RESUMEN
The radiation field required to produce a dose distribution in rotation therapy may, in a certain approximation, be calculated using an integral equation, that is, the solution of the equation predicts the intensities needed to produce the dose distribution. The nature of this approximation is discussed and is shown to be connected with a Radon-type problem for circles through the origin provided the beam can be continuously modified during the rotation. The lowest order approximation provides a vivid geometrical way of looking at treatment planning which may be useful in novel situations and which will persist, to some extent, in higher-order approximations. Questions of scattering, and of the extension of the problem to a full three dimensional treatment are discussed.
Asunto(s)
Radioterapia/métodos , Humanos , Matemática , Modelos Biológicos , Dosificación RadioterapéuticaRESUMEN
We give the equations which need to be solved to extend the work of Brahme, Roos, and Lax to dose distributions which are not circularly symmetrical. These equations do not contain the linear absorption coefficient, mu, explicitly so they are valid in principle for any mu. The general solution of these equations has not been found, but the solution given by Brahme, Roos, and Lax is used to extend their work to simple dose distributions with an axis of symmetry. Some examples are given and discussed.
Asunto(s)
Dosificación Radioterapéutica , Humanos , Modelos Teóricos , Rayos XRESUMEN
An attempt has been made to see whether energetic protons (158 MeV) could be used instead of X-rays in computerized axial tomography to detect density differences of the order of those at which commercial X-ray tomographs cease to be useful. A circularly symmetrical phantom consisting of Lucite and sugar solutions was used, and density differences of 0-5% were reconstructed with reasonable accuracy from data obtained with very simple equipment. Discontinuities in either density or chemical composition, or both, seem to cause artifacts in the reconstruction. These may be related to the West-Sherwood effect.