| dc.description.abstract | A comprehensive study of the substitute materials used in clinical
radiation dosimetry has shown that many of the existing products
give poor simulation for both photon and electron interactions•
Those materials with known composition were classified according
to the errors in their attenuation and energy absorption coefficients,
stopping and angular scattering powers compared to those for the
material being simulated Large discrepancies were found at low
photon energies, with lung and bone substitutes giving poor results.
The existing selection procedures were evaluated and two new
techniques were evolved, namely, the BASIC DATA METHOD and
the EXTENDED Vx) METHOD. The first procedure was based
on the attenuation and absorption quantities, while the second method
used an extension of the popular, but misused, concept of effective
atomic number.
A thorough analysis of the dependence of photon and electron
interactions on atomic number was made so that the effective atomic
number data could be manipulated more accurately.
Computer programs based on the new procedures were written
and, using a library of some 1040 materials, produced 77 new
formulations including muscle, fat, lung, bone, skin, breast,
liver, thyroid and air substitutes.
Techniques were developed for the manufacture and quality testing
of 35 of these new materials.
The results of a series of 'narrow-beam photon attenuation
measurements, nominally from 10 keV to 1 MeV, verified the high
precision of the selection procedures and provided useful data on
the contaminants present in some of the base materials.
Finally, the applications of the new substitutes in practical
dosimetry were investigated. | en_US |
