1,000-Curie Cobalt-60 Units for Radiation Therapy

Abstract

TELETHERAPY units using radium are limited in usefulness by the low radiation intensities produced by the small amounts of radium which can be used. To secure an adequate dosage-rate, the distance between the source and the tumour cannot be more than a few centimetres, and therefore the dose delivered to the skin lying between the source and the tumour is much higher than that delivered to the tumour. The dose-rate below the surface, expressed as a percentage of the dose-rate at the skin, decreases very rapidly with increasing depth. Thus the percentage depth-dose is influenced primarily by the inverse square law, and one of the chief advantages of high-energy radiation, namely, its small attenuation by the tissue between the source and the tumour, is not realized.