RESUMEN
The system of modified tissue phantom ratio (called tissue standard factor, or TSF, in this paper) was introduced to facilitate the calculation of monitor units in isocentric configurations. Twenty-five years later, TSFS have been measured at 6 MV on different linear accelerators, and are in agreement with the original values, highlighting the property of machine independence. The utility of TSF is shown by the simplicity of the equation for calculating dose per monitor unit at any depth, field size and distance from source. New equations are given for relating isocentric systems to fixed-SSD systems, and the table of TSFS is extended to include a symbolic zero-area column, which is shown to be the primary-dose component of TSF in electronic equilibrium.
Asunto(s)
Modelos Teóricos , Radioterapia , Humanos , Matemática , Aceleradores de Partículas , Dispersión de RadiaciónRESUMEN
A transillumination computed tomography system has been developed for studies of the breast, testes, neonatal skull and peripheral limbs. Initial experiments on test objects have emphasised the problems of scattering and geometrical dependence of lesion detection that are likely to be encountered in conventional diaphanography, but have demonstrated the feasibility of computed tomography as a means of improving the sensitivity of the transillumination technique. The problems of transillumination computed tomography have been addressed and further areas of research identified.
Asunto(s)
Tomografía Computarizada por Rayos X/métodos , Transiluminación/métodos , Humanos , Dispersión de RadiaciónRESUMEN
The Meditech M250 computerised tomography (CT) machine was evaluated during the first half of 1984. Measurements were made of noise, modulation transfer function, slice width, radiation dose profile, uniformity and linearity of CT number, effective photon energy and parameters relating to machine specification, such as pixel size and scan time. All breakdowns were logged to indicate machine reliability. A comparison with the established EMI CT1010 and CT5005 was made for noise, resolution and multislice radiation dose, as well as the dose efficiency or quality (Q) factor for both head and body modes of operation. The M250 was found to perform to its intended specification with an acceptable level of reliability.