Radionuclidic Explorations in Opthalmology

Radioimmunoscintigraphy with melanoma-associated monoclonal antibody fragments in choroidal melanoma

A prospective pilot study on radioimmunoscintigraphy with monoclonal antibody fragments against cutaneous melanoma (MoAb 225.28S) was carried out in 17 patients with a clinical diagnosis of choroidal melanoma. Monoclonal antibodies against melanoma-associated antigen were labeled with 740 mBq 99mTc and injected IV; images were made with a gamma camera at 6 h after injection. With a double-pinhole collimator, radioactivity was counted thrice in both eyes at 6 h after injection. In 6 of 16 patients (37.5%), the melanoma could be imaged with the gamma camera. With the double-pinhole collimator, a significantly higher activity was measured in the melanomatous eye in 13 of 16 patients (82.4%). In two patients a false negative result was obtained, and in one patient the difference between the left and right eye was not significant. Considering these results, radioimmunoscintigraphy may be valuable in ocular melanoma diagnostics, but the specificity of MoAb 225.28S needs to be assessed.

Potential radiopharmaceuticals for the detection of ocular melanoma. Part II. Iodoquinoline derivatives and 67Ga-citrate

The uptake and distribution of several 4-(substituted amino)-iodoquinolines, 131I-labelled, and of 67Ga-citrate were investigated in Syrian golden hamsters with Greene melanomas. Because of its uptake in the melanoma (tumour/eye ratio 8.9), 4-(dimethylamino-ethylamino)-7-iodoquinoline (NM113) was selected for further investigations as a possible radiopharmaceutical for ocular scintigraphy when labelled with 123I. High uptake of NM113 turned out to be incidental and could not be favourably influenced by several pharmacological pretreatments. Affinity for melanin, as shown in in vitro experiments, unfavourably influences NM113 tumour-to-eye ratios. In comparison with 67Ga-citrate, the latter, with a high tumour-to-eye ratio (44.8 after 24 h) is more promising in patient studies in which NM113 123I was not.

L-3-123I-alpha-methyltyrosine for melanoma detection: a comparative evaluation

L-3-123I-alpha-methyltyrosine (IMT) was compared to [67Ga]citrate, [203Pb]Tris and [131I]iodochloroquine (ICQ) with respect to their potential as melanoma seeking radiopharmaceuticals in two tumor lines, a malignant melanotic melanoma of the Sofia type and a malignant amelanotic melanoma of the Greene-Harvey type, transplanted onto Syrian Golden hamsters. [203Pb]Tris and ICQ showed significant accumulation only in melanotic melanoma. In contrast, [67Ga]citrate and IMT accumulated in both tumor lines. [67Ga]citrate has very high tumor-to-skin, tumor-to-eye, and tumor-to-blood ratios at 48 h after injection, but has low selectivity for melanoma and unfavorable physical (high gamma-energy) and biological (half-time) characteristics. IMT has a convenient gamma-energy at 159 keV and a short biological half-time. Maximum of melanoma accumulation is reached at 1-2h after application; tumor-to-tissue ratios are suitable for scintigraphy.

Noncontact detection of experimental amelanotic ocular melanoma with L-3-123I-iodo-alpha-methyltyrosine

An application of L-3-123I-iodo-alpha-methyltyrosine for the detection of ocular melanoma is presented. In rabbits with malignant Greene amelanotic melanoma transplanted to the anterior chamber of the eye, all tumors were detected in positive contrast using a gamma camera with a single pinhole collimator. The smallest tumor identified weighed 65 mg. Our data are compared with those obtained with 32PO4, 67Ga, 203Pb or labelled iodochloroquine.

[Noncontact detection of intraocular lesions by means of a gamma scintillation camera]

A gamma scintillation camera is used for noncontact detection of intraocular mass lesions. A double aperture pinhole collimator was designed for this special application. The collimator projects a magnified image of the radioactivity present in each eye onto the detector crystal of the camera. Details of the collimator design are described. The image-making properties of a double aperture pinhole collimator for ocular scintigraphy in regard to resolution and response were studied and demonstrated by phantom experiments. So far we have studied 50 cases with this new nuclear medicine procedure, using mainly technetium-pertechnetate as the radioindicator. Case histories and records of some typical results are presented. Better designed radiopharmaceuticals with appropriate tumor-seeking properties should be developed. Labeled melanin precursors are promising for detection of these lesions.