PT - JOURNAL ARTICLE AU - Michael Gabriel AU - Andreas Oberauer AU - Georg Dobrozemsky AU - Clemens Decristoforo AU - Daniel Putzer AU - Dorota Kendler AU - Christian Uprimny AU - Peter Kovacs AU - Reto Bale AU - Irene J. Virgolini TI - <sup>68</sup>Ga-DOTA-Tyr<sup>3</sup>-Octreotide PET for Assessing Response to Somatostatin-Receptor–Mediated Radionuclide Therapy AID - 10.2967/jnumed.108.053421 DP - 2009 Sep 01 TA - Journal of Nuclear Medicine PG - 1427--1434 VI - 50 IP - 9 4099 - http://jnm.snmjournals.org/content/50/9/1427.short 4100 - http://jnm.snmjournals.org/content/50/9/1427.full SO - J Nucl Med2009 Sep 01; 50 AB - 68Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N′′,N′′′-tetraacetic acid-d-Phe1-Tyr3-octreotide (DOTA-TOC) PET has proven its usefulness in the diagnosis of patients with neuroendocrine tumors. Radionuclide therapy (90Y-DOTA-TOC or 177Lu-DOTA-octreotate) is a choice of treatment that also requires an accurate diagnostic modality for early evaluation of treatment response. Our study compared 68Ga-DOTA-TOC PET with CT or MRI using the Response Evaluation Criteria in Solid Tumors. Furthermore, standardized uptake values (SUVs) were calculated and compared with treatment outcome. Methods: Forty-six patients (29 men, 17 women; age range, 34–84 y) with advanced neuroendocrine tumors were investigated before and after 2–7 cycles of radionuclide therapy. Long-acting somatostatin analogs were not applied for at least 6 wk preceding the follow-up. Data were acquired with a dedicated PET scanner. Emission image sets were acquired at 90–100 min after injection. 68Ga-DOTA-TOC PET images were visually interpreted by 2 experienced nuclear medicine physicians. For comparison, multislice helical CT scans and 1.5-T MRI scans were obtained. Attenuation-corrected PET images were used to determine SUVs. Repeated CT evaluation and other imaging modalities, for example, 18F-FDG, were used as the reference standard. Results: According to the reference standard, 68Ga-DOTA-TOC PET and CT showed a concordant result in 32 patients (70%). In the remaining 14 patients (30%), discrepancies were observed, with a final outcome of progressive disease in 9 patients and remission in 5 patients. 68Ga-DOTA-TOC PET was correct in 10 patients (21.7%), including 5 patients with progressive disease. In these patients, metastatic spread was detected with the follow-up whole-body PET but was missed when concomitant CT was used. On the other hand, CT confirmed small pulmonary metastases not detected on 68Ga-DOTA-TOC in 1 patient and progressive liver disease not detected on 68Ga-DOTA-TOC in 3 patients. Quantitative SUV analysis of individual tumor lesions showed a large range of variability. Conclusion: 68Ga-DOTA-TOC PET shows no advantage over conventional anatomic imaging for assessing response to therapy when all CT information obtained during follow-up is compared. Only the development of new metastases during therapy was detected earlier in some cases when whole-body PET was used. SUV analysis of individual lesions is of no additional value in predicting individual responses to therapy.