International Commission On Radiological Protection Model Research Articles

Incidence risk assessment of secondary cancer due to radiotherapy of women with rectal cancer using BEIR VII, EPA, and ICRP models.

Radiotherapy has a significant side effect known as radiation-induced secondary cancer. This study aims to evaluate the dose and secondary cancer risk for women with rectal cancer treated with three-dimensional conformal radiation therapy (3D-CRT) to the organs at risk (OARs) and some sensitive organs using different types of radiation-induced cancer risk prediction models, including Biological Effects of Ionizing Radiation (BEIRVII), Environmental Protection Agency (EPA) and International Commission on Radiological Protection (ICRP), and compare the results of the different models for same organs. Thirty female patients with rectal cancer were considered and dose calculations were based on the PCRT-3D treatment planning system, while the radiotherapy of the patients had been performed using Shinva linear accelerator with a total dose of 45 Gy at 25 fractions. Planning target volume (PTV), OARs, and some sensitive organs were contoured, three models were used to evaluate secondary cancer risk (SCR) using the excess relative risk (ERR) and excess absolute risk (EAR). The bladder presents the highest risk, in terms of ERR, and the femur head and uterus in terms of EAR from the three models (BEIR VII, EPA, and ICRP). Based on the obtained results, radiotherapy of rectal cancer is relatively higher for the bladder and femur head, compared to the risk for other organs, the kidney risk is significantly lower. It was observed that the SCR from the ICRP model was higher compared to BEIR VII and EPA models.

A filter-based system mimicking the particle deposition and penetration in human respiratory system for secondhand smoke generation and characterization

Introduction Secondhand smoke endangers both the environment and the health of nonsmokers. Due to the scarcity of repeatable data generated by human subjects, a system capable of generating representative secondhand smoke is essential for studying smoke properties. This work presents the design and validation of a filter-based system that could mimic the particle deposition and penetration in human respiratory system for secondhand smoke generation and characterization. Methods Guided by our study on characterizing size-dependent filtration efficiency of common materials, we identified three filter media that generate similar particle deposition efficiencies compared to different regions of the human respiratory system over a wide submicron size range. We demonstrated the performance of the proposed filter-based system using various operating conditions. Additionally, we compared the properties of secondhand smoke particles to those of primary smoke particles. Results The difference in aerosol deposition efficiencies between the filter-based system and the International Commission on Radiological Protection (ICRP) model was less than 10% in the size range of 30 to 500 nm. High concentrations of metals were detected in the secondhand smoke. The contents of Ni and Cr generated from the secondhand electronic cigarettes are at least 20 and 5 times above the regulated daily maximum intake amount. Conclusion Given the agreement in aerosol respiratory deposition between the filter-based system and the ICRP model, such a system can facilitate laboratory studies of secondhand smoke due to its simple structure, high repeatability, and ease of control while remaining free of human subjects.

Biokinetic model for the calculation of dose coefficients for oral and intravenous administration of 14C labeled drugs

Abstract A first order biokinetic model is presented for the calculation of dose coefficients from human activity excretion data after intravenous and oral administration of 14C labeled drugs. It is intended for the dose estimation in human studies in drug research, where the number of measurements is low and their uncertainty rather high. The model depends on only 6 parameters that are to be adjusted with the help of the measurement data. A comparison of measured and calculated activities in excreta of four human studies on 14C labeled drugs revealed considerable agreement, although some limitations have to be accepted. In contrast to the biokinetic model for 14C in organic compounds recommended by the International Commission on Radiological Protection (ICRP) the present model does not assume a fixed biological half-life of 40 days, but follows the experimental data. In consequence, the resulting dose coefficients differ from the ICRP value. For experimental data tested and assuming uniform activity distribution, the committed effective doses amount between one twenty-fifth to one fiftieth of the values calculated from the ICRP model. The uncertainty of the derived dose coefficients is estimated to be about ± 50%.

