thiouracil and Choroid-Neoplasms

Various aspects of radiotherapeutic techniques used in treating ocular tumors are discussed. Previous and current "standard" modalities are briefly reviewed, including beta and gamma emitters, 60Co, 125I, and charged particles. In particular, emphasis is placed upon techniques under development that use biomolecules to physiologically target radioactive or stable isotopes to ocular melanoma. These procedures include 35S-thiouracil, 127I-deoxyuridine in conjunction with irradiation with photons from 145Sm, neutron capture therapy, and various combinations of the above. Thiouracil shows particular promise because of its incorporation during malanin synthesis in growing melanoma. Radiosensitization and stimulation of Auger cascades via introduction of iodine in DNA followed by irradiation with activating photons of appropriate energy (from 145Sm) has been shown to be effective in vitro. Various molecules may be used to transport boron to ocular melanoma, including thiouracil, thus allowing selective irradiation of tumor cells via 10B (n, alpha) 7Li reaction.

Topics: Antibodies, Monoclonal; Choroid Neoplasms; Cobalt Radioisotopes; Deoxyuridine; Dose-Response Relationship, Radiation; Eye Neoplasms; Helium; Humans; Iodine Radioisotopes; Melanins; Melanoma; Methods; Ophthalmology; Protons; Radioisotopes; Thiouracil

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.

Topics: Animals; Choroid Neoplasms; Cricetinae; Iodine Radioisotopes; Melanoma; Mesocricetus; Radionuclide Imaging; Thiouracil

[123I]-5-iodo-2-thiouracil (123I-ITU) was evaluated as a radiopharmaceutical for tumor detection in 10 patients with proven choroidal melanoma. Uptake of 123I-ITU was measured with a specially designed single eye probe collimator, 24 h after administration of 123I-ITU. Increased uptake in the tumor-bearing eye as compared to the fellow nontumor bearing eye was found in 7 out of 10 cases when the probe was located 3.5 cm in front of the eye (p less than 0.01). By using a double pinhole collimator tests were positive in 3 out of 10 123I-ITU studies only. Tests with 123I-ITU were compared with 67Ga tests in the same patients. The 67Ga tests with the single eye probe collimator were positive in 6 out 10 cases when the probe was located 6 cm in front of the eye. With the double pinhole collimator tests were positive in 7 out of 10 67Ga studies. It is concluded that 123I-labeled thiouracil is at least as useful as a radiopharmaceutical for ocular melanoma diagnosis as 67Ga-citrate, provided measurements are performed with a single eye probe.

Topics: Choroid Neoplasms; False Positive Reactions; Gallium Radioisotopes; Humans; Melanoma; Radionuclide Imaging; Thiouracil