University of California Replacement of Cesium Irradiators with Alternative Technologies

The University of California possesses a large number of Cs irradiators that are used in a wide variety of medical and research applications. The university president made a system-wide decision to reduce the potential threat of malevolent use of Cs by switching wherever feasible to x-ray irradiators over a 3-y period of time. A Radioactive Source Replacement Working Group of involved faculty was formed to study the topic and to make recommendations as to when alternative technologies could offer equivalency. The Working Group concluded that x-ray irradiators could replace Cs irradiators in most applications, with some likely exceptions. They found that the depth dose curve for the 320 kVp x-ray irradiator was found to be nearly identical to that of Cs down to a depth in tissue of 4 cm. It was concluded that x rays (energies ≤320 keV) are more biologically effective than Cs gamma rays, suggesting that lower doses of x rays will be required to achieve the same biological endpoint as Cs gamma rays. A simple conversion factor for equating x-ray effects to Cs effects was not recommended because relative biological effectiveness depends on multiple factors. They concluded that each experiment should be individually calibrated when converting from Cs irradiators to x-ray irradiators. The lessons learned from implementing the project to date have shown the importance of having senior management buy-in, involving the research community in the decision making process and allowing for exceptions where equivalency of Cs to x ray cannot be established.

Characterization of Ivoclar Vivadent Dental Restoration Material for 137CS Retrospective Radiation Dosimetry

Retrospective dosimetry is the method of using materials on or near a person who is exposed to ionizing radiation to determine the amount of radiation received by the person. A possible candidate material for retrospective dosimetry is Ivoclar Vivadent IPS e.max® CAD ceramic dental restoration material, which exhibits radiation-induced thermoluminescence when exposed to gamma- and x-ray radiation from a Cs source. The purpose of this paper is to characterize the material and study the behavior of the thermoluminescence signal with radiation dose and with delay time between radiation exposure and thermoluminescence measurement. The first glow peak is well-modeled by a first-order glow curve deconvolution formula. The height of the first glow peak is approximately linear with dose. The fading of the signal with time is approximately described by a power law curve with cutoff. The material appears to be suitable for retrospective radiation dosimetry.

Screening Internal Contamination of Inhaled and Ingested Radionuclides with Hand-held Survey Meters

During the aftermath of a radiological accident or attack, the rapid identification of individuals who have internalized medically significant amounts of material is paramount to guide medical and public health decisions. This paper explores the utility of hand-held, pancake GM detectors to determine if an individual has inhaled Sr, Cs, Pu, Pu, or Am in quantities requiring treatment. Additionally, ingestion of Sr or Cs was considered. Both Sr and Cs were modeled in equilibrium with their progeny, but the progeny of Pu, Pu, and Am were excluded. Treatment thresholds are defined using the National Council on Radiation Protection & Measurements' (NCRP) clinical decision guides (CDGs). Using Monte Carlo N-Particle (MCNP) modeling software, a human phantom and detector were modeled to determine the activity required to achieve a detector reading of twice background 1, 7, or 30 d post-ingestion or post-inhalation. Modeling found that inhaled Pu, Pu, and Am are detectable only if the contaminated individual inhaled thousands-fold more material than the CDG. This lack of detectability means that hand-held GM detectors are inappropriate for initial screening for americium or plutonium and that more intensive screening is necessary to confirm suspected contamination. Cesium-137, by contrast, could be detected at levels 10- to 100-fold lower than the amount requiring treatment, allowing quick differentiation between contaminated and uncontaminated individuals. Surprisingly, Sr was detectable within a factor of 2 of the amount requiring treatment. Detection of Sr was due primarily to bremsstrahlung radiation from beta interactions with calcium in bone. While rapid screening could identify individuals contaminated by Cs and possibly with Sr, further screening of identified individuals is necessary to establish medical need. However, these contaminated individuals could still be prioritized for further testing and possible presumptive treatment. Based on the findings of this study, concepts of operation for the use of hand-held survey meters should be developed for the screening of individuals potentially internally contaminated with Cs and Sr.

Biological characterization of a novel in vitro cell irradiator

To evaluate the overall robustness of a novel cellular irradiator we performed a series of well-characterized, dose-responsive assays to assess the consequences of DNA damage. We used a previously described novel irradiation system and a traditional ¹³⁷Cs source to irradiate a cell line. The generation of reactive oxygen species was assessed using chloromethyl-H₂DCFDA dye, the induction of DNA DSBs was observed using the comet assay, and the initiation of DNA break repair was assessed through γH2AX image cytometry. A high correlation between physical absorbed dose and biologic dose was seen for the production of intracellular reactive oxygen species, physical DNA double strand breaks, and modulation of the cellular double stand break pathway. The results compared favorably to irradiation with a traditional ¹³⁷Cs source. The rapid, straightforward tests described form a reasonable approach for biologic characterization of novel irradiators. These additional testing metrics go beyond standard physics testing such as Monte Carlo simulation and thermo-luminescent dosimeter evaluation to confirm that a novel irradiator can produce the desired dose effects in vitro. Further, assessment of these biological metrics confirms that the physical handling of the cells during the irradiation process results in biologic effects that scale appropriately with dose.

[Impact of Radioactive Elements on Microbial Complexes in Cryogenic Soils of Yakutia]

It has been found that microorganisms in cryogenic soils of Yakutia are resistant to the long-term impact of cesium and thorium. The number of microorganisms in the studied ecological-trophic groups does not depend on the concentrations of radioactive elements. Differences in the number of microorganisms are determined by the physicochemical conditions that are created in different horizons of the soils studied. The long-term impact of radiation (for 36 and 66 years) on microorganisms inhabiting the permafrost soils of Yakutia has developed their adaptive capacity to high concentrations of these radioactive elements.

Comparison of Cesium-137 and X-ray Irradiators by Using Bone Marrow Transplant Reconstitution in C57BL/6J Mice

Mice are used extensively in transplantation studies involving bone marrow ablation. Due to the increasing security issues and expenses involved with γ irradiators, self-contained X-ray irradiators have been increasing in popularity. We hypothesized that bone marrow ablation by irradiation of mice with a (137)Cs irradiator would be comparable to that from an X-ray source irradiator. A lethal-dose curve was obtained by irradiating C57BL/6J mice with 500, 700, 900, and 1100 cGy from either source. These data were used to determine the lethal radiation exposure range for a noncompetitive bone marrow engraftment curve for each source. At 90 d after reconstitution, the bone marrow engraftment curves revealed significant differences between the 2 sources in the establishment of B cell, myeloid, and T cell lineages. Murine B cell reconstitution after exposure to a (137)Cs source was greater than that after X-ray exposure at each dose level, whereas the converse was true for myeloid cell reconstitution. At the 1050- and 1100-cGy doses, mice irradiated by using the X-ray source demonstrated higher levels of T cell reconstitution but decreased survival compared with mice irradiated with the (137)Cs source. We concluded that although both sources ablated endogenous bone marrow sufficiently to enable stem cell engraftment, there are distinct physiologic responses that should be considered when choosing the optimal source for use in a study and that irradiation from the (137)Cs source was associated with lower overall morbidity due to opportunistic infection.

