Dosimetric effects of contrast media for catheter-based intravascular brachytherapy

The purpose of this work is to calculate the dose perturbations due to the presence of iodine contrast media in catheter-based intravascular brachythe rapy (IVBT). The EGSnrc Monte Carlo system was used to perform the calculat ion for the two most commonly used beta and gamma sources (Sr-90 and Lr-192 as well as for a variety of monoenergetic photon and electron sources. Var ious contrast media with cylindrical-shell shapes were considered. The dose perturbations due to the presence of iodine contrast media were found to b e significant for IVBT. In the region outside of the contrast media (usuall y the treatment target region for IVBT), the dose is generally increased fo r the gamma source, while it is decreased for the beta source. In the prese nce of a 1.0-mm-thick common clinical contrast medium, the dose enhancement can be as high as 30% for the Ir-192 source, while the dose can be reduced by up to 25% for the Sr-90 source. The dose enhancement region for the gam ma source extends approximately 1.0 mm away from the contrast medium, while the dose reduction for the beta source affects the entire target region. T he dose perturbation depends on (1) the volume (thickness) of the contrast medium, (2) the iodine concentration in contrast media, and (3) the type an d energy of radioactive source. The dose effects due to the contrast medium as well as the differences between beta and gamma sources, revealed in thi s study, should be recognized and may be considered in the dose prescriptio n for intravascular brachytherapy. These effects should also be taken into account in analyzing the treatment outcome for those IVBT clinical trials i nvolving a contrast medium. (C) 2001 American Association of Physicists in Medicine.