Dosimetric effect of contrast media for catheter-based intravascular brachytherapy

The purpose of this work is to calculate the dose perturbation in the presence of iodine contrast media during the procedure of catheter-based intravascular brachytherapy. The calculation was performed for two most commonly used β and γ sources (⁹⁰ Sr and ¹⁹²Ir) using EGS4 Monte Carlo system. A carefully chosen set of EGS4 transport parameters for the small geometry in question was used in the calculation, various contrast media with cylindrical-shell shape were considered. Calculations for a variety of monoenergetic sources were also included. Dose effects of iodine concentration, thickness (volume) of contrast media, energy of radioactive sources were studied. It is found that the dose perturbation due to a contrast medium is very significant. In the target region (the region beyond the contrast media), dose is generally increased (by up to 35%) for the γ source, while it is decreased (by 20-50%) for the β source. The dose enhancement is primarily due to the production of iodine K-edge characteristic X-rays. The dose perturbation strongly depends on (1) volume (thickness) of the contrast medium, (2) iodine concentration, and (3) type and energy of radioactive source. These dose effects due to a contrast medium should be recognized and may be considered in the dose prescription of intravascular brachytherapy