POS1275 A RETROSPECTIVE STUDY ON UVEITIS FLARES FOLLOWING COVID19 VACCINATION: SHARING EXPERIENCE FROM A TEACHING HOSPITAL COMBINED RHEUMATOLOGY AND UVEITIS CLINIC

Background

Uveitis is a sight threatening disease caused by inflammation of the uveal tract of the eye. Uveitis is a manifestation of many autoimmune conditions and is associated with seronegative axial spondyloarthritis, reactive arthritis, Behçet’s disease, inflammatory bowel disease, and psoriatic arthritis. Acute anterior uveitis is the most common presentation and is most commonly idiopathic or associated with the HLA-B27 gene (around 20% of cases). Studies have shown that anterior uveitis frequently recurs in patients after it has previously remitted. (1) Patients suffering from autoimmune conditions are frequently prescribed immunosuppressant drugs to control their illness, thus leaving them more susceptible to bacterial and viral illnesses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Previous studies have shown that some patients suffer exacerbation of their autoimmune condition after coronavirus vaccination, including uveitis(2). We aim to evaluate our cohort of patients suffering from autoimmune conditions treated at Leicester Uveitis Service at Leicester Royal Infirmary and explore any proposed link.

Objectives

To assess if COVID19 vaccination is associated with uveitis flares in immunosuppressed patients.

Methods

A retrospective study, to determine if patients diagnosed with autoimmune conditions suffered from uveitis following COVID-19 vaccination. A data collection sheet was used to document demographic and clinical data: age, sex, ethnicity, autoimmune condition, dates of COVID-19 vaccination(s), type of vaccine, medication at the time of vaccine, symptoms of autoimmune recurrence, date of uveitis onset and number of days between uveitis onset and latest vaccine. We used an already existing uveitis database with an active register of 2346 patients, of which 246 were on immunomodulation.

Results

After reviewing the first 50 patients on immunosuppression for uveitis, we found a total of 4 patients had a uveitis flare despite tight control previously; 3 are female and 1 male, their median age was 39.5 years. They experienced a recurrence of uveitis in the last 6 months. Of these 4 patients 3 were on synthetic DMARDS (2 mycophenolate mofetil, 1 azathioprine), 1 was on steroids and 1 was on a biological DMARD (adalimumab). 2 of the patients suffered from posterior uveitis and 2 from anterior uveitis. All the 50 patients had been vaccinated against COVID19 however there was no clear record of booster dose.

Conclusion

Our study showed that of 50 immunosuppressed patients, 4 had a uveitis flare following vaccination. Clinicians need to be aware of uvetis flares in rheumatology patients following vaccination. This is a small retrospective analysis of our cohort however a large observational study on flare of uveitis following COVID-19 primary vaccination and booster vaccination would be useful to get meaningful data.

References

[1]Grunwald L, Newcomb CW, Daniel E, Kaçmaz RO, Jabs DA, Levy-Clarke GA, Nussenblatt RB, Rosenbaum JT, Suhler EB, Thorne JE, Foster CS, Kempen JH; Systemic Immunosuppressive Therapy for Eye Diseases Cohort Study. Risk of relapse in primary acute anterior uveitis. Ophthalmology. 2011 Oct;118(10):1911-5. doi: 10.1016/j.ophtha.2011.02.044. Epub 2011 Jun 16. PMID: 21680024; PMCID: PMC3179829.

[2]Bolletta E, Iannetta D, Mastrofilippo V, De Simone L, Gozzi F, Croci S, Bonacini M, Belloni L, Zerbini A, Adani C, Fontana L, Salvarani C, Cimino L. Uveitis and Other Ocular Complications Following COVID-19 Vaccination. J Clin Med. 2021 Dec 19;10(24):5960. doi: 10.3390/jcm10245960. PMID: 34945256; PMCID: PMC8704915.

Disclosure of Interests

None declared

The Importance and Quantification of Plutonium Binding in Human Lungs

Epidemiological studies have shown that the main risk arising from exposure to plutonium aerosols is lung cancer, with other detrimental effects in the bone and liver. A realistic assessment of these risks, in turn, depends on the accuracy of the dosimetric models used to calculate doses in such studies. A state-of-the-art biokinetic model for plutonium, based on the current International Commission on Radiological Protection biokinetic model, has been developed for this purpose in an epidemiological study involving the plutonium exposure of Mayak workers in Ozersk, Russia. One important consequence of this model is that the lung dose is extremely sensitive to the fraction (fb) of plutonium, which becomes bound to lung tissue after it dissolves. It has been shown that if just 1% of the material becomes bound in the bronchial region, this will double the lung dose. Furthermore, fb is very difficult to quantify from experimental measurements. This paper summarizes the work carried out thus far to quantify fb. Bayesian techniques have been used to analyze data from different sources, including both humans and dogs, and the results suggest a small, but nonzero, fraction of < 1%. A Bayesian analysis of 20 Mayak workers exposed to plutonium nitrate suggests an fb between 0 and 0.3%. Based on this work, the International Commission on Radiological Protection is currently considering the adoption of a value of 0.2% for the default bound fraction for all actinides in its forthcoming recommendations on internal dosimetry. In an attempt to corroborate these findings, further experimental work has been carried out by the US Transuranium and Uranium Registries. This work has involved direct measurements of plutonium in the respiratory tract tissues of workers who have been exposed to soluble plutonium nitrate. Without binding, one would not expect to see any activity remaining in the lungs at long times after exposure since it would have been cleared by the natural process of mucociliary clearance. Further supportive study of workers exposed to plutonium oxide is planned. This paper ascertains the extent to which these results corroborate previous inferences concerning the bound fraction.

The Mayak Worker Dosimetry System (MWDS 2013): Soluble Plutonium Retention in the Lungs of An Occupationally Exposed USTUR Case

For the first time, plutonium retention in human upper airways was investigated based on the dosimetric structure of the human respiratory tract proposed by the International Commission on Radiological Protection (ICRP). This paper describes analytical work methodology, case selection criteria, and summarizes findings on soluble (ICRP 68 Type M material) plutonium distribution in the lungs of a former nuclear worker occupationally exposed to plutonium nitrate [239Pu(NO3)4]. Thirty-eight years post-intake, plutonium was found to be uniformly distributed between bronchial (BB), bronchiolar (bb) and alveolar-interstitial (AI) dosimetric compartments as well as between the left and right lungs. 239+240Pu and 238Pu total body activity was estimated to be 2333 ± 23 and 42.1 ± 0.7 Bq, respectively. The results of this work provide key information on the extent of plutonium binding in the upper airways of the human respiratory tract.

