Brachytherapy in choroid tumors

Abstract Even though brachytherapy has been used for many years to treat choroidal tumors, it is not a widespread technique because it requires much organization and operators skills. The most common methods use 60Cobalt and 106Rutenium plaques, or custom-made plaques with 125Iodine loaded seeds. Another, less common, technique uses 192Iridium wires loaded on custom-made plaques. The technique we used to treat 4 retinoblastomas and 2 choroidal melanomas uses 192Iridium wires loaded on custom-made plaques. The applicator is made of a quick drying paste poured over a sphere the same size as the eye-ball: plastic tubes are inserted, according to preliminary dosimetric measurements, to house the Iridium wires. The applicator is positioned on the eye-ball corresponding to tumor site by surgery. The Iridium sources are inserted into the plastic tubes at the end of surgical placement: this afterloading technique guarantees maximal staff protection. 192Iridium (320 keV gamma emitter) allows the dose to be transmitted deeper than with 125Iodine (30 keV gamma-emitter) and 106Rutenium (3540 keV beta-emitter). Therefore, with Iridium, the dose delivered is lower on the eye-ball surface for the same tumor dose. On the other hand, the use of 60Cobalt (1250 keV gamma-emitter) gives the healthy surrounding tissues higher doses. To conclude, this method allows us to customize the application to every single case, to reach posterior sites, to ensure radioactive protection to staff thanks to afterloading and to obtain a good depth to surface dose ratio.