Considerations on the ICRP model predictions of the transfer of (137)Cs from food to the milk and urine of lactating mothers

A recent work has shown that the current ICRP biokinetic model for the transfer of caesium radionuclides from food to human breast milk was able to describe with satisfactory accuracy (137)Cs activity concentrations in human breast samples collected a few weeks after the Chernobyl accident as well as in samples collected some years later. However, systematic discrepancies were observed for the predictions of the activity concentrations in urine samples. In the present work, modifications to the model were investigated with the aim of improving the agreement between model predictions and data. It turned out that the disagreement for the urine data was ascribable to the mathematical simplifications used by the ICRP to describe urinary excretion in the first few days after delivery. However, the predictive performances of the model remained unchanged even when differences in the bioavailability of caesium from the ingested food types were considered or metabolic interactions between caesium and potassium were introduced into the model formulation.

Reconstruction of long-lived radionuclide intakes for Techa riverside residents: 137Cs

Radioactive contamination of the Techa River (Southern Urals, Russia) occurred from 1949-1956 due to routine and accidental releases of liquid radioactive wastes from the Mayak Production Association. The long-lived radionuclides in the releases were Sr and Cs. Contamination of the components of the Techa River system resulted in chronic external and internal exposure of about 30,000 residents of riverside villages. Data on radionuclide intake with diet are used to estimate internal dose in the Techa River Dosimetry System (TRDS), which was elaborated for the assessment of radiogenic risk for Techa Riverside residents. The Sr intake function was recently improved, taking into account the recently available archival data on radionuclide releases and in-depth analysis of the extensive data on Sr measurements in Techa Riverside residents. The main purpose of this paper is to evaluate the dietary intake of Cs by Techa Riverside residents. The Cs intake with river water used for drinking was reconstructed on the basis of the Sr intake-function and the concentration ratio Cs-to-Sr in river water. Intake via Cs transfer from floodplain soil to grass and cows' milk was evaluated for the first time. As a result, the maximal Cs intake level was indicated near the site of releases in upper-Techa River settlements (8,000-9,000 kBq). For villages located on the lower Techa River, the Cs intake was significantly less (down to 300 kBq). Cows' milk was the main source of Cs in diet in the upper-Techa River region.

The metabolomic approach identifies a biological signature of low-dose chronic exposure to cesium 137

Reports have described apparent biological effects of (137)Cs (the most persistent dispersed radionuclide) irradiation in people living in Chernobyl-contaminated territory. The sensitive analytical technology described here should now help assess the relation of this contamination to the observed effects. A rat model chronically exposed to (137)Cs through drinking water was developed to identify biomarkers of radiation-induced metabolic disorders, and the biological impact was evaluated by a metabolomic approach that allowed us to detect several hundred metabolites in biofluids and assess their association with disease states. After collection of plasma and urine from contaminated and non-contaminated rats at the end of the 9-months contamination period, analysis with a LC-MS system detected 742 features in urine and 1309 in plasma. Biostatistical discriminant analysis extracted a subset of 26 metabolite signals (2 urinary, 4 plasma non-polar, and 19 plasma polar metabolites) that in combination were able to predict from 68 up to 94% of the contaminated rats, depending on the prediction method used, with a misclassification rate as low as 5.3%. The difference in this metabolic score between the contaminated and non-contaminated rats was highly significant (P = 0.019 after ANOVA cross-validation). In conclusion, our proof-of-principle study demonstrated for the first time the usefulness of a metabolomic approach for addressing biological effects of chronic low-dose contamination. We can conclude that a metabolomic signature discriminated (137)Cs-contaminated from control animals in our model. Further validation is nevertheless required together with full annotation of the metabolic indicators.

Influence on the mouse immune system of chronic ingestion of 137Cs

The aim of this work was to determine the possible occurrence of damage to the immune system during the course of chronic ingestion of (137)Cs. BALB/C mice were used, with (137)Cs intake via drinking water at a concentration of 20 kBq l(-1). Adults received (137)Cs before mating and offspring were sacrificed at various ages between birth and 20 weeks. Phenotypic analysis of circulating blood cells and thymocytes did not show any significant modification of immune cell populations in animals ingesting (137)Cs as compared with control animals, with the exception of a slight increase in Treg percentage at the age of 12 weeks. Functional tests, including proliferative response to mitogens such as phytohaemagglutinin, response to alloantigens in mixed lymphocyte reaction and immunoglobulin response to vaccine antigens such as tetanus toxin and keyhole limpet haemocyanin did not show any significant functional modification of the immune system in (137)Cs-ingesting animals as compared with control animals. Overall, our results suggest that chronic ingestion of a low concentration of (137)Cs in drinking water in the long term does not have any biologically relevant effect on the immune system.

Reconstruction of radiation doses in a case-control study of thyroid cancer following the Chernobyl accident

A population-based case-control study of thyroid cancer was carried out in contaminated regions of Belarus and Russia among persons who were exposed during childhood and adolescence to fallout from the Chernobyl accident. For each study subject, individual thyroid doses were reconstructed for the following pathways of exposure: (1) intake of 131I via inhalation and ingestion; (2) intake of short-lived radioiodines (132I, 133I, and 135I) and radiotelluriums (131mTe, 132Te) via inhalation and ingestion; (3) external dose from radionuclides deposited on the ground; and (4) ingestion of 134Cs and 137Cs. A series of intercomparison exercises validated the models used for reconstruction of average doses to populations of specific age groups as well as of individual doses. Median thyroid doses from all factors for study subjects were estimated to be 0.37 and 0.034 Gy in Belarus and Russia, respectively. The highest individual thyroid doses among the subjects were 10.2 Gy in Belarus and 5.3 Gy in Russia. Iodine-131 intake was the main pathway for thyroid exposure. Estimated doses from short-lived radioiodines and radiotelluriums ranged up to 0.53 Gy. Reconstructed individual thyroid doses from external exposure ranged up to 0.1 Gy, while those from internal exposure due to ingested cesium did not exceed 0.05 Gy. The uncertainty of the reconstructed individual thyroid doses, characterized by the geometric standard deviation, varies from 1.7 to 4.0 with a median of 2.2.

