[Consideration of inhomogeneities in irradiation planning. 2. Influence of inhomogeneities on the shape of the depth dose curve in water with 42 MeV X-rays (author's transl)].

With 42 MeV high-energy radiation, inhomogeneities such as bones, fat, plaster or palacos have no particular influence upon the depth dose curve in water because of the relatively insignificant differences of their atomic numbers, and there is no need to consider them in calculation of the focal dose. Metallic inhomogeneities, however, their effective atomic numbers being relatively high, show a different behaviour in 42 MeV X-ray bremsstrahlung: Just behing the metallic inhomogeneity an increase of the dose as compared to water is to be seen (e.g. directly behind a metallic plate, 4.5 mm thick, the augmentation of the dose amounts to 17%). This difference between 42 MeV X-ray bremsstrahlung and 60Co gamma rays (see part I of the present study) in the shape of the depth dose curve following permeation of metal by the radiations is due to enhanced pair formation within the high-energy radiation of 42 MeV photons.