Scintigraphy plays role in detecting metastatic thyroid cancer
Specialists have long questioned indium-111-based somatostatin receptor scintigraphy?s (SRS) value for detection of metastatic thyroid cancer. That controversy may be over, according to University of Texas researchers.
Investigators compared In-111 DTPA octreotide SRS?s sensitivity with that of FDG-PET and extensive conventional imaging -- namely CT, MRI, and high-resolution neck ultrasound -- for metastatic thryroid cancer detection in 21 patients. They found that, even though SRS?s sentivity is moderate, the modality can occasionally detect lesions that neither FDG-PET nor conventional imaging can. They published their findings in the March issue of Clinical Nuclear Medicine.
?Our study has a value in quelching the controversy of whether SRS is of any use in patients with metastatic thyroid carcinoma, especially when whole-body I-131 (RAI) imaging is not helpful,? said lead author Dr. Nicholas J. Sarlis, until recently at the National Institutes of Health and currently an associate professor of medicine at UT?s M.D. Anderson Cancer Center in Houston.
Using conventional imaging, FDG-PET, and SRS combined, researchers detected 105 metastatic lesions. Sensitivity for SRS was 49.5% versus 67.6% for PET. The lesion detection concordance rates were the following: · conventional imaging vs. FDG-PET: 80.8% · conventional imaging vs. SRS: 74.2% · FDG-PET vs. SRS: 58.6%
Sensitivities for metastatic lesion detection were always higher with both conventional and FDG-PET imaging. SRS, however, detected five unexpected lesions that neither PET nor conventional imaging could find. In addition, two patients showed a statistically significant correlation of lesional In-111 DTPA octreotide uptake and PET SUV in eight lesions.
A ?universal statement? of SRS?s value in this setting is inappropriate and potentially misleading outside of the setting of a clinical research study, Sarlis said. Nevertheless, SRS still has a place in imaging disease deposits in metastatic thyroid carcinoma and in selected cases can even be complementary to FDG-PET scanning.
From a molecular oncology standpoint, different lesions? expression of somatostatin receptors and that of glucose transporters can differ a lot, even within the same patient, and occasionally within different parts of the very same lesion. Clinicians should consider this factor when analyzing or interpreting non-RAI-based cancer-targeting radionuclide scans, Sarlis said.
SRS is a useful alternative when PET results are inconclusive. It?s also more widely available than PET and has better reimbursement. Only one PET application for thyroid cancer was recently approved by the Centers for Medicare and Medicaid Services, out of four requested by PET proponents. SRS is also more cost-effective and, when combined with SPECT, may be superior for detection of lesions smaller than 4 to 5 mm than extensive multimodality conventional imaging, he said.
In agreement with several other studies, Sarlis reinforced that FDG-PET should be the method of choice for detecting metastatic thyroid carcinoma when RIA whole-body scans are uninformative. But SRS can be used in selected patients with lesions suspected by anatomical imaging that do not show on PET scans. It can also be used as an alternative in settings where FDG-PET is unavailable or its cost is prohibitive.