Distribution of 137Cs in rat tissues after various schedules of chronic ingestion

The aim of this work was to compare the distribution of 137Cs in organisms after chronic ingestion following different schedules. Rats were contaminated through drinking water containing 6,500 Bq L(-1) of 137Cs, starting either at birth, at weaning, or upon reaching adult age (13 wk). Animals were then sacrificed after different durations of ingestion. 137Cs content of organs and excreta were determined by gamma counting. A slight decrease in 137Cs elimination through urine was observed according to the age of animals. All organs tested showed similar 137Cs content, with the exception of striated muscles and the thyroid at certain ages, which showed the highest accumulation of 137Cs. The lowest 137Cs concentration was found in the blood, which acts as a transfer compartment after absorption in the intestine. Substructures of the central nervous system showed a homogeneous level of 137Cs accumulation, except for the olfactive bulbs. In these structures, an increased concentration of 137Cs was observed, suggesting a possible direct route of intake through the nasal epithelium. Overall, these results are in agreement with current models for the biokinetics of 137Cs. However, these results also suggest that the thyroid should be taken into account in future models of 137Cs biokinetics.

Hepatic cholesterol metabolism following a chronic ingestion of cesium-137 starting at fetal stage in rats

The Chernobyl accident released many radionuclides in the environment. Some are still contaminating the ground and thus the people through dietary intake. The long-term sanitary consequences of this disaster are still unclear and several biological systems remain to be investigated. Cholesterol metabolism is of particular interest, with regard to the link established between atherosclerosis and exposure to high-dose ionizing radiations. This study assesses the effect of cesium-137 on cholesterol metabolism in rats, after a chronic exposure since fetal life. To achieve this, rat dams were contaminated with cesium-137-supplemented water from two weeks before mating until the weaning of the pups. Thereafter, the weaned rats were given direct access to the contaminated drinking water until the age of 9 months. After the sacrifice, cholesterol metabolism was investigated in the liver at gene expression and protein level. The cholesterolemia was preserved, as well as the cholesterol concentration in the liver. At molecular level, the gene expressions of ACAT 2 (a cholesterol storage enzyme), of Apolipoprotein A-I and of RXR (a nuclear receptor involved in cholesterol metabolism) were significantly decreased. In addition, the enzymatic activity of CYP27A1, which catabolizes cholesterol, was increased. The results indicate that the rats seem to adapt to the cesium-137 contamination and display modifications of hepatic cholesterol metabolism only at molecular level and within physiological range.

An empirical multivariate log-normal distribution representing uncertainty of biokinetic parameters for 137Cs

A simplified biokinetic model for (137)Cs has six parameters representing transfer of material to and from various compartments. Using a Bayesian analysis, the joint probability distribution of these six parameters is determined empirically for two cases with quite a lot of bioassay data. The distribution is found to be a multivariate log-normal. Correlations between different parameters are obtained. The method utilises a fairly large number of pre-determined forward biokinetic calculations, whose results are stored in interpolation tables. Four different methods to sample the multidimensional parameter space with a limited number of samples are investigated: random, stratified, Latin Hypercube sampling with a uniform distribution of parameters and importance sampling using a lognormal distribution that approximates the posterior distribution. The importance sampling method gives much smaller sampling uncertainty. No sampling method-dependent differences are perceptible for the uniform distribution methods.

Reconstruction and forecast of doses due to ingestion of 137Cs and 90Sr after the Chernobyl accident

The assessment doses due to ingestion of (137)Cs and (90)Sr for the population suffering from the Chernobyl accident was performed on the basis of the new mechanistic ecological model for assessment of radiological consequences of agricultural lands contamination (EMARC). The EMARC model allows estimation of internal doses based on ecological factors influencing the contamination of foodstuff, for the post-accidental years in the countries of the former Soviet Union. The EMARC model allows estimation of all quantities required in radiation hygiene practice. For example, the proposed analytical method may be used for both retrospective dose reconstruction and prospective estimates of annual dose and integrated "life-time" dose, for different age intervals. According to the EMARC model, estimated reference "life-time" doses for adults are between 7 and 269 microSv kBq(-1) m(2) for (137)Cs, and between 25 and 235 microSv kBq(-1) m(2) for (90)Sr. Maximal doses were estimated for persons who were 3, 9 and 11 years old, at the time of the accident and these doses exceed those for adults by a factors of 1, 5 for (90)Sr, and 1.4 for (137)Cs.

Effects of chronic 137Cs ingestion on barrier properties of jejunal epithelium in rats

Environmental contamination by 137Cs is of particular public health interest because of the various sources of fallout originating from nuclear weapons, radiological source disruptions, and the Chernobyl disaster. This dispersion may lead to a chronic ecosystem contamination and subsequent ingestion of contaminated foodstuffs. The aim of this study was to thus determine the impact of a chronic ingestion of low-dose 137Cs on small intestine functions in rats. The animals received 150 Bq per day in drinking water over 3 mo. At these environmental doses, 137Cs contamination did not modify the crypt and villus architecture. In addition, epithelial integrity was maintained following the chronic ingestion of 137Cs, as demonstrated by histological analyses (no breakdown of the surface mucosa) and electrical transepithelial parameters (no change in potential difference and tissue conductance). Furthermore, cesium contamination seemed to induce contradictory effects on the apoptosis pathway, with an increase in the gene expression of Fas/FasL and a decrease in the apoptotic cell number present in intestinal mucosa. No marked inflammation was observed following chronic ingestion of 137Cs, as indicated by neutrophil infiltration and gene expression of cytokines and chemokines. Results indicated no imbalance in the Th1/Th2 response induced by cesium at low doses. Finally, evaluation of the functionality of the jejunal epithelium in rats contaminated chronically with 137Cs did not demonstrate changes in the maximal response to carbachol, nor in the cholinergic sensitivity of rat jejunal epithelium. In conclusion, this study shows that chronic ingestion of 137Cs over 3 mo at postaccidental doses exerts few biological effects on the epithelium of rat jejunum with regard to morphology, inflammation status, apoptosis/proliferation processes, and secretory functions.