Korean-specific biokinetic model for iodine in radiological protection

The International Commission on Radiological Protection (ICRP) recently adopted a detailed biokinetic model for systemic iodine with reference transfer coefficients based on typical worldwide dietary intakes of stable iodine. The regional data provided demonstrate that the ICRP reference thyroidal biokinetics may differ substantially across regions with atypically low or high dietary intakes of stable iodine. Importantly, the design of the ICRP model facilitates modifications of reference thyroidal kinetics based on regional dietary iodine intake. The present study extended the ICRP model to the South Korean population, whose dietary iodine intake is much higher than the global mean. The following three transfer coefficients were selected as targets for Korean-specific values: thyroidal uptake rate (λ 1), hormonal secretion rate (λ 4) and leakage rate of thyroidal organic iodine as inorganic iodide (λ 5). The Korean-specific values for λ 1, λ 4 and λ 5 were determined to be 4.48, 0.0086 and 0.0171 d−1, respectively, to yield the measurements of thyroidal iodine and physiological status of Korean adults. The determined λ 1 and λ 5 values differed noticeably from the ICRP values, whereas the λ 4 value was comparable to that of the ICRP. Compared with the ICRP reference model, the Korean model, in which the Korean-specific transfer coefficients were adopted, predicted noticeably lower thyroidal uptake and faster decrease of thyroidal iodine. In addition, the predicted cumulative activities of radioiodine in the thyroid were substantially lower (40–80%) than those predicted by the ICRP model. The Korean model developed in this study demonstrates that the iodine biokinetics for Koreans (i.e. a population with a high iodine consumption) obviously differ from the prediction of the ICRP model. Hence, the Korean model may serve to improve the accuracy of thyroid dose estimation for Koreans and will lead to practical changes in matters concerned with radiological protection.

Development of carbon-based metabolic models for estimation of doses of organically bound tritium ingested in humans

The tritium dose coefficient is an important parameter for assessment of the radiation safety of nuclear facilities such as fusion reactors. The dose coefficient for dietarily derived organically bound tritium (OBT) for members of the public is recommended by the International Commission on Radiological Protection (ICRP), which makes some assumptions regarding the human metabolism in calculating this value, because metabolic data for tritium is limited. The objective of this study is to develop biokinetic models for OBT based on metabolic data to validate the current ICRP-recommended dose coefficient for OBT. In contrast to the ICRP model, by modifying biokinetic models for 14C developed in a previous study, the models described in this study consider OBT activity in a range of nutrient molecules. The dose coefficient estimated using these OBT models ((2.4 ± 0.1) × 10−11 Sv Bq-1) was smaller than the value recommended by the ICRP (4.2 × 10−11 Sv Bq-1), suggesting that human metabolic data support its recommendations. However, the conservative estimation considering uncertainties in metabolic data was significantly larger ((9.7 ± 3.5) × 10−11 Sv Bq-1) than the ICRP recommended value; therefore, further studies to reduce the uncertainties are required.

Assessment of exposure after injection of 99mTc-labeled intact monoclonal antibodies and their fragments into humans.

Human pharmacokinetics and internal radiation dosimetry of normal organs after injection with the 99mTc-labeled monoclonal antibody (intact and fragments) are simulated by the WinAct program and IDAC (Internal Dose Assessment by Computer) software. The WinAct program is used to calculate the cumulative activity in organs and tissues. The calculated cumulative activity is inputted to the IDAC software, an internal dosimetry program for nuclear medicine based on the International Commission on Radiological Protection (ICRP) adult reference voxel phantom, and the absorbed doses by the organs and tissues are estimated. The obtained absorbed doses for the 99mTc-labeled monoclonal antibody (intact and fragments) are compared with the published figures by ICRP-128. The WinAct program method to calculate the cumulative activity is more accurate, as the fraction distribution, Fs, is described and calculated for organs, not only for intake, as in the ICRP model, but also for elimination.

A Biokinetic Model for Systemic Nickel.

The International Commission on Radiological Protection (ICRP) is updating its suite of reference biokinetic models for internally deposited radionuclides. This paper reviews data for nickel and proposes an updated biokinetic model for systemic (absorbed) nickel in adult humans for use in radiation protection. Compared with the ICRP's current model for nickel, the proposed model is based on a larger set of observations of the behavior of nickel in human subjects and laboratory animals and provides a more realistic description of the paths of movement of nickel in the body. For the two most important radioisotopes of nickel, Ni and Ni, the proposed model yields substantially lower dose estimates per unit of activity reaching blood than the current ICRP model.

