Estimation (RADRUE) method. We then used a conditional logistic regression model to estimate excess relative risk of leukemia per gray (ERR/Gy) of radiation dose.

RESULTS

We found a significant linear dose response for all leukemia [137 cases, ERR/Gy = 1.26 (95% CI: 0.03, 3.58]. There were nonsignificant positive dose responses for both CLL and non-CLL (ERR/Gy = 0.76 and 1.87, respectively). In our primary analysis excluding 20 cases with direct in-person interviews < 2 years from start of chemotherapy with an anomalous finding of ERR/Gy = -0.47 (95% CI: < -0.47, 1.02), the ERR/Gy for the remaining 117 cases was 2.38 (95% CI: 0.49, 5.87). For CLL, the ERR/Gy was 2.58 (95% CI: 0.02, 8.43), and for non-CLL, ERR/Gy was 2.21 (95% CI: 0.05, 7.61). Altogether, 16% of leukemia cases (18% of CLL, 15% of non-CLL) were attributed to radiation exposure.

CONCLUSIONS

Exposure to low doses and to low dose-rates of radiation from post-Chornobyl cleanup work was associated with a significant increase in risk of leukemia, which was statistically consistent with estimates for the Japanese atomic bomb survivors. Based on the primary analysis, we conclude that CLL and non-CLL are both radiosensitive.

Methodological approach to developing of double dosimetry algorithms and its application in the interventional cardiology

STUDY OBJECTIVES

to develop taking into account the specifity of exposure conditions a new algorithm for interventional cardiologists who use the X-ray protective clothes.

MATERIALS AND METHODS

modelling of the typical conditions of radiation exposure of interventional cardiologist wearing protective clothes during the interventions, providing Monte-Carlo computations of organ doses and dosimeters readouts.

RESULTS

partial dose values for all possible radiation conditions and relative frequency weight coefficients for each condition were obtained by Monte-Carlo method.

CONCLUSIONS

flexible and adaptive methodology for algorithm developing was proposed, a more specific algorithm was obtained for typical radiation conditions occuring under the interventional cardiology procedures. This algorithm well corresponded to experimental measurements demonstrating at that less conservatism comparing to other known algorithms.

Multiple myeloma among Chornobyl accident clean-up workers - state and perspectives of analytical study

The objective of the study was to analyze the Multiple Myeloma (MM) incidence in clean-up workers preparing the information background for consequent analytical study with a dose-dependent risk estimates.

MATERIALS AND METHODS

The Cohort Database was linked to the Ukrainian National Cancer Registry to identify the MM cases in a cohort of 152 520 male clean-up workers.

RESULTS

The 64 MM cases were identified in the studied Cohort for the 1987-2012 period. Fifty-eight of them were included to the preliminary incidence analysis accounting for the 10-years lag-period. According to the preliminary data analysis the MM incidence rate in studied clean-up workers Cohort did not exceed the corresponding rate in general population of Ukraine along the 21 years after the catastrophe.

CONCLUSIONS

Standardized incidence ratio for the 2008-2012 period, that is 22-26 years after the accident, demonstrated the significant excess of MM incidence among male clean-up workers in comparison with general population of Ukraine of corresponding age and gender (SIR 1.61, 95% CI 1.01;2.21).

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

BACKGROUND

Although high doses of ionizing radiation have long been linked to circulatory disease, evidence for an association at lower exposures remains controversial. However, recent analyses suggest excess relative risks at occupational exposure levels.

OBJECTIVES

We performed a systematic review and meta-analysis to summarize information on circulatory disease risks associated with moderate- and low-level whole-body ionizing radiation exposures.

METHODS

We conducted PubMed/ISI Thomson searches of peer-reviewed papers published since 1990 using the terms "radiation" AND "heart" AND "disease," OR "radiation" AND "stroke," OR "radiation" AND "circulatory" AND "disease." Radiation exposures had to be whole-body, with a cumulative mean dose of < 0.5 Sv, or at a low dose rate (< 10 mSv/day). We estimated population risks of circulatory disease from low-level radiation exposure using excess relative risk estimates from this meta-analysis and current mortality rates for nine major developed countries.