AFCF and clinoptilolite use in reduction of (137)Cs deposition in several days' contaminated broiler chicks

The objective of this study was to investigate the binding efficiency of AFCF and clinoptilolite, mixed to the feed and administered orally using gastric tube to chronically (137)Cs alimentary contaminated broiler chicks. Seventy-five male Hybro broiler chicks, between 35 and 47 days of age were divided into five groups (15 birds per group) reared in cages (five birds in a cage) and fed a standard diet. Every day during 13 days of the experimental period all chicks received orally 1 ml CsCl water solution with activity of 1310 Bq ml(-1)(137)Cs (gastric tube). Group 1 was the control group and received no binders. The experimental groups received the binders. Group 2 received 0.2 g of AFCF in the form of water solution (gastric tube); group 3 received 0.2% AFCF in the feed; group 4 received 2g clinoptilolite in the form of water suspension (gastric tube) and group 5 received 2% clinoptilolite in the feed. Five chicks from each group were sacrificed on days 4, 10 and 13 of the experimental period. Using gamma spectrometric methods specific activity of (137)Cs was determined in the samples of breast meat, liver and gizzard. The results obtained showed that administering binders to the chronically contaminated broiler chicks significantly (p<0.01) reduced (137)Cs transfer and deposition in breast meat, liver and gizzard. Decreasing deposition of (137)Cs in breast meat and internal organs increased with time of contamination and binders' administration. With AFCF as a cesium binder, on day 13 of measuring the (137)Cs activity in breast meat was 80-83% lower than that in the control group, 89% in liver and 83-84% in gizzard. Natural clinoptilolite demonstrated lower binding efficiency. On day 13 of measuring the (137)Cs activity in breast meat was 53-69% lower than that in the control group, 67-60% in liver and 59-71% in gizzard.

The transfer of radiocaesium to ewes through a breeding cycle--an illustration of the pitfalls of the transfer coefficient

A study to measure the transfer of radiocaesium to adult female sheep through a breeding cycle is described. The transfer of radiocaesium from the diet to muscle (estimated as the equilibrium transfer coefficient) was significantly lower to pregnant, and especially lactating, animals compared to non-lactating and barren animals. High dry matter intake rates were also associated with significantly lower transfer coefficients. Known relationships between dry matter intake rates and protein turnover could credibly explain some of these differences. However, when described as the concentration ratio, radiocaesium transfer to meat was apparently highest during lactation. The apparent difference in results obtained by the two approaches of determining transfer is the consequence of daily dry matter intake being a denominator within the estimation of transfer coefficient. A wider discussion of transfer coefficients and concentration ratios leads us to suggest that the concentration ratio is the more robust and potentially generic parameter.

Increase of regional total cancer incidence in north Sweden due to the Chernobyl accident?

STUDY OBJECTIVE

Is there any epidemiologically visible influence on the cancer incidence after the Chernobyl fallout in Sweden?

DESIGN

A cohort study was focused on the fallout of caesium-137 in relation to cancer incidence 1988-1996.

SETTING

In northern Sweden, affected by the Chernobyl accident in 1986, 450 parishes were categorised by caesium-137 deposition: < 3 (reference), 3-29, 30-39, 40-59, 60-79, and 80-120 kiloBecquerel/m(2).

PARTICIPANTS

All people 0-60 years living in these parishes in 1986 to 1987 were identified and enrolled in a cohort of 1 143 182 persons. In the follow up 22 409 incident cancer cases were retrieved in 1988-1996. A further analysis focused on the secular trend.

MAIN RESULTS

Taking age and population density as confounding factors, and lung cancer incidence in 1988-1996 and total cancer incidence in 1986-1987 by municipality as proxy confounders for smoking and time trends, respectively, the adjusted relative risks for the deposition categories were 1.00 (reference < 3 kiloBecquerel/m(2)), 1.05, 1.03, 1.08, 1.10, and 1.21. The excess relative risk was 0.11 per 100 kiloBecquerel/m(2) (95% CI 0.03 to 0.20). Considering the secular trend, directly age standardised cancer incidence rate differences per 100 000 person years between 1988 to 1996 and the reference period 1986-1987, were 30.3 (indicating a time trend in the reference category), 36.8, 42.0, 45.8, 50.1, and 56.4. No clear excess occurred for leukaemia or thyroid cancer.

CONCLUSIONS

Unless attributable to chance or remaining uncontrolled confounding, a slight exposure related increase in total cancer incidence has occurred in northern Sweden after the Chernobyl accident.

Short-term distribution of 134Cs in relation to 51Cr-EDTA after intravenous dose in goats

AIM

The aim of this study was to gather information about the short-term rate of caesium uptake (incorporation) in different animal tissues and explain them with known physiological mechanisms affecting ion distribution.

METHODS

Six goats were given an intravenous bolus containing (134)Cs as a tracer and (51)Cr-EDTA as an extracellular marker. After 30 min, the animals were killed and the activity concentration of radioactive isotopes in different tissues and fluid compartments were measured.

RESULTS

The highest relative activity concentration of (134)Cs was found in kidney cortex, with a tissue/plasma-ratio around 50. In urine, the ratio varied between 5 and 28. In the salivary gland, cardiac muscle and small intestine the ratio was around 11, 7 and 6, respectively. The contents of small intestine had an average activity concentration five times that of plasma. In skeletal muscle the terminal activity concentration was surprisingly low, with a tissue/plasma ratio mostly far less than unity. Even in connective tissue and cartilage the terminal activity concentration was generally higher than in skeletal muscle.

CONCLUSION

The rate of uptake of caesium varies widely from tissue to tissue. Many of these differences can be explained with differences in Na,K-ATPase activity. Also, perfusion and accessibility play a role in some tissues, like brain and possibly part of the skeletal muscles. The short-term distribution of caesium differs distinctly from the long-term distribution reported in literature.

[Contamination of the food chain with caesium-137 and strontium-90 in Switzerland]

One task of the field physiology of nutrition is the monitoring of the quality of feedstuffs. Rations may consequently be prepared with unadulterated components. This review uses the example of contamination with the radionuclides caesium-137 und strontium-90 and shows how these two unwanted substances reach the end host via the food chain and how their untoward effects are expressed in animals and humans. The extent of the contamination with artificial radioactivity is followed with periodical measurements according to the program of the Division for Radiological Protection of the Swiss Federal Office of Public Health. The interpretation of the measurements and the directives of this division are designed to protect primarily human health, but also that of animals.

