AbstractID: 7765 Title: Investigation of Density and Linear Attenuation Coefficient Changes in
Polymer Gel Dosimeters
There has been a large body of work in the past decade on the development of three-dimensional polymer gel dosimeters. Some
of this work has involved investigations into extracting absorbed dose information by x-ray computed tomography (CT) [1]. The
contrast in the CT image is due to an increase in the linear attenuation coefficient, µ, of the irradiated polymer gel dosimeter. In
this work we investigate the cause of the change in µ of the polymer gel dosimeter by comparing direct measurement in the
laboratory using narrow beam geometry with measurements of changes in physical density, ρ. It is shown that the increase in µ
and ρ are proportional. A linear fit of µ plotted against ρ gives a r2 value of 0.99877, a P value of <0.0001. The change in density
of the polymer gel dosimeter during irradiation may introduce uncertainties into the absorbed dose as the radiation attenuation
properties change. There is no mass lost from the gel during irradiation, therefore the increase in density must be related to a
reduction in the volume of the irradiated gel. Initial measurements show that the change in volume is within acceptable levels to
meet spatial resolution requirements of ICRU 42 [2].
1. Trapp, J.V. et al 2001. An experimental study of the dose response of polymer gel dosimeters imaged with x-ray computed
tomography. Phys. Med. Biol. 46 2939-2951.
2. ICRU Report No 42. Use of Computers in External Beam Radiotherapy Procedures with High-Energy Photons and Electrons.
1987, ICRU Publications: Betesda, MD.