A New Design 6 MeV Linear Accelerator System for Supervoltage Radiotherapy

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Abstract
A description is given of a new and compact megavoltage therapy system which combines a cantilevered treatment couch with an isocentrically mounted accelerator capable of rotating completely around a recumbent patient. In addition, provision is made for therapy techniques which require patient rotation. This linear accelerator system introduces a new standard of compactness and flexibility as related to patient treatment. The overall height of the accelerator is less than 240 cm while a 100 cm FSD is retained. The patient support assembly includes a plastic portal device for irradiation from beneath the couch, three-dimensional positioning of the patient, and snap-off wheel assemblies which enable the patient to be lowered to floor level on an electrically operated pedestal for large field techniques. These features ensure rapid, precise, and consistent patient set-up procedures. Representative techniques are illustrated. Use of the actual treatment couch for patient transportation is an operational convenience. The application of this accelerator system for diagnostic radiography is discussed. Physical measurements indicate a high degree of beam flatness and a surface dose of less than 20 percent of the maximum which occurs at about 15 mm depth. High X-ray intensity permits large FSD techniques. Approximately 600 watts of electron beam power can be made available through the X-ray beam defining system by a simple conversion. Some characteristics of the electron beam are discussed to enable evaluation for sterilisation and radiobiological applications.