An 8-MeV linear accelerator for X-ray therapy

The paper gives a general account of a 4-year research and development programme which has resulted in the installation at Hammersmith Hospital of a new type of super-voltage therapy equipment. This machine produces 8-MV X-rays, and stabilized outputs of up to 200 r/min at 1 m are available after filtration. Acceleration of the electrons is obtained by a 3-m length of corrugated waveguide energized by a magnetron giving a pulsed output of approximately 2 MW peak power at a free-space wavelength of 10 cm. Since the accelerating unit is fixed with its axis horizontal, the electron beam is deflected through a right angle before reaching the target, and the deflector system is made rotatable, to give variable direction of the X-ray beam. Many clinical facilities are available, and, in addition, the electron beam may easily be extracted. Early Sections of the paper deal with the background to the programme, the underlying principles and the basic design. These are followed by a description of the equipment and some details of its construction. The investigation of the performance is covered in some detail, and certain improvements in the understanding of the properties of the accelerating waveguide are discussed. Finally, a comparison is made between measured and calculated performance and the agreement is shown to be satisfactory.