Positive thyroid cancer scintigraphy using technetium-99m methoxyisobutylisonitrile

Use of 99mTc-sestamibi SPECT/CT when conventional imaging studies are negative for localizing suspected recurrence in differentiated thyroid cancer: a method and a lesson for clinical management

PURPOSE

The detection of recurrent disease in differentiated thyroid cancer (DTC) patients with elevated or rising serum thyroglobulin (Tg) levels and multiple negative conventional imaging studies can be challenging, especially when ¹⁸F-FDG PET/CT scan is also negative. We report a patient and review the literature on the diagnostic use of ^99mTc-sestamibi scans to identify the source of elevated or rising Tg in patients with negative conventional imaging including negative ¹⁸F-FDG PET/CT scans.

PATIENT AND METHODS

A 73-year-old woman was referred for widely-invasive metastatic follicular thyroid cancer with bone metastasis to her left mandible. She had a total thyroidectomy, left mandibular resection, and ¹³¹I therapy of 145 mCi (5.4 GBq) and her subsequent unstimulated serum Tg level was 29 ng/ml (TgAb negative). At six months' follow-up, her stimulated Tg was 527 ng/ml (TSH 188 mIU/L, TgAb negative). All imaging studies performed within the prior 12 months were reported as negative for recurrence or metastasis; this included neck ultrasound, diagnostic radioiodine scan, chest CT and, ¹⁸F-FDG PET/CT. The patient was injected with 24.6 mCi (910 MBq) of ^99mTc-sestamibi intravenously, and whole-body and SPECT/CT images were acquired.

RESULTS

The ^99mTc-sestamibi whole-body posterior image demonstrated abnormal focal uptake in the right posterior calvarium and corresponded to an occipital lytic bone lesion on the SPECT/CT. The patient underwent surgical resection of the skull metastasis, and pathology confirmed metastatic follicular thyroid cancer. Five months post-surgery, the suppressed Tg was markedly reduced and remained stable at ~3.2 ng/ml. With the knowledge of the DTC recurrence location, the two sets of ¹⁸F-FDG images were re-evaluated. The more thorough and targeted interpretation underscored the importance of structured image reporting. The current literature on the utility of ^99mTc-sestamibi scans when radioiodine, ¹⁸F-FDG PET/CT, and other imaging studies are negative is sparse and inconsistent.

CONCLUSIONS

^99mTc-sestamibi may have a role in thyroid cancer localization when physical exam, neck ultrasound, radioiodine scan, chest/abdomen CT, and ¹⁸F-FDG PET/CT does not identify the source of elevated Tg levels in DTC.

99mTc Sestamibi Thyroid Scan in Amiodarone-Induced Thyrotoxicosis Type I

Amiodarone-induced thyrotoxicosis (AIT) type I describes inducement of clinical hyperthyroidism by excessive thyroidal iodine in the setting of latent Graves disease, and therapy differs from that used for AIT type II. A 65-year-old man previously on amiodarone for atrial fibrillation developed clinical hyperthyroidism. Diagnosis of AIT was made, but the type was not clear. Tc sestamibi thyroid scan showed diffusely increased uptake and retention in an enlarged thyroid gland, a pattern consistent with AIT type I. Methimazole was initiated and controlled the thyrotoxicosis. I iodide thyroid scan and uptake study performed later was consistent with Graves disease.

The value of I-131 SPECT in the detection of recurrent differentiated thyroid cancer

AIM

The aim of this study is to assess the additional value of radioiodine-131 (I-131) single-photon emission computed tomography (SPECT) to whole-body scintigraphy (WBS) in the detection of recurrent differentiated thyroid cancer.

MATERIALS AND METHODS

Eighty-seven consecutive patients with differentiated thyroid cancer, who had undergone a diagnostic SPECT WBS study, were included. In all patients, posttreatment scans, computed tomography scanning or ultrasonography were used to assess positive results, whereas follow-up was used in patients with a negative scan result. General data, such as primary tumor, histology and biochemical parameters were also gathered.

RESULTS

In this study cohort, nine positive diagnostic WBS were found compared with 31 positive SPECT scans. In eight of the nine (89%) positive WBS, recurrent thyroid cancer was found at the same location on the SPECT scan. In 56 patients SPECT and WBS were negative. Moreover, eight patients with a positive SPECT study had a serum thyroglobulin level less than 1 microg/l, which, in our hospital, was the cut-off level for treatment. On the basis of the serum thyroglobulin measurements and the WBS, 9% of the patients would not have been treated.