RESULTS

Estimated excess population risks for all circulatory diseases combined ranged from 2.5%/Sv [95% confidence interval (CI): 0.8, 4.2] for France to 8.5%/Sv (95% CI: 4.0, 13.0) for Russia.

CONCLUSIONS

Our review supports an association between circulatory disease mortality and low and moderate doses of ionizing radiation. Our analysis was limited by heterogeneity among studies (particularly for noncardiac end points), the possibility of uncontrolled confounding in some occupational groups by lifestyle factors, and higher dose groups (> 0.5 Sv) generally driving the observed trends. If confirmed, our findings suggest that overall radiation-related mortality is about twice that currently estimated based on estimates for cancer end points alone (which range from 4.2% to 5.6%/Sv for these populations).

The Chernobyl experience in the area of retrospective dosimetry

The Chernobyl accident, which occurred on 26 April 1986 at a nuclear power plant located less than 150 km north of Kiev, was the largest nuclear accident to date. The unprecedented scale of the accident was determined not only by the amount of released activity, but also by the number of workers and of the general public involved, and therefore exposed to increased doses of ionising radiation. Due to the unexpected and large scale of the accident, dosimetry techniques and practices were far from the optimum; personal dosimetry of cleanup workers (liquidators) was not complete, and there were no direct measurements of the exposures of members of the public. As a result, an acute need for retrospective dose assessment was dictated by radiation protection and research considerations. In response, substantial efforts have been made to reconstruct doses for the main exposed cohorts, using a broad variety of newly developed methods: analytical, biological and physical (electron paramagnetic resonance spectroscopy of teeth, thermoluminescence of quartz) and modelling. This paper reviews the extensive experience gained by the National Research Center for Radiation Medicine, Academy of Medical Sciences, Ukraine in the field of retrospective dosimetry of large cohorts of exposed population and professionals. These dose reconstruction projects were implemented, in particular, in the framework of epidemiological studies, designed to follow-up the medical consequences of the Chernobyl accident and study health effects of ionizing radiation, particularly Ukrainian-American studies of cataracts and leukaemia among liquidators.

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

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

Risk of hematological malignancies among Chernobyl liquidators

A case-control study of hematological malignancies was conducted among Chernobyl liquidators (accident recovery workers) from Belarus, Russia and Baltic countries to assess the effect of low- to medium-dose protracted radiation exposures on the relative risk of these diseases. The study was nested within cohorts of liquidators who had worked around the Chernobyl plant in 1986-1987. A total of 117 cases [69 leukemia, 34 non-Hodgkin lymphoma (NHL) and 14 other malignancies of lymphoid and hematopoietic tissue] and 481 matched controls were included in the study. Individual dose to the bone marrow and uncertainties were estimated for each subject. The main analyses were restricted to 70 cases (40 leukemia, 20 NHL and 10 other) and their 287 matched controls with reliable information on work in the Chernobyl area. Most subjects received very low doses (median 13 mGy). For all diagnoses combined, a significantly elevated OR was seen at doses of 200 mGy and above. The excess relative risk (ERR) per 100 mGy was 0.60 [90% confidence interval (CI) -0.02, 2.35]. The corresponding estimate for leukemia excluding chronic lymphoid leukemia (CLL) was 0.50 (90% CI -0.38, 5.7). It is slightly higher than but statistically compatible with those estimated from A-bomb survivors and recent low-dose-rate studies. Although sensitivity analyses showed generally similar results, we cannot rule out the possibility that biases and uncertainties could have led to over- or underestimation of the risk in this study.

