CT-based interstitial HDR brachytherapy

Purpose: Development, application and evaluation of a CT-guided implantatio n technique and a fully CT-based treatment planning procedure for brachythe rapy. Methods and Materials: A brachytherapy procedure based on CT-guided implant ation technique and CT-based treatment planning has been developed and clin ical evaluated. For this purpose a software system (PROMETHEUS) for the 3D reconstruction of brachytherapy catheters and patient anatomy using only CT scans has been developed. An interface for the Nucletron PLATO BPS treatme nt planning system for optimization and calculation of dose distribution ha s been devised. The planning target volume(s) are defined as sets of points using contouring tools and are used for optimization of the 3D dose distri bution. Dose-volume histogram based analysis of the dose distribution (COIN analysis) enables a clinically realistic evaluation of the brachytherapy a pplication to be made. The CT-guided implantation of catheters and the CT-b ased treatment planning procedure has been performed for interstitial brach ytherapy and for different tumor sites in 197 patients between 1996 and 199 7. Results: The accuracy of the CT reconstruction was tested using first a qua lity assurance phantom and second, a simulated interstitial implant of 12 n eedles. These were compared with the results of reconstruction using radiog raphs. Both methods gave comparable results with regard to accuracy, but th e CT based reconstruction was faster. Clinical feasibility was proved in pr e-irradiated recurrences of brain tumors, in pretreated recurrences or meta static disease, and in breast carcinomas. The tumor volumes treated were in the range 5.1 to 2,741 cm(3). Analysis of implant quality showed a slightl y significant lower COIN value for the bone implants, but no differences wi th respect to the planning target volume. Conclusions: The Offenbach system, incorporating the PROMETHEUS software fo r interstitial HDR brachytherapy has proved to be extremely valuable in rou tine clinical practice for many tumor sites. Our CT-guided implantation tec hnique together with a fully CT-based planning system has enabled conformal brachytherapy treatment to become routine.