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A number of authors have calculated x-ray energies for mammography using, as a criterion, the maximum signal-to-noise ratio (SNR) obtainable per unit dose to the breast or conversely the minimum exposure for constant SNR. The predicted optimum energy increases with increasing breast thickness. Tungsten anode x-ray spectra have been measured with and without various added filter materials to determine how close the resultant spectra can be brought to the predicted optimum energies without reducing the x-ray output to unacceptable levels. The proportion of the total number of x-rays in a measured spectrum lying within a narrow energy band centred on the predicted optimum has been used as an optimum energy index. The effect of various filter materials on the measured x-ray spectra has been investigated both experimentally and theoretically. The resulting spectra have been compared with molybdenum anode, molybdenum filtered x-ray spectra normally used for mammography. It is shown that filters with K-absorption edges close to the predicted optimum energies are the most effective at producing the desired spectral shape. The choices of filter thickness and Vp are also explored in relationship to their effect on the resultant x-ray spectral shape and intensity.

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The photorl flus spectra from two 6 Mev Linear Accelerators and a 2 JIev Van do Graaff Generator which are in normal use for radiotherapy, have been measured using a 7.5 x i . 5 c m Sa1 (Tl) crystal spectrometer. The x-ray beam was scattered by aluminium sheets to reduce the intensity and energy range, and the primary spectra calculated from the measured scattered spectra using the Klein-Nishina formula. The crystal spectrometer was calibrated from theoretical Monte Carlo calculations which wele compared with experimentally obtained isotope spectra. The measured pulse height speotra were converted to photon flux spectra by a digital computer. Photon flux spectra wpre obtained for different field sizes and under dlfferenG operating condit,ions, a,nd the variation in the spectra over the x-ray field was investigated. The results Twre compared with theoretically calculated thick target spectra using published formulae for the bremsstrahlung cross-sectio!is.

This paper describes a low cost mobile measurement system for the determination of gold in vivo base around a 153Gd radiation source and a hyper pure germanium detector. Early clinical results are also presented to demonstrate the efficacy of the system.