Over the years, different techniques have been used to ensure that the radioactive plaque, sutured to the scleral surface, covers the tumor base with the required tumor-free margin. The first step is to locate the intraocular tumor, which for anteriorly located tumors can be achieved relatively easily by transpupillary or transocular transillumination.
2 Melanin-containing tumor tissue absorbs the transilluminated light and casts a distinct shadow onto the eyewall so that its margin can be marked on the episclera. For more posteriorly located tumors, however, the procedure is more complicated, necessitating the use of indirect ophthalmoscopy combined with scleral depression or transscleral transillumination.
3 For this purpose, Damato et al.
4 developed a dummy plaque with small holes for the insertion of a right-angled transilluminator. To ensure proper localization of the radioactive plaque both during and after primary surgery, several techniques have been described in published reports, such as 2- and 3-dimensional ultrasonography,
5–8 magnetic resonance imaging,
9,10 and plaque-mounted light-emitting diodes.
11,12 Nevertheless, for choroidal melanomas located in the posterior pole or juxtapapillary area, it is challenging to locate the tumor and to position the plaque correctly, which may explain why radiation failure is more common in this location.
13 Furthermore, initially well-localized plaques may become displaced or tilted away from the sclera during the time the plaque is sutured to the eye (typically 3–7 days), which could reduce radiation dose to the tumor and cause local tumor recurrence.
14 Current methods to determine the correct plaque position are time consuming and demanding and rather inaccurate due to generally low image resolution and different types of imaging errors.
15 Thus, there is a need for improved methods to facilitate and document proper plaque placement both at the time of insertion and during the course of treatment.