Development of miniature 125I sources for the treatment of eye and prostate cancers

The aim of the present work was to develop a technology for the fabrication of 125I brachytherapy sources for their potential application in the treatment of eye and prostrate cancers. Several methods of incorporating the 125I activity in solid core were investigated and the best among them, in terms of low leachability, ease of preparation and encapsulation in titanium capsules and reproducibility was chosen. Two kinds of cores, namely rod/cylinder shaped wires and spherical balls, were envisaged for introduction into the titanium capsule. Two procedures for depositing the 125I activity on rod shaped core were explored; namely anodic deposition of 125I on silver wire and physicochemical adsorption of 125I on palladium chloride coated silver wire. Similarly, two methods for depositing 125I on spherical source cores were studied. In the first case, alumina microspheres were used as the core on which 125I was impregnated as iodate (IO-3) using a solid-solution interface technique. In the second, 125I was adsorbed on palladium coated silver beads of 0.5 mm. Various physical and chemical parameters were optimized to obtain quantitative uptake of 125I and firm adsorption that would result in negligible iodine leachability (≤ 0.01%). The source cores prepared by various methods were encapsulated in indigenously fabricated titanium capsules [4.5mm (l) 0.8mm (OD) and 0.05mm (thickness)]. These capsules were in accordance with the ISO specifications for use as low energy brachytherapy sources. The welding of the capsules was optimized by changing welding parameters such as energy, frequency and pulse duration to obtain neat and leak-proof welded capsules. Integrity of the welding was ascertained by metallographic examination and leak testing. Quality assurance tests such as leak testing and dosimetry that are essential before clinical use were conducted. All the above methods were compared and the one which was easy to prepare in large scale was adopted for preparation of the sources for clinical trials. (author)