A Gamma Ray Probe for the Detection of Ocular Melanomas

A specially designed scintillation probe has been assembled and applied in a promising diagnostic study of malignant melanoma in the human eye. When used in conjunction with a new radiopharmaceutical agent recently developed at The University of Michigan, 125I labeled chloroquine analog, the probe permits simple and nonsurgical gamma ray counting as a substitute for more elaborate techniques required in 32p beta scanning for the same prupose. Preferential uptake of the agent in ocular melanomas has been previously reported using a modified 5-inch NaI (Tl) crystal scanner as the detector. We have realized a substantial improvement in both sensitivity and reproducibility by substituting a hand-held probe placed in contact with the patient\´s closed eyelid. The counting rate over each eye is followed for a period ranging from 3 to 21 days after dosage. A melanoma in one eye gives rise to an enhanced rate over that eye. Data are presented on a total of 12 patients, including two with confirmed ocular melanomas. In both of these cases, the involved eye consistently shows a significantly greater activity than the opposite eye. In the remaining cases considered "negative", measured eye-to-eye asymmtries are much lower, and a measure of the variance associated with these cases is presented.