Stunning phenomenon after a radioactive iodine- ¹³¹I diagnostic whole-body scan: Is it really a point of clinical consideration?

Statistical and radiobiological analysis of the so-called thyroid stunning

Background

The origin of the reduction in thyroid uptake after a low activity iodine scan, so-called stunning effect, is still controversial. Two explanations prevail: an individual cell stunning that reduces its capability to store iodine without altering its viability, and/or a significant cell-killing fraction that reduces the number of cells in the tissue still taking up iodine. Our aim is to analyze whether this last assumption could explain the observed reduction.

Methods

The survival fraction after administration of a small radioiodine activity was computed by two independent methods: the application of the statistical theory underlying tissue control probability on recent clinical studies of thyroid remnant ¹³¹I ablation and the use of the radiosensitivities reported in human thyroid cell assays for different radioiodine isotopes.

Results

Both methods provided survival fractions in line with the uptake reduction observed after a low ¹³¹I activity scan. The second method also predicts a similar behavior after a low ¹²³I or ¹²⁴I activity scan.

Conclusions

This study shows that the cell-killing fraction is sufficient to explain the uptake reduction effect for ¹³¹I and ¹²³I after a low activity scan and that even if some still living cells express a stunning effect just after irradiation (as shown in vitro), they will mostly die with time. As the β/α value is very low, this therapy fractionation should not impact the patient outcome in agreement with recent studies. However, in case of huge uptake heterogeneity, pre-therapy scan could specifically kills high-uptake cells and by the way could reduce the cross irradiation to the low-uptake cells during the therapy, resulting in a reduction of the ablation success rate.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0144-9) contains supplementary material, which is available to authorized users.

Usefulness of (99m)Tc-pertechnetate whole body scan with neck and chest SPECT/CT for detection of post-surgical thyroid remnant and metastasis in differentiated thyroid cancer patients

OBJECTIVE

The aim of the study was to evaluate the usefulness of (99m)Tc-pertechnetate whole body scan (WBS) with neck and chest SPECT/CT for detection of post-surgical thyroid remnant and metastasis in differentiated thyroid cancer (DTC) patients.

METHODS

Fifty-six post total thyroidectomy patients were included. All patients were prospectively imaged with (99m)Tc-pertechnetate WBS with neck and chest SPECT/CT before (131)I ablation. The post-ablative (131)I WBS with SPECT/CT was performed at 5-7 days after receiving (131)I. Both scans were directly compared to determine the concordance of sites and number of remnant and metastasis.

RESULTS

Overall per-patient analysis, the percentage of concordance between two scans was 96.4%. In thyroid bed, lymph node, lung and bone subgroups, the percentage of concordance between two scans was 96.4, 92.9, 98.2 and 100%, respectively. All of them show good correlation with unweighted kappa between 0.7 and 1. Overall per-lesion analysis, the percentage of concordance between two scans was 84%. In thyroid bed, lymph node, lung and bone subgroups, the percentage of concordance between two scans was 89.5, 55, 82.6 and 50%, respectively.

CONCLUSIONS

Pre-ablative pertechnetate WBS with neck and chest SPECT/CT has good correlation for the detection of post-surgical thyroid remnant, cervical node and discrete lung nodule metastasis as compared to (131)I WBS with SPECT/CT per-patient basis. Because (131)I therapeutic activity is desired base on metastatic site and less concerning about the number of lesions, pre-ablative (99m)Tc-pertechnetate WBS with SPECT/CT was a good alternative tool to avoid radioiodine stunning in post-surgical DTC patients.

Is thyroid stunning clinically relevant? A retrospective analysis of 208 patients

OBJECTIVE

Current guidelines have advised against the performance of (131)I-iodide diagnostic whole body scintigraphy (dxWBS) to minimize the occurrence of stunning, and to guarantee the efficiency of radioiodine therapy (RIT). The aim of the study was to evaluate the impact of stunning on the efficacy of RIT and disease outcome.

SUBJECTS AND METHODS

This retrospective analysis included 208 patients with differentiated thyroid cancer managed according to a same protocol and followed up for 12-159 months (mean 30 ± 69 months). Patients received RIT in doses ranging from 3,700 to 11,100 MBq (100 mCi to 300 mCi). Post-RIT-whole body scintigraphy images were performed 10 days after RIT in all patients. In addition, images were also performed 24-48 hours after therapy in 22 patients. Outcome was classified as no evidence of disease (NED), stable disease (SD) and progressive disease (PD).

RESULTS

Thyroid stunning occurred in 40 patients (19.2%), including 26 patients with NED and 14 patients with SD. A multivariate analysis showed no association between disease outcome and the occurrence of stunning (p = 0.3476).

CONCLUSION

The efficacy of RIT and disease outcome do not seem to be related to thyroid stunning.