Usefulness of 99mTc-pertechnetate single-photon emission computed tomography in remnant mass estimation of postsurgical patients of differentiated thyroid cancer during internal dosimetry

Prognostic value of star-shaped intense uptake of 131I in thyroid cancer patients

OBJECTIVE

After ¹³¹I treatment in patients with differentiated thyroid carcinoma (DTC), we sometimes find a star-shaped intense uptake of ¹³¹I on therapeutic whole body scans (Rx-WBS), called star artifacts. Therefore, we analyzed the relevant clinical factors and prognostic value of star artifacts in DTC patients.

METHODS

809 DTC patients who received ¹³¹I treatment were retrospectively evaluated and divided into 2 groups of patients with and without star artifacts. We evaluated the therapeutic response which was divided into excellent response (ER), biochemical incomplete response (BIR), indeterminate response (IR), and structural incomplete response (SIR). Clinical factors for the presence of star artifacts were analyzed. We also compared the rate of ER, BIR, IR, SIR and recurrence rate between group 1 and group 2.

RESULTS

The major clinical factors included stimulated thyroglobulin (sTg)>1.8ng/ml, 24h radioiodine uptake (RAIU)>2.2%, and positive ^99mTcO4^- thyroid imaging for the presence of star artifacts. In patients with sTg levels>10ng/ml, patients in group 1 had a higher rate of ablation success and ER than patients in group 2 (80.2% vs 65.6%, P=0.038, 31.6% vs 13.1%, P=0.008, respectively) and had a similar rate of BIR, IR, SIR. Recurrence rate was similar between group 1 and group 2 (5.2% vs 3.1%, P=0.13).

CONCLUSION

More remnant thyroid tissue is one of the factors associated with the presence of star artifacts on Rx-WBS. Patients with star artifacts exhibit a better therapeutic response (ER) when sTg levels are >10ng/ml. However, star artifacts have no effect on the recurrence rate.

Routine Intraoperative Neuromonitoring of the Recurrent Laryngeal Nerve to Facilitate Complete Resection and Ensure Safety in Thyroid Cancer Surgery

Routine use of intraoperative neuromonitoring (IONM) in thyroid cancer surgery is controversial. We aimed to investigate whether it improves the completeness of thyroidectomy and ensures safety. This retrospective study included 380 thyroid cancer patients who underwent thyroidectomy, by one surgeon, between July 2006 and November 2015. Patients were grouped according to the surgeon's adaptation of IONM, as follows: none (period 1; n = 92), early (period 2; n = 141), and late (period 3; n = 147). The operative time and rates of vocal cord palsy were determined. Surgical completeness was assessed by technetium-99m imaging of the thyroid remnant and serum thyroglobulin measurement before ablation. The rate of recurrent laryngeal nerve (RLN) palsy showed a decreasing trend over time. No permanent RLN palsies occurred in nerves not invaded by tumor after routine IONM was introduced. Technetium-99m uptake (periods 1–3, 0.62 vs 0.32 vs 0.20; P < 0.01) and thyroglobulin levels (periods 1 and 2, 37.93 vs 8.98 ng/mL, respectively; P = 0.034; period 3, 9.10 ng/mL) progressively decreased. The mean thyroglobulin level dropped significantly after introduction of routine IONM. We conclude that routine IONM during thyroid cancer surgery improves surgical completeness and might prevent permanent RLN palsy over time.

The role of postoperative Tc-99m pertechnetate scintigraphy in estimation of remnant mass and prediction of successful ablation in patients with differentiated thyroid cancer

OBJECTIVE

Surgery and radioactive iodine (RAI) ablation constitute the mainstay of the treatment of differentiated thyroid carcinoma (DTC). In this study, we aimed to evaluate the diagnostic value of postoperative early Tc-99m pertechnetate scanning to detect remnant thyroid tissue and predict ablation success.

METHODS

DTC patients evaluated with postoperative Tc-99m pertechnetate scintigraphy and treated with RAI between January 2007 and December 2014 were recruited. The results of Tc-99m pertechnetate scanning were compared with therapeutic I-131 whole-body scanning (TxWBS) and diagnostic I-131 whole-body scanning (DxWBS) performed 6-9 months after RAI.

RESULTS

There were 154 (21.5%) male and 563 (78.5%) female patients, with a mean age of 49.11±12.35 years. Postoperative Tc-99m pertechnetate scanning was positive in 499 patients (69.6%) and negative in 218 (30.4%) patients. There were 673 (93.9%) patients with a positive TxWBS scan and 44 (6.1%) patients with negative TxWBS scan. Considering TxWBS as the standard test, sensitivity, specificity, positive predictive value, and negative predictive value of Tc-99m pertechnetate scanning were 72.2, 70.5, 97.4, and 14.2%, respectively. DxWBS was positive in 57 (9.0%) and negative in 564 (91%) patients. Ablation dose was higher and preablation thyroglobulin was lower in patients with negative DxWBS (P=0.001 and 0.04, respectively). Overall, 171 (92.9%) of 184 patients with negative Tc-99m pertechnetate had negative DxWBS.

CONCLUSION

Postoperative Tc-99m pertechnetate scintigraphy has a high positive predictive value to detect remnant tissue in patients with DTC. Although negative Tc-99m pertechnetate scanning does not indicate removal of all thyroid tissue, it is related to successful ablation in more than 90% of patients.

