Palladium-103 versus iodine-125 for ophthalmic plaque radiotherapy.
OBJECTIVE
A dosimetry study comparing the use of I-125 vs. Pd-103 radioactive seeds for ophthalmic plaque brachytherapy.


METHODS
Palladium-103 (Pd-103) seeds in ophthalmic plaques were used to treat 15 patients with intraocular malignant melanoma. Computer-aided simulations were performed to evaluate the intraocular dose distribution of I-125 versus Pd-103 ophthalmic plaques (delivering equivalent apex doses). Seven target points were selected. Starting at the outer scleral surface, four were located along the central axis of the plaque: the 1 mm point (the inner sclera), the 6 mm point, the tumors apex, and the opposite eye wall. We also evaluated the fovea, optic nerve, and the lens because they were considered to be critical structures.


RESULTS
These studies demonstrated that the lower energy photons generated by Pd-103 seeds (average 21 KeV) in ophthalmic plaques were more rapidly absorbed in tissue than photons generated by I-125 (average 28 KeV). Therefore, during ophthalmic plaque radiotherapy, Pd-103 photons were found to be more rapidly absorbed within the tumor and less likely to reach most normal ocular structures. On average, the use of Pd-103 decreased the dose to the fovea by 5.7%, to the optic nerve by 8.4%, to the lens by 26%, and to the opposite eye wall by 38.4%.


CONCLUSIONS
Palladium-103 ophthalmic plaque brachytherapy resulted in slightly more irradiation of the tumor and less radiation to most normal ocular structures.
Finger
P T
PT
Department of Ophthalmology, North Shore University Hospital-Cornell University Medical College, Manhasset, NY 11030.
Lu
D
D
Buffa
A
A
DeBlasio
D S
DS
Bosworth
J L
JL
D001918:Brachytherapy; D002830:Choroid Neoplasms / Q000532:radiotherapy*; D003198:Computer Simulation; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008545:Melanoma / Q000532:radiotherapy*; D010165:Palladium / Q000627:therapeutic use*; D011868:Radioisotopes / Q000627:therapeutic use*; D011879:Radiotherapy Dosage
D007457:Iodine Radioisotopes; D011868:Radioisotopes; D010165:Palladium