Practical aspects of intra-arterial brachytherapy

A wealth of experience exists in brachytherapy delivered in a variety of methods. Both beta and gamma sources have been used in the form of wires, pellets and liquids introduced through specially designed catheters. In addition, stents have been used and work with radioactive gases proposed. A significant issue in such interventional work is dosimetry. Presently, many methods and systems are still under development undergoing clinical trials and refinement. There is considerable uncertainty in the determination of appropriate target volumes and dose prescriptions. It is not known whether treatment of only the lumen wall is sufficient, or whether the media and adventitia must also be irradiated. Clinical trials suggest success depends on delivering adequate dose to target tissues (8-20 Gy) while limiting normal tissue dose to 30-40 Gy. Some trials indicate that a mimimal dose of 8-10 Gy has to be given to the whole media and the upper limit is determined by the tolerance of the intima (localized doses of approximately 90 Gy have been applied without complications). The requirements for the source for endovascular brachytherapy and the small lumen diameters involved compound the problems of achieving accurate dosimetry. Discussion of the aspects of radiation physics and the sources of dosimetric uncertainty together with the methodology used to calculate the dose is presented.