Diagnostic 131I SPECT/CT Scans Detect Unsuspected Metastases after Thyroidectomy for DTC
Jerome M. Hershman
Avram AM, Fig LM, Frey KA, Gross MD, Wong KK. Preablation 131-I scans with SPECT/CT in postoperative thyroid cancer patients: what is the impact on staging? J Clin Endocrinol Metab 2013;98:1163-71. Epub February 21, 2013.
SUMMARY • • • • • • • • • • • • • • • • • • • • • • • •
Background
After surgery for differentiated thyroid cancer (DTC), routine post operative radioiodine scans have largely been abandoned for several reasons. First, the use of relatively large doses of radioiodine may “stun” residual thyroid tissue and prevent the uptake of a subsequent therapeutic dose. Second, in young patients with tumors
Methods
Between April 2007 and April 2011, all patients with DTC at the University of Michigan who were referred for postoperative 131I therapy underwent preablation 131I planar and SPECT/CT imaging after a 2-week preparation with a low-iodine diet under conditions of thyroid hormone withdrawal. Images were acquired 24 hours after the administration of 1 mCi 131I. Data were analyzed according to TNM staging and age
Results
Data were acquired on 320 patients; 43% were
The two observers agreed on interpretation of the scans in 84% of the cases. In 138 patients <45, the SPECT/CT detected distant metastases in 5 (4%), restaging them to stage 2, and nodal metastases in 61 (44%), of whom 24 were not considered to have nodal metastases at surgery. In 182 patients ≥45, the SPECT/CT detected distant metastases in 18 (10%) and nodal metastases in 51 (28%). Incorporation of these findings led to upstaging of the disease in 25% of the older patients.
In 67 patients with tumors of 1 to 2 cm, nodal metastases were found by SPECT/CT in 35 (52%) and distant metastases in 3 (4.5%). In 49 patients with tumors
In 303 patients, the diagnostic scan results were compared with the posttherapy scans. The results were concordant in 92%. In 6%, additional foci were found on the posttherapy scans, but new metastatic lesions were found in only 1.4%.
Conclusions
Diagnostic preablation SPECT/CT scans detected regional metastases in 35% of patients and distant metastases in 8% of patients. This information changed staging in 4% of younger and 25% of older patients.
ANALYSIS AND COMMENTARY • • • • • •
This study could dramatically alter the use of diagnostic 131I scans after thyroidectomy in patients who have undergone surgery for DTC. However, there is one major caveat. The group of patients studied were highly selected because they were referred to a nuclear medicine unit for 131I ablation therapy, even though 43% were younger patients and less than one-half had nodal disease. The patients had more aggressive tumors than the usual group of patients with DTC. Pathology showed that 30% had vascular invasion, 63% had capsular invasion, and 26% had positive surgical margins.
The SPEC/CT showed an impressive number of patients with residual nodal disease. The finding of distant metastases on the scans in over one fourth of older patients is very surprising. There was no information provided with regard to how many of these new findings occurred in the patients with more aggressive pathologic results. In addition, there was no information concerning correlation with serum thyroglobulin in this group with distant metastases. Although the scans were read to include the classification of uptake in the thyroid bed, there was no comment on the frequency of this finding.
In patients selected for 131I ablation, the positive findings on diagnostic SPECT/CT could influence the amount of the dose for ablation. Others have claimed utility for diagnostic 131I scans before ablation (1). One study reported that SPECT/CT performed after radioablation was much more sensitive than planar imaging and detected nodal involvement in one fourth of patients with papillary thyroid carcinoma (2).
If the improved sensitivity for finding residual disease by SPECT/CT is confirmed in an unselected group of patients with DCT, then the wheel will have come full circle by returning to routine 131I diagnostic scans in virtually all patients, a practice largely abandoned over a decade ago based on data showing that stimulated thyroglobulin and neck ultrasound are more sensitive diagnostic tools than 131I scans. In the meantime, this study influences me to consider SPECT/CT for patients who are classified as low risk and who are not selected for 131I ablation because a negative result would give the patient a very good prognosis. Of course cost considerations would influence the decision to use SPECT/CT in such a patient.
References
- Van Nostrand D, Aiken M, Atkins F, Moreau S, Garcia C, Acio E, Burman K, Wartofsky L. The utility of radioiodine scans prior to iodine 131 ablation in patients with well-differentiated thyroid cancer. Thyroid 2009;19:849-55.
- Mustafa M, Kuwert T, Weber K, Knesewitsch P, Negele T, Haug A, Linke R, Bartenstein P, Schmidt D. Regional lymph node involvement in T1 papillary thyroid carcinoma: a bicentric prospective SPECT/CT study. Eur J Nucl Med Mol Imaging 2010;37:1462-6. Epub April 1, 2010.
CLINICAL THYROIDOLOGY • APRIL 2013 VOLUME 25 • ISSUE 4• © 2013
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