Biological dosimetry in a group of radiologists by the analysis of dicentrics and translocations

The results of a cytogenetic study carried out in a group of nine radiologists are presented. Chromosome aberrations were detected by fluorescence plus Giemsa staining and fluorescence in situ hybridization. Dose estimates were obtained by extrapolating the yield of dicentrics and translocations to their respective dose-effect curves. In seven individuals, the 95% confidence limits of the doses estimated by dicentrics did not include 0 Gy. The 99 dicentrics observed in 17,626 cells gave a collective estimated dose of 115 mGy (95% confidence limits 73-171). For translocations, five individuals had estimated doses that were clearly higher than the total accumulated recorded dose. The 82 total apparently simple translocations observed in 9722 cells gave a collective estimated dose of 275 mGy (132-496). The mean genomic frequencies (x100 +/- SE) of complete and total apparently simple translocations observed in the group of radiologists (1.91 +/- 0.30 and 2.67 +/- 0.34, respectively) were significantly higher than those observed in a matched control group (0.53 +/- 0.10 and 0.87 +/- 0.13, P < 0.01 in both cases) and in another occupationally exposed matched group (0.79 +/- 0.12 and 1.14 +/-0.14, P < 0.03 and P < 0.01, respectively). The discrepancies observed between the physically recorded doses and the biologically estimated doses indicate that the radiologists did not always wear their dosimeters or that the dosimeters were not always in the radiation field.     

The effects of exposure to different clastogens on the pattern of chromosomal aberrations detected by FISH whole chromosome painting in occupationally exposed individuals

The pattern of chromosomal aberrations (CA) was studied by fluorescence in situ hybridization (FISH) technique (whole chromosomes #1 and #4 painting) in workers occupationally exposed to any of the four following conditions: acrylonitrile (ACN), ethyl benzene (EB), carcinogenic polycyclic aromatic hydrocarbons (c-PAHs), and irradiation in nuclear power plants (NPP), respectively. Decrease in the relative frequency of translocations was observed in EB group, and an increase in reciprocal translocations in ACN and NPP-exposed groups. An increase in a relative number of insertions was registered under all four conditions (significant at ACN, EB, c-PAHs, quasisignificant at NPP-exposed groups). Significant differences in the percentage of lymphocytes with aberrations on chromosome #1 (58.8+/-32.7%, versus 73.8+/-33.6% in the controls, P < 0.05), and chromosome #4 (47.0+/-34.1%, versus 29.4+/-32.2%, P < 0.01) were found in workers exposed to ACN. Similarly, a decrease in the proportion of cells with aberration on chromosome #1 (61.0+/-24.0%, versus 73.8+/-33.6%, P < 0.05) and an increase on chromosome #4 (45.6+/-24.6%, versus 29.4+/-32.2%, P < 0.05) were observed in workers exposed to EB. Frequency of aberrant cells (%AB.C.) as well as genomic frequency of translocations (F(G)/100) increased with age (P < 0.001). Aging also increased the percentage of translocations and reciprocal translocations (P < 0.05), but decreased the relative number of acentric fragments (P < 0.01). Smoking led to significantly increased F(G)/100 (P < 0.05), but did not affect the pattern of chromosomal aberrations. Our results seem to indicate that different carcinogens may induce a different pattern of chromosomal aberrations.     

Induction of chromatid-type aberrations in peripheral lymphocytes of hospital workers exposed to very low doses of radiation

Radiological personnel represent workers exposed to low cumulative doses of radiation. As their surveillance is generally based on physical dosimetry, there is little or inconclusive information on biological effects due to radiation exposure at these doses. We aimed to explore the extent of chromosomal damage in circulating lymphocytes of hospital workers (technicians, nurses and physicians) chronically exposed to a very low level of radiation using conventional and molecular cytogenetic analyses (chromosome painting with chromosomes #2, #3 and #10 as probe cocktail). Compared with controls, exposed workers displayed a significant increase in the frequency of aberrant lymphocytes (1.26+/-0.11/100 cells versus 1.63+/-0.17/100 cells). In particular, exposed technicians showed significantly higher mean values than nurses or physicians (3.68+/-1.17/100 cells versus 1.36+/-0.18/100 cells and 1.36+/-0.09/100 cells, respectively). Interestingly, we found that the chromosomal damage was prevalently expressed as chromatid-type aberrations. Chromosome painting indicated that the frequency of chromosome rearrangements (CR; translocations and dicentrics pooled together) was approximately comparable between radiological workers and the control group. Moreover, we did not detect any significant difference due to radiation exposure when CR rates were considered separately for each of the three chromosomes in the probe cocktail.     

