The Usefulness of CT Contrast Agent with 166 Ho-based Radiation Brachytherapy Sources

Since coronary angioplasty using a liquid radiation source is performed with a computed tomography(CT) angiography, use of a CT contrast agent is a good alternative to see if the balloon has close contact with the blood vessel wall for the delivery of a sufficient radiation dose to the stenotic artery. This study was designed to estimate the usefulness of the CT contrast agent as a diluent of a liquid radiation source. Physicochemical studies and in vivo stability studies using animals were implemented. For this study, three CT contrast agents, Hexabrix(320), Iomeron(350) and Visipaque(320) were used. 166 Ho was radiolabeled with the component of Hexabrix(320) and the 166 Ho-complex was proposed to be 166 Ho-EDTA. However, as for Iomeron(350) and Visipaque(320), no other 166 Ho-complex was formed. In the case where 166 Ho-EDTA was administrated to rabbits, only 10 % of the administered dose was excreted. In the case where 166 Ho was added to a vial containing DTPA and EDTA, its half excretion (T1/2) was similar to that of 166 Ho-EDTA with the assumption that 166 Ho was trans-chelated with EDTA/DTPA. However, in the animal experiment where Hexabrix(320) was added to the 166 Ho-DTPA vial with the volume ratio of 1: 1, most of the injected dose was excreted via the urinary system within 30 mins. The similar results were acquired in the case where Iomeron(350) or Vispaque(320) was added to 166 Ho-DTPA. It is more preferable to use the CT contrast agents as a diluent of 166 Ho-based radiation brachytherapy sources having the characteristics of high stability in vivo and the fast renal excretion. As for Hexabrix(320), the volume used as a diluent of 166 Ho-DTPA should be minimized only to visualize the balloon catheter