Technical Methods in X-Ray Therapy 227 



of light along what is later the X-ray beam axis. A tube with 

 cross wires and sighting aperture, at the other side of the room, 

 is aligned with this light beam. The tube can also throw a light 

 beam back in the same direction, so that, when the patient is 

 adjusted to the applicator, a light spot on the patient shows the 

 position of emergence of the beam. The use of this appliance 

 in the treatment of esophageal growths is described by Adams. ^ 

 It eliminates error due to whip in mechanical callipers, but has 

 the disadvantage that the patient must be adjusted to the ap- 

 plicator, which must not be moved out of line with the light 

 beam. 



By *'jig" is meant an appliance which can l)e fitted to a patient 

 in a reproducible position, and which has surfaces or sockets in 

 correct positions, to which the applicator is adjusted. A simple 

 illustration is the jig to insure that two wedge fields are applied 

 to a patient correctly at right angles. The jig is formed of two 

 "perspex" (transparent plastic) plates, each the size of the ap- 

 plicator end, and fixed at right angles to each other. It is ad- 

 justed on the patient so that the block of tissue it is desired 

 to treat is within the right angle. Skin markings are made so 

 that it can be replaced in the same position. A metal replica is 

 substituted for the perspex one, and any space between it and 

 the skin is filled with "radium compo" (see below), a thermo- 

 plastic material. The radium-compo mold is detached from the 

 metal replica, and used in the same position in the perspex jig. 

 The fact that the radium compo has taken the shape of the body, 

 together wnth the skin markings, makes it easy to replace the 

 jig in the same position for each treatment. It is a simple matter 

 to bring the X-ray-tube applicator into contact with each plane 

 surface in turn. 



Flood and Smithers ^^ illustrate a nose built up with a wax 

 mold to form a parallel-sided slab to aid in the correct adjust- 

 ment of two opposed fields. 



Another method is to produce a rigid shell, to fit the part of 

 the patient's body under treatment, from plastic materials — 

 nidrose, plaster bandage, or bexoid — and to cast on it wax 

 sockets into which the applicator will slip in correct positions.*'* 



