Technical Methods in X-Ray Therapy 



223 



of tissue of which the two fields are adjacent sides. The dose 

 dechnes rapidly outside this block. The single field with the 

 wedge-filter, and the two fields added at right angles, are shown 

 in figures 4a and 4b. To produce a field like 4a, the wedge must 

 cause a very considerable absorption, so that the useful dose rate 

 is seriously diminished. However, if adequate dose rate is avail- 

 able, the arrangement is very convenient for the irradiation of 

 lesions situated a few centimeters deep to the skin, and is specially 

 suitable to use with a jig to give accurate direction of the beams. 

 When a number of fields are chosen to give a uniform dose 

 distribution, a complete set should be administered to a patient 

 at one treatment, and not at intervals of a day or so. 



cm 



10 



FIG. 4a. IsoDOSE Curves as Modified by a Brass Wedge-Filter of Maximum 

 Thickness 6.3 mm. Field 8X8 cm, Focus-Skin Distance HVL of th^ Radiation 

 1,5 mm Copper (Ellis and Miller 7) 



