The Paris System in Interstitial Radiation Therapy

The introduction of after-loading methods for flexible lg21r wires in interstitial therapy has brought renewed interest in this modality of radiation therapy throughout the world (cf.HILARIS 1975).While a major advantage to the therapist and the staff has been the improved radiation protection, the use of these techniques has also allowed a new dosimetry to be evolved, the 'Paris System', better suited to the characteristics of flexible wire implants than the previous dosage systems which were associated with rigid sources of finite length ( PIERQUIN 1971, DUTREIX et coll., in press).The techniques for the use of these methods have been described previously ( PIERQUIN 1964, PAINE 1972, PIERQUIN et coll.1977).The purpose of this article is to describe the system of dosimetry, which has now been found satisfactory in clinical use for over 15 years, and to show the current practice in day to day implant construction, dose calculation and prescription.Although some 90 per cent of the applications are calculated easily by the methods to be described, it seems right to say that in a very small number it is not possible to distribute the sources in such a way that this system can be accurately applied, usually