Published in:
01-03-2008 | Original Article
Disseminated iodine-avid lung metastases in differentiated thyroid cancer: a challenge to 124I PET
Published in: European Journal of Nuclear Medicine and Molecular Imaging | Issue 3/2008
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Aim
This study assessed the ability of visual and quantitative 124-iodine positron emission tomography (124I PET) data to detect disseminated iodine-avid lung metastases (DILM) of differentiated thyroid cancer (DTC).
Materials and methods
Using “post-therapy” 131-iodine (131I) whole-body scintigraphy (TxWBS) and thoracic computed tomography (CT), we retrospectively divided 70 consecutive DTC patients undergoing 124I PET dosimetry ∼1 week before 131I therapy into subgroups positive (n = 7) or negative (n = 63) for DILM, defined as lung metastases visible on TxWBS but not thoracic CT. To determine whether 124I PET data could distinguish patients with versus without DILM, we compared these data with the TxWBS findings. The 124I PET data were acquired via whole-body PET scans ∼24 h after oral administration of 124I, 24 ± 2 MBq. Quantitative data comprised absolute lung 124I activity concentrations and lung-to-background (L/B) 124I uptake ratios.
Results
Only 1/7 DILM-positive patients had visible disseminated lung uptake. Absolute 124I lung uptake activities overlapped considerably between both groups and did not differ significantly (P = 0.150). Mean L/B ratios, however, differed significantly between the DILM-positive and negative groups (P < 0.001). Nevertheless, L/B ratios overlapped between the groups (0.62–1.37 versus 0.13–0.69).
Conclusion
Quantitative analysis of 124I PET data using the L/B ratio is a promising tool to detect patients suspicious for DILM. However, L/B ratios overlapped between the groups to an extent that an unequivocal diagnosis based solely on this criterion was impossible in some patients. In those cases, additional diagnostic tests are necessary for diagnosis.