Effect of age and radiation exposure on the frequency of translocations and dicentrics detected by FISH method in human lymphocytes

The frequencies of translocations and dicentrics detected by "chromosome painting" in lymphocytes were estimated in 115 healthy donors and in 273 people exposed to uncontrolled irradiation at low doses 1-4 years ago. Age responses of both types of exchanges at the age range from 3 to 85 years fit to quadratic model. The frequency of translocations grew faster with age than the frequency of dicentrics. The yields of stable exchanges in exposed people was significantly higher than those in control donors of corresponding ages.     

The in vivo dose rate effect of chronic gamma radiation in mice: translocation and micronucleus analyses

The in vivo effects of chronic, ultra low dose rates of gamma radiation in mice were evaluated using fluorescence in situ hybridization and the in vivo micronucleus test. SWR×C57BL/6 mice were divided into nine exposure groups and continuously exposed to 0.5, 2.0 or 4.0 cGy ¹³⁷Cs per day for 30, 60 or 90 days; unexposed control mice were also included. Following exposure, blood samples were taken from each animal and the frequencies of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE) were determined using flow cytometry. Peripheral blood lymphocytes were cultured and analyzed by chromosome painting to determine translocation frequencies. A significant dose rate response was seen in translocations and both MPCE and MNCE. Comparisons were made between the three chronic dose rates and it was determined that there was no significant difference among translocation frequencies for each rate. However, a significant difference was found between the chronic exposures reported here and the fractionated daily exposures reported previously. Dose rate reduction effects, ranging from 3 at low doses to 14 at high doses, were found for chronic versus acute exposures. The possibility of gender effects was investigated in both micronucleus and translocation data. No gender effect was found in translocation induction, but a slight effect was suggested in micronucleus induction.     

Sister-chromatid exchanges and chromosomal aberrations in a population exposed to pesticides

Sister-chromatid exchanges (SCE) and chromosomal aberrations were studied in a population of floriculturists occupationally exposed to organophosphorus, carbamate and organochlorine pesticides. Blood samples from 36 individuals from a community of 154 persons of asiatic origin were obtained. Among the group sampled, 21 individuals exhibited at least one symptom of chronic intoxication. SCE analysis was performed in 14 symptomatic and 13 asymptomatic persons. The asymptomatic group showed a SCE frequency of 5.47 +/- 1.03 and the symptomatic group a frequency of 6.45 +/- 1.19. Comparison between both groups with the Mann-Whitney 'U' test revealed a significant difference (p 0.0409). Case-control analysis of 9 pairs matched by sex and age also showed significant differences between both groups (p 0.0104). In contrast, the frequencies of chromosomal aberrations were not correlated with intoxication symptomatology, though a significant increment of exchange-type aberrations in relation to a group of non floriculturists was observed in the population studied.     

Genetic injury in hybrid male mice exposed to low doses of 60Co gamma-rays or fission neutrons. III. Frequencies of abnormal sperm and reciprocal translocations measured during and following long-term weekly exposures

Male B6CF1 mice were exposed to either fission neutrons or 60Co gamma-rays at once-weekly doses approaching occupational levels for periods up to 60 weeks. Both during and after the irradiation sequence, the mice were screened to determine the incidence of abnormal epididymal sperm and of reciprocal chromosome translocations in metaphase spermatocytes. Abnormal sperm frequencies equilibrated with dose/week by 10 weeks and also showed an additive nonlinear seasonal increment. The relative biological effectiveness (RBE) for these damages is 12 +/- 1. After exposures ended, sperm frequencies in gamma-irradiated mice quickly returned to near-normal levels. Neutron-irradiated males showed a significantly elevated level of abnormalities for approximately 30 weeks--a paradoxical finding--as no clear evidence of cumulative injury was seen during exposure. When assayed at 10 and 25 weeks of exposure but not later, translocation frequencies demonstrated an increment, significant in the neutron series, attributed to irradiated spermatocytes. Dose-response analysis with cumulative dose up to the 60-week maximum gave an RBE of 45 +/- 10. Post exposure, the incidence of translocations subsided slightly, but the RBE remained above 30.     