Reduction of radiocaesium transfer to broiler chicken meat by the hexacyanoferrate-cellulose binder "Bifezh"

The influence of Bifezh (a hexacyanoferrate compound as veterinary feed additive) on the transfer of (137)Cs to meat was investigated in broiler chickens after application of an artificially contaminated feed mixture. The reduction factors reached 2.23 and 8.46 for single and multiple (137)Cs administration, respectively. The elimination rate of (137)Cs in the decontamination period was only slightly increased by Bifezh. The reduction effect of Bifezh was considerably and positively limited by various amounts of the additive during both radiocaesium accumulation and decontamination. No significant differences in the reduction effect between breast and thigh meat were observed. In conclusion, the hexacyanoferrate-cellulose binder Bifezh can be recommended as an alternative chemical measure for reducing (137)Cs contamination of broiler chicken meat, although administration rates may need to be enhanced over those currently recommended.

Absorption, retention and tissue distribution of radiocaesium in reindeer: effects of diet and radiocaesium source

Radiocaesium absorption and retention in reindeer (Rangifer tarandus) calves was compared in groups fed diets containing different proportions of lichen and concentrates, and different chemical forms of radiocaesium ((134)CsCl in solution or fallout from the Chernobyl accident). Daily intakes of fallout radiocaesium were 15-23 kBq, while daily intakes of (134)CsCl ranged from 70 kBq to 1,160 kBq. The half-life for radiocaesium in red blood cells (RBC) in animals fed with a pure lichen diet exceeded that in animals fed with a combined diet of lichen and concentrates by 40% (17.8+/-0.7 days vs. 12.7+/-0.4 days). Corresponding differences in the half-lives for urinary and faecal excretion were about 60% and 40%, respectively. Transfer coefficients (F(f)) to reindeer meat were estimated to be 0.25+/-0.01 days kg(-1) for fallout radiocaesium and 1.04+/-0.03 days kg(-1) for (134)CsCl, reflecting differences in both radiocaesium bioavailability and retention. The bioavailability of the Chernobyl radiocaesium in lichen in 1988 was estimated at ca. 35% compared to (134)CsCl.

Caesium(137) implant as sole radiation therapy for operable breast cancer: a phase II trial

BACKGROUND AND PURPOSE

Clinical trials have indicated the need for irradiation of the tumour-bearing quadrant in patients with operable breast cancer treated by conservation therapy even under circumstances where there has been complete pathologic clearance. The aim of this phase II trial was to replace whole breast irradiation with brachytherapy to the tumour bed.

PATIENTS AND METHODS

A series of 50 patients with operable breast cancers measuring <==4 cm diameter were treated by combination therapy comprising tumour excision axillary clearance and synoperative insertion of a rigid implant to the tumour bed. The implant was after-loaded with medium dose rate Cs(137) sources giving a dose of 45 Gy in daily four fractions of about 6 h duration. No external beam radiotherapy was given.

RESULTS

After a median follow-up of 6.3 years, of the 49 evaluable patients, 80% were alive without relapse. Of the 9 patients (18%) who developed a breast relapse, the site of recurrence was in the index quadrant in 7 cases (78%). Of the series, 26 (81%) gave a subjective rating of cosmetic outcome which was excellent or good. Objectively the treated breast was deemed to be normal in 11 (42%) and abnormal in 15 (58%).

CONCLUSIONS

This phase II study suggests that in a selected group of patients with early breast cancer, external whole breast radiotherapy can be replaced by interstitial irradiation to the tumour bed without compromising local disease control and giving an excellent or good cosmetic outcome in the majority of cases.

Concentrations of 137Cs and 40K in mushrooms consumed in Japan and radiation dose as a result of their dietary intake

Mushrooms are known to accumulate radiocesium. To estimate the intake of radiocesium through the eating of mushrooms, about 30 samples belonging to 4 commonly consumed species (Lentinula edodes, Hypsizigus marmoreus, Grifola frondosa, and Tricholoma matsutake), were analyzed for (137)Cs and (40)K. The concentration ranges were 0.060-29 Bq kg(-1) (wet wt) for (137)Cs and 38-300 Bq kg(-1) (wet wt) for (40)K. The geometric mean concentration for (137)Cs was 0.56 Bq kg(-1) (wet wt), and the mean concentration for (40)K was 92 Bq kg(-1) (wet wt). The (137)Cs concentrations in L. edodes cultivated in mushroom beds (sawdust-rice bran media) were lower than those cultivated on bed logs (natural wood with bark). The annual intake of (137)Cs per person through mushrooms was calculated, by using the current analytical results and food consumption data in Japan, to be 3.1 Bq for (137)Cs, which is about 28% of the total dietary intake of this nuclide. The effective dose equivalent of (137)Cs through mushrooms was estimated to be 4.0 currency 10(-8) Sv, which is about the half the value obtained in our previous study. The decrease of the (137)Cs intake through mushrooms is probably related to changes in cultivation methods in recent years, from the use of bed logs to mushroom beds.

Uncertainties in dose coefficients from ingestion of 131I, 137Cs, and 90Sr

Quantification of uncertainties in doses from intakes of radionuclides is important in risk assessments and epidemiologic studies of individuals exposed to radiation. In this study, the uncertainties in the doses per unit intake (i.e., dose coefficients) for ingestion of 131I, 137Cs, and 90Sr by healthy individuals have been determined. Age-dependent thyroid dose coefficients were derived for 131I. The analysis for 131I uses recent measurements of thyroid volume obtained by ultrasonography, which indicate a thyroid mass lower than that previously obtained using autopsy measurements. The coefficients for 137Cs are determined using the relationship between the biological half-lives and the amount of potassium in the human body. The most recent International Commission on Radiological Protection biokinetic model was employed to determine the uncertainties for 90Sr. For 137Cs and 90Sr, the dose coefficients represent exposure in adulthood and they were determined for all organs of radiological importance. The uncertainty in the estimated dose coefficients represent state of knowledge estimates for a reference individual, and they are described by lognormal distributions with a specified geometric mean (GM) and geometric standard deviation (GSD). The estimated geometric means vary only slightly from the dose coefficients reported by ICRP publications. The largest uncertainty is observed in the dose coefficients for bone surface (GSD = 2.6), and red bone marrow (GSD = 2.4) in the case of ingestion of 90Sr. For most other organs, the uncertainty in the 90Sr dose coefficients is characterized by a GSD of 1.8 (or less for some organs). For 131I, the uncertainty in the thyroid dose coefficients is well represented by a GSD of 1.7 for both sexes and all ages other than infants for whom a GSD of 1.8 is more appropriate. The lowest uncertainties are obtained for the dose coefficients from ingestion of 137Cs (GSD = 1.24 for males; 1.4 for females). A dominant source of uncertainty in the ingestion dose coefficients is the variation of the biokinetic parameters. For 131I, the largest contribution to the uncertainty comes from the variation in the thyroid mass, but the contribution of the biokinetic parameters is comparable. The biokinetic parameters with the largest contribution to the uncertainty are (a) the fractional uptake from blood to thyroid in the case of ingestion of 131I, (b) the absorbed fraction from the gastrointestinal tract (f1) in the case of 90Sr, and (c) the amount of potassium in the body for 137Cs. The contribution to the uncertainty of the absorbed fraction (which accounts for the fraction of energy deposited in the target organ) is the smallest contributor to the uncertainty in the dose coefficients for most organs. To reduce the uncertainty in the dose estimated for a real individual, one should determine the above-mentioned parameters for the specified individual rather than to rely on assumptions for a reference individual.

