Iodine-125 ophthalmic applications with monolithic active insert

A prototype ophthalmic applicator for conservative treatment of intraocular tumors was designed in 1985 by Klemp et al. This served to retain a number of 'seed-type' sources of iodine-125. Such applicator consists of two major parts: a seed-holding acrylic insert, spherically shaped, with drilled trenches on the convex side to accommodate the seeds, and a stainless steel shell capsule serving as radiation shield. This design proved to be difficult and hazardous to assemble and dismantle after usage. As these problems appeared likely to persist if not attended to, development of the applicator was undertaken in order to eliminate the necessity of using iodine seeds. The investigations preformed comprised uniform adsorption of iodine-125 on the concave surface of the silver shell and its hermetic sealing inside spherically shaped acrylic insert. The method of fixing iodine-125 on silver as well as the technique of its sealing in acryl is described. The results of the classification testing for performance requirements of the assembled applicator are quoted. Comparative measurements of the energy spectra of the radiation emitted by both the seed-less and seed-containing applicators are presented. From the results of the depth dose rate measurements it follows that the total activity incorporated in a seed-less applicator can be much lower than in seed-containing one without decrease in the dose rate value. (author)