Cytogenetic monitoring by use of the micronucleus assay among hospital workers exposed to low doses of ionizing radiation

The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation. We used the cytokinesis-block micronucleus (CBMN) assay in the peripheral lymphocytes of 132 exposed workers compared with 69 controls matched for gender, age and smoking habits. The CBMN assay was combined with fluorescence in situ hybridization with a human pan-centromeric DNA probe in 32 exposed subjects and 30 controls randomly chosen from the initial populations. Occupational dosimetry records were collected over the last 10-year period and revealed very low exposure levels. The average binucleated micronucleated cell rate (BMCR) was significantly higher in the exposed subjects than in the controls (14.9 per thousand+/-8.1 versus 11.8 per thousand+/-6.5; P=0.011). About one-third of the micronuclei were centromere-negative in the exposed and control groups. BMCR significantly positively correlated with donor age in the exposed population; this correlation was at the border of significance in the control group. In the two groups, BMCR was significantly greater in females than in males, and the significant correlation between age and BMCR was observed in the female population, but not in the male one. No effect of smoking habits emerged. Univariate analysis revealed a possible influence of familial cancer history and diagnostic medical radiation dose (estimated from examinations reported in the questionnaire) on BMCR. Multiple regression analysis, taking into account all the previous confounding factors, showed that only occupational exposure status, gender and age had a significant effect on BMCR. In conclusion, the present study shows that chromosomal damage leading to micronucleated lymphocytes is more frequent in hospital workers exposed to ionizing radiation than in controls, despite the very low levels of exposure.     

An evaluation of several methods for assessing the effects of occupational exposure to radiation

Several methods for the analysis of occupational radiation exposure data, including procedures based on Cox's proportional hazards model, are presented and evaluated. Issues of interest include the contribution of an external control, the effective handling of highly skewed exposure data, and the potential for detecting effects in populations occupationally exposed to radiation. Expressions for evaluating the power of various procedures are derived and applied to data from the Hanford population in order to determine power curves for detecting leukemia effects, with both additive and multiplicative linear models being used. It is found that the introduction of an external control can increase power, although not when an overall adjustment factor must be estimated from the data or when death rates for the study population are substantially lower than those for the control population. It is also found that very little power is lost if exposures are grouped. Finally, the power calculations indicate, as expected, that in analyses of occupationally exposed populations, such as the Hanford workers, there is very little chance of detecting radiation effects at the levels of our current estimates. However, power is reasonably good for detecting effects that are 10 to 15 times larger.     

Microsporogenesis and meiotic abnormalities in the hybrid complex of Phlomis composita (Lamiaceae)

The extent of chromosome structural differences such as permanent translocations and paracentric inversions has been studied in the hybrid complex of Phlomis composita and its putative parental taxa P. lychnitis and P. crinita . They are detected as meiotic abnormalities during microsporogenesis. In total, 117 plants from 19 populations in Andalusia (southern Spain) and Levante (eastern Spain) were studied for ploidy level, chromosome clumping, multivalent or univalent formation, late bivalent disjunction with bridges, chromatin bridges and fragments, irregular polysporads and variable pollen size. All individuals had the diploid chromosome number 2 n  = 20, with no significant difference in the frequencies of the above meiotic abnormalities either at taxon or population levels. However, very different frequencies were observed on the regional scale between populations in Andalusia and Levante. The results are discussed within the theoretical framework of homoploid hybrid or recombinational speciation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 79−85.     

The micronucleus assay in exfoliated buccal cells: application to occupational exposure to polycyclic aromatic hydrocarbons.