Adapting the ICRP model to predict regional deposition of the pharmaceutical aerosols inhaled through DPIs and nebulizers

Using inhaler devices, drug delivery to the lung has been practiced for a long time to treat respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). The key question in this practice is how to deliver the drug to the regions of interest efficiently. Significant efforts have been made to develop models of depositional behavior of inhaled particles. The semi-experimental International Commission on Radiological Protection (ICRP) model is frequently used to predict depositional behavior of inhaled particles. Here, we have tried to adapt this model for predicting deposition of pharmaceutical particles that are inhaled through dry powder inhalers (DPIs) and nebulizers. We attempted to use a more proper extrathoracic deposition formula accounting for breath holding and bolus timing (in case of DPIs) and possible evaporation of droplets (in case of nebulizers). Two computer programs for DPIs and nebulizers were developed which can be freely accessed through e-mail contact to the first author.

A review of hygroscopic growth factors of submicron aerosols from different sources and its implication for calculation of lung deposition efficiency of ambient aerosols

Hygroscopic properties are an important parameter in determining the atmospheric behaviour of aerosols and their optical properties, influencing the direct and indirect effect of aerosols upon climate. As a result, particle hygroscopicity has received much attention with a rapid increase of publications in recent years. Likewise, hygroscopicity is an important characteristic influencing the deposition efficiency of particles in the human respiratory tract by affecting the particle size. The object of this study is to review the existing knowledge on the hygroscopic growth factor (Gf) of atmospheric submicron particles and its influence on the lung deposition calculation. The study briefly reviews first the Gf values of particles generated from various sources, including nucleation, traffic emissions and biomass burning, discussing the spatial and temporal variations. It then summarises Gf values of submicron particles and number fraction of each hygroscopic group measured in different ambient environments. These include marine, roadside, urban background and rural environments. The study concludes by estimating the lung deposition efficiency of ambient particles using a modified version of the International Commission on Radiological Protection (ICRP) model for hygroscopic particles. Furthermore, the effect of hygroscopicity on lung deposition efficiency of ambient particles has been estimated. The ICRP model seems to predict well the deposition efficiency (DE) values for small ambient particles in the extra-thoracic and tracheo-bronchial region, but not the alveolar region, where they are overestimated. However, for larger particles (D p > 200 nm), the ICRP model underestimates the DE values, with the extra-thoracic region the most affected of the three. Hygroscopic atmospheric particles with a small diameter (D p < 200 nm) showed a lower total lung deposition than hydrophobic particles of the same initial size due to their hygroscopic properties. On the other hand, larger hygroscopic particles (D p > 200 nm) showed much higher lung deposition than hydrophobic particles.

Development of a computer code to calculate the distribution of radionuclides within the human body by the biokinetic models of the ICRP.

This paper describes the Basic Radionuclide vAlue for Internal Dosimetry (BRAID) code, which was developed to calculate the time-dependent activity distribution in each organ and tissue characterised by the biokinetic compartmental models provided by the International Commission on Radiological Protection (ICRP). Translocation from one compartment to the next is taken to be governed by first-order kinetics, which is formulated by the first-order differential equations. In the source program of this code, the conservation equations are solved for the mass balance that describes the transfer of a radionuclide between compartments. This code is applicable to the evaluation of the radioactivity of nuclides in an organ or tissue without modification of the source program. It is also possible to handle easily the cases of the revision of the biokinetic model or the application of a uniquely defined model by a user, because this code is designed so that all information on the biokinetic model structure is imported from an input file. The sample calculations are performed with the ICRP model, and the results are compared with the analytic solutions using simple models. It is suggested that this code provides sufficient result for the dose estimation and interpretation of monitoring data.

