A modified dummy plaque for the accurate placement of ruthenium-106 plaques in brachytherapy of intraocular tumours

Abstract

Purpose: To present a new technique to ensure the correct positioning of ruthenium plaques in episcleral brachytherapy. Materials and Methods: An acrylic dummy plaque is made opaque by sanding both sides with sandpaper, and its edge is covered by a black marking tape. This modified plaque is temporarily sutured to the sclera overlying the choroidal tumour site. The tip of an endoillumination probe is placed at the anterior edge of the plaque, yielding a strong light scattering within the opaque acrylic material. Due to the light-absorbing tape around the plaque border, the scattered light is confined within the plaque, and its perimeter can be observed by indirect ophthalmoscopy as a circle of transilluminated light surrounding the tumour. When the correct position has been found, the dummy plaque is replaced by a ruthenium-106 plaque. Results: The technique was successfully applied in 5 patients with posterior choroidal melanoma. Compared to standard focal transillumination, its main advantage is that the position of the entire plaque and tumour can be observed simultaneously in one field without any movement or manipulation of the light probe or plaque. Conclusion: The described transillumination technique and modified dummy plaque facilitate the correct positioning of ruthenium plaques in brachytherapy of choroidal melanoma.