Many polycyclic aromatic hydrocarbons (PAHs) have been identified as cancer-inducing chemicals for animals and/or humans. Also, there is sufficient evidence that exposures in the occupational settings are carcinogenic or probably carcinogenic to human. Engine exhaust and used engine oils are major PAH sources in engine repair workshops and traffic. Analysis of micronucleus (MN) in exfoliated buccal cells is a sensitive method for monitoring genetic damage in human populations. In our study, we used three different occupational groups (Group 1; engine repair workers, Group 2; taxi drivers, Group 3; traffic police) and two controls (Control I for Group 1 and Control II for Group 2 and Group 3) for the exposed groups. We analysed MN frequencies in exfoliated buccal cells and compared the exposed groups (Group 1; n=34, Group 2; n=17, Group 3; n=15) and subjects not occupationally exposed to PAH (Control I; n=28, Control II; n=20). The mean (+/-S.D.) MN (%) frequencies in exfoliated buccal cells from Group 1 and Control I were 0.07+/-0.05 and 0. 05+/-0.04, respectively (p>0.05; Table 2). The mean (+/-S.D.) MN (%) frequencies in exfoliated buccal cells from Group 2, 3 and Control II were 0.12+/-0.05, 0.10+/-0.05 and 0.03+/-0.03, respectively (p<0. 0001, p<0.05; Table 2) Smokers and nonsmokers do not differ with respect to the incidence of MN in all groups.     

Cytogenetic monitoring of industrial radiographers using the micronucleus assay

Industrial radiography is the process of using either gamma-emitting radionuclide sources or X-ray machines to examine the safety of industrial materials. Industrial radiographers are among the radiation workers who receive the highest individual occupational radiation doses. To assess occupationally induced chromosomal damage, we performed the cytokinesis-block micronucleus (CBMN) assay in peripheral lymphocytes of 29 male industrial radiographers, exposed to ionizing radiation for 12.8 years+/-11.2, in comparison with 24 gender-, age-, and smoking habits-matched controls. The CBMN assay was combined with fluorescent in situ hybridization with a pan-centromeric DNA probe in 17 exposed subjects and 17 controls randomized from the initial populations. The mean cumulative equivalent dose, recorded by film dosimeters, was 67.2 mSv+/-49.8 over the past 5 years. The mean micronucleated binucleated cell rate (MCR) was significantly higher in the industrial radiographers than in the controls (10.7 per thousand +/-5.2 versus 6.6 per thousand +/-3.1, P=0.009); this difference was due to a significantly higher frequency of centromere-negative micronuclei (C-MN) in exposed subjects than in controls (8.5 per thousand +/-4.9 versus 2.2 per thousand +/-1.6, P<0.001). The two populations did not significantly differ in centromere-positive micronuclei (C+MN) frequency. These findings demonstrate a clastogenic effect in lymphocytes of industrial radiographers. MCR significantly positively correlated with age in the two groups. After correction for the age effect, MCR did not correlate with duration of occupational exposure. No correlation between radiation doses and MCR, C-MN, and C+MN frequencies was observed. In addition to physical dosimetry records, the enhanced chromosomal damage in lymphocytes of industrial radiographers emphasizes the importance of radiation safety programs.     

The persistence of sister-chromatid exchange frequencies in men occupationally exposed to vinyl chloride monomer.

The persistence of sister-chromatid exchange frequencies in a population occupationally exposed to the well known chemical mutagen vinyl chloride monomer was studied. It was shown that increased values of sister-chromatid exchange frequencies were still present in the lymphocytes of workers who had not been exposed for 8-120 days and retired persons for 5-10 years after exposure. The possible ability of vinyl chloride monomer alkylating metabolites to cause long-lasting damage of the DNA molecule is discussed.     

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay.

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.     