Biokinetic models for radiocaesium and its progeny

The International Commission on Radiological Protection (ICRP) is preparing a series of reports that will provide updated biokinetic and dosimetric models and dose coefficients for occupational intake of radionuclides. The biokinetic modelling scheme continues a trend in ICRP reports towards physiologically realistic descriptions of the time-dependent behaviour of absorbed radionuclides and their radioactive progeny. This paper proposes systemic biokinetic models for caesium isotopes and their ingrowing chain members and examines the dosimetric implications of the proposed models. Comparisons of D68 = tissue dose per unit input to blood based on current ICRP models for workers (ICRP Publication 68, 1994) with DP = corresponding values based on the proposed biokinetic models (but using the dosimetry models of Publication 68) yields the following ranges of the ratios DP:D68 for the tissues addressed in Publication 68: 0.5–25 for 130Cs (T1/2 = 29.2 min), 0.6–9.5 for 134mCs (2.9 h), 0.7–1.7 for 131Cs (9.69 d), 0.7–1.1 for 134Cs (2.06 y), 0.5–1.9 for 137Cs (30.2 y) and 0.2–3.7 for 135Cs (2.3 × 106 y). The large differences in the derived dose coefficients for some tissues and caesium isotopes, particularly short-lived isotopes, result mainly from differences in predictions of the time-dependent distributions of caesium in the body. For example, the proposed model and the current ICRP model for occupational intake of caesium predict peak kidney contents of ∼22% and ∼0.4%, respectively, following intravenous injection of stable caesium. Based on the proposed models for caesium and its progeny, the only dosimetrically significant chain members of caesium isotopes with half-life ≥10 min are 137mBa, which represents 32–85% of the estimated tissue doses from injected 137Cs, and 134Cs, which represents 4–53% of the estimated tissue doses from injected 134mCs.

In Vitro Particle Size Distributions in Electronic and Conventional Cigarette Aerosols Suggest Comparable Deposition Patterns

Electronic cigarette users ("vapers") inhale aerosols of water, nicotine, and propylene glycol (PG) or vegetable glycerin (VG). Aerosol particle sizes should affect deposition patterns in vapers and bystanders. Aerosols were generated by a smoking machine and an electronic cigarette filled with 16mg/ml nicotine in aqueous PG or VG solution. A scanning mobility particle sizer (SMPS) counted particles of 10-1,000 nm diameters. A single puff experiment counted particles immediately and after aging 10 and 40 s. A steady-state experiment counted particles emitted from a collection chamber, untreated and after desiccation or organic vapor removal. The International Commission on Radiological Protection (ICRP) human respiratory tract model was used to estimate deposition. Results were compared to similar data from reference cigarettes. Puffs generated peak particle counts at (VG) 180 nm and (PG) 120 nm. Steady-state peaks occurred around 400 nm. Organic vapor removal eliminated small particles and reduced the size and number of large particles. Desiccation reduced the total volume of particles by 70% (VG, small PG) to 88% (large PG). The ICRP model predicted 7%-18% alveolar delivery; 9%-19% venous delivery, mostly in the head; and 73%-80% losses by exhalation. Reference cigarettes generated more particles initially, but were otherwise similar; however, in vivo smoke particle deposition is higher than the model predicts. Nicotine delivery may depend on vaping technique, particle evolution, and cloud effects. Predicted 10% arterial and 15% venous delivery may describe bystander exposure better than vapers exposure.

