Smithsonian Report, 1948.—Trump PLATE 4 
This circular radiograph and the two shown on plate 5 illustrate the technique 
of cross-firing with one- three- and continuous-portal radiation, as described 
under each of the separate illustrations. 
A 2-million-volt beam of X-rays passing through a 20-centimeter cylinder of 
Masonite representing a phantom patient. In deep X-ray therapy the beam 
of radiation must enter through the skin and pass through the intervening 
healthy tissue before it reaches the tumor itself. Supervoltage X-rays pro- 
duce relatively little reaction on the radiation-sensitive skin, and, because of 
the higher penetration and lower scattering, are capable of delivering a higher 
dose to a deep tumor than can be achieved with lower-voltage X-rays. 
