II. The Patient and the Röntgen. Part I

The problem involved in translating the röntgen from the standardising laboratory to the patient is reviewed. Some recent measurements of central axis percentage depth doses at 1·7 mm Cu and 1·06 mm Cu H.V.L. agree well with the H.P.A. Survey figures (1953) except at 20 cm2 for which the Survey values are significantly higher. Evidence is given for utilising the concept of surface dose-rate factor rather than back-scatter factor in the assessment of surface dose-rates. Measurements have been made of the effect on the tumour dose of a plaster shell and wax applicator seating. The optimum correction is considered to be zero rather than 5 per cent as hitherto widely assumed. Heterogeneous phantoms representing the skull and the thorax have been built and dosage has been investigated on and in these phantoms. The results are expressed in terms of both percentage depth doses and absolute doses, as compared with corresponding points in a water phantom.