CONCLUSION

I-131 SPECT of the head and neck region and chest has a complementary role for planar imaging in the follow-up of patients treated for differentiated thyroid cancer. Therefore, its use in addition to WBS is strongly recommended in clinical practice.

Role of 99mTc-Tetrofosmin delayed scintigraphy and color Doppler sonography in characterization of solitary thyroid nodules

OBJECTIVES

A study was undertaken to evaluate the diagnostic efficiency of Tc-Tetrofosmin scan and color Doppler in the characterization of benign and malignant solitary thyroid nodules.

METHODS

Fifty-two patients found to have a cold solitary thyroid nodule on Tc-pertechnetate scintigraphy were included in this study. All patients underwent a single-injection dual-phase (30 min and 120 min) Tc-Tetrofosmin scan. The intranodular vascularity was measured using color Doppler sonography. Fine-needle aspiration cytology was performed on all the patients. In the following days and weeks all patients underwent surgery.

RESULTS

Thirteen out of 15 patients with thyroid cancer showed delayed retention of radiotracer (on 120 min images as compared to the initial 30 min image). Thirty-six out of 37 patients harboring benign solitary nodules showed significant washout of tracer on delayed images. Sensitivity, specificity, positive predictive value and negative predictive value of delayed Tc-Tetrofosmin scintigraphy were found to be 86.6, 97.2, 92.8 and 94.7%, respectively. The Doppler study was able to demonstrate increased vascularity in the center of 8 of the 15 malignant nodules. Thirty-two patients harboring a benign solitary nodule showed normal or increased peripheral vascularity on Doppler study. Sensitivity, specificity, positive predictive value and negative predictive value of color Doppler were found to be 53.5, 86.4, 61.5 and 82%, respectively.

CONCLUSION

Delayed Tc-Tetrofosmin scintigraphy is a highly sensitive and specific method for characterizing solitary thyroid nodules, while color Doppler has a low sensitivity but relatively high specificity in differentiating benign from malignant thyroid lesions.

Clinical importance of technetium-99m-methoxyisobutylisonitrile (MIBI) scintigraphy in differentiated thyroid carcinoma patients with elevated thyroglobulin levels and negative I-131 scanning results

AIMS AND BACKGROUND

The aim of this study was to evaluate the potential contribution of Tc-99m-MIBI scintigraphy to the follow-up of patients with differentiated thyroid carcinoma, who had elevated Tg levels and negative I-131 whole-body scan results.

MATERIALS AND METHODS

In this retrospective study, we evaluated 28 patients with differentiated thyroid carcinoma, who had total or near total thyroidectomy followed by an ablative dose of I-131 at various time intervals (15 women, 13 men; mean age 43 +/- 17 years). All patients were treated with T4 suppression. After a mean follow-up period of 6.1 years (range 3-15) all patients were determined to have a high serum Tg concentrations (>2 ng/ml) and previous negative I-131 WBS results. All patients were examined for metastatic sites using Tc-99m-MIBI scan. Scans were visually evaluated for detecting lymph node metastases and/or local recurrence, lung metastases and skeletal metastases.

RESULTS

Tc-99m-MIBI scan demonstrated lesions in 23 patients (83.3%). In five patients with negative Tc-99m-MIBI scan findings (FN results): Chest CT showed small-sized mediastinal LN metastases in 2 patients and lung metastases in another 2 patients (<1 cm). Neck CT showed small-sized cervical LN involvement in 1 patient. The sensitivity of detection for neck was 94.4%, for lung 63.6%, and for bone lesions 100%. For all scan sites taken together, the sensitivity of disease detection was 83.3%, the specificity was 50%, positive predictive value (PPV) was 96.2%, and finally negative predictive value (NPV) was 16.7%.

CONCLUSION

We concluded that Tc-99m-MIBI scan should be considered as a supplementary scintigraphic method for the follow-up of patients with high serum Tg levels and negative I-131 WBS results, and it can help clinicians in making the decision to treat these patients.

Radioiodine whole-body scans, thyroglobulin levels, 99mTc-MIBI scans and computed tomography: results in patients with lung metastases from differentiated thyroid cancer

OBJECTIVES

The correlation between a 131I whole-body scan (WBS), a 99mTc sestamibi (99mTc-MIBI) WBS, a computed tomography (CT) scan and the value of routine follow-up for 131I WBS and thyroglobulin (Tg) levels in patients with lung metastases from differentiated thyroid cancer was assessed.