Effect of U and 137Cs chronic contamination on dopamine and serotonin metabolism in the central nervous system of the rat

Following the Chernobyl accident, the most significant problem for the population of the former Soviet Union for the next 50-70 years will be chronic internal contamination by radionuclides. One of the few experiments carried out in this field reported that neurotransmitter metabolism in the central nervous system of the rat was disturbed after feeding with oats contaminated by 137Cs for 1 month. The present study assessed the effect of chronic contamination by depleted U or 137Cs on the metabolism of two neurotransmitters in cerebral areas of rats. Dopamine and serotonin were chosen because their metabolism has been shown to be disturbed after external irradiation, even at moderate doses. Dopamine, serotonin, and some of their catabolites were measured by high-pressure liquid chromatography coupled with an electrochemical detector in five cerebral structures of rats contaminated over a 1-month period by drinking water (40 mg U·L–1 or 6500 Bq 137Cs·L–1). In the striatum, hippocampus, cerebral cortex, thalamus, and cerebellum, the dopamine, serotonin, and catabolite levels were not significantly different between the control rats and rats contaminated by U or 137Cs. These results are not in accordance with those previously described.Key words: uranium, caesium, dopamine, serotonin, HPLC.

[Radioactivity for 137Cs, 125I, 131I, 59Fe, y 57Co windows from foods included in the basic alimentary basket and in the water, consumed in the state of Carabobo, Venezuela]

One of the input ways of radionucleids into the organism is through food intake. The aim of the present study is to measure the radioactivity levels in food and water samples within energy windows corresponding to 137Cs, 125I, 131I, 59Fe, and 57Co. Samples were taken from local and imported food belonging to the venezuelan basic alimentary basket and included: beef meat, hen egg, chicken bone, tomato, black bean, rice, powder milk from local dealers or imported from Italy and New Zeeland, potable water from the Valencia city aqueduct and bottled water from local sources or imported from Portugal. Radioactivity was measured with a well type Nal (TI) scintillation counter. Analyzed foods and water presented levels lower than the minimal detectable activity for 137Cs, 131I, 59Fe, 57Co, but it was detected in the Valencia city aqueduct water and in bottled water imported from Portugal, levels greater than the minimal detectable activity for the 125I energy window. These results strongly suggest the need of repeated multienergy windows monitoring of radioactivity of basic alimentary basket foods and potable water.

Activity levels of 137Cs and 40K in the skin and the cutaneous organs of a cow

We have performed an extensive study to determine the activity distributions of radiocesium (137Cs) and of the radioisotope 40K of potassium in the whole body of a cow. ICRP assumes that cesium and potassium are distributed homogeneously throughout the whole body of an organism. The current investigation measured concentrations of 137Cs and 40K in components of the skin, horns, and hooves of a cow. Activity levels of 137Cs were caused by the long-term ingestion following the Chernobyl fallout, whereas the naturally occurring potassium (40K) is an essential part of cow's normal diet. The cow was born at the time of the fallout following the Chernobyl accident and had ingested heavily contaminated forage during its entire lifetime. Activities of 137Cs and 40K were determined simultaneously by gamma spectrometry. All activities are related to the day of slaughter and include also corrections for self attenuation of photons caused by the different densities of the samples. Radionuclide concentrations in samples were corrected for moisture losses incurred during freezing and sample preparation. Surface contamination on the skin was estimated by rinsing it in heated water followed by removal of the epidermis and hair. In comparison with the activities of the components of the skin we observed a considerable amount of external contamination on the surface of the skin. But with respect to whole body countings of the animal this amount of external contamination appears to be negligible. It was found that activity ratios of 137Cs to 40K are greater than 1 in all measured components. The average activity concentrations of 137Cs and 40K in the common integument are 23.3 Bq kg(-1) and 13.3 Bq kg(-1), respectively. The highest activity concentrations of 137Cs and 40K were measured in clean hair and hypodermis. Despite being its largest organ, the cow's skin contains probably less than 1% of the animal's whole body 137Cs activity.

Validation of biokinetic models of Cs and I using their daily dietary intakes and organ contents in an adult Indian population

The daily dietary intakes and total contents of Cs and I in skeletal muscle and thyroid, respectively, for an average Indian adult were estimated by determining their concentrations in the total cooked diet and tissue samples using instrumental neutron activation analysis. These data were then used to predict the biological half-lives of Cs and I and their radioactive counterparts for the Reference Indian Man. The predicted biological half-lives of Cs and I for Reference Indian Man were found to be comparable with the reported values for the ICRP Reference Man.

Review of methods and computer codes for interpretation of bioassay data

Internal dose determination is an essential component of individual monitoring programmes for workers or members of the public exposed to radionuclides, and methods and computer programs are required for dose assessment. A recent international European Radiation Dosimetry Group (EURADOS) intercomparison has shown unacceptably large ranges in the results assessment. An ICRP working party has been initiated to consider what guidance ICRP can give on the use of models and interpret bioassay data in terms of intake/dose. In this field, six codes for bioassay data interpretation, which implement the current ICRP publication 78 biokinetic models, have been reviewed against several criteria with different levels of importance: minor criteria such as the practical use of the code and the graphical capabilities, and major criteria such as the choice of available parameters, peculiarities of data fitting and interpretation, the choice of biokinetic models and the use of uncertainties. All these criteria were assessed using one artificial set of data and two examples extracted from the previous international EURADOS intercomparison.

