Physical Measurements in High Voltage X-ray Therapy

Abstract

In the Mozelle Sassoon High Voltage X-ray Therapy Department at St. Bartholomew's Hospital, the physical aspects of X rays excited at 700 K.V. have been investigated mainly from the point of view of their use in therapy. Clinical experience with 700 K.V. X-rays was considered desirable before proceeding to the full 1,000 K.V. for which the apparatus was designed. Much work has, of course, been done on the technical problems associated with the behaviour and operation of the installation, with the design of measuring instruments, diaphragms, applicators and accessory equipment in general, and with X-ray protection measures. The present paper, however, will be confined to reporting the physical measurements of intensity, absorption, quality, scatter and percentage depth dose; it is not proposed to discuss the significance of the results obtained, since further investigations at higher voltages are in progress. A full description of the design and operation of the apparatus will be published elsewhere; it will therefore suffice to say that the X-ray tube is of the continuously evacuated type, with a water-cooled gold target, and is supplied from 600 K.V. constant potential positive and negative generators. The operating voltage has been measured in three ways:— (a) By the manufacturer's calibration from the primary voltage of the transformers. (b) By 50 cm. sphere-gaps mounted at each end of the X-ray tube. (c) By oil-immersed resistance voltmeters.