The impact of 99mTc-DTPA orbital SPECT in patient selection for external radiation therapy in Graves' ophthalmopathy.

OBJECTIVE

In Graves' ophthalmopathy (GO), there is a demand to differentiate the immunologically active disease state, when immunosuppressive therapy is necessary, from the inactive state, when the patient would not benefit from it. We measured the inflammatory activity in the retrobulbar region using Tc-diethylene triamine pentaacetic acid (DTPA) SPECT before and after external radiation to determine whether this method is suitable for predicting the effectiveness of this therapy.

MATERIALS AND METHODS

Thirty-two patients with suspected active GO were involved in this retrospective study. The initial image, DTPA uptake value (UV) and its change after therapy were assessed to monitor the effect of the therapy and investigate whether a pretreatment scan is capable of predicting the outcome.

RESULTS

Depending on the change in DTPA UV after radiotherapy, three patient groups were formed: decreased, increased or minimally changed (less than 1×10 injected dose (ID)/ml). The initial DTPA UVs of these groups were significantly different (P<0.001). Improvement was observed mainly in patients with higher initial values. When comparing the groups with low (<12×10 ID/ml) versus high (≥12×10 ID/ml) initial uptake, an unexpected increase was observed in the first group after therapy (mean: +2.89±2.66×10 ID/ml), whereas the average change in the DTPA UV was negative in the latter group as anticipated (-2.24±4.47×10 ID/ml, P<0.00001).

CONCLUSION

We found that in GO patients a high DTPA UV may predict the response to orbital radiation therapy. DTPA orbital SPECT may be a suitable technique for the selection of GO patients for radiation therapy.