Effects of low chronic doses of ionizing radiation on antioxidant enzymes and G6PDH activities in Stipa capillata (Poaceae)

Stipa capillata (Poaceae) seeds were harvested from a control area (displaying a gamma dose rate of 0.23 micro Sv h(-1)) (C plants) and from two contaminated areas (5.4 and 25 micro Sv h(-1)) on the Semipalatinsk nuclear test site (SNTS) in Kazakhstan. The plants were grown for 124 d in a greenhouse under controlled conditions and exposed to three different treatments: (0) control; (E) external gamma irradiation delivered by a sealed 137Cs source with a dose rate of 66 micro Sv h(-1); (E+I) E treatment combined with internal beta irradiation due to contamination by 134Cs and 85Sr via root uptake from the soil. The root uptake led to a contamination of 100 Bq g(-1) for 85Sr and 5 Bq g(-1) for 134Cs (of plant dry weight) as measured at harvest. The activity of SOD, APX, GR, POD, CAT, G6PDH, and MDHAR enzymes was measured in leaves. Under (0) treatment, all enzymes showed similar activities, except POD, which had higher activity in plants originating from contaminated areas. Treatment (E) induced an enhancement of POD, CAT, GR, SOD, and G6PDH activities in plants originating from contaminated areas. Only control plants showed any stimulation of APX activity. Treatment (E+I) had no significant effect on APX, GR, CAT, and POD activities, but MDHAR activity was significantly reduced while SOD and G6PDH activities were significantly increased. The increase occurred in plants from all origins for SOD, with a greater magnitude as a function of their origin, and it occurred only in plants from the more contaminated populations for G6PDH. This suggests that exposure to a low dose rate of ionizing radiation for almost a half century in the original environment of Stipa has led to natural selection of the most adapted genotypes characterized by an efficient induction of anti-oxidant enzyme activities, especially SOD and G6PDH, involved in plant protection against reactive oxygen species.

Uptake of cesium-137 and strontium-90 from contaminated soil by three plant species; application to phytoremediation

A field test was conducted to determine the ability of three plant species to extract 137Cs and 90Sr from contaminated soil. Redroot pigweed (Amaranthus retroflexus L.), Indian mustard [Brassica juncea (L.) Czern.], and tepary bean (Phaseolus acutifolius A. Gray) were planted in a series of spatially randomized cells in soil that was contaminated in the 1950s and 1960s. We examined the potential for phytoextraction of 90Sr and 137Cs by these three species. Concentration ratios (CR) for 137Cs for redroot pigweed, Indian mustard, and tepary bean were 2.58, 0.46, and 0.17, respectively. For 90Sr they were substantially higher: 6.5, 8.2, and 15.2, respectively. The greatest accumulation of both radionuclides was obtained with redroot pigweed, even though its CR for 90Sr was the lowest, because of its relatively large biomass. There was a linear relationship between the 137Cs concentration in plants and its concentration in soil only for redroot pigweed. Uptake of 90Sr exhibits no relationship to 90Sr concentrations in the soil. Estimates of time required for removal of 50% of the two contaminants, assuming two crops of redroot pigweed per year, are 7 yr for 90Sr and 18 yr for 137Cs.

A case of repeated accidental inhalation contamination of a male subject with 137Cs

Two consecutive incidents of internal contamination occurred within a 13-mo period when a male worker (56 y, 70 kg) briefly entered and stayed (during a breakdown of control apparatus for air contamination) in a radioisotope storeroom with air contaminated by an explosion of old ampules containing 137Cs solution. Monitoring of the first contamination began on day 34 and that of the second one within 1 h after inhalation. According to the two-exponential model, long-term biological half-times of 92 and 93 d were obtained for the first and second contaminations, respectively. The short-term biological half-time for the second contamination was calculated as 3.0 d. The mean value of the fraction of 137Cs excreted in daily urine to that in total excreta was 0.88 for the first contamination and 0.89 for the second one.

[Lipid peroxidation and regulation of it in rat blood and liver under the experimental alimentary radionuclide effect]

Effect of alimentary radionuclide load (137Cs, 700 Bq for animal per day during 7, 14 and 22 days) on the lipid peroxidation intensity and blood and liver enzymatic and non-enzymatic antioxidant system in the Wistar male-rats was investigated. It was found that considerable change of antioxidant system activity in plasma and erythrocytes of experimental animals was already noticeable on the 7th day of radionuclide load. After 22 days of experiment the reliability of glutathione-dependent antioxidant system in blood was essentially decreased and lipid hydroperoxide content was increased. The increase of lipid peroxidation intensity was also found in the experimental animals liver but at the same time the activities of all studied enzymes of antioxidant system were significantly higher than they were in the control rats.

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. SWRxC57BL/6 mice were divided into nine exposure groups and continuously exposed to 0.5, 2.0 or 4.0cGy 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.

Cesium-137 source strength verification

Over the years, the protocol for Cesium-137 source calibration has undergone a number of revisions based on updated data. The 3M Corporation issued product alerts and a revision of the calibration protocol in the early 1980s. We verified the activity of clinically used cesium tubes and found the difference with the activity stated by 3M in the range of 6-13%, which exceeds the recommended by 3M adjustment of 5% for all sources issued before 1979. Therefore, the verification and adjustment of activity should be recommended for each affected tube individually.

Monte Carlo calculations of dose rate distributions around the Amersham CDCS-M-type 137Cs source

The Amersham CDCS-M-type 137Cs stainless-steel encapsulated source is widely used in low dose rate brachytherapy with manual afterloading. However there is a need for more accurate dosimetry data. In this study we present Monte Carlo calculations of absolute dose rate in water around this source using the Monte Carlo code GEANT, discuss dosimetric features of these data, and compare them with Krishnaswamy's results for 137Cs intracavitary sources. Dose rate distributions are presented in the form of along-away tables and in the TG43 formalism. Simulated absolute dose rate values can be used as benchmark data to verify the treatment planning system calculation results or directly as input data for treatment planning. Best-fit values of attenuation coefficients suitable for use in Sievert integral type calculations have been derived comparing dose rate distributions calculated using this algorithm with those obtained from Monte Carlo calculations.

Combined experimental and Monte Carlo verification of 137Cs brachytherapy plans for vaginal applicators

Dose rates in a phantom around a shielded and an unshielded vaginal applicator containing Selectron low-dose-rate 137Cs sources were determined by experiment and Monte Carlo simulation. Measurements were performed with thermoluminescent dosimeters in a white polystyrene phantom using an experimental protocol geared for precision. Calculations for the same set-up were done using a version of the EGS4 Monte Carlo code system modified for brachytherapy applications into which a new combinatorial geometry package developed by Bielajew was recently incorporated. Measured dose rates agree with Monte Carlo estimates to within 5% (1 SD) for the unshielded applicator, while highlighting some experimental uncertainties for the shielded applicator. Monte Carlo calculations were also done to determine a value for the effective transmission of the shield required for clinical treatment planning, and to estimate the dose rate in water at points in axial and sagittal planes transecting the shielded applicator. Comparison with dose rates generated by the planning system indicates that agreement is better than 5% (1 SD) at most positions. The precision thermoluminescent dosimetry protocol and modified Monte Carlo code are effective complementary tools for brachytherapy applicator dosimetry.

