Million-Volt Therapy 



255 



All these physical improvements make posible many altera- 

 tions and refinements in techniques developed for 200 kilovolt 

 therapy, and some methods quite inapplicable at 200 kilovolts 

 have been introduced. There is one other factor which has to 



lo 12 14 16 le 20 cm 

 Tissue Depth in cm 

 FIG. 4. 



Abscissae = tissue depth in cm 



Ordinates = ratio tissue dose 1,000 kv X-rays 



tissue dose 200 kv X-rays 



Ratio of the tissue dose with 1,000 kv DC. X-rays (9.0 mm Cu 



HVL) to that with 200 kv DC. X-rays (2.0 mm Cu HVL) for the 



same input skin dose at 100 cm FSD and various field sizes 



be brought in, out of sequence, before it is possible to discuss 

 alterations in treatment technique, viz., skin reaction. 



Alteration in Skin Reaction 



Tests were carried out on corresponding skin surfaces on 

 patients with X-ray beams of identical dimensions under the 

 same physical conditions except for the beam qualities. The 

 control beam was one of 300 kilovolts (3.35 millimeters Cu 



