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Abstract: Objective: A promising radiopharmaceutical 99mTc-HYNIC-TOC (99mTc-HYNIC-Octreotide) can be applied for somatostatin receptor scintigraphy with the potential to replace Indium-111 labeled somatostatin analogus. Here we evaluate whether orbital 99mTc-HYNIC-TOC scintigraphy can be used as a Graves’ ophthalmopathy (GO) activity parameter to predict the retrobulbar irradiation response. Methods: Orbital 99mTc-HYNIC-TOC scintigraphy was performed on 14 consecutive patients demonstrating moderated to severe Graves’ ophthalmopathy. The patients were treated with retrobulbar irradiation following the octreoscan and the response to this therapy was assessed at 3 months after the start of treatment. The orbital 99mTc-HYNIC-TOC uptake was calculated to assess the effects of treatment. Results: Among the 14 GO patients, eight (57.1%) responded to retrobulbar radiotherapy; six (42.9%) showed no change. We compared the eight responders and six non-responders in terms of orbital 99mTc-HYNIC-TOC uptake, using the orbital/occipital ratio. On the 4-h 99mTc-HYNIC-TOC scintigraphy, responders had a higher orbital/occipital uptake ratio than the no-responders (P = 0.001). A significant correlation was found between the orbital/occipital ratio and the clinical activity score (CAS) (P = 0.034). The Receiving-Operator-Characteristic curve showed the best threshold for discriminating active and inactive disease was 1.40 (sensitivity, 100%; specificity, 83.3%). In the responders group, all these eight patients had positive scintigraphy. While there were five patients who had negative scintigraphy in the non-responders group. Conclusion: Orbital 99mTc-HYNIC-TOC scintigraphy can be a useful method for the estimation of disease activity and prediction the response to subsequent radiotherapy in GO patient. And the patients with positive octreoscan were more likely to respond to irradiation.