Abstract
Gadolinium (Gd)-containing microcapsules designed for neutron-capture therapy (NCT) were prepared by a spouted bed coating process. Microcapsules were designed as Gd-reservoir. They were prepared with the following properties : particle size was smaller than 50 μm, Gd-content was as high as possible, and release of Gd was suppressed as long as possible. Calcium carbonate (20-32 μm) was selected as a seed particle. As a Gd-source, gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) or a synthesized water-insoluble Gd-DTPA derivative, Gd-DTPA-distearylamide (Gd-DTPA-SA), was layered onto the seed particles. The release-suppressing layer was composed of aqueous acrylic latex of 9 : 9 : 4 poly(ethyl acrylate/methyl methacrylate/2-hydroxyethyl methacrylate). In preliminary studies, Gd/DTPA microcapsules with 41-45 μm (mass median diameter) were prepared; they released Gd with a short lag-time and 3 h-prolongation. Complete release suppression was, however, difficult to achieve because of high water-solubility of Gd-DTPA. Hence, a hydrophobic derivative, Gd-DTPA-SA, was next used as a Gd source. Gd-DTPA-SA microcapsules could be prepared with a mass median diameter of 52 μm. Gd-DTPA-SA content of the microcapsulles was 38% and release of Gd was suppressed to less than 0.2% over 60 d.
