68Ga-DOTA-Tyr3-Octreotide PET for Assessing Response to Somatostatin-Receptor–Mediated Radionuclide Therapy
Michael Gabriel 1*,
Andreas Oberauer 1,
Georg Dobrozemsky 1,
Clemens Decristoforo 1,
Daniel Putzer 1,
Dorota Kendler 1,
Christian Uprimny 1,
Peter Kovacs 2,
Reto Bale 2,
and
Irene J. Virgolini 1
1 Department of Nuclear Medicine, Innsbruck Medical University, Innsbruck, Austria
2 Department of Radiology, Innsbruck Medical University, Innsbruck, Austria
* To whom correspondence should be addressed. E-mail: michael.gabriel{at}i-med.ac.at.
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Abstract |
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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.
Key Words:
PET, radionuclide therapy, neuroendocrine, gallium-68, neuroendocrine tumors, peptide-related radionuclide therapy
