Echographic findings in uveal melanomas treated with the Leksell gamma knife

Between June 1992 and July 1995, 29 uveal melanomas were treated radiosurgically with the Leksell gamma unit at the University of Graz. The aim of this retrospective study was to examine the pattern of regression and the extent and time period of the decrease in tumour size.

The Leksell gamma knife, model B, was used. Patients were divided into three groups according to marginal dose: group 1: eight patients with a marginal dose > 50 Gy, group 2: 15 patients with a marginal dose = 50 Gy, and group 3: six patients with a marginal dose = 45 Gy. For the retrospective study two groups were examined: group A, tumours < 5 mm and group B, tumours > or = 5 mm.

No significant correlation was found between tumour regression and the marginal dose. Tumour shrinkage depends on the pretreatment height. In the group of eight patients with an initial tumour prominence of less than 5 mm, no prominence was found after therapy. In the group of patients with an original tumour prominence of 5 mm and more, only two tumours formed a flat scar while a residual prominence was found in 18 patients. Increase in reflectivity combined with a decrease in size appears to be a good criterion for the effectiveness of the treatment. In five patients with tumours showing low reflectivity, over a longer period of time metastases were found. An enucleation was performed in two patients because of uncertain tumour regression and in one patient as a result of an increase in tumour size.

The pattern of echographic reflectivity and decrease in size is similar to brachytherapy and is one of the most important diagnostic variables for evaluation of tumour regression. An increase in reflectivity as well as a decrease in tumour size in the first 6-8 months can be considered a therapeutic success.