Study of the cytogenetic effects of occupational exposure to pesticides on sanitation workers in Belo Horizonte, Brazil

Sanitation workers handling pesticides in the control of disease vectors constitute an occupationally exposed population to genotoxic substances. The aim of the present study was to investigate the relation between the occupational exposure to various pesticides and the presence of cytogenetic damage. Fifty-nine men were selected (29 sanitation workers and 30 control individuals) with ages varying between 18-57 years who lived and worked in the same area in Belo Horizonte (Brazil). The following parameters were determined for all individuals using the cytokinesis-block micronucleus (MN) assay in peripheral blood lymphocytes: MN/1000 binucleated cells (BC), BC with MN (BCMN)/1000 BC, nucleoplasmic bridges (NB)/1000 BC, apoptotic and necrotic cells/500 cells and nuclear division index. The analysis of covariance showed significantly higher (p < 0.05) mean frequencies of MN (15.81 +/- 1.31 vs 4.71 +/- 0.42), BCMN (15.10 +/- 1.22 vs 4.62 +/- 0.44), NB (4.59 +/- 0.76 vs 1.00 +/- 0.34), and necrotic cells (12.07 +/- 1.45 vs 5.17 +/- 0.70) in the exposed group when compared to the control group. There was no significant difference in the apoptotic cell frequency between the two groups, while the nuclear division index was significantly lower (1.49 +/- 0.02 vs 1.61 +/- 0.02) in the control group. Neither the time of exposure nor the smoking or alcohol drinking habit influenced the cytogenetic parameters examined. According to these results, occupational exposure to pesticides induced genotoxic and cytotoxic effects in sanitation workers.     

Micronuclei in humans induced by exposure to low level of ionizing radiation: influence of polymorphisms in DNA repair genes

Understanding the risks deriving from protracted exposure to low doses of ionizing radiation has remarkable societal importance in view of the large number of work settings in which sources of IR are encountered. To address this question, we studied the frequency of micronuclei (MN), which is an indicator of DNA damage, in a population exposed to low levels of ionizing radiation and in matched controls. In both exposed population and controls, the possible influence of single nucleotide polymorphisms in XRCC1, XRCC3 and XPD genes on the frequency of micronuclei was also evaluated. We also considered the effects of confounding factors, like smoking status, age and gender. The results indicated that MN frequency was significantly higher in the exposed workers than in the controls [8.62+/-2.80 versus 6.86+/-2.65; P=0.019]. Radiological workers with variant alleles for XRCC1 or XRCC3 polymorphisms or wild-type alleles for XPD exon 23 or 10 polymorphisms showed a significantly higher MN frequency than controls with the same genotypes. Smoking status did not affect micronuclei frequency either in exposed workers or controls, while age was associated with increased MN frequency in the exposed only. In the combined population, gender but not age exerted an influence on the yield of MN, being higher in females than in males. Even though there is a limitation in this study due to the small number of subjects, these results suggest that even exposures to low level of ionizing radiation could have genotoxic effects and that XRCC3, XRCC1 and XPD polymorphisms might contribute to the increased genetic damage in susceptible individuals occupationally exposed to chronic low levels of ionizing radiation. For a clear conclusion on the induction of DNA damage caused by protracted exposure to low doses of ionizing radiation and the possible influence of genetic polymorphism in DNA repair genes larger studies are needed.     

Five polymorphisms of the apolipoprotein B gene in healthy Bulgarians

Five APOB polymorphisms (I/D in the promoter region, XbaI [codon 24881, MspI [codon 3611], EcoRI [codon 41541, and 3' VNTRs) were studied in a population sample of 147 healthy normolipemic Bulgarians. For all biallelic loci, the observed genotype distributions do not deviate from Hardy-Weinberg equilibrium. In Bulgaria the insertion allele and the MspI+ allele of APOB presented the highest allelic frequencies (0.793 +/- 0.024 and 0.959 +/- 0.012, respectively) among the European population groups studied so far. The allele frequencies of the other two biallelic polymorphisms (XbaI and EcoRI) found in the Bulgarian population are similar to those previously described in other Caucasian populations. Analysis of the 3' VNTR polymorphism revealed 11 different alleles. Like studies in other Caucasian populations, this study found bimodal allele-size distribution and a high level of heterozygosity. The frequency of allele *31 (0.162 +/- 0.022) among Bulgarians is higher than that of any other European population group studied so far. Genetic distances between Bulgarians and each of six populations from southeastern Europe for which 3' VNTR allele frequencies are available showed an increase in the order: Albanians相似文献   

Aromatic DNA adduct levels in coke oven workers: correlation with polymorphisms in genes GSTP1, GSTM1, GSTT1 and CYP1A1