[Evaluation of relative biological effectiveness of tritium oxide based on biochemical indices of blood in rats]

The influence of tritium oxide injected peritoneally of the range of activity of 5.5 MBq/g to 111 MBq/g versus gamma-radiation of 137Cs with decreasing dose rate in biochemical parameters of blood in rats was compared. It was shown that relative biological effectiveness of tritium oxide was higher than that for metabolism and it was equal to 1.5 in average.

[Kinetics of metabolism and mechanisms of formation of absorbed doses in the mouse testis from incorporated Cs-137]

The process of accumulation of absorbed doses from incorporated 137Cs in the body and gonads of male mice was investigated in our experiments. The radionuclide accumulated in gonads has very long time of excretion, and as result the radionuclide can be treated as long lasting and permanent source of alpha- and beta-radiation in gonads. The rates of total exposed doses in gonads were in 2.0-3.0 times higher then the average total exposed dose in hole body.

[Several parameters of the state of the nervous, immune and endocrine systems in newborn rats exposed to irradiation during the preimplantation period of embryogenesis]

Protracted prenatal irradiation of animals at the preimplantation stage of embryogenesis is shown to produce disturbances in the development of regulation systems, with their consequences persisting up to sexually mature period of postnatal life. Unknown before, these effects of preimplantation irradiation give the experimental confirmation to the main statement of the previously proposed theoretical concept of the "systemic teratogenesis": the ultimate effect of prenatal irradiation is a distortion of the structure of postnatal neuroimmunoendocrine regulation in the direction of overdevelopment of its endocrine component with the following coadaptive underdevelopment of the nervous and immune components.

[Behavior of fuel hot particles in the body of cows at oral intake]

It was studied the behaviour of fuel hot particles (analogous to Chernobyl) in gastrointestinal tract of cows. The values of caesium and strontium radionuclides transfer to the cows organism and its transition parameters to milk after the single per oral intake to the organism of animals are estimated. It is shown, that the biological simplicity of radionuclides in the fuel hot particles at two parameters lower, than the same radionuclides in washed phases.

The use of comparative 137Cs body burden estimates from environmental data/models and whole body counting to evaluate diet models for the ingestion pathway

Rongelap and Utirik Atolls were contaminated on 1 March 1954, by a U.S. nuclear test at Bikini Atoll code named BRAVO. The people at both atolls were removed from their atolls in the first few days after the detonation and were returned to their atolls at different times. Detailed studies have been carried out over the years by Lawrence Livermore National Laboratory (LLNL) to determine the radiological conditions at the atolls and estimate the doses to the populations. The contribution of each exposure pathway and radionuclide have been evaluated. All dose assessments show that the major potential contribution to the estimated dose is 137Cs uptake via the terrestrial food chain. Brookhaven National Laboratory (BNL) has carried out an extensive whole body counting program at both atolls over several years to directly measure the 137Cs body burden. Here we compare the estimates of the body burdens from the LLNL environmental method with body burdens measured by the BNL whole body counting method. The combination of the results from both methods is used to evaluate proposed diet models to establish more realistic dose assessments. Very good agreement is achieved between the two methods with a diet model that includes both local and imported foods. Other diet models greatly overestimate the body burdens (i.e., dose) observed by whole body counting. The upper 95% confidence limit of interindividual variability around the population mean value based on the environmental method is similar to that calculated from direct measurement by whole body counting. Moreover, the uncertainty in the population mean value based on the environmental method is in very good agreement with the whole body counting data. This provides additional confidence in extrapolating the estimated doses calculated by the environmental method to other islands and atolls.

[The effect of long-term ionizing radiation exposure on retinal function]

An experimental investigation designed to study the nervous tunic of eyeball of those animals who had been exposed to low levels of radiation for a long time revealed dystrophic-destructive changes in cellular elements of the above tunic. Its ganglial layer exhibited most marked changes such as destruction of gangliocytes against the background of pronounced pericelmomer edema. Changes in the system of photoreceptors were characterized by suppression of protein-synthesizing function of cells and, to a lesser extent, energy-producing one. An important observation is to our mind practically complete absence of processes of intracellular regeneration, which fact is a bad prognostic sign in respect of recovery of morphofunctional status of retina of the eye. Probability of development of dystrophic events in retina of those individuals having been under combined exposure to low levels of radiation gets higher.

Chromosome aberrations in Syrian hamsters following very low radiation doses in vivo

This paper addresses a report of a large increase (approximately 6- to 11-fold) in chromosome aberrations in lymphocytes of persons in Salzburg attributed to their exposure to fallout from the Chernobyl cloud. Their additional exposure, approximately 0.3 mGy in 1 year, comprised about a 30% increase in their normal background radiation dose. The report has attracted considerable attention because, if correct, it seriously challenges assumptions of linearity in the low-dose response for chromosomal damage and, by implication, the linear, no-threshold hypothesis for risk of induced cancer. An experiment has been carried out with Syrian hamsters treated with caesium-137 to produce a range of doses comparable with those calculated for the persons in Salzburg. No significant elevation in lymphocyte aberration yields was found in the hamsters, thus arguing against the conclusions of the Salzburg study.

Algorithms for the process management of sealed source brachytherapy

Incidents and misadministrations suggest that brachytherapy may benefit from clarification of the quality management program and other mandates of the U.S. Nuclear Regulatory Commission. To that end, flowcharts of step by step subprocesses were developed and formatted with dedicated software. The overall process was similarly organized in a complex flowchart termed a general process map. Procedural and structural indicators associated with each flowchart and map were critiqued and pre-existing documentation was revised. "Step-regulation tables" were created to refer steps and subprocesses to Nuclear Regulatory Commission rules and recommendations in their sequences of applicability. Brachytherapy algorithms were specified as programmable, recursive processes, including therapeutic dose determination and monitoring doses to the public. These algorithms are embodied in flowcharts and step-regulation tables. A general algorithm is suggested as a template from which other facilities may derive tools to facilitate process management of sealed source brachytherapy.