The Mayak Worker Dosimetry System (MWDS-2013): Implementation of the Dose Calculations

The calculation of internal doses for the Mayak Worker Dosimetry System (MWDS-2013) involved extensive computational resources due to the complexity and sheer number of calculations required. The required output consisted of a set of 1000 hyper-realizations: each hyper-realization consists of a set (1 for each worker) of probability distributions of organ doses. This report describes the hardware components and computational approaches required to make the calculation tractable. Together with the software, this system is referred to here as the 'PANDORA system'. It is based on a commercial SQL server database in a series of six work stations. A complete run of the entire Mayak worker cohort entailed a huge amount of calculations in PANDORA and due to the relatively slow speed of writing the data into the SQL server, each run took about 47 days. Quality control was monitored by comparing doses calculated in PANDORA with those in a specially modified version of the commercial software 'IMBA Professional Plus'. Suggestions are also made for increasing calculation and storage efficiency for future dosimetry calculations using PANDORA.

The Mayak Worker Dosimetry System (MWDS-2013): How to Reduce Hyper-Realisations to Realisations

Two important aspects in which the MWDS-2013 output (absorbed dose to organs calculated in each calendar year) differs from previous data bases (MWDS-2008 and DOSES-2005) are that they have been designed to (a) deal explicitly with uncertainties in model parameters, and (b) differentiate parameters that are considered to be shared (unknown, but having the same value for all workers) and unshared (unknown, but having different values between workers). A multiple-realisation approach is used to preserve information on the effects of shared and unshared parameters both for internal and external doses. Previously, a single realisation (a set of organ doses: one for each worker in the cohort) was calculated using the best estimates of parameter values only. In MWDS-2013, a set of 1000 realisations is produced, to reflect the uncertainty in assumed model parameters: each realisation using a different set of parameter values. Within each realisation, shared parameter values are fixed throughout the cohort, while unshared parameters are allowed to vary between workers. One problem is that because the calculation of organ dose is Bayesian, the estimate for each organ dose is not just a single value, but is itself a distribution (hyper-dose). Technically, it is the probability density of dose given the sampled set of parameter values and given the data for that worker. Thus, in our case, the realisations consist not of single doses, but distributions of doses. The term hyper-realisation is used to differentiate this from the more conventional realisation. Although the multiple hyper-realisation in principle contains all of the necessary information on parameter uncertainty, including shared and unshared parameters, in order to make preliminary epidemiological analyses tractable, and also for consistency with the external doses, it was required to convert the hyper-realisations to realisations. The aim of this paper is to discuss the different approaches that were considered to do this, and to define the method that was eventually chosen. Single spot (point) estimates of dose (for each worker) were also calculated to support the epidemiological analysis. The different methods for obtaining these and the implications are also discussed.

The Mayak Worker Dosimetry System (MWDS-2013): Internal Dosimetry Results

The distribution of calculated internal doses has been determined for 8043 Mayak Production Associate (Mayak PA) workers. This is a subset of the entire cohort of 25 757 workers, for whom monitoring data are available. Statistical characteristics of point estimates of accumulated doses to 17 different tissues and organs and the uncertainty ranges were calculated. Under the MWDS-2013 dosimetry system, the mean accumulated lung dose was 185 ± 594 mGy (geometric mean = 28 mGy; geometric standard deviation = 9.32; median value = 31 mGy; maximum value = 8980 mGy). The ranges of relative standard uncertainty were from 40 to 2200% for accumulated lung dose, from 25-90% to 2600-3000% for accumulated dose to different regions of respiratory tract, from 13-22% to 2300-2500% for systemic organs and tissues. The Mayak PA workers accumulated internal plutonium lung dose is shown to be close to log normal. The accumulated internal plutonium dose to systemic organs was close to a log triangle. The dependency of uncertainty of accumulated absorbed lung and liver doses on the dose estimates itself is also shown. The accumulated absorbed doses to lung, alveolar-interstitial region, liver, bone surface cells and red bone marrow calculated both with MWDS-2013 and MWDS-2008 have been compared. In general, the accumulated lung doses increased by a factor of 1.8 in median value, while the accumulated doses to systemic organs decreased by factor of 1.3-1.4 in median value. For the cases with identical initial data, accumulated lung doses increased by a factor of 2.1 in median value, while accumulated doses to systemic organs decreased by 8-13% in median value. For the cases with both identical initial data and all of plutonium activity in urine measurements above the decision threshold, accumulated lung doses increased by a factor of 2.7 in median value, while accumulated doses to systemic organs increased by 6-12% in median value.

The Mayak Worker Dosimetry System (MWDS-2013): A Bayesian Analysis to Quantify Pulmonary Binding of Plutonium in Lungs Using Historic Beagle Dog Data

The revised human respiratory tract model, published in Part 1 of the International Commission on Radiological Protection's (ICRP) report on Occupational Intakes of Radionuclides (OIR), includes a bound fraction, fb, to represent radionuclides that have become chemically bound in the lungs following dissolution of particulates in lung fluid. Bound radionuclides are not subject to particle transport clearance but can be absorbed to blood at a rate, sb. The occurrence of long-term binding of plutonium can greatly increase lung doses, particularly if it occurs in the bronchial and bronchiolar regions. However, there has been little evidence that currently supports the existence of a long-term bound state for plutonium. The present work describes the analysis of measurements of lung data obtained from a life span study of Beagle dogs that were exposed by inhalation to different concentrations of plutonium-239 (239Pu) nitrate aerosol at Pacific Northwest Laboratories, USA. The data have been analysed to assess whether a bound state was required to explain the data. A Bayesian approach was adopted for the analysis that accounts for uncertainties in model parameter values, including uncertainties in the rates of particle transport clearance. Furthermore, it performs the analysis using two different modelling hypotheses: a model based on the current ICRP human respiratory tract model and its treatment of alveolar particle transport clearance; and a model of particle transport clearance that is based on the updated model developed by ICRP to calculate dose coefficients for the OIR. The current model better represents clearance in dogs at early times (up to 1 year following intake) and the latter better represents retention at greater times (>5 years following intake). The results indicate that a long-term bound fraction of between 0.16 and 1.1%, with a mean value of between 0.24 and 0.8% (depending on the model) is required to explain the data.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS-2013) FOR INTERNALLY DEPOSITED PLUTONIUM: AN OVERVIEW

The Mayak Worker Dosimetry System (MWDS-2013) is a system for interpreting measurement data from Mayak workers from both internal and external sources. This paper is concerned with the calculation of annual organ doses for Mayak workers exposed to plutonium aerosols, where the measurement data consists mainly of activity of plutonium in urine samples. The system utilises the latest biokinetic and dosimetric models, and unlike its predecessors, takes explicit account of uncertainties in both the measurement data and model parameters. The aim of this paper is to describe the complete MWDS-2013 system (including model parameter values and their uncertainties) and the methodology used (including all the relevant equations) and the assumptions made. Where necessary, Supplementary papers which justify specific assumptions are cited.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS-2013): TREATMENT OF UNCERTAINTY IN MODEL PARAMETERS

Different dose estimates have been produced for the Mayak PA workforce over recent years (DOSES-2000, DOSES-2005, MWDS-2008). The dosimetry system MWDS-2013 described here differs from previous analyses, in that it deals directly with uncertainty in the assumed model parameters. This paper details the way in which uncertainty is dealt with within MWDS-2013 to produce the final output represented by a multiple hyper-realisation of organ doses. More specifically, the paper describes: Application of the WeLMoS method to calculate Bayesian posterior probability distributions of organ doses.Extension of the WeLMoS method for dealing with multiple intake regimes.How shared and unshared parameters are dealt with using a multiple realisation method.A practical algorithm for the generation of multiple hyper-realisations.How to deal with uncertainty in the intake and the intake regime. The resulting multiple hyper-realisation contains all of the information required to take account of model parameter uncertainty and the effects of shared and unshared parameters in any epidemiological analysis, which uses this information, although it is acknowledged that in practice, certain data simplifications may be required to make such analyses tractable, and comparable to previous analyses. Such simplifications are outside the scope of this paper.

