A Wedge Filter Approach with 4 MV Radiation to the Treatment of Carcinomata of the Alveolus and Antrum

poor depth dose and the loss of wedge angulation created problems of prescription when treating at depth. Some of these have since been solved by Cohen (1959), but even so, from considerations of the differential absorption in bone, conventional therapy could never be.a serious contender where alternative treatment by radium was available. Following the introduction of 4 MV radiation, the position immediately changed. Theoretically at least, here was radiation with physical characteristics ideally suited for use with wedge filters. The relative absence of lateral scatter results in a more or less direct relationship between the dose at a point and the intensity of the primary beam through that point. Thus, attenuation of the primary beam, as by a wedge, is reflected accurately by the isodoses. The wedge angulation is thus maintained into depth. From this same argument the depth dose at any point below an oblique surface is simply calculated, and the necessary correction for such obliquity may be incorporated in the prescription. Correction by use of bolus becomes less important, but may still be necessary in certain sites. In such cases a beam compensator such as that introduced by Ellis et al. (1959) might be used with advantage. Despite the great advantage of skin sparing with megavoltage radiation, the danger of tumour involvement near the surface must be borne in mind. With 4 MV radiation in the treatment of tumours around the mouth, it is surprising how often bolus is necessary for this