RELIABILITY OF A NEW BIOKINETIC MODEL OF ZIRCONIUM IN INTERNAL DOSIMETRY: PART I, PARAMETER UNCERTAINTY ANALYSIS

The reliability of biokinetic models is essential in internal dose assessments and radiation risk analysis for the public, occupational workers, and patients exposed to radionuclides. In this paper, a method for assessing the reliability of biokinetic models by means of uncertainty and sensitivity analysis was developed. The paper is divided into two parts. In the first part of the study published here, the uncertainty sources of the model parameters for zirconium (Zr), developed by the International Commission on Radiological Protection (ICRP), were identified and analyzed. Furthermore, the uncertainty of the biokinetic experimental measurement performed at the Helmholtz Zentrum München-German Research Center for Environmental Health (HMGU) for developing a new biokinetic model of Zr was analyzed according to the Guide to the Expression of Uncertainty in Measurement, published by the International Organization for Standardization. The confidence interval and distribution of model parameters of the ICRP and HMGU Zr biokinetic models were evaluated. As a result of computer biokinetic modelings, the mean, standard uncertainty, and confidence interval of model prediction calculated based on the model parameter uncertainty were presented and compared to the plasma clearance and urinary excretion measured after intravenous administration. It was shown that for the most important compartment, the plasma, the uncertainty evaluated for the HMGU model was much smaller than that for the ICRP model; that phenomenon was observed for other organs and tissues as well. The uncertainty of the integral of the radioactivity of Zr up to 50 y calculated by the HMGU model after ingestion by adult members of the public was shown to be smaller by a factor of two than that of the ICRP model. It was also shown that the distribution type of the model parameter strongly influences the model prediction, and the correlation of the model input parameters affects the model prediction to a certain extent depending on the strength of the correlation. In the case of model prediction, the qualitative comparison of the model predictions with the measured plasma and urinary data showed the HMGU model to be more reliable than the ICRP model; quantitatively, the uncertainty model prediction by the HMGU systemic biokinetic model is smaller than that of the ICRP model. The uncertainty information on the model parameters analyzed in this study was used in the second part of the paper regarding a sensitivity analysis of the Zr biokinetic models.

Human biokinetic data and a new compartmental model of zirconium — A tracer study with enriched stable isotopes

Biokinetic models describing the uptake, distribution and excretion of trace elements are an essential tool in nutrition, toxicology, or internal dosimetry of radionuclides. Zirconium, especially its radioisotope 95Zr, is relevant to radiation protection due to its production in uranium fission and neutron activation of nuclear fuel cladding material. We present a comprehensive set of human data from a tracer study with stable isotopes of zirconium. The data are used to refine a biokinetic model of zirconium. Six female and seven male healthy adult volunteers participated in the study. It includes 16 complete double tracer investigations with oral ingestion and intravenous injection, and seven supplemental investigations. Tracer concentrations were measured in blood plasma and urine collected up to 100 d after tracer administration. The four data sets (two chemical tracer forms in plasma and urine) each encompass 105–240 measured concentration values above detection limits. Total fractional absorption of ingested zirconium was found to be 0.001 for zirconium in citrate-buffered drinking solution and 0.007 for zirconium oxalate solution. Biokinetic models were developed based on the linear first-order kinetic compartmental model approach used by the International Commission on Radiological Protection (ICRP). The main differences of the optimized systemic model of zirconium to the current ICRP model are (1) recycling into the transfer compartment made necessary by the observed tracer clearance from plasma, (2) different parameters related to fractional absorption for each form of the ingested tracer, and (3) a physiologically based excretion pathway to urine. The study considerably expands the knowledge on the biokinetics of zirconium, which was until now dominated by data from animal studies. The proposed systemic model improves the existing ICRP model, yet is based on the same principles and fits well into the ICRP radiation protection approach.

Enhancement effect of relative humidity on the formation and regional respiratory deposition of secondary organic aerosol

In this study, we investigated the effect of relative humidity (RH) on the formation of secondary organic aerosol (SOA) generated from the ozonolysis of d-limonene in an environmental chamber. The mass yield and the number concentration of SOA increased seven and eight times, respectively, when the RH increased from 18% to 82%. The measured total loss rates (apparent loss rates) of the number and mass concentration of SOA in the chamber ranged from 1.70 to 1.77 h −1 and from 2.51 to 2.61 h −1, respectively, at a controlled ventilation rate of 0.72 ± 0.04 h −1. The wall-deposition-loss-rate coefficient observed (1.00 ± 0.02 h −1) was approximate to the estimated value based on Zhao and Wu's model [1] which includes the factors of turbulence, Brownian diffusion, turbophoresis and surface roughness. According to the ICRP (International Commission on Radiological Protection) model, the inhaled SOA particles are deposited primarily in the alveoli of the lung. The integrated alveolar deposited dose of the mass (surface area) of SOA over 3 h accounted for 74.0–74.8% (74.3–74.9%) of the total deposited dose at the investigated RH. Raising the RH resulted in the growth of SOA particle sizes and increment of the deposition dose but did not cause significant changes in the ratio of regional to the total respiratory deposition of SOA.

