V. Dosage Control in Interstitial Gamma-ray Therapy

The object of this contribution is to review the progress of the past 15 years in a branch of radiotherapeutic physics which has received probably more attention in this country than in others. It might be objected that it is no longer a matter of importance since other methods, especially those using supervoltage X rays may already, or soon will, have supplanted interstitial methods. This is not the view, however, of many radiologists in this and other countries. In spite of the fact that implantation involves surgical interference and its concomitant risks, they regard the radium implant as an excellent method of delivering a high dose of γ rays to a limited volume of tissue. The tumour zone receives a high dose, the surrounding tissues very little (see, for example, Paterson, 1948). The implantation method being accepted, the need for efficient methods of dosage control is imperative, for good results can only be obtained by using correct radiation doses, and the knowledge of what are the correct doses can only be obtained from accumulated experience of many treatments at known doses. Essentially what we want to know is the rate at which radiation is being delivered so that the treatment time for any desired dose can be found. Probably the most important progress in interstitial therapy in general, and in the estimation of dosage rate in particular, came with the publication of the dosage system of Paterson and Parker (1938).