Some Data Concerning the Use of X-ray Beams in Direct (Cross-Firing) Opposition

Abstract

A Technique widely used in deep X-ray therapy (e.g., for irradiation of the axilla, pelvis, whole limbs, neck, etc.) is that which utilises two identical beams cross-firing through opposite fields or portals. One of the chief reasons for this wide use is that the technique represents one of the simplest methods of achieving (a) a large dose at the centre point between the fields1 relative to that received by the skin surface—it is in this region that the disease is usually situated and (b) a high degree of dosagė homogeneity between the two fields. The latter is of the utmost importance in the treatment of many cases where the disease is extensive. It is of value to the radiologist using such a technique to know how the dosage conditions provided by it depend upon the various physical factors, radiation quality, focus-skin distance, field size and separation of the opposing fields. The last of these is usually equal to the maximum thickness of the part to be irradiated. A few specific cases of this method...