CENTRALIZED MULTIINSTITUTIONAL POSTIMPLANT ANALYSIS FOR INTERSTITIAL PROSTATE BRACHYTHERAPY

Purpose: To investigate the feasibility and utility of performing cent ralized postimplant analysis for transperineal interstitial permanent prostate brachytherapy (TIPPB) by conducting a pilot study that compar es the results obtained from I-125 implants conducted at five differen t institutions. Methods and Materials: Dose-volume histogram (DVH) ana lysis was performed on 10 postimplant CT scans from each of five insti tutions. This analysis included the total implanted activity of I-125, ultrasound, and CT volumes of the prostate, target-volume ratios, dos e homogeneity quantifiers, prostate dose coverage indices, and rectal doses. As a result of the uncertainty associated with the delineation of the prostatic boundaries an a CT scan, the contours were redrawn by a single, study center physician, and a repeat DVH analysis was perfo rmed. This provided the basis for comparison between institutions in t erms of implant technique and quality. Results: By comparing total act ivity to preimplant ultrasound volume we clearly demonstrated that dif ferences exist in implant technique among these five institutions. The difficulty associated with determining glandular boundaries on CT sca ns was apparent, based upon the variability in prostate volumes drawn by the various investigators compared to those drawn by the study cent er physician. This made no difference, of course, in the TVR or homoge neity quantifiers that are independent of target location. Furthermore , this variability made surprisingly little difference in terms of dos e coverage of the prostate gland. Rectal doses varied between institut ions according to the various implant techniques. Conclusions: Central ized, outcome-based evaluation of transperineal interstitial permanent prostate brachytherapy is viable and appropriate. Such an approach co uld be reasonably used in the conduct of multiinstitutional trials use d to study the efficacy of the procedure. (C) 1998 Elsevier Science In c.