Whole-remnant and maximum-voxel SPECT/CT dosimetry in 131 I-NaI treatments of differentiated thyroid cancer

PURPOSE

To investigate the possible differences between SPECT/CT based whole-remnant and maximum-voxel dosimetry in patients receiving radio-iodine ablation treatment of differentiated thyroid cancer (DTC).

METHODS

Eighteen DTC patients were administered 1.11 GBq of 131 I-NaI after near-total thyroidectomy and rhTSH stimulation. Two patients had two remnants, so in total dosimetry was performed for 20 sites. Three SPECT/CT scans were performed for each patient at 1, 2, and 3-7 days after administration. The activity, the remnant mass, and the maximum-voxel activity were determined from these images and from a recovery-coefficient curve derived from experimental phantom measurements. The cumulated activity was estimated using trapezoidal-exponential integration. Finally, the absorbed dose was calculated using S-values for unit-density spheres in whole-remnant dosimetry and S-values for voxels in maximum-voxel dosimetry.

RESULTS

The mean absorbed dose obtained from whole-remnant dosimetry was 40 Gy (range 2-176 Gy) and from maximum-voxel dosimetry 34 Gy (range 2-145 Gy). For any given patient, the activity concentrations for each of the three time-points were approximately the same for the two methods. The effective half-lives varied (R = 0.865), mainly due to discrepancies in estimation of the longer effective half-lives. On average, absorbed doses obtained from whole-remnant dosimetry were 1.2 ± 0.2 (1 SD) higher than for maximum-voxel dosimetry, mainly due to differences in theS-values. The method-related differences were however small in comparison to the wide range of absorbed doses obtained in patients.

CONCLUSIONS

Simple and consistent procedures for SPECT/CT based whole-volume and maximum-voxel dosimetry have been described, both based on experimentally determined recovery coefficients. Generally the results from the two approaches are consistent, although there is a small, systematic difference in the absorbed dose due to differences in the S-values, and some variability due to differences in the estimated effective half-lives, especially when the effective half-life is long. Irrespective of the method used, the patient absorbed doses obtained span over two orders of magnitude.

Tc-99m imaging in thyroidectomized differentiated thyroid cancer patients immediately before I-131 treatment

PURPOSE

The aim of this study was to evaluate the clinical role of technetium-99m pertechnetate (Tc-99m) imaging in thyroidectomized differentiated thyroid cancer patients immediately before radioiodine-131 (I-131) treatment (Tx).

PATIENT AND METHODS

Eighty-six consecutive post-total-thyroidectomy patients (15 men, 71 women; mean age: 46.8 years) with pathologically diagnosed differentiated thyroid cancer were retrospectively studied. Tc-99m imaging immediately before I-131 Tx using both patient-based and lesion-based measurements were analyzed and were further compared with those of post-Tx I-131 whole-body scans.

RESULTS

For patients with unequivocally positive Tc-99m uptake, the sensitivity was 77% (patient-based) and 59% (site-based). The positive predictive value (PPV) was 100% for both patient-based and site-based measurements. If equivocal Tc-99m uptake was counted as positive, the sensitivity was 83 and 67%, and the PPV was 100 and 99% for patient-based and site-based measurements, respectively.

CONCLUSION

(a) To increase sensitivity yet maintaining high PPV, equivocal Tc-99m uptake should be considered a positive finding. (b) The nearly 100% PPV of Tc-99m imaging immediately before I-131 Tx for remnant detection suggests that Tc-99m imaging not only serves as an alternative to low-dose I-131 scanning in the low-risk post-thyroidectomy patients but also provides a clue for the subsequent I-131 therapeutic dosage and even for the outcome prediction.

Prediction of the success of thyroid remnant ablation using preablative 99mTc pertechnetate scintigraphy and postablative dual 131I scintigraphy

OBJECTIVE

The aim of this study was to predict the success of 131I ablation using preablative 99mTc pertechnetate salivary scintigraphy and a postablative dual 131I scan in differentiated thyroid cancer (DTC).

PATIENTS AND METHODS

A total of 168 DTC patients who underwent 131I ablation with preablative salivary scintigraphy and a postablative dual (early and delayed) 131I scan were enrolled. For salivary scintigraphy, the thyroid remnant uptake was visually assessed. For the dual 131I scan, the thyroid remnant to background uptake ratios (TBRs) on early and delayed scans were measured and the percentage change in TBR (TBRΔ) was calculated.

RESULTS

Thyroid remnant uptake was seen in 69 (41%) patients on salivary scintigraphy and in 162 (96%) patients on the dual 131I scan. The success rate of ablation was higher in patients with negative remnant uptake on salivary scintigraphy (86%) than in patients with positive remnant uptake (58%, P=0.0001). The success rate of ablation was 100% in patients with no remnant uptake on both salivary scintigraphy and the dual 131I scan. The success rate of ablation was higher in patients with TBRΔ 0 or more than in patients with TBRΔ less than 0, irrespective of remnant uptake on salivary scintigraphy (91 vs. 70%, P=0.03, for patients without remnant uptake on salivary scintigraphy; 74 vs. 48%, P=0.05, for patients with remnant uptake on salivary scintigraphy).

CONCLUSION

The success of thyroid remnant ablation in DTC can be predicted by the presence of remnant uptake on preablative 99mTc pertechnetate scintigraphy and change in remnant uptake on the postablative dual 131I scan.

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.