Cerenkov Luminescence Imaging for Accurate Placement of Radioactive Plaques in Episcleral Brachytherapy of Intraocular Tumors

PURPOSE. The purpose of this study was to determine the feasibility of using Cerenkov luminescence imaging (CLI) to facilitate plaque placement during episcleral brachytherapy of intraocular tumors. METHODS. Ruthenium-106 (Ru-106) decays to rhodium-106, which in turn emits high-energy beta particles. When the electrons propagate through the eyewall, the so-called Cerenkov effect leads to emission of weak light, which can be captured by high-sensitivity charge-couple device (CCD) cameras. Enucleated porcine eyes were prepared with tumor phantoms made of melanin-containing gelatin. The anterior portion of the globe was removed, and different Ru-106 plaque types (designated CCA, CCB, COB, and CIA) with activities ranging from 6.8 to 16.7 MBq were sutured to the sclera overlying the tumor phantom. The globe was placed in a transparent container with saline. CLI was performed through the anterior opening of the eye using a cooled electron-multiplying CCD camera. RESULTS. Exposure times between 5 and 60 seconds produced good quality images of the Cerenkov light. There was a linear relationship between plaque activity and Cerenkov radiance. The perimeters of the CCA and CCB plaques could be seen clearly as circles of light symmetrically surrounding the tumor phantoms. Notched COB and CIA plaques led to images revealing their actual positions in relation to the optic disc and ciliary body, respectively. Simulated plaque tilting resulted in diffuse demarcation of the light. CONCLUSIONS. The study indicates that CLI is a feasible method to ensure accurate placement of Ru-106 plaques in brachytherapy of intraocular tumors. CLI may offer a new tool to improve and document plaque placement, both perioperatively and postoperatively.