Million-Volt Therapy 245 



tubes became an economical proposition. These tubes had walls 

 and envelopes electrically better than those of the sealed-off 

 tubes, but they had previously been barred by their prolonged 

 gassing.^' ^' ^ 



Million-volt Equipment at St. Bartholomew's 

 Hospital, London 



The hospital is indebted to the foresight of its Radium 

 Committee, the generosity of Mrs. Meyer Sassoon, and the 

 technical skill of the Research Department of Messrs. Metro- 

 politan-Vickers Electrical Co., Ltd., Manchester, for envisaging 

 and making available the million-volt plant installed in the 

 hospital in 1936. The equipment was guaranteed to operate at 

 600 kilovolts d.-c. 3 milliamperes, with the proviso that con- 

 tinuous operation at one million volts would be aimed at. In 

 the first hour after final erection, 700 kilovolts 4 milliamperes 

 was attained, but at voltages greater than this, the tube became 

 unstable in operation.^ 



During the next two years, while many modifications and 

 additions were made to the tube, treatments were carried out 

 at 700 kilovolts, giving the medical and physical staff an insight 

 into the problems to be encountered at higher voltages. By 1938, 



a Rotable applicator cylinder 



b Moving floor 



c Adjustable diaphragm for limiting size of emergent beam 



d 8-ton lead protection cylinder, used as sbutter by rotating 



e Steel tube vacuum envelope 



/ Gold or copper target head 



g Aperture in lead cylinder 



h Lead block suspended from roof, blocking upwards beam, when shutter 



in "safe" position (as shown) 



i Parallel plate ionization chamber across beam 



/ Cathode support tube 



k Six-element filament assembly 



I Negative mid-potential steel sheath 



tn Target support tube 



n Positive mid-potential steel sheath 



Support insulators 



p 04 (vacuum) pumping plants 



q Treatment couch 



r Control pedestal for tube angulation and floor movement 



X Barytes X-ray protection walls between treatment room and H.T. rooms 



