The effect of contrast medium and balloon shape on dosimetry for arterial irradiation with 188Re

The radiation dosimetry associated with the use of the beta particle emitter 188Re in an angioplasty balloon is investigated for the case when the balloon has an elliptical rather than circular cross section and when iodinated x-ray contrast medium is included inside the balloon. It is found that the elliptical cross section introduces significant dose corrections when the eccentricity of the ellipse is equal to or greater than 0.7. However, for cases where the artery is nearly circular in cross section, the corrections are likely to be small. As expected, the dose is reduced along the major axis of the ellipse and increased along the minor axis. The corrections are greatest at larger distances from the surface of the balloon. The effect on dose of contrast in the balloon is significant for 33% Omnipaque in saline. Since this is a typical concentration of contrast that is used for imaging the radiation-filled balloon, correction for the effects of contrast medium in the balloon should in general be applied. To enable corrections to be readily applied for other types and concentrations of contrast media, formulas have been derived that allow the dose correction to be calculated for a range of balloon diameters and at various distances from the surface of the balloon. To undertake this calculation, the elemental composition and density of the material in the balloon needs to be known.