1. NAME AND TITLE

TIMED: Calculation of Cumulated Activity of a Radionuclide in the Organs of the Human Body at a Given Time After Deposition.

2. CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV and Assembler language; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

TIMED is designed to calculate cumulated activity in various source organs at a specified time, t, after deposition. TIMED embodies a system of differential equations which describes activity transfer in the body. Activity transfer is based on the concept of a system of compartments with constant rates of transfer to other compartments of the body. The pathways of transfer and transfer constants for the lungs and gastrointestinal tract are those described in ICRP Publication 19 and Publication 2. The models for activity transfer to other organs of the body must be supplied by the user. The code is sufficiently general to allow for radioactive daughters born in the body and also handles branching of decay schemes.

5. METHOD OF SOLUTION

The solution of the ordinary differential equation (ODE) is calculated using a subroutine package which is based on a program written by C. W. Gear for the solution of initial value problems for a system of ODE's. A prime feature of the GEAR package is the ability to solve stiff ODE problems. The basic method used is a linear multistep method. The method is implemented in a manner which allows both the step size and the order to vary in a dynamic way throughout the problem.

6. RESTRICTIONS OR LIMITATIONS

The code is limited to 12,000 differential equations, i.e., compartments in the model. The maximum number of nonzero entries in a row of the coefficient matrix is 52. The maximum number of radionuclides in a chain is 10.

The user may include up to 10 source organs other than lungs and gastrointestinal tract. Each source organ may include up to 10 compartments.

7. TYPICAL RUNNING TIME

For compilation, the FORTRAN routines require about 7.5 seconds; the Assembler language routines 0.7 seconds. Execution time depends upon many factors: the number of differential equations, the number of nonzero entries in the coefficient matrix, the length of the time period of integration, etc. The execution time for a complicated chain of four radionuclides involving 116 differential equations is about 5.8 seconds.

8. COMPUTER HARDWARE REQUIREMENTS

The code is operable on the IBM 360/370 and requires about 310 K for execution.

9. COMPUTER SOFTWARE REQUIREMENTS

A FORTRAN IV and Assembler compiler is required.

10. REFERENCES

S. B. Watson, W. S. Snyder, and M. R. Ford, "TIMED: A Computer Program for Calculating Cumulated Activity of a Radionuclide in the Organs of the Human Body at a Given Time, t, After Deposition," ORNL/CSD/TM-17 (December 1976).

J. M. Langsted, "Investigations of Several Task Group Lung Model Modifications to More Accurately Describe Pulmonary Clearance of In Vivo Produced Daughter Products," M. S. Thesis, U. Washington (1977).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code and sample problem input and output.

12. DATE OF ABSTRACT

December 1981.