METHOD

Pulmonary metastases were detected in 32 patients out of 583 with differentiated thyroid cancer (DTC) who were admitted to our clinic between 1985 and 2004 (age range, 22-79 years; mean, 58 +/- 19 years; 15 women and 17 men). Pulmonary metastases were diagnosed by considering the 131I WBS, increased Tg levels and/or other positive radiological findings. Papillary carcinoma was diagnosed in 15/32 patients and follicular carcinoma in 13/32. A mixed type found in 4/32 patients was classified histopathologically. A total of 3.7-53.65 GBq (100-1450 mCi) 131I was given to each patient. The duration of follow-up ranged from 36 to 240 months. A 131I WBS, the determination of Tg levels and/or a CT scan were carried out in the assessment of a diagnosis and follow-up of patients with lung metastases. A 99mTc-MIBI WBS was performed on 19 patients who were chosen at random from the 583.

RESULTS

Nineteen of 32 patients had lung metastases before they received the first 131I treatment. Six of the 32 had distant-organ metastases other than in the lungs. Four of these six patients had only lung and bone metastases. Pulmonary metastases were observed on the 131I WBS patients 31/32 (96.8%) whereas no pulmonary metastases, were detected on the CT scans in 3/32 patients. The last diagnostic whole-body scan (DWBS) was normal in 13/32 patients. At the first examination, the Tg levels in 27/32 (84.4%) patients were below 30 ng . ml(-1). At the final examination, 20/32 (62.5%) patients had Tg levels higher than 30 ng . ml(-1), while Tg levels were lower than 30 ng . ml(-1) in 12/32 patients. Tg levels decreased in 21/32 and increased in 3/32 patients. The 131I WBS continued to be abnormal in 2/3 patients with increased Tg levels but became normal in one patient whose CT scan still showed macro-nodular lesions. Tg levels did not change significantly in 8/32 patients. The 131I WBS became normal in 5/8 patients, while the CT scans for 4/5 showed micro-nodules. Metastases were detected in 12/19 patients who underwent 99mTc-MIBI whole-body scanning: 18/19 showed metastases on the 131I WBSs and 17/19 on the CT scans. Of the seven patients without a sign of metastasis on the 99mTc-MIBI WBS, one was negative in terms of metastasis on the 131I WBS and one on the CT scan. Fibrosis was observed on the CT scans of 2/32 patients. One patient developed dedifferentiation, as determined by the negative 131I WBS and positive CT scan.

CONCLUSION

131I whole-body scanning and the determination of Tg levels are the most important procedures for the evaluation of lung metastases in differentiated thyroid cancer. Computed tomography is a useful addition to 131I whole-body scanning. MIBI imaging alone may not be enough to detect lung metastases from differentiated thyroid cancer.

Indium-111-Octreotide scintigraphy in differentiated thyroid carcinoma metastases that do not respond to treatment with high-dose I-131

AIM

Differentiated thyroid cancer is characterized by a very good prognosis in the majority of the patients. The therapy of choice is surgery followed by ablation with Iodine-131 (I-131). However, some patients have metastases that have lost the capability of concentrating I-131, even when it is given in therapeutic doses. In the present study, we describe the value of Indium-111 Octreotide (Octreoscan) in differentiated thyroid cancer patients with increased Tg levels who failed to demonstrate a response to treatment with high-dose I-131.

METHOD

Fifteen consecutive patients with progressive differentiated thyroid cancer (ten female, five male) (mean age: 59 years, range 13-81 years; eight papillary, six follicular, and one Hürthle cell carcinoma) were studied. Progression was based on increasing Tg levels and was confirmed by radiological evaluation. Whole body scintigraphy (WBS) was performed after the administration of 200 MBq of Indium-111-Octreotide. The images were assessed by two experienced observers and compared with post-treatment I-131 WBS.

RESULTS

In seven out of 15 patients distant metastases were already present at initial stage, whereas in ten patients the primary tumor stage was T3 or T4 indicating that the majority of the patients had advanced disease. In two out of five patients with a positive I-131 WBS, Indium-111-Octreotide was false negative. In nine out of ten patients with a negative I-131 WBS, Indium-111-Octreotide demonstrated multiple metastases. In those patients with a positive SSR-scintigraphy, metastases were found in the lungs ( n=14), bone ( n=7), mediastinum ( n=3), liver ( n=2), brains ( n=1), and cutis ( n=1). Overall, three out of 15 