Ring filter to locate external boundaries in SPECT using scattered radiation.

A novel form of filter for SPECT is described, in which, after back projection and summation, the reconstructed signal is a measure of the total activity within a ring of specified radius, centre and width. The filter is applied to the problem of using Compton scattered radiation to locate external boundaries. In the simple case of the determination of the radius of a circular scattering body of known centre, the filter output would identify a transition region and define an appropriate threshold as the boundary was crossed.

Experimental 3D dosimetry around a high-dose-rate clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter.

It is well known that the experimental dosimetry of brachytherapy sources presents a challenge. Depending on the particular-dosimeter used, measurements can suffer from poor spatial resolution (ion chambers), lack of 3D information (film) or errors due to the presence of the dosimeter itself distorting the radiation flux. To avoid these problems, we have investigated the dosimetry of a clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter.