Optimal source position for irradiation of coronary bifurcations in endovascular brachytherapy with catheter based beta or iridium-192 sources.

ABSTRACT

BACKGROUND AND PURPOSE: Intracoronary brachytherapy after percutaneous transluminal coronary angioplasty (PTCA) is usually performed with catheter-based treatment techniques in a straight vessel segment. There is a growing interest for treatment of bifurcations, which requires consecutive positioning of the source in main vessel and side branch. MATERIALS AND METHODS: In-house developed software (IC-BT doseplan) is used to explore the optimal positioning of the source in modelled bifurcations with different shape for the source types available in our hospital, i.e. (90)Sr/(90)Y, (32)P and (192)Ir. The results were summarised in look-up tables. The usefulness of these look-up tables was tested on various clinical examples. RESULTS: Tabulated results for the modelled bifurcations yield an estimation of the distance between the sources (gap width) in relation to the geometry and source type (90)Sr/(90)Y gap range 3-8.5 mm, (32)P gap range 2-7 mm and (192)Ir gap range 3.5-8 mm. The average dose relative to 2 mm from the source axis is (90)Sr/(90)Y, (mean+/-SD) 120+/-40%; (32)P, 125+/-50% and (192)Ir, 120+/-22%. The look-up tables also provide the coarse location and value of maximum and minimum dose (90)Sr/(90)Y, 220-60%, (32)P, 230-55% and (192)Ir, 170-85%. It appeared that the look-up tables provide a good approximation of the optimal gap width in the clinical examples. CONCLUSIONS: Tabulated optimal gap widths are very useful for quick estimation of the required gap width for a given bifurcation and source type, in case the prescribed dose in both vessels is the same. In unfavourable geometries there is a risk of local underdosage. Individual treatment planning using a program such as IC-BT doseplan is then recommended.