The Ukrainian-American study of leukemia and related disorders among Chornobyl cleanup workers from Ukraine: II. Estimation of bone marrow doses

After the accident that took place on 26 April 1986 at the Chornobyl nuclear power plant, hundreds of thousands of cleanup workers were involved in emergency measures and decontamination activities. In the framework of an epidemiological study of leukemia and other related blood diseases among Ukrainian cleanup workers, individual bone marrow doses have been estimated for 572 cases and controls. Because dose records were available for only about half of the study subjects, a time-and-motion method of dose reconstruction that would be applicable to all study subjects, whether dead or alive, was developed. The doses were calculated in a stochastic mode, thus providing estimates of uncertainties. The arithmetic mean individual bone marrow doses were found to range from 0.00004 to 3,300 mGy, with an average value of 87 mGy over the 572 study subjects. The uncertainties, characterized by the geometric standard deviation of the probability distribution of the individual dose, varied from subject to subject and had a median value of about 2. These results should be treated as preliminary; it is likely that the dose calculations and particularly the uncertainty estimates will be improved in the follow-up of this effort.

Physical dosimetry of chernobyl cleanup workers

This paper presents a critical review of dosimetric monitoring practices during Chernobyl cleanup from 1986 to 1990. Dosimetric monitoring is considered in time evolution with respect to legislative background (including dose limits), methods of dose assessment, and coverage of workers with radiation monitoring programs as well as availability of data on individual doses of liquidators. Four large independent dosimetry services (Administration of Construction No. 605, Chernobyl Nuclear Power Plant, Production Association "Combinat," and the troops) had operated in Chernobyl covering different cohorts of cleanup workers with dosimetric monitoring of variable quality and comprehension. Extremes in this range were presented by the highly professional dosimetry service of the Administration of Construction No. 605 (USSR Ministry of Medium Machinery), which had provided total coverage of workers with high quality individual thermoluminescent dosimeter monitoring, and military (troops of the USSR Ministry of Defense) who had received the least precise group dosimetry, which, however, had covered the whole population of military cleanup workers. The main groups of liquidators are considered from the point of view of completeness and quality of their dosimetric data. Main gaps in dosimetric data and limitations of existing dose records are identified. The issues of evolution of dose limits and problems of monitoring internal and beta exposure are considered from the point of view of significance of these components and the need for missing information.

Dosimetry for a Study of Low-Dose Radiation Cataracts among Chernobyl Clean-up Workers

A cohort of 8,607 Ukrainian Chernobyl clean-up workers during 1986-1987 was formed to study cataract formation after ionizing radiation exposure. Study eligibility required the availability of sufficient exposure information to permit the reconstruction of doses to the lens of the eye. Eligible groups included civilian workers, such as those who built the "sarcophagus" over the reactor, Chernobyl Nuclear Power Plant Workers, and military reservists who were conscripted for clean-up work. Many of the official doses for workers were estimates, because only a minority wore radiation badges. For 106 military workers, electron paramagnetic resonance (EPR) measurements of extracted teeth were compared with the recorded doses as the basis to adjust the recorded gamma-ray doses and provide estimates of uncertainties. Beta-particle doses to the lens were estimated with an algorithm devised to take into account the nature and location of Chernobyl work, time since the accident, and protective measures taken. A Monte Carlo routine generated 500 random estimates for each individual from the uncertainty distributions of the gamma-ray dose and of the ratio of beta-particle to gamma-ray doses. The geometric mean of the 500 combined beta-particle and gamma-ray dose estimates for each individual was used in the data analyses. The median estimated lens dose for the cohort was 123 mGy, while 4.4% received >500 mGy.

