Evaluation and characterization of parallel plate microchamber's functionalities in small beam dosimetry.

A parallel plate microchamber (PPMC) has been designed to specifically address the problems of small beam dosimetry. The chamber's extremely small volume and tissue equivalency theoretically make it possible for the chamber to perform an ideal measurement for small field dosimetry. Results show the PPMC to be a simple and reproducible detector for the measurements of total scattering factors, percentage depth doses, and off-axis ratios.

A conducting plastic simulating brain tissue.

A new conducting plastic has been composed which accurately simulates the photon and neutron absorption properties of brain tissue. This tissue-equivalent (TE) plastic was formulated to match the hydrogen and nitrogen constituents recommended by ICRU Report #44 for brain tissue. Its development was initiated by the inability of muscle tissue-equivalent plastic to closely approximate brain tissue with respect to low-energy neutron interactions.

Dose descriptors for computed tomography.

A weakness in the dose descriptor, the computed tomography dosimetry index, is discussed and an alternate descriptor is proposed. The new descriptor, the equivalent rectangular width, conveniently expresses the spatial spread of dose and is simply derived from customary dose measurements. A measure of performance, which expresses the relative size of the volume being imaged with respect to the volume receiving the dose, is suggested for computed tomography.