A novel ionization chamber for dosimetry in intravascular brachytherapy

A novel ionization chamber for the dosimetry and quality assurance program of beta particle emitting radioactive sources (in the form of wires or seed trains) used in the intravascular brachytherapy of coronary disease has been devised and investigated. It has a cylindrical shape, and a catheter, housing the source (a wire or seeds), passes through the chamber along its axis. The new type of ionization chamber is called the ring ionization chamber (RIC). Owing to its similarity to a cylindrical ionization chamber, the well-established dosimetric protocol can be applied to determine the absorbed dose-to-air chamber calibration factor, ND, as well as the absorbed dose-to-water calibration factor, ND,W. Owing to this similarity, the overall uncertainty in the standardization of the absorbed dose for beta radioactive sources used in intravascular brachytherapy could be substantially reduced compared with that presently achieved. The RIC can be implemented into a new code of practice for dose standardization and quality assurance in intravascular brachytherapy. An example of practical application of a model of RIC for dosimetry of 32P radioactive source is presented.