A generic biokinetic model for Carbon-14

The generic biokinetic model currently recommended by the International Commission on Radiological Protection (ICRP) for the treatment of systemic radiocarbon assumes uniform distribution of activity in tissues and a biological half-time of 40 d. This model is intended to generate cautiously high estimates of dose per unit intake of C-14 and, in fact, generally predicts a much higher effective dose than systemic models that have been developed on the basis of biokinetic studies of specific carbon compounds. The simplistic model formulation precludes its application as a bioassay model or adjustment to fit case-specific bioassay data. This paper proposes a new generic biokinetic model for systemic radiocarbon that is less conservative than the current ICRP model but maintains sufficient conservatism to overestimate the effective dose coefficients generated by most radiocarbon-compound-specific models. The proposed model includes two systemic pools with different biological half-times representing an initial systemic form of absorbed radiocarbon, a submodel describing the behaviour of labelled carbon dioxide produced in vivo, and three excretion pathways: breath, urine and faeces. Generic excretion rates along each path are based on multi-phase excretion curves observed in experimental studies of radiocarbons. The generic model structure is designed so that the user may adjust the level of dosimetric conservatism to fit the information at hand and may adjust parameter values for consistency with subject-specific or site-specific bioassay data.

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.

Biokinetic and dosimetric modelling in the estimation of radiation risks from internalemitters

The International Commission on Radiological Protection (ICRP) has developed biokineticand dosimetric models that enable the calculation of organ and tissue doses for a wide range ofradionuclides. These are used to calculate equivalent and effective dose coefficients (dose inSv Bq−1 intake), considering occupational and environmental exposures. Dose coefficients have alsobeen given for a range of radiopharmaceuticals used in diagnostic medicine. Usingequivalent and effective dose, exposures from external sources and from differentradionuclides can be summed for comparison with dose limits, constraints and referencelevels that relate to risks from whole-body radiation exposure. Risk estimates are derivedlargely from follow-up studies of the survivors of the atomic bombings at Hiroshima andNagasaki in 1945.New dose coefficients will be required following the publication in 2007 of new ICRPrecommendations. ICRP biokinetic and dosimetric models are subject to continuing reviewand improvement, although it is arguable that the degree of sophistication of some of themost recent models is greater than required for the calculation of effective dose to areference person for the purposes of regulatory control. However, the models arealso used in the calculation of best estimates of doses and risks to individuals, inepidemiological studies and to determine probability of cancer causation. Models arethen adjusted to best fit the characteristics of the individuals and populationunder consideration. For example, doses resulting from massive discharges ofstrontium-90 and other radionuclides to the Techa River from the Russian Mayakplutonium plant in the early years of its operation are being estimated usingmodels adapted to take account of measurements on local residents and otherpopulation-specific data. Best estimates of doses to haemopoietic bone marrow, in uteroand postnatally, are being used in epidemiological studies of radiation-induced leukaemia.Radon-222 is the one internal emitter for which control of exposure is based on directinformation on cancer risks, with extensive information available on lung cancer inductionby radon progeny in mines and consistent data on risks in homes. The dose per unit 222Rn exposure can be calculated by comparing lung cancer risk estimates derived for 222Rn exposure and for external exposure of the Japanese survivors. Remarkably similar valuesare obtained by this method and by calculations using the ICRP model of the respiratorytract, providing good support for model assumptions. Other informative comparisons withrisks from external exposure can be made for Thorotrast-induced liver cancer andleukaemia, and radium-induced bone cancer. The bone-seeking alpha emitters,plutonium-239 and radium isotopes, are poorer leukaemogens than predicted by models.ICRP dose coefficients are published as single values without consideration of uncertainties.However, it is clear that full consideration of uncertainties is appropriate when consideringbest estimates of doses and risks to individuals or specific population groups. Anunderstanding of the component uncertainties in the calculation of dose coefficients can beseen as an important goal and should help inform judgements on the control of exposures.The routine consideration of uncertainties in dose assessments, if achievable, would be ofquestionable value when doses are generally maintained at small fractions of limits.

