Radio-iodine-labelled 5-iodo-2-thiouracil: a potential radiopharmaceutical for establishing the viability of ocular melanoma after radiation therapy.

Radio-iodine-labelled thiouracil has been evaluated as a radiopharmaceutical for establishing the viability of ocular melanoma after radiation treatment. The uptake of 125I-5-iodo-2-thiouracil (125I-ITU) was studied in X-ray irradiated and non-irradiated melanotic melanomas implanted in Syrian golden hamsters. Uptake of 125I-ITU in melanomas 4 days after irradiation with 40 Gy X-ray was 25% of the value found in non-irradiated controls, 12 days after such treatment it was 10% of that value. Twenty-one days after radiation treatment the melanomas showed regrowth and uptake of 125I-ITU was about equal to that in non-treated controls. Uptake of 125I-ITU in melanomas after 10 Gy X-ray irradiation was higher and uptake in tumours after 20 Gy was only slightly lower than the uptake by non-irradiated melanomas. The results indicate that the iodine labelled-thiouracil uptake test may be useful as an additional diagnostic issue for assessing the viability of ocular melanoma after radiation therapy.