Technetium-99m (V) dimercaptosuccinic acid uptake by choroidal melanoma before and after iodine-125 brachytherapy

The value of the new tumour-seeking agent technetium-99m (V) dimercaptosuccinic acid (99mTc (V) DMSA), is assessed by the visualization of choroidal melanoma before and after iodine-125 episcleral plaque brachytherapy.

A prospective study was conducted on 12 consecutive patients with choroidal melanoma that was to be treated with plaque brachytherapy. The pre-operative mean (+/- SD) maximal tumour basal diameter was 12.9+/-2.9 mm and the mean tumour height was 8.2+/-2.9 mm. Each patient had planar scintigraphy and single-photon emission computed tomography using 99mTc (V) DMSA 2 days before treatment and 8 months following plaque removal. The calculated tumour to background ratios of these two tests were compared.

The pre-operative tumour to background ratio was 1.8+/-0.4 and all tumours could be correctly identified. At the time of postoperative imaging, all melanomas showed varying degrees of regression. The mean tumour height was 4.4+/-2.1 mm. The tumour to background ratio was 1.4+/-0.3. The difference between the two scintigraphic results was statistically significant (P = 0.002).

Technetium-99m (V) DMSA scintigraphy can accurately detect choroidal melanoma and document tumour response following episcleral radioactive plaque therapy. As such, this test can be an alternative ancillary investigative tool in the rare event of opaque media or diagnostic uncertainty.