Million-Volt Therapy 247 



the plant was operating continuously at one million volts and 

 since then some 10,000 hours of operation have been accom- 

 plished in spite of many near misses by bombs and V-weapons. 

 Although there was considerable damage to the buildings on 

 many occasions, the plant suffered little and at no time were 

 treatments not carried out on schedule, except when power 

 supplies were interrupted. 



The equipment is so designed that, as far as possible, methods 

 of treatment previously employed at 200 kilovolts can be repeated 

 with the new tube . The tube (figure 1 a, b) spans the treatment 

 room (X to X) and from the center of its span can emerge the 

 X-ray beam, the direction of which can be varied from pointing 

 vertically downwards to 110° upwards. This is accomplished 

 by rotation of the outer sheath of the tube (a). Adjustment of 

 the patient to the tube beam is accomplished by making the 

 center part of the treatment room floor (b) under the tube 

 traversible vertically through 7 feet [about 2.2 meters]. This is 

 necessary, since it would have been difficult to traverse the 32 

 feet long [about 9.75 meters] tube, which weighs nearly 12 tons 

 [about 12,192 kilograms]. The minimum FSD obtainable with 

 ease is 60 centimeters, comparable with that used at 200 kilovolts. 



Beam limitation at 200 kilovolts is done by lead-lined boxes 

 called applicators, fitted with end limiting stops of the required 

 size. At a million volts and 100 centimeters FSD, such appli- 

 cators, to be effective, would weigh some 200 pounds [91 kilo- 

 grams] and would be rather expensive and difficult to change. 

 An adjustable diaphragm (c) was therefore fitted on to the 

 tube outer sheath, built up of twin 1.5 inch [about 3.8 centi- 

 meters] thick adjustable lead stops, giving any beam size from 

 5 X 5 to 40 X 40 centimeters at 100 centimeters FSD. It is pos- 

 sible to use the diaphragm down to 60 centimeters FSD, but 

 beam positioning then becomes awkward. The diaphragm has 

 a light-beam device attached, indicating the size and position 

 of the X-ray beam in space. The X-ray beams obtained from 

 the diaphragm are not perfect, since they have penumbral edges 

 caused by combination of a large focal spot, 2.5 centimeters, 

 with the position of the stops at half the distance from the focus. 



