The Use of Wedge Filters in Deep X-ray Therapy

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Abstract
In the treatment of tumours by X-ray beams when the lesion is situated only a few centimetres deep to the skin, it is a matter of some difficulty to irradiate the tumour uniformly, using a cross-fire technique with the normal type of beam. This is especially so if it is desirable to avoid irradiating normal tissue deeper than the tumour. The irradiation of a tumour confined to one side of the floor of the mouth, for example, is not easy if it is desired to avoid strong irradiation of the other side of the mouth. The beams must then be confined to the affected side. The use of two or more normal fields directed at the tumour from one side of it gives an uneven dose distribution with a region of high dose near the surface. For a few years we have employed at the Sheffield Radium Centre a technique which we have called a “Wedge Technique” in an attempt to obtain uniformity of dosage in these circumstances without irradiating normal tissue more than necessary. The general principle is to introduce into the beam a wedge-shaped absorber. This is arranged so that the absorber thickness increases gradually from one side of a rectangular field to the opposite edge. The dose in any plane at right-angles to the central ray is thus reduced progressively in passing across the field.

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