The aim of this study was to use DNA adducts levels, detected by 32P-postlabelling, as a biomarker to assess human exposure to polycyclic aromatic hydrocarbons (PAHs) from a coke oven plant and explore the possible association between CYP1A1 MspI, GSTP1, GSTM1 and GSTT1 genotypes, and smoking status on bulky DNA adduct formation. A large amount of inter-individual variation in adduct level was observed among workers with the same job and the same smoking habits. No significant differences were observed in DNA adduct levels between the coke oven workers and control group. Smokers in the control group had significantly higher DNA adducts than the non-smokers in the same group (35.13+/-21.11 versus 11.18+/-8.00, per 10(8) nucleotides, P=0.003). In this group, the correlation between the level of DNA adducts and the cigarettes smoked was strongly significant (r=0.70, P<0.0005), but no correlation was found among the coke oven workers. Among non-smokers there was a significant difference between the control group and the coke oven workers (11.18+/-8.00 versus 24.62+/-15.20, per 10(8) nucleotides, P=0.03). These results suggests that tobacco smoke could behave as a confounding factor for evaluation of DNA adducts arising from occupational exposure. The levels of DNA adducts in smokers not occupationally exposed to PAHs is dependent on the polymorphisms CYP1A1 MspI in the 3' non-coding region (49.04+/-22.18 versus 25.85+/-15.87, per 10(8) nucleotides, P<0.05), but no effect was observed for the GST genotypes studied.     

Biological monitoring of workers in the rubber industry. I. Chromosomal aberrations and sister-chromatid exchanges in lymphocytes of vulcanizers

To evaluate the possible genetic consequences of the industrial exposure among the vulcanizers of a rubber plant we measured the in vivo levels of chromosomal aberrations and sister-chromatid exchanges in peripheral lymphocytes of 34 vulcanizers and in an adequate control population. The observed chromosomal aberration frequencies were 1.9 +/- 1.4 aberrations/100 cells in the exposed group and 2.1 +/- 1.5 aberrations/100 cells in the controls. No difference was found between the two groups for the mean value of sister-chromatid exchanges (5.2 +/- 1.3 in the exposed, 5.2 +/- 0.7 in the control group). Cigarette-smoking was clearly associated with increased sister-chromatid exchange frequencies both in the exposed and in the control groups, while chromosomal aberration frequencies were not correlated with smoking habits.     

Retrospective biodosimetry among United States radiologic technologists

Measurement of chromosome translocations in peripheral blood lymphocytes has been used to quantify prior exposure to ionizing radiation, including for workers exposed to low, chronic doses. We assessed translocation frequencies in a subset of U.S. radiologic technologists to substantiate ionizing radiation dose estimates developed for 110,418 technologists who worked between 1916 and 1984. From 3,441 cohort members known to have begun working before 1950, we selected a sample of 152, stratified by estimated cumulative dose, over-sampling from higher-dose categories and excluding persons with a prior cancer diagnosis, a personal or family history of chromosomal instability disorders, or a current history of smoking. Estimates of film-badge dose ranged from less than 10 cSv to more than 30 cSv. Blood samples, obtained in 2004, were analyzed by fluorescence in situ hybridization (FISH) whole chromosome painting by simultaneously labeling chromosomes 1, 2 and 4 in red and 3, 5 and 6 in green. Translocations were scored in 1800 well-spread metaphase cells and expressed per 100 cell equivalents (CE) per person. Linear Poisson regression models with allowance for overdispersion were used to assess the relationship between estimated occupational red bone marrow absorbed dose in cGy and translocation frequency, adjusted for age, gender and estimated red bone marrow absorbed dose score from personal diagnostic procedures. We observed 0.09 excess translocations per 100 CE per cGy red bone marrow dose (95% CI: -0.01, 0.2; P = 0.07), which is similar to the expected estimate based on previous cytogenetic studies (0.05 excess translocations per 100 CE per cGy). Despite uncertainty in the estimates of occupational red bone marrow absorbed doses, we found good general agreement between the doses and translocation frequencies, lending support to the credibility of the dose assessment for this large cohort of U.S. radiologic technologists.