Post-irradiation changes in the linear attenuation coefficient, μ, of polymer gel dosimeters give rise to a change which can be measured with x-ray computed tomography. Polymer gel dosimeters were manufactured consisting of 3% (by weight) acrylamide and 3% N,N′-methylene-bis-acrylamide comonomers dissolved in aqueous gelatin (5% gelatin by total weight and 89% de-ionized distilled water). μ was measured in a collimated radiation beam of photons from an 241Am source. Density, ρ, of polymer gel dosimeters was measured using volumetric flasks with capillary stoppers. The measured post-irradiation data of μ was plotted against the data of ρ for different batches, and linear least squares fits gave r2 values of 0.996 05 and 0.999 53, with P values of less than 0.001. This confirms that the post-irradiation change in μ is proportional to that of ρ. The change in ρ implies a change in volume regardless of the evaluation modality of the polymer gel dosimeter.