1. NAME AND TITLE
FANTOM: Monte Carlo Calculation of the Response of an External Detector to a Photon
Source in the Lungs of a Heterogeneous Phantom.
Bhabha Atomic Research Centre Hospital, Bombay, India.
3. CODING LANGUAGE AND COMPUTER
Fortran IV; BESM-6.
4. NATURE OF PROBLEM SOLVED
FANTOM calculates the response of a 20-cm-diameter phoswich (3 mm NaI(Tl) primary detector)
to a source of low energy photons distributed in the lungs of a heterogeneous MIRD phantom,
approximating ICRP Reference Man. The program considers the trunk region of the MIRD phantom
which is made up of three types of tissues with different densities: skeletal tissue (1.85), lung tissue
(0.3) and soft tissue (1). Each organ in the thorax region is described by simple quadratic equations,
with respect to a Cartesian coordinate system (X,Y,Z), the origin of which is located at the center of
the base of the trunk, with positive Z-axis, Y-axis, and X-axis directed toward the head, posterior, and
left side of the phantom, respectively.
5. METHOD OF SOLUTION
FANTOM is designed for a 241Am source (60,000 disintegrations) uniformly distributed in the
lungs of the phantom. Monte Carlo techniques are employed to generate photons and trace their fates
in the thorax of the phantom. FANTOM starts by tracing 18,000 histories (9,000 in each lung) of
photons belonging to each of the four main energies of the 241Am nuclide. Each photon is assigned a
weight in proportion to its yield. The acceptable points of photon interactions (photoelectric and
Compton) in skeletal, lung, and ordinary tissue are determined by the Coleman technique. The
calculations yield the exit photon energy spectrum, which is then smeared with an experimentally
determined Gaussian resolution function to convert into the pulse-height spectrum observable with the
detector. The program has provisions for incorporating the effects of the iodine K X-ray escape as
well as the variable intrinsic efficiency of the detector.
6. RESTRICTIONS OR LIMITATIONS
The calculated calibration factors are valid only for body builds typical of the MIRD phantom.
There appear to be certain discrepancies regarding the estimates of the body-build parameters for the
MIRD phantom. There also appear to be wide variations between experimental observations made on
human volunteers and the results of Monte Carlo calculations on the MIRD phantom.
7. TYPICAL RUNNING TIME
No study has been made by RSIC of typical running times for FANTOM.
8. COMPUTER HARDWARE REQUIREMENTS
The code is designed to execute on the BESM-6 computer.
9. COMPUTER SOFTWARE REQUIREMENTS
A Fortran IV compiler is required.
S. Bhati, R. C. Sharma, and S. Somasundaram, "Monte Carlo Calculations of the Response of an
External Detector to a Photon Source in the Lungs of a Heterogeneous Phantom," Health Phys. 37,
145-159 (July 1979).
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.
12. DATE OF ABSTRACT
February 1982; revised February 1983.
KEYWORDS: MONTE CARLO; MODEL MAN; PHANTOM; GAMMA-RAY