68Ga-DOTA-Tyr3-octreotide PET for assessing response to somatostatin-receptor-mediated radionuclide therapy.
(68)Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotide (DOTA-TOC) PET has proven its usefulness in the diagnosis of patients with neuroendocrine tumors. Radionuclide therapy ((90)Y-DOTA-TOC or (177)Lu-DOTA-octreotate) is a choice of treatment that also requires an accurate diagnostic modality for early evaluation of treatment response. Our study compared (68)Ga-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. (68)Ga-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, (18)F-FDG, were used as the reference standard.


RESULTS
According to the reference standard, (68)Ga-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. (68)Ga-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 (68)Ga-DOTA-TOC in 1 patient and progressive liver disease not detected on (68)Ga-DOTA-TOC in 3 patients. Quantitative SUV analysis of individual tumor lesions showed a large range of variability.


CONCLUSIONS
(68)Ga-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.
Gabriel
Michael
M
Department of Nuclear Medicine, Innsbruck Medical University, Innsbruck, Austria; and 2Department of Radiology, Innsbruck Medical University, Innsbruck, Austria. michael.gabriel@i-med.ac.at
Oberauer
Andreas
A
Dobrozemsky
Georg
G
Decristoforo
Clemens
C
Putzer
Daniel
D
Kendler
Dorota
D
Uprimny
Christian
C
Kovacs
Peter
P
Bale
Reto
R
Virgolini
Irene J
IJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000532:radiotherapy*; D015282:Octreotide / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D009942:Organometallic Compounds / Q000493:pharmacokinetics / Q000627:therapeutic use*; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use; D017481:Receptors, Somatostatin / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D017481:Receptors, Somatostatin; C513399:gallium Ga 68 dotatate; C496730:90Y-octreotide, DOTA-Tyr(3)-; C447941:lutetium Lu 177 dotatate; D015282:Octreotide