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...
A method of dose calculation with applications to moving-field therapy.
A simple numerical system of dosage estimation is described. By analysing the dose into primary and secondary components the dose at any point can be found quickly. Tables based on recent central axis depth dose data are presented to assist the calculations in the range 1–3·5 mm Cu H.V.L., and their use is illustrated by examples. The methods are applied to problems of moving-field therapy and are shown to offer a rapid solution to most problems of are therapy.
The Absorption of X-Rays of Wave-Length 50 ≤ λ 150 X.U. by Elements of Low Atomic Number
With a 600 kv x-ray source and a two-crystal spectrometer especially designed for short wave-length x-rays, the mass absorption coefficients for C(6), Na(11), Al(13), S(16), K(19), Ni(28), Cu(29) were determined for wavelengths from 50 to 209 X.U. A small $\ensuremath{\delta}\ensuremath{\lambda}$ interval was used. The results are estimated to be in error by no more than two percent. The present results are compared with the few overlapping measurements of other observers. The values of the electronic scattering coefficient predicted by the Klein-Nishina formula are in excellent agreement with the experimental values of the scattering by carbon in the region $40\ensuremath{\le}\ensuremath{\lambda}\ensuremath{\le}100$ X.U., which confirms the Klein-Nishina formula for this wave-length region. The photoelectric absorption in copper was found to be proportional to ${\ensuremath{\lambda}}^{2.83}$.