Calculation Of Dose Coefficients Research Articles

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%.

Cálculo de H(50) y E(50) para 90sr - 90y utilizando el hatm y los modelos voxelizado de la mujer y hombre adultos de referencia de la ICRP

La Comisión Internacional de Protección Radiológica, ICRP, propuso una nueva metodología para el cálculo de coeficientes de dosis para trabajador ocupacionalmente expuesto que cambia la propuesta en las publicaciones 60 y 78 de la misma comisión. En este trabajo se reprodujeron los valores AF para hombre adulto reportados en la publicación 100 de la ICRP utilizando el software MCNPx y se calcularon con la misma metodología los SAFs para los compartimentos del HATM de mujer adulta, para electrones monoenergéticos dentro del rango de energías de 0.01 a 4 MeV. Se calcularon los SAFs en phantom voxelizados para hombre y mujer adulto, cuya estructura anatómica se reporta en la publicación 110 de la misma Comisión, usando la misma metodología de cálculo con el software MCNPx. Con estos datos se calcularon los coeficientes h(50) y e(50) para incorporación única por ingestión del 90Sr – 90Y, dada su importancia dosimétrica. Se consideraron las fracciones de absorción en intestino delgado reportados por la ICRP 78 y la metodología recomendada por la publicación 103 de la ICRP, encontrando valores de e(50) menores que los reportados por la ICRP en sus publicaciones. Finalmente se comparan los valores obtenidos con los reportados por Wei Bo Li et al.

ICARE software for calculation of dose coefficients and retained/excreted fractions of intake

ICARE software for calculation of dose coefficients and retained/excreted fractions of intake

Doses from radiation exposure

Practical implementation of the International Commission on Radiological Protection’s (ICRP) system of protection requires the availability of appropriate methods and data. The work of Committee 2 is concerned with the development of reference data and methods for the assessment of internal and external radiation exposure of workers and members of the public. This involves the development of reference biokinetic and dosimetric models, reference anatomical models of the human body, and reference anatomical and physiological data. Following ICRP’s 2007 Recommendations, Committee 2 has focused on the provision of new reference dose coefficients for external and internal exposure. As well as specifying changes to the radiation and tissue weighting factors used in the calculation of protection quantities, the 2007 Recommendations introduced the use of reference anatomical phantoms based on medical imaging data, requiring explicit sex averaging of male and female organ-equivalent doses in the calculation of effective dose. In preparation for the calculation of new dose coefficients, Committee 2 and its task groups have provided updated nuclear decay data (ICRP Publication 107) and adult reference computational phantoms (ICRP Publication 110). New dose coefficients for external exposures of workers are complete (ICRP Publication 116), and work is in progress on a series of reports on internal dose coefficients to workers from inhaled and ingested radionuclides. Reference phantoms for children will also be provided and used in the calculation of dose coefficients for public exposures. Committee 2 also has task groups on exposures to radiation in space and on the use of effective dose.

Voxel2mcnp

Voxel2MCNP is a program that sets up radiation protection scenarios with voxel models and generates corresponding input files for the Monte Carlo code MCNPX. Its technology is based on object-oriented programming, and the development is platform-independent. It has a user-friendly graphical interface including a two- and three-dimensional viewer. A row of equipment models is implemented in the program. Various voxel model file formats are supported. Applications include calculation of counting efficiency of in vivo measurement scenarios and calculation of dose coefficients for internal and external radiation scenarios. Moreover, anthropometric parameters of voxel models, for instance chest wall thickness, can be determined. Voxel2MCNP offers several methods for voxel model manipulations including image registration techniques. The authors demonstrate the validity of the program results and provide references for previous successful implementations. The authors illustrate the reliability of calculated dose conversion factors and specific absorbed fractions. Voxel2MCNP is used on a regular basis to generate virtual radiation protection scenarios at Karlsruhe Institute of Technology while further improvements and developments are ongoing.

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.

Recent developments in biokinetic models and the calculation of internal dose coefficients

In most cases the measurement of radioactivity in an environmental or biological sample will be followed by some estimation of dose and possibly risk, either to a population or an individual. This will normally involve the use of a dose coefficient (dose per unit intake value) taken from a compendium. In recent years the calculation of dose coefficients has seen many developments in both biokinetic modelling and computational capabilities. ICRP has recommended new models for the respiratory tract and for the systemic behavior of many of the more important elements. As well as this, a general age-dependent calculation method has been developed which involves an effectively continuous variation of both biokinetic and dosimetric parameters, facilitating more realistic estimation of doses to young people. These new developments were used in work for recent ICRP, IAEA and CEC compendia of dose coefficients for both members of the public (including children) and workers. This paper presents a general overview of the method of calculation of internal doses with particular reference to the actinides. Some of the implications for dose coefficients of the new models are discussed. For example it is shown that compared with data in ICRP Publications 30 and 54: the new respiratory tract model generally predicts lower deposition in systemic tissues per unit intake; the new biokinetic models for actinides allow for burial of material deposited on bone surfaces; age-dependent models generally feature faster turnover of material in young people. All of these factors can lead to substantially different estimates of dose and examples of the new dose coefficients are given to illustrate these differences. During the development of the new models for actinides, human bioassay data were used to validate the model. Thus, one would expect the new models to give reasonable predictions of bioassay quantities. Some examples of the bioassay applications, e.g., excretion data for the plutonium model, are discussed briefly.