The Mayak Worker Dosimetry System (MWDS-2013): Plutonium Binding in the Lungs-An Analysis of Mayak Workers

Estimates of plutonium lung doses from urine bioassay are highly dependent on the rate of absorption from the lungs to blood assumed for the inhaled aerosol. Absorption occurs by dissolution of particles in lung fluid followed by uptake to blood. The latter may occur either rapidly or dissolved ions may first become temporarily bound within airway tissue. The presence of long-term binding can greatly increase lung doses, particularly if it occurs in the bronchial and bronchiolar regions. Analyses of autopsy data from Beagle dogs and USTUR Case 0269, obtained following exposure to plutonium nitrate, suggest that a small fraction of 0.2-1.1 and 0.4-0.7%, respectively, of plutonium becomes permanently bound within the lungs. The present work performs a further analysis using autopsy data of former plutonium workers of the Mayak Production Association to determine values of the bound fraction that are supported by these data. The results suggest a bound fraction value of 0-0.3%. The results also indicate that the Mayak worker population median values of the particle transport clearance parameters from the alveolar-interstitial region are largely consistent with expected values, but suggest the rate from the alveolar region to the interstitium may be lower than initially thought.

The Mayak Worker Dosimetry System (MWDS-2013): Uncertainty in the Measurement of Pu Activity in a 24-Hour Urine Sample of a Typical Mayak PA Worker

In the Mayak Worker Dosimetry System (MWDS-2013), intakes of plutonium and organ doses are assessed on the basis of measurements made on the plutonium content of 56 400 urine samples. Altogether, there were urine bioassays for 7591 (29%) of the 25 757 cohort members who were employed any time at Mayak between 1948 and 1982. These measurements are subject to uncertainty due to many factors (e.g. whether or not creatinine is measured, the volume of the sample, whether diethylenetriaminepentaacetic acid was administered, etc.) and this uncertainty will affect not only the uncertainty in the estimated doses, but also the values of the doses themselves. Therefore, it is important for the estimated uncertainty to be as accurate as possible. The input to the dose calculation requires an estimate of the plutonium activity in a true 24-hour sample. The uncertainty in this activity is approximated by a lognormal distribution. The aim of this paper is to describe and justify how the parameters of this lognormal distribution are derived from the raw data. Histograms of the distribution of sample volumes are given for both sexes. The method of calculation of the decision threshold and relative standard uncertainty (RSU) of a measurement result for Pu activity in a worker's urine sample is shown. Diagrams of correlation between Pu activity in collected urine and its RSU are given.

The Mayak Worker Dosimetry System (MWDS-2013): How to Weight the Absorbed Dose to Different Lung Regions in the Calculation of Lung Dose

In the Mayak Worker Dosimetry System-2013, lung dose is calculated as an average of the three absorbed doses to the bronchial, the bronchiolar and the alveolar regions. Previous epidemiological studies involving Mayak Workers have used a lung dose calculated as the total energy deposited in the lungs divided by the mass. These two definitions lead to very different estimates of lung dose, especially for radon dosimetry. This paper uses the results of recent epidemiological studies to justify the use of a regionally weighted lung dose (wi = 1/3, I = 1, 3) over the use of an 'average lung' dose.

THE MAYAK WORKER DOSIMETRY SYSTEM-2013 (MWDS-2013): PHASE II-QUALITY ASSURANCE OF ORGAN DOSE CALCULATIONS

In order to check developed software tools, it was necessary to compare estimates of statistical characteristics of annual absorbed plutonium internal doses obtained by PANDORA and IMBA software with the same original data. The results were compared from dose calculations of five cases with different initial data on plutonium inhalation intake, lifetime measurements of plutonium activity in daily urine and post-mortem measurements in lungs, lung lymph nodes, liver and skeleton. Estimates of geometric mean and geometric standard deviation of annual regionally weighted lung dose and bone surface dose were compared. Satisfactory agreements of the estimates of statistical characteristics of annual doses to two critical organs for the selected cases were shown. One hundred individual hyper-realizations (forward model evaluations) are sufficient to calculate MWDS-2013 if only measurements of plutonium activity in daily urine are used, and 2000 individual hyper-realizations if both urine and autopsy measurement results are used.

The Mayak Worker Dosimetry System-2013: Treatment of Organ Masses in the Calculation of Organ Doses

Previous Mayak worker epidemiological studies designed to quantify the risk of cancer following exposure to airborne plutonium have calculated organ doses by dividing the organ-absorbed energy by the individual's estimated organ mass. For living workers, this was done by using a relationship between organ mass and total mass and height. For autopsy cases, this was measured directly. In the Mayak Worker Dosimetry System-2013 study, organ doses are calculated by dividing this energy by a population average organ mass. The reasons for departing from previous methodologies are described in this note. The average organ masses that were used in the final analysis are tabulated for males and females.

Mayak Worker Dosimetry System (MWDS-2013): Phase I-Quality Assurance of Organ Doses and Excretion Rates From Internal Exposures of Plutonium-239 for the Mayak Worker Cohort

The calculation of reliable and realistic doses for use in epidemiological studies for the quantification of risk from internal exposure to radioactive material is fundamental to the development of advice, guidance and regulations for the control and use of radioactive material. Thus, any programme of work carried out which requires the calculation of doses for use by epidemiologists ideally should contain a rigorous program of quality assurance (QA). This paper describes the initial QA (Phase I) implemented by Public Health England (PHE) and the Southern Urals Biophysics Institute (SUBI) as part of the work programme on internal dosimetry in the Joint Coordinating Committee for Radiation Effects Research Project 2.4 for the 2013 Mayak Worker Dosimetry System. SUBI designed and implemented new software (PANDORA) to include the latest Mayak Worker Dosimetry System and to calculate organ burdens, urinary excretion rates, intakes and absorbed doses, while PHE modified their commercially available IMBA Professional Plus software package. Comparisons of output from the two codes for the Mayak Worker Dosimetry System 2013 showed calculated values of absorbed doses, intakes, organ burdens and urinary excretion agreed to within 1%. The 1% discrepancy can be explained by the approximation used in IMBA to speed up dose calculations.

