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A Birchall

Publications and source records attributed to A Birchall.

8 recordsLinked to original sources
PubMed1989

A microcomputer algorithm for solving first-order compartmental models involving recycling.

A general algorithm for solving first-order compartmental models including recycling systems has been developed and its implementation on a microcomputer is described. Matrix algebra is used to obtain for any compartmental model an analytical solution, which is expressed as the exponential of a matrix of rate constants. A special technique is used in the algorithm to enable this exponential to be evaluated with a rapidly converging series. Truncation errors incurred in this process are estimated automatically. Thus, in an extreme case, where these errors may be significant, the appropriate action can be taken. Given a particular model, the user enters the model parameters into a rate matrix according to a simple rule. The algorithm then uses this matrix to solve the model, and thus no specialized mathematical knowledge is needed. The algorithm is given in a short BASIC program (60 lines) listed in an appendix. No additional software is required. By running this program on a standard microcomputer, the user can solve models of any complexity: those up to 15 compartments in seconds and those up to 30 compartments within a minute. The algorithm is thus ideally suited to solve kinetic models describing the transport of radionuclides in the environment or the translocation of elements in biological systems such as the metabolic models recommended by the International Commission on Radiological Protection (ICRP). Given the initial amount of material in each compartment at time t = 0, together with its radioactive decay constant, the algorithm gives both the amount in each compartment at any future time t and the number of disintegrations that will have occurred in each compartment up to time t. The computer program, shown in an appendix, could easily be used to calculate disintegrations over any time interval of interest, or to predict the quantities or fractions of an intake expected to be present in any in vivo or excretion compartments of interest. Thus, the algorithm can be useful in both the design and conduct of bioassay and internal dose assessment procedures.

Algorithms↗
PubMed1989

Sensitivity testing of an age-related, multicompartment dosimetric model for bone-surface-seeking radionuclides in man.

The sensitivity testing of an age-related dosimetric model and its application to the dosimetry of 239Pu are described. The model is used to calculate the committed dose received by the skeleton and liver to age 70 y, following intakes of 239Pu by an adult aged 20 y and by children aged 0 and 10 y. The model is biologically based and takes account of the age-dependent transfer of Pu between the different organs of the body and between the different components of the skeleton. It consists of 22 compartments, 16 of which are skeletal, each connected by transfer pathways defined by age-dependent rate constants. The sensitivity of the predictions of the model, as applied to adults, to changes in the assumed values of rate constants were tested. The results of the tests applied suggested that the age-related model is relatively robust and is not particularly sensitive to changes in the assumed values of many of the rate constants used.

Adult↗
PubMed1989

The current approach of the ICRP Task Group for modeling doses to respiratory tract tissues.

For radiation protection purposes, the International Commission on Radiological Protection (ICRP) Task Group proposes to apportion radiation risk within the respiratory tract according to the tumor mortality rates observed in the different anatomical regions. This approach requires that doses absorbed by extrathoracic tissues must be considered, in addition to those in the lung. For the extrathoracic region, the tissues at highest potential risk are the pharyngeal parts of the nasopharynx and oropharynx and a part of the larynx. In the lung, all tissues are potentially at risk, and it is necessary to consider doses absorbed by bronchial tissues, the lung parenchyma, and lymph nodes. This paper outlines the methods proposed by the Task Group to evaluate the heterogeneous doses absorbed by sensitive cells in these tissues from radioactive decays of alpha-emitters. The objective is to evaluate doses to broad regions of the respiratory tract, where the regions are defined to reflect substantial differences in potential risk when taking into account deposition and clearance behavior. The Task Group proposes to represent the respiratory tract by three generic regions: an extrathoracic region and two thoracic regions, one clearing fast and one slowly. The models of aerosol deposition and clearance applied for each region are outlined. To illustrate the use of the model, doses are evaluated for the key cases of short-lived radionuclides and long-lived insoluble alpha-emitters and are discussed with regard to current ICRP recommendations.

Aerosols↗
PubMed1986

A microcomputer algorithm for solving compartmental models involving radionuclide transformations.

An algorithm for solving first-order non-recycling compartment models is described. Given the initial amounts of a radioactive material in each compartment and the fundamental transfer rate constants between each compartment, the algorithm gives both the amount of material remaining at any time t and the integrated number of transformations that would occur up to time t. The method is analytical, and consequently, is ideally suited for implementation on a microcomputer. For a typical microcomputer with 64 kilobytes of random access memory, a model containing up to 100 compartments, with any number of interconnecting translocation routes, can be solved in a few seconds; providing that no recycling occurs. An example computer program, written in 30 lines of Microsoft BASIC, is included in an appendix to demonstrate the use of the algorithm. A detailed description is included to show how the algorithm is modified to satisfy the requirements commonly encountered in compartment modelling, for example, continuous intake, partitioning of activity, and transformations from radioactive progeny. Although the algorithm does not solve models involving recycling, it is often possible to represent such cases by a non-recycling model which is mathematically equivalent.

Computers↗