Radiotherapeutic physics. VII. An instrument for dosage estimation with fields of any size and shape.
In the preceding paper in this symposium the need was stressed for a system of dosage estimation with beamed radiations of more general application than those at present use, and in particular one that could be used for the routine estimation of dose with fields of irregular shape. Brief mention was made of a machine which could fulfil this function, and the purpose of the present paper is to describe more fully the construction and mode of operation of this device. The basic principle of the device is one which has been discussed by various workers—that the analysis of the way in which the dose of scattered radiation at given points on the central axis of a circular field varies with field diameter can be made the basis of the estimation of dose at any point of the volume irradiated by an irregularly shaped field. The essential procedure in this estimation has in the past been one of integration, graphical or otherwise, of a rather cumbersome nature and not well fitted for routine work. However, in the p...
Applications of Wheatley's optical integrator.
In 1951 Wheatley of the Royal Cancer Hospital described an instrument which greatly facilitates the calculation of dosage due to X-ray fields of any size and shape. Experience with such a machine has led to extensions of its use in the solving of a large number of dosage problems which arise in the radiotherapy department. The basis of all the calculations of X-ray dosage below is the analysis, due to Meredith and Neary (1944), of scattered radiation, and reference should be made to these papers for an explanation of the symbols used.
The absorption of the γ-rays of radium
Summary From the theory of Klein and Nishina on the scattering, that of Hulme c.s. on the photo-absorption and that of Bethe and Heitler on the creation of pairs, we calculated the total absorption coefficients for the wavelengths corresponding to the various components of the gamma radiation of radium. With the aid of these theoretical absorption coefficients and of the intensities of these components found by Ellis and Aston we calculated the absorption curves for Al, Fe, Cu, Sn and Pb. The results of these calculations were found to be in perfect agreement with the absorption measurements of Kohlrausch (1917) .