The Mayak Worker Dosimetry System (Mwds-2013): Plutonium Dissolution in The Lungs-An Analysis of Mayak Workers

Lung doses resulting from inhalation of plutonium aerosols are highly dependent on the assumed rate of particle clearance, which occurs by two competing processes: (1) particle transport clearance to the alimentary tract and to the thoracic lymph nodes and (2) clearance to systemic tissues, which occurs by dissolution of particles in lung fluid followed by uptake to blood, which is a process collectively known as absorption. Unbiased and accurate estimates of the values of lung absorption parameters are required to obtain reliable estimates of lung dose, particularly those inferred from urine bioassay. Parameter values governing the rate of absorption are best estimated from data, such as autopsy measurements of plutonium in the lungs and systemic tissues, which directly relate to the exposed workers of interest. However, because the mathematical models that determine clearance from the lungs and systemic tissues are complex and consist of many parameters, estimates of model parameter values are subject to significant uncertainties. With this in mind, this paper uses a Bayesian approach to estimate one of the most important dissolution parameters: the slow rate of dissolution. This is estimated for both plutonium nitrate and plutonium oxide bearing aerosols in the lungs of former workers of the Mayak Production Association. A value of 2.6 × 10-4 d-1 is estimated for plutonium nitrates, and 4.7 × 10-5 d-1 for plutonium oxides.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS 2013): A RE-ANALYSIS OF USTUR CASE 0269 TO DETERMINE WHETHER PLUTONIUM BINDS TO THE LUNGS

Radionuclides in ionic form can become chemically bound in the airways of the lungs following dissolution of inhaled particulates in lung fluid. The presence of long-term binding can greatly increase lung doses from inhaled plutonium, particularly if it occurs in the bronchial and bronchiolar regions. However, the only published evidence that plutonium binding occurs in humans comes from an analysis of the autopsy and bioassay data of United States Transuranium and Uranium Registries Case 0269, a plutonium worker who experienced a very high (58 kBq) acute inhalation of plutonium nitrate. This analysis suggested a bound fraction of around 8 %, inferred from an unexpectedly low ratio of estimated total thoracic lymph node activity:total lung activity, at the time of death. However, there are some limitations with this study, the most significant being that measurements of the regional distribution of plutonium activity in the lungs, which provide more direct evidence of binding, were not available when the analysis was performed. The present work describes the analysis of new data, which includes measurements of plutonium activity in the alveolar-interstitial (AI) region, bronchial (BB) and bronchiolar (bb) regions, and extra-thoracic (ET) regions, at the time of death. A Bayesian approach is used that accounts for uncertainties in model parameter values, including particle transport clearance, which were not considered in the original analysis. The results indicate that a long-term bound fraction between 0.4 and 0.7 % is required to explain this data, largely because plutonium activity is present in the extra-thoracic (ET2), bronchial and bronchiolar airways at the time of death.

Risk of Lung Cancer Mortality in Nuclear Workers from Internal Exposure to Alpha Particle-emitting Radionuclides

BACKGROUND

Carcinogenic risks of internal exposures to alpha-emitters (except radon) are poorly understood. Since exposure to alpha particles-particularly through inhalation-occurs in a range of settings, understanding consequent risks is a public health priority. We aimed to quantify dose-response relationships between lung dose from alpha-emitters and lung cancer in nuclear workers.

METHODS

We conducted a case-control study, nested within Belgian, French, and UK cohorts of uranium and plutonium workers. Cases were workers who died from lung cancer; one to three controls were matched to each. Lung doses from alpha-emitters were assessed using bioassay data. We estimated excess odds ratio (OR) of lung cancer per gray (Gy) of lung dose.

RESULTS

The study comprised 553 cases and 1,333 controls. Median positive total alpha lung dose was 2.42 mGy (mean: 8.13 mGy; maximum: 316 mGy); for plutonium the median was 1.27 mGy and for uranium 2.17 mGy. Excess OR/Gy (90% confidence interval)-adjusted for external radiation, socioeconomic status, and smoking-was 11 (2.6, 24) for total alpha dose, 50 (17, 106) for plutonium, and 5.3 (-1.9, 18) for uranium.

CONCLUSIONS

We found strong evidence for associations between low doses from alpha-emitters and lung cancer risk. The excess OR/Gy was greater for plutonium than uranium, though confidence intervals overlap. Risk estimates were similar to those estimated previously in plutonium workers, and in uranium miners exposed to radon and its progeny. Expressed as risk/equivalent dose in sieverts (Sv), our estimates are somewhat larger than but consistent with those for atomic bomb survivors.See video abstract at, http://links.lww.com/EDE/B232.

Reconstruction of Internal Doses for the Alpha-Risk Case-Control Study of Lung Cancer and Leukaemia Among European Nuclear Workers

The Alpha-Risk study required the reconstruction of doses to lung and red bone marrow for lung cancer and leukaemia cases and their matched controls from cohorts of nuclear workers in the UK, France and Belgium. The dosimetrists and epidemiologists agreed requirements regarding the bioassay data, biokinetic and dosimetric models and dose assessment software to be used and doses to be reported. The best values to use for uncertainties on the monitoring data, setting of exposure regimes and characteristics of the exposure material, including lung solubility, were the responsibility of the dosimetrist responsible for each cohort. Among 1721 subjects, the median absorbed dose to the lung from alpha radiations was 2.1 mGy, with a maximum dose of 316 mGy. The lung doses calculated reflect the higher levels of exposure seen among workers in the early years of the nuclear industry compared to today.

A multicentre study of the precision and accuracy of the TruSlice and TruSlice Digital histological dissection devices

BACKGROUND

Five key factors enabling a good surgical grossing technique include a flat uniformly perpendicular specimen cutting face, appropriate immobilisation of the tissue specimen during grossing, good visualisation of the cutting tissue face, sharp cutting knives and the grossing knife action. TruSlice and TruSlice Digital are new innovative tools based on a guillotine configuration. The TruSlice has plastic inserts whilst the TruSlice Digital has an electronic micrometre attached: both features enable these dissection factors to be controlled. The devices were assessed in five hospitals in the UK.

MATERIAL AND METHODS

A total of 267 fixed tissue samples from 23 tissue types were analysed, principally the breast (n = 32) skin (30), rectum (28), colon (27) and cervix (17). Precision and accuracy were evaluated by measuring the defined thickness, and the consistency of achieving the defined thickness of tissue samples taken respectively. Both parameters were expressed as a total percentage of compliance for the cohort of samples accessed.

RESULTS

Overall, the mean (standard deviation) score for precision was 81 (11) % whilst the accuracy score was 82 (11) % (both p < 0.05, chi-squared test), although this varied with type of tissue. Accuracy and precision were strongly correlated (r_p = 0.83, p < 0.001).

CONCLUSION

The TruSlice Digital devices offer an assured precision and accuracy performance which is reproducible across an assortment of tissue types. The use of a micrometre to set tissue slice thickness is innovative and should comply with laboratory accreditation requirements, alleviating concerns of how to tackle issues such as the 'measurement of uncertainty' at the grossing bench.

