MILLION- VOLT THERAPY 



G. S. INNES, B.Sc, A.M.I.E.E., A.Inst.P. 



Physicist and Engineer to the Sassoon Department, 



St. Bartholomew^ s Hospital 



Introduction 



UP TO the year 1930, the maximum voltage X-ray equip- 

 ment available for X-ray therapy was of the order of 200 

 kilovolts. With such equipment, it had been demonstrated 

 that in some types of cancer it was possible to attain a cure 

 without irreparably damaging the patient. It was not known 

 whether the failure in many lesions in certain sites was due to a 

 difference in radiosensitivity, or whether it was due to the im- 

 possibility of delivering a sufficiently high dose to the lesion. 

 The problem was not a simple one, being complicated by many 

 factors. 



No matter how high a dose is administered to a lesion, there 

 are always some malignant cells left intact, and these have to 

 be overcome by local normal cells if the lesion is to be eradicated. 

 This can take place only if the normal cells have been less dam- 

 aged by the radiations than have the malignant ones — that is, 

 if the normal cells are less radiosensitive. Whether this radio- 

 sensitivity factor varied with the wave length of the radiations 

 was not known, but the hope that this might be the case war- 

 ranted investigation into the unexplored shorter wave lengths. 



For optimum results, damage to the normal tissue surrounding 

 the malignant zone should be reduced to a minimum, otherwise 

 blood supplies to the normal cells in the zone of destruction will 

 be cut, reducing their effectiveness. This requires a rapid de- 

 cline of the X-ray dose outside the zone of required destruction, 

 and it was forecast that this could be accomplished with the 



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