Influence of human biokinetics of strontium on internal ingestion dose of 90Sr and absorbed dose of 89Sr to organs and metastases

The objective of the present work is to apply the plasma clearance parameters to strontium, previously determined in our laboratory, to improve the biokinetic and dosimetric models of strontium-90 ((90)Sr) used in radiological protection; and also to apply this data for the estimation of the radiation doses from strontium-89 ((89)Sr) after administration to patients for the treatment of the painful bone metastases. Plasma clearance and urinary excretion of stable strontium tracers of strontium-84 ((84)Sr) and strontium-86 ((86)Sr) were measured in GSF-National Research Center for Environment and Health (GSF) in 13 healthy German adult subjects after intravenous injection and oral administration. The biological half-life of strontium in plasma was evaluated from 49 plasma concentration data sets following intravenous injections. This value was used to determine the transfer rates from plasma to other organs and tissues. At the same time, the long-term retention of strontium in soft tissue and whole body was constrained to be consistent with measured values available. A physiological urinary path was integrated into the biokinetic model of strontium. Parameters were estimated using our own measured urinary excretion values. Retention and excretion of strontium were modeled using compartmental transfer rates published by the International Commission on Radiological Protection (ICRP), the SENES Oak Ridge Inc. (SENES), and the Urals Research Center for Radiation Medicine (TBM). The results were compared with values calculated by applying our GSF parameters (GSF). For the dose estimation of (89)Sr, a bone metastases model (GSF-M) was developed by adding a compartment, representing the metastases, into the strontium biokinetic model. The related parameters were evaluated based on measured data available in the literature. A set of biokinetic parameters was optimized to represent not only the early plasma kinetics of strontium but also the long-term retention measured in soft tissue and whole body. The ingestion dose coefficients of (90)Sr were computed and compared with different biokinetic model parameters. The ingestion dose coefficients were calculated as 2.8 x 10(-8), 2.1 x 10(-8), 2.5 x 10(-8) and 3.8 x 10(-8) Sv Bq(-1) for ICRP, SENES, TBM and GSF model parameters, respectively. Moreover, organ absorbed dose for the radiopharmaceutical of (89)Sr in bone metastases therapy was estimated based on the GSF and ICRP biokinetic model parameters. The effective doses were 3.3, 1.8 and 1.2 mSv MBq(-1) by GSF, GSF-M, and ICRP Publication 67 model parameters, respectively, compared to the value of 3.1 mSv MBq(-1) reported by ICRP Publication 80. The absorbed doses of red bone marrow and bone surface, 17 and 21 mGy MBq(-1) calculated by GSF parameters, and 7.1 and 8.8 mGy MBq(-1) by GSF-M parameters, are comparable to the clinical results of 3-19 mGy MBq(-1) for bone marrow and 16 mGy MBq(-1) for bone surface. Based on the GSF-M model, the absorbed dose of (89)Sr to metastases was estimated to be 434 mGy MBq(-1). The strontium clearance half-life of 0.25 h from the plasma obtained in the present study is obviously faster than the value of 1.1 h recommended by ICRP. There are no significant changes for ingestion dose coefficients of (90)Sr using different model parameters. A model including the metastases was particularly developed for dose estimation of (89)Sr treatment for the pain of bone metastases.

Comparisons of 239Pu inhalation doses calculated with ICRP 67 and proposed systemic models

The International Commission on Radiological Protection (ICRP) has issued an age-specific systemic biokinetic model for plutonium (Pu), which was later modified to give better agreement with measured urinary excretion data. Recently, the current ICRP systemic Pu model was improved by Leggett et al. based on recently developed data. Incorporation of 239Pu in the human body may result in significant internal radiation exposure. In the present work, the retentions in organs and tissues, the equivalent dose and effective dose from 239Pu for workers and members of the public were estimated and compared under the current ICRP and the proposed models. 239Pu contents in liver and in other soft tissue calculated with the proposed model are higher than predicted by the ICRP model, whereas bone content is lower than predicted by the ICRP model. Based on the proposed model, the inhalation equivalent dose coefficient in some organs, e.g. liver and kidneys, is increased, but there is no significant change in the effective inhalation dose coefficients of 239Pu for workers and members of the public.