A CONFORMAL INDEX (COIN) TO EVALUATE IMPLANT QUALITY AND DOSE SPECIFICATION IN BRACHYTHERAPY

Purpose: To propose a new index (COIN) that can be easily understood a nd computed to assess high dose rate (HDR) brachytherapy interstitial implant quality and dose specification and is an improvement on existi ng indexes, Methods and Materials: The COIN index is based on an exten sion of dose-volume histograms and employs an analogous concept to tha t of cost-benefit analysis, which has already been applied to quality- of-life assessments for two alternative treatment protocols, The COIN index calculation methodology is shown for two cases: with and without critical structures. An analysis is given of dose distributions for t wo planning treatment volumes (PTV) of simple geometrical shape, apply ing both the rules of the Paris system and that of the ''Offenbach'' s ystem. 40 patients who have received interstitial implants form the cl inical material, With current HDR brachytherapy technology both for do se delivery, using remote afterloaders, and for three-dimensional (3D) treatment planning, it is now possible to relatively easily plan conf ormal brachytherapy treatments that would have been impossible with ma nual afterloading techniques and two-dimensional (2D) treatment planni ng, Results: Examples of the use of the COIN index are presented for e xperimental and clinical data, Conclusions: The results show that COIN is a useful and practical index to improve the quality of treatment o f interstitial brachytherapy implants, Further work will be undertaken with a larger population of implanted cancer patients and a subdivisi on of the results by treatment site. (C) 1998 Elsevier Science Inc.