Cataracts among Chernobyl Clean-up Workers: Implications Regarding Permissible Eye Exposures

The eyes of a prospective cohort of 8,607 Chernobyl clean-up workers (liquidators) were assessed for cataract at 12 and 14 years after exposure. The prevalence of strictly age-related cataracts was low, as expected (only 3.9% had nuclear cataracts at either examination), since 90% of the cohort was younger than 55 years of age at first examination. However, posterior subcapsular or cortical cataracts characteristic of radiation exposure were present in 25% of the subjects. The data for Stage 1 cataracts, and specifically for posterior subcapsular cataracts, revealed a significant dose response. When various cataract end points were analyzed for dose thresholds, the confidence intervals all excluded values greater than 700 mGy. Linear-quadratic dose-response models yielded mostly linear associations, with weak evidence of upward curvature. The findings do not support the ICRP 60 risk guideline assumption of a 5-Gy threshold for "detectable opacities" from protracted exposures but rather point to a dose-effect threshold of under 1 Gy. Thus, given that cataract is the dose-limiting ocular pathology in current eye risk guidelines, revision of the allowable exposure of the human visual system to ionizing radiation should be considered.

The Chornobyl Accident: Estimation of Radiation Doses Received by the Baltic and Ukrainian Cleanup Workers

During the first day after the explosion, the Chornobyl accident of April 26, 1986 exposed a few hundred emergency workers to high dose levels ranging up to 16 Gy, resulting in acute radiation syndrome. Subsequently, several hundred thousand cleanup workers were sent to the Chornobyl power plant to mitigate the consequences of the accident. Depending on the nature of the work to be carried out, the cleanup workers were sent for periods ranging from several minutes to several months. The average dose from external radiation exposure that was received by the cleanup workers was about 170 mGy in 1986 and decreased from year to year. The radiation exposure was mainly due to external irradiation from gamma-ray-emitting radionuclides and was relatively homogeneous over all organs and tissues of the body. To assess the possible health consequences of external irradiation at relatively low dose rates, the U.S. National Cancer Institute is involved in two studies of Chornobyl cleanup workers: (1) a study of cancer incidence and thyroid disease among Estonian, Latvian and Lithuanian workers, and (2) a study of leukemia and other related blood diseases among Ukrainian workers. After an overview of the sources of exposure and of the radiation doses received by the cleanup workers, a description of the efforts made to estimate individual doses in the Baltic and Ukrainian studies is presented.

[The experience of FISH technique application for reconstruction of individual radiation doses in Chernobyl liquidators in the framework of Ukrainian-American project "Leukemia"]

The results of proper investigations received under the cytogenetic examination of 225 persons (control groups, Chernobyl liquidators exposed to different radiation doses, oncogematology patients) had been summarized and analyzed. The conclusion concerning possibilities and limitations of FISH technique usage for retrospective biodosimetry of human radiation exposure has been presented.

High precision EPR dosimetry as a reference tool for validation of other techniques

We present here a particular application area for EPR dosimetry with teeth--use as a source of reference dose values for validation/verification of other retrospective dosimetry techniques and existing dose records. The conditions of application of EPR dosimetry in this role as well as practical design of such studies are shown. Particular attention is given to the requirements to the techniques in terms of precision and throughput, as well as to the issue of availability of samples for analysis and practical solution of this problem. Practical application of this approach is illustrated by several examples of completed validation sub-studies, which were performed in the framework of large-scale post-Chernobyl epidemiological studies.

Variability of parameters in retrospective EPR dosimetry with teeth for Ukrainian population

Variability of EPR signal parameters in retrospective dosimetry with teeth has been studied among five different oblasts (regions) of Ukraine. It was found that the native signal in enamel is region-invariant and has peak-to-peak width of 0.85+/-0.01 mT and intensity of 1.0+/-0.20 normalized units. Low-frequency background signals in the spectra of enamel, expressed in terms of dose were estimated to represent 1520 mGy. Variability of radiation sensitivity among different teeth (inter-sample variability measured using 100 mg aliquots) was (+/-)4% while among different parts of one tooth (intra-sample variability measured using 5-10 mg aliquots)--(+/-)7%.