Doses and lung cancer risks from exposure to radon and plutonium

PURPOSE

Epidemiological studies of the French uranium miners and the plutonium workers at the Mayak nuclear facility have provided excess relative risk (ERR) estimates per unit absorbed lung dose from alpha radiation. The aim of this paper was to review these two studies and to derive values of the relative biological effectiveness (RBE) of alpha particles for the induction of lung cancer.

MATERIALS AND METHODS

We examined and compared the dosimetry assumptions and methodology used in the epidemiological studies of uranium miners and the plutonium workers. Values of RBE were obtained by comparing risk coefficients including comparison of lifetime risks for a given population. To do this, preliminary calculations of lifetime risks following inhalation of plutonium were carried out.

RESULTS AND CONCLUSIONS

Published values of risk per unit dose following inhalation of radon progeny and plutonium were in agreement despite the very different dose distributions within the lungs and the different ways the doses were calculated. Values of RBE around 10-20 were obtained by comparing ERR values, but with wide uncertainty ranges. Comparing lifetime risks gave similar values (10, 19 and 21). This supports the use of a radiation weighting factor of 20 for alpha particles for radiation protection purposes.

An intake prior for the Bayesian analysis of plutonium and uranium exposures in an epidemiology study

In Bayesian inference, the initial knowledge regarding the value of a parameter, before additional data are considered, is represented as a prior probability distribution. This paper describes the derivation of a prior distribution of intake that was used for the Bayesian analysis of plutonium and uranium worker doses in a recent epidemiology study. The chosen distribution is log-normal with a geometric standard deviation of 6 and a median value that is derived for each worker based on the duration of the work history and the number of reported acute intakes. The median value is a function of the work history and a constant related to activity in air concentration, M, which is derived separately for uranium and plutonium. The value of M is based primarily on measurements of plutonium and uranium in air derived from historical personal air sampler (PAS) data. However, there is significant uncertainty on the value of M that results from paucity of PAS data and from extrapolating these measurements to actual intakes. This paper compares posterior and prior distributions of intake and investigates the sensitivity of the Bayesian analyses to the assumed value of M. It is found that varying M by a factor of 10 results in a much smaller factor of 2 variation in mean intake and lung dose for both plutonium and uranium. It is concluded that if a log-normal distribution is considered to adequately represent worker intakes, then the Bayesian posterior distribution of dose is relatively insensitive to the value assumed of M.

A revised model for the deposition and clearance of inhaled particles in human extra-thoracic airways

The International Commission on Radiological Protection (ICRP) Task Group that developed the Human Respiratory Tract Model for Radiological Protection (HRTM) identified a lack of published information on aspects of the clearance of inhaled particles deposited in the human nasal passage. Using the results of a recent human volunteer study on the clearance of inhaled particles from the nose, a revised model of clearance from the extra-thoracic (ET) airways has been developed that addresses important issues for which simplifying assumptions had to be made in the ICRP Publication 66 HRTM ET model. This ET clearance model has been adopted by ICRP for inclusion in the revised HRTM. The derivation of the model and parameter values from the experimental data are explained.

A Bayesian analysis of uncertainties on lung doses resulting from occupational exposures to uranium

In a recent epidemiological study, Bayesian estimates of lung doses were calculated in order to determine a possible association between lung dose and lung cancer incidence resulting from occupational exposures to uranium. These calculations, which produce probability distributions of doses, used the human respiratory tract model (HRTM) published by the International Commission on Radiological Protection (ICRP) with a revised particle transport clearance model. In addition to the Bayesian analyses, point estimates (PEs) of doses were also provided for that study using the existing HRTM as it is described in ICRP Publication 66. The PEs are to be used in a preliminary analysis of risk. To explain the differences between the PEs and Bayesian analysis, in this paper the methodology was applied to former UK nuclear workers who constituted a subset of the study cohort. The resulting probability distributions of lung doses calculated using the Bayesian methodology were compared with the PEs obtained for each worker. Mean posterior lung doses were on average 8-fold higher than PEs and the uncertainties on doses varied over a wide range, being greater than two orders of magnitude for some lung tissues. It is shown that it is the prior distributions of the parameters describing absorption from the lungs to blood that are responsible for the large difference between posterior mean doses and PEs. Furthermore, it is the large prior uncertainties on these parameters that are mainly responsible for the large uncertainties on lung doses. It is concluded that accurate determination of the chemical form of inhaled uranium, as well as the absorption parameter values for these materials, is important for obtaining unbiased estimates of lung doses from occupational exposures to uranium for epidemiological studies. Finally, it should be noted that the inferences regarding the PEs described here apply only to the assessments of cases provided for the epidemiological study, where central estimates of dose were sought. Approved dosimetry service assessments of exposures are unlikely to yield significant underestimates, as pessimistic assumptions of lung solubility would almost always be used.

Application of Bayesian inference to the bioassay data from long-term follow-up of two refractory PuO2 inhalation cases

The dominant contribution to the uncertainty in internal dose assessment can often be explained by the uncertainty in the biokinetic model structure and parameters. The International Commission on Radiological Protection (ICRP) is currently updating its biokinetic models, including the Human Respiratory Tract Model (HRTM). Gregoratto et al. (2010) proposed a physiologically-based particle transport model that simplifies significantly the representation of particle clearance from the alveolar interstitial region. Bayesian inference using the Weighted Likelihood Monte-Carlo Sampling (WeLMoS) method is applied to the bioassay and autopsy data from the U.S. Transuranium and Uranium Registries' (USTUR) tissue donors 0202 and 0407 exposed to "high fired," refractory PuO2 aerosols in order to examine the applicability of the revised model and to estimate the uncertainties in model parameters and the lung doses as expressed by the posterior probability distributions. It is demonstrated that, with appropriate adjustments, the Gregoratto et al. particle transport model can describe situations involving exposure to highly insoluble particles. Significant differences are observed in particle clearance pattern characteristics to these two individuals' respiratory systems. The respiratory tract of registrant 0202 was most likely compromised by his prior occupational exposure to coal dust, smoking habit, and chronic obstructive pulmonary disease, while donor 0407 was a non-smoker and had no prior history of lung disorder. However, the central values of the particle transport parameter posterior distributions for both cases are found to be still within the 68% probability range for the inter-subject variability derived by Gregoratto et al. PuO2 particles produced by the plutonium fire were extremely insoluble, with about 99% absorbed into blood at a rate of approximately 4.8 × 10 d (Case 0202) and 5.1 × 10 d (Case 0202). When considering this type of plutonium material, doses to other body organs are small in comparison to those to tissues of the respiratory tract. More than 95% of the total committed weighted equivalent dose is contributed by the lungs.

