The design and the dosimetry of bi-nuclide radioactive ophthalmic applicators

A novel type of applicator for the treatment of intra-ocular tumors has been developed, based on the two radionuclides Ru-106/Rh-106 and I-125. The dose distribution of this ophthalmic plaque combines advantageous features of both radionuclides and can be optimally adapted to a tumor thickness in the range 6.5-9 mm, a size which is beyond the dosimetric limitations of the Ru-106/Rh-106 plaque therapy. Compared with I-125 plaques a bi-nuclide plaque allows to maintain the tumor dosage while the dose in the irradiated volume outside of the target volume is significantly reduced. Consequently, radiosensitive structures within the eye can be spared more effectively. Dedicated methods have been developed for the dosimetry of this plaque. These methods are based on our own extensive dosimetric investigations with plastic scintillators. The precondition was the availability, developed in recent years, of a more accurate determination of the absolute dose rate to water of beta- and low energy emitters. (C) 2004 American Association of Physicists in Medicine.