MR technique for localization and verification procedures in episcleral brachytherapy

Spatial definition of an intraocular tumor and subsequent determination of the actual position of an implanted eye plaque are essential for adequate ocular brachytherapy treatment planning. However, a method for verification of the plaque placement which would provide required 3-dimensional information is not available at present. In addition, tumor localization procedures, including ultrasonography and CT techniques, cannot always offer the precision needed for 3-dimensional definition of an intraocular target. This communication describes a magnetic resonance imaging technique specifically developed for both localization and verification procedures. A 1.5 Tesla magnetic resonance scanner, spin-echo pulse sequence (echo time 30 msec, repetition time 700 msec), and commercially available surface coil were used to obtain a series of transverse, coronal, and sagittal images of a slice thickness of 3 mm. Usually, eight scans in each of the three planes were needed for adequate coverage of the orbit. The required patient set-up and data acquisition time did not exceed 40 minutes. With a data matrix size of 256 X 256 pixels and 13 cm field of view, localization and verification were accomplished with a precision of 0.5 mm. Our results suggest that the magnetic resonance imaging technique permits precise integration of diagnostic and therapeutic procedures, and in addition provides adequate data for accurate treatment planning. We conclude that magnetic resonance imaging is the preferred diagnostic technique for episcleral brachytherapy.