Relationship between protection and operational quantities in dosimetry of photon external exposure-deficiencies of Hp(10)

It is commonly assumed that, for a variety of conditions, the E/Hp(10) conversion coefficient is below unity, i.e., Hp(10) can be used as a conservative surrogate of effective dose. The validity of this assumption was checked by Monte Carlo simulation of E and Hp(10) as determined by a practical dosemeter. The calculations concerned irradiation by parallel photon beams with directions varying within a 4pi solid angle and energy ranging from 50 keV to 1 MeV. Observed dependences of conversion coefficients on irradiation geometry, photon energy and dosemeter position demonstrate that in strongly anisotropic radiation fields straightforward application of Hp(10) for assessment of effective dose may lead to significant underestimation of the latter. For photon energy of 80 keV this underestimation may be up to 16-fold. For simulation of real life situations, irradiation by photons coming within broad cones (with solid angle pi) was considered. It was found that even for this irradiation geometry, E/Hp(10) may be as high as 4.3. At the same time, for radiation coming from the frontal hemisphere, the values of the conversion coefficient for a typically positioned (i.e., the left chest pocket) personal dosemeter do not exceed unity. The conclusion was reached that prior to application of Hp(10) as a surrogate of effective dose, the information regarding angular distribution of radiation fields must be taken into account.

Uncertainties in alanine dosimetry in the therapeutic dose range

A method for evaluating the overall uncertainty of alanine EPR transfer dosimetry in the therapeutic dose range is described. The method uses experimental data on EPR signal reproducibility from replicate dosimeters irradiated to low doses (1-5 Gy), estimates of Type B uncertainties, and Monte Carlo simulations of heteroscedastic orthogonal linear regression. A Bruker ECS106 spectrometer and Bruker alanine dosimeters have been used for this evaluation. The results demonstrate that alanine dosimetry can be used for transfer dosimetry in that range with the overall uncertainty 1.5-4% (1sigma) depending on the dose, the number of replicate dosimeters. and the duration of the calibration session (the session should not exceed one working day).

Some aspects of EPR dosimetry of liquidators

Doses of few hundred liquidators were reconstructed using EPR dosimetric technique, developed and routinely used in SCRM. Both cumulative and accidental dose values were determined. Obtained results are analyzed and discussed.

Emerging technological bases for retrospective dosimetry

In this article we discuss examples of challenging problems in retrospective dosimetry and describe some promising solutions. The ability to make measurements by accelerator mass spectrometry and luminescence techniques promises to provide improved dosimetry for regions of Belarus, Ukraine and Russian Federation contaminated by radionuclides from the Chernobyl accident. In addition, it may soon be possible to resolve the large neutron discrepancy in the dosimetry system for Hiroshima through novel measurement techniques that can be used to reconstruct the fast-neutron fluence emitted by the bomb some 51 years ago. Important advances in molecular cytogenetics and electron paramagnetic resonance measurements have produced biodosimeters that show potential in retrospective dosimetry. The most promising of these are the frequency of reciprocal translocations measured in chromosomes of blood lymphocytes using fluorescence in situ hybridization and the electron paramagnetic resonance signal in tooth enamel.

Estimation of 131I thyroid doses for the evacuees from Pripjat

The thyroid doses of 49,360 inhabitants of Pripjat evacuated after the accident at Chernobyl were reconstructed. During their evacuation most of the evacuees passed through highly contaminated territories. The evaluation of a large-scale public survey showed that only about 50% of the evacuees had left the contaminated areas within 5 days and that 30% of them stayed there for more than 30 days. As a first step, the model of dose estimations was improved, and thyroid doses were assessed for the group of evacuees for whom the 131I activity in the thyroids was measured. The 131I incorporation during the first 5 days after the accident was described by a single-intake model (inhalation); later incorporations were assumed to be proportional to the radioiodine activity in milk. As a second step, the correlation between the calculated doses and individual parameters (place of residence in Pripjat, intake of stable iodine, and age at the time of the accident) was described by an empirical equation. This equation was applied to all evacuees who completed the questionnaires of the public survey. Previous dose assessments were found to overestimate the thyroid doses especially for the younger evacuees. On the basis of these estimations, collective doses and the resulting radiation risks for thyroid cancer were assessed for different age groups.