Dosimetry calculation for a novel phosphorus-32-impregnated balloon angioplasty catheter for intravascular brachytherapy.

PURPOSE

A phosphorus-32-impregnated balloon angioplasty catheter was used in a novel technique of simultaneous angioplasty and vessel irradiation. The 32P radionuclides were distributed on the surface of the balloon so that a certain amount of radiation was delivered while angioplasty was performed. Three-dimensional dosimetry and dose-time relationship needs to be established for the catheter so that quantitative dosimetric information is available for both clinical treatment and research investigation.

METHODS AND MATERIALS

The 32P-impregnated balloon of an angioplasty catheter was assumed to have a cylindrical shape, and the radionuclides were assumed to be distributed uniformly on the curved surface of the cylinder. The dose rate at a point in space was computed by integrating the point dose-rate kernel of 32P over the radioactive surface of the balloon. The point dose-rate kernel was computed with Monte Carlo simulation of radiation transport. The energy spectra of 32P based on a mathematical model was used in the calculations. The three-dimensional dose distributions and dose-time relationships were calculated for balloons of various lengths and radii.

RESULTS

At a short radial distance (e.g., 0.2 mm) away from the balloon surface, the dose distribution was uniform across a large portion of the balloon along the longitudinal axis, and dropped off rapidly at both ends of the balloon. Uniformity became worse as the radial distance increased. Uniformity was almost independent of balloon radius. The underdosed length at each end of the balloon was also almost independent of balloon length. In the central transverse plane, the dose reached a maximum at the surface of the balloon and then dropped off rapidly as the distance increases. Relative dose coverage outside the balloon was approximately independent of balloon radius and length, and the absolute dose coverage was approximately inversely proportional to balloon radius and length, assuming same total activity.

CONCLUSIONS

Point dose-rate kernel of 32P beta emitter and the three-dimensional dose distributions of a 32P-impregnated balloon from an novel angioplasty catheter were calculated. A rule of thumb for dose calculation and dose coverage was established for simultaneous angioplasty and vascular brachytherapy with a 32P-impregnated balloon catheter.