Mayak Worker Dosimetry System 2008 (MWDS-2008): assessment of internal dose from measurement results of plutonium activity in urine

A new modification of the prior human lung compartment plutonium model, Doses-2005, has been described. The modified model was named "Mayak Worker Dosimetry System-2008" (MWDS-2008). In contrast to earlier models developed for workers at the Mayak Production Association (Mayak PA), the new model more correctly describes plutonium biokinetics and metabolism in pulmonary lymph nodes. The MWDS-2008 also provides two sets of doses estimates: one based on bioassay data and the other based on autopsy data, where available. The algorithm of internal dose calculation from autopsy data will be described in a separate paper. Results of comparative analyses of Doses-2005 and MWDS-2008 are provided. Perspectives on the further development of plutonium dosimetry are discussed.

A method for calculating Bayesian uncertainties on internal doses resulting from complex occupational exposures

Estimating uncertainties on doses from bioassay data is of interest in epidemiology studies that estimate cancer risk from occupational exposures to radionuclides. Bayesian methods provide a logical framework to calculate these uncertainties. However, occupational exposures often consist of many intakes, and this can make the Bayesian calculation computationally intractable. This paper describes a novel strategy for increasing the computational speed of the calculation by simplifying the intake pattern to a single composite intake, termed as complex intake regime (CIR). In order to assess whether this approximation is accurate and fast enough for practical purposes, the method is implemented by the Weighted Likelihood Monte Carlo Sampling (WeLMoS) method and evaluated by comparing its performance with a Markov Chain Monte Carlo (MCMC) method. The MCMC method gives the full solution (all intakes are independent), but is very computationally intensive to apply routinely. Posterior distributions of model parameter values, intakes and doses are calculated for a representative sample of plutonium workers from the United Kingdom Atomic Energy cohort using the WeLMoS method with the CIR and the MCMC method. The distributions are in good agreement: posterior means and Q(0.025) and Q(0.975) quantiles are typically within 20 %. Furthermore, the WeLMoS method using the CIR converges quickly: a typical case history takes around 10-20 min on a fast workstation, whereas the MCMC method took around 12-72 hr. The advantages and disadvantages of the method are discussed.

Disaggregating measurement uncertainty from population variability and Bayesian treatment of uncensored results

In making low-level radioactivity measurements of populations, it is commonly observed that a substantial portion of net results is negative. Furthermore, the observed variance of the measurement results arises from a combination of measurement uncertainty and population variability. This paper presents a method for disaggregating measurement uncertainty from population variability to produce a probability density function (PDF) of possibly true results. To do this, simple, justifiable and reasonable assumptions are made about the relationship of the measurements to the measurands (the 'true values'). The measurements are assumed to be unbiased, that is, that their average value is the average of the measurands. Using traditional estimates of each measurement's uncertainty, a likelihood PDF for each individual's measurand is produced. Then using the same assumptions and all the data from the population of individuals, a prior PDF of measurands for the population is produced. The prior PDF is non-negative, and the average is equal to the average of the measurement results for the population. Using Bayes's theorem, posterior PDFs of each individual measurand are calculated. The uncertainty in these bayesian posterior PDFs appears to be all Berkson with no remaining classical component. The method is applied to baseline bioassay data from the Hanford site. The data include (90)Sr urinalysis measurements of 128 people, (137)Cs in vivo measurements of 5337 people and (239)Pu urinalysis measurements of 3270 people. The method produces excellent results for the (90)Sr and (137)Cs measurements, since there are non-zero concentrations of these global fallout radionuclides in people who have not been occupationally exposed. The method does not work for the (239)Pu measurements in non-occupationally exposed people because the population average is essentially zero relative to the sensitivity of the measurement technique. The method is shown to give results similar to classical statistical inference when the measurements have relatively small uncertainty.

Uncertainties on lung doses from inhaled plutonium

In a recent epidemiological study, Bayesian uncertainties on lung doses have been calculated to determine lung cancer risk from occupational exposures to plutonium. These calculations used a revised version of the Human Respiratory Tract Model (HRTM) published by the ICRP. In addition to the Bayesian analyses, which give probability distributions of doses, point estimates of doses (single estimates without uncertainty) were also provided for that study using the existing HRTM as it is described in ICRP Publication 66; these are to be used in a preliminary analysis of risk. To infer the differences between the point estimates and Bayesian uncertainty analyses, this paper applies the methodology to former workers of the United Kingdom Atomic Energy Authority (UKAEA), who constituted a subset of the study cohort. The resulting probability distributions of lung doses are compared with the point estimates obtained for each worker. It is shown that mean posterior lung doses are around two- to fourfold higher than point estimates and that uncertainties on doses vary over a wide range, greater than two orders of magnitude for some lung tissues. In addition, we demonstrate that uncertainties on the parameter values, rather than the model structure, are largely responsible for these effects. Of these it appears to be the parameters describing absorption from the lungs to blood that have the greatest impact on estimates of lung doses from urine bioassay. Therefore, accurate determination of the chemical form of inhaled plutonium and the absorption parameter values for these materials is important for obtaining reliable estimates of lung doses and hence risk from occupational exposures to plutonium.

Plutonium worker dosimetry

Epidemiological studies of the relationship between risk and internal exposure to plutonium are clearly reliant on the dose estimates used. The International Commission on Radiological Protection (ICRP) is currently reviewing the latest scientific information available on biokinetic models and dosimetry, and it is likely that a number of changes to the existing models will be recommended. The effect of certain changes, particularly to the ICRP model of the respiratory tract, has been investigated for inhaled forms of (239)Pu and uncertainties have also been assessed. Notable effects of possible changes to respiratory tract model assumptions are (1) a reduction in the absorbed dose to target cells in the airways, if changes under consideration are made to the slow clearing fraction and (2) a doubling of absorbed dose to the alveolar region for insoluble forms, if evidence of longer retention times is taken into account. An important factor influencing doses for moderately soluble forms of (239)Pu is the extent of binding of dissolved plutonium to lung tissues and assumptions regarding the extent of binding in the airways. Uncertainty analyses have been performed with prior distributions chosen for application in epidemiological studies. The resulting distributions for dose per unit intake were lognormal with geometric standard deviations of 2.3 and 2.6 for nitrates and oxides, respectively. The wide ranges were due largely to consideration of results for a range of experimental data for the solubility of different forms of nitrate and oxides. The medians of these distributions were a factor of three times higher than calculated using current default ICRP parameter values. For nitrates, this was due to the assumption of a bound fraction, and for oxides due mainly to the assumption of slower alveolar clearance. This study highlights areas where more research is needed to reduce biokinetic uncertainties, including more accurate determination of particle transport rates and long-term dissolution for plutonium compounds, a re-evaluation of long-term binding of dissolved plutonium, and further consideration of modeling for plutonium absorbed to blood from the lungs.

A Monte Carlo method for calculating Bayesian uncertainties in internal dosimetry

This paper presents a novel Monte Carlo method (WeLMoS, Weighted Likelihood Monte-Carlo sampling method) that has been developed to perform Bayesian analyses of monitoring data. The WeLMoS method randomly samples parameters from continuous prior probability distributions and then weights each vector by its likelihood (i.e. its goodness of fit to the measurement data). Furthermore, in order to quality assure the method, and assess its strengths and weaknesses, a second method (MCMC, Markov chain Monte Carlo) has also been developed. The MCMC method uses the Metropolis algorithm to sample directly from the posterior distribution of parameters. The methods are evaluated and compared using an artificially generated case involving an exposure to a plutonium nitrate aerosol. In addition to calculating the uncertainty on internal dose, the methods can also calculate the probability distribution of model parameter values given the observed data. In other words, the techniques provide a powerful tool to obtain the estimates of parameter values that best fit the data and the associated uncertainty on these estimates. Current applications of the methodology, including the determination of lung solubility parameters, from volunteer and cohort data, are also discussed.

Internal dosimetry: towards harmonisation and coordination of research

The CONRAD Project is a Coordinated Network for Radiation Dosimetry funded by the European Commission 6th Framework Programme. The activities developed within CONRAD Work Package 5 ('Coordination of Research on Internal Dosimetry') have contributed to improve the harmonisation and reliability in the assessment of internal doses. The tasks carried out included a study of uncertainties and the refinement of the IDEAS Guidelines associated with the evaluation of doses after intakes of radionuclides. The implementation and quality assurance of new biokinetic models for dose assessment and the first attempt to develop a generic dosimetric model for DTPA therapy are important WP5 achievements. Applications of voxel phantoms and Monte Carlo simulations for the assessment of intakes from in vivo measurements were also considered. A Nuclear Emergency Monitoring Network (EUREMON) has been established for the interpretation of monitoring data after accidental or deliberate releases of radionuclides. Finally, WP5 group has worked on the update of the existing IDEAS bibliographic, internal contamination and case evaluation databases. A summary of CONRAD WP5 objectives and results is presented here.

Development, implementation and quality assurance of biokinetic models within CONRAD

The work of the Task Group 5.2 'Research Studies on Biokinetic Models' of the CONRAD project is presented. New biokinetic models have been implemented by several European institutions. Quality assurance procedures included intercomparison of the results as well as quality assurance of model formulation. Additionally, the use of the models was examined leading to proposals of tuning parameters. Stable isotope studies were evaluated with respect to their implications to the new models, and new biokinetic models were proposed on the basis of their results. Furthermore, the development of a biokinetic model describing the effects of decorporation of actinides by diethylenetriaminepentaacetic acid treatment was initiated.

Internal dose assessments: uncertainty studies and update of ideas guidelines and databases within CONRAD project

The work of Task Group 5.1 (uncertainty studies and revision of IDEAS guidelines) and Task Group 5.5 (update of IDEAS databases) of the CONRAD project is described. Scattering factor (SF) values (i.e. measurement uncertainties) have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Based upon this work and other published values, default SF values are suggested. Uncertainty studies have been carried out using both a Bayesian approach as well as a frequentist (classical) approach. The IDEAS guidelines have been revised in areas relating to the evaluation of an effective AMAD, guidance is given on evaluating wound cases with the NCRP wound model and suggestions made on the number and type of measurements required for dose assessment.

Dosimetric models used in the Alpha-Risk project to quantify exposure of uranium miners to radon gas and its progeny

The European project Alpha-Risk aims to quantify the cancer and non-cancer risks associated with multiple chronic radiation exposures by epidemiological studies, organ dose calculation and risk assessment. In the framework of this project, mathematical models have been applied to the organ dosimetry of uranium miners who are internally exposed to radon and its progeny as well as to long-lived radionuclides present in the uranium ore. This paper describes the methodology and the dosimetric models used to calculate the absorbed doses to specific organs arising from exposure to radon and its progeny in the uranium mines. The results of dose calculations are also presented.

Comparison of dose estimation from occupational exposure to 239Pu using different modelling approaches

Several approaches are available for bioassay interpretation when assigning Pu doses to Mayak workers. First, a conventional approach is to apply ICRP models per se. An alternative method involves individualised fitting of bioassay data using Bayesian statistical methods. A third approach is to develop an independent dosimetry system for Mayak workers by adapting ICRP models using a dataset of available bioassay measurements for this population. Thus, a dataset of 42 former Mayak workers, who died of non-radiation effects, with both urine bioassay and post-mortem tissue data was used to test these three approaches. All three approaches proved to be adequate for bioassay and tissue interpretation, and thus for Pu dose reconstruction purposes. However, large discrepancies are observed in the resulting quantitative dose estimates. These discrepancies can, in large part, be explained by differences in the interpretation of Pu behaviour in the lungs in the context of ICRP lung model. Thus, a careful validation of Pu lung dosimetry model is needed in Mayak worker dosimetry systems.

Evaluation of scattering factor values for internal dose assessment following the IDEAS guidelines: preliminary results

The IDEAS Guidelines for the assessment of internal doses from monitoring data suggest default measurement uncertainties (i.e. scattering factors, SFs) to be used for different types of monitoring data. However, these default values were mainly based upon expert judgement. In this paper, SF values have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Results are presented.

Avoiding biased estimates of dose when nothing is known about the time of intake

A common problem in internal dosimetry occurs in routine monitoring, when it is required to estimate an intake from a measurement made at the end of a monitoring interval, and the time of intake is unknown. ICRP suggests that it should be assumed that the intake occurred in the middle of the monitoring period. However, it has been shown that this will, in the long-term, lead to biased estimates of a worker's intake and dose. In order to overcome this biasing, the United States Department of Energy (USDOE) recommends a different method based on calculating the intakes for all possible intake times in the interval and then taking an arithmetic average. In a recent paper, it has been shown that both the ICRP and USDOE methods were biased and that the only unbiased estimator of the true intake was obtained by assuming a constant chronic intake throughout the monitoring interval. In all of the analyses carried out to date on this 'Constant Chronic' method, it was assumed that the measurements were exact. In this paper, the effects of assuming either normally or log-normally distributed measurement errors are explored, and the effect on the bias of the intake estimate is investigated.

Estimating uncertainty on internal dose assessments

The estimation of uncertainty on doses broadly falls into three categories. (1) Estimating the uncertainty on prospective doses. Here, the intake is known and the uncertainties in individual parameter values must be propagated through the calculated dose. (2) Estimating the error or uncertainty on dose assessments made from single measurements. Here, intake, model parameter and measurement uncertainties are propagated into the measurement, but default ICRP parameter values are used to estimate the intake and dose from the measurement. (3)Estimating the probability distribution of an individual's dose from a set of monitoring data. Here, Bayesian inference methods must be used to estimate the uncertainty on the estimated dose. A computer code is being developed that performs all three types of uncertainty analysis using Monte Carlo simulation. The software samples biokinetic parameters from probability density functions and then calculates doses from these parameters by calling the dosimetry code IMBA Professional Plus. A description of the methodology, together with an example application of the software, is included in this paper.

Application of IDEAS guidelines: the IDEAS/IAEA intercomparison exercise on internal dose assessment

As part of the EU Fifth Framework Programme IDEAS project 'General Guidelines for the Evaluation of Incorporation Monitoring Data', and in collaboration with the International Atomic Energy Agency, a new intercomparison exercise for the assessment of doses from intakes of radionuclides was organised. Several cases were selected, to cover a wide range of practices in the nuclear fuel cycle and medical applications. The cases were: (1) acute intake of HTO, (2) acute inhalation of the fission products 137Cs and 90Sr, (3) acute inhalation of 60Co, (4) repeated intakes of 131I, (5) intake of enriched uranium and (6) single intake of Pu isotopes and 241Am. This intercomparison exercise especially focused on the effect of the Guidelines proposed by the IDEAS project for harmonisation of internal dosimetry.

Coordination of research on internal dosimetry in Europe: the CONRAD project

The EUropean RAdiation DOSimetry Group (EURADOS) initiated in 2005 the CONRAD Project, a Coordinated Network for Radiation Dosimetry funded by the European Commission (EC), within the 6th Framework Programme (FP). The main purpose of CONRAD is to generate a European Network in the field of Radiation Dosimetry and to promote both research activities and dissemination of knowledge. The objective of CONRAD Work Package 5 (WP5) is the coordination of research on assessment and evaluation of internal exposures. Nineteen institutes from 14 countries participate in this action. Some of the activities to be developed are continuations of former European projects supported by the EC in the 5th FP (OMINEX and IDEAS). Other tasks are linked with ICRP activities, and there are new actions never considered before. A collaboration is established with CONRAD Work Package 4, dealing with Computational Dosimetry, to organise an intercomparison on Monte Carlo modelling for in vivo measurements of (241)Am deposited in a knee phantom. Preliminary results associated with CONRAD WP5 tasks are presented here.

Comparison of radon lung dosimetry models for the estimation of dose uncertainties

In order to investigate the degree of dose uncertainty produced by different models, three dosimetry models were compared with each other, representing different classes of models: (i) The RADEP/IMBA model based on the ICRP Human Respiratory Tract Model, a deterministic regional compartment model, (ii) the RADOS model, a deterministic airway generation model and (iii) the IDEAL dosimetry model, a stochastic airway generation model. The outputs of the three models for defined mining exposure conditions were compared at three different levels: deposition fractions for attached and unattached radon progeny; nuclear transformations, reflecting the combined effect of deposition and clearance; and resulting cellular doses. Resulting dose exposure conversion factors ranged from 7.8 (median) mSv/WLM (IDEAL) to 11.8 mSv/WLM (RADEP/IMBA), with 8.3 mSv/WLM (RADOS) as an intermediate value. Despite methodological and computational differences between the three models, resulting dose conversion factors do not appreciably differ from each other, although predictions by the two generation models are consistently smaller than that for the RADEP/IMBA model.

IMBA Professional Plus: a flexible approach to internal dosimetry

IMBA (Integrated Modules for Bioassay Analysis) is a suite of software modules that implement the current ICRP biokinetic and dosimetric models for estimation of intakes and doses. The IMBA modules have gone through extensive quality assurance, and are now used for routine formal dose assessment by Approved Dosimetry Services throughout the UK. HPA has continued to develop the IMBA modules. In addition, several projects, sponsored by organisations both in the USA and in Canada, have resulted in the development of customised user-friendly interfaces (IMBA Expert 'editions'). These enable users not only to use the standard ICRP models, but also to change many of the parameter values from ICRP defaults, and to apply sophisticated data handling techniques to internal dose calculations. These include: fitting measurement data with the maximum likelihood method; using multiple chronic and acute intakes; and dealing with different data types, such as urine, faces and whole body simultaneously. These interfaces were improved further as a result of user-feedback, and a general 'off-the-shelf' product, IMBA Professional, was developed and made available in January 2004. A new version, IMBA Professional Plus, was released in April 2005, which is both faster and more powerful than previous software. The aim of this paper is to describe the capabilities of IMBA Professional Plus, and the mathematical methods used.

The autocorrelation coefficient as a tool for assessing goodness of fit between bioassay predictions and measurement data

Project IDEAS has produced guidelines for internal dose assessment. An integral part of this process is assessing the goodness of fit of biokinetic models to bioassay data. It is recommended that a fit should only be accepted if (a) it is close enough to the data not to be rejected by a chi2 test and (b) if it looks acceptable to 'the eye'. The latter criterion was added to enable the assessor to reject fits which seemed to display some sort of systematic bias. However, there are problems with both of these tests: (a) the chi2 test is dependent on the assumed uncertainties which are often unknown, (b) 'by eye' assessment is subjective. In this paper, another statistic, the autocorrelation coefficient of the residuals, rho, is investigated. The main advantages of the rho statistic are that it is objective, very sensitive to biasing and independent of the assumed errors.

The work of the CONRAD task group 5.2: research studies on biokinetic models

The objective of this Task Group is the coordination of research studies on biokinetic models and the evaluation of the implications of new biokinetic models on dose assessment and safety standards. For this the new ICRP models, which will be used for a revision of ICRP Publications 30, 54, 68 and 78, are implemented into six different computer codes in five European countries and quality assured by intercomparison procedures. The work has started with the implementation of the new ICRP Alimentary Tract Model. New systemic models and the new NCRP wound model will follow. The work also includes the evaluation of experimental results in terms of formulation by the new model structures and a quality assurance of model formulation.

Obtaining an unbiased estimate of intake in routine monitoring when the time of intake is unknown

A common problem in internal dosimetry occurs in routine monitoring, when it is required to estimate an intake from a measurement made at the end of a monitoring interval, and the time of intake is unknown. ICRP suggests that, in these cases, it should be assumed that the intake occurred in the middle of the monitoring period. However, it has been shown that this will, in the long term, lead to biased estimates of a worker's intake and dose. In order to overcome this biasing, the United States Department of Energy (USDOE) recommends a different method based on calculating the intakes for all possible intake-times in the interval, and then taking an arithmetic average. In this paper, it is shown that both the ICRP and USDOE methods are biased. An alternative method is suggested, which assumes a constant chronic intake throughout the monitoring interval. Monte Carlo simulations are used to estimate the magnitude of bias for two realistic monitoring programmes using all three methods. It is shown that the proposed method is unbiased and also yields estimates of intake that are generally closer to the actual intake, than the other two. The Monte Carlo conclusions are backed up by a theoretical analysis of bias. Finally, the source of bias in the apparently intuitive approach of the USDOE method is revealed by viewing the problem from a Bayesian perspective.

Uncertainties in doses from intakes of radionuclides assessed from monitoring measurements

The evaluation of uncertainties in doses from intakes of radionuclides is one of the most difficult problems in internal dosimetry. In this paper, the process of assessing internal doses from monitoring measurements is reviewed and the major sources of uncertainty are discussed. Methods developed independently at HPA and at IRSN for the determination of uncertainties in internal doses assessed from monitoring measurements are described. Both use a Monte Carlo simulation approach. Results are described for three illustrative examples. An alternative method developed at the Los Alamos National Laboratory that uses Bayesian statistical methods is also described briefly.