Mass Production of Source Core for Iodine-125 Seed

Abstract

Nowadays, brachytherapy using a sealed source called a ‘seed’ has drawn attention for the treatment of various cancers. Generally, Iodine-125 (I) has been used for the seed in the radiation therapy of eye disease and prostate cancer. I has a half-life of 59.4 days, and emits 27 keV and 31 keV X-rays, and a 35 keV γ-ray through an internal conversion process. An I seed of 4.5 mm (l) × 0.8 mm (O) has a structure composed of an inner source core and an outer shell capsule. I is adsorbed on the source core’s surface and a titanium capsule surrounds it. The seed is directly inserted into the human body to treat cancer cells, and the seed may be permanently left in tissues owing to the low activity and the excellent biocompatibility of Ti capsule (Fig. 1). The diverse materials and preparation of the source core have been reported for many years, for example, a palladium (Pd) coated silver wire, a silver (Ag) rod and a porous ceramic tube etc. The Korea Atomic Energy Research Institute (KAERI) previously used a bare ceramic rod and an Ag+Al2O3 rod 12 as the core. With regard to the preparation of an I seed, the electro deposition technique was used for adsorption of iodine on the silver surface. In addition, a chemical adsorption on the Pd coated silver wire, the impregnation into ceramics and iodine substitution after forming an intermediate having chloride (Cl) or bromide (Br) were reported. In our previous investigation, the effect of the various intermediates (N3 −, CO3 , C2O4 , AsO4 , Cl− and PO4 ) using each set of 10 Ag rods were reported. Among them, Ag rods modified using phosphate (PO4 ) showed the highest adsorption ability with the good substitution effect of iodine. On the basis of this technique, the studies on mass production using 100 Ag rods and leachability test of a finished source core prior to encapsulation were performed in this work. The uniformity of iodide adsorption on every silver rod in the same batch is important for mass production to reduce the number of abandoned rods. For this reason, we developed a cutting device (Fig. 2) precisely manufacturing the silver rods in 3 mm (l) and compared the iodide adsorption with the handmade rods. A silver wire of 0.5 mm (O) passes through a syringe needle (d) of 0.584 mm (O), and the wire is softened through the heating part (b). The length of this wire is adjusted with the help of micrometer (c) and can quickly cut to a uniform shape by using a steel blade (a). In the case of handmade rods, the wire was cut by using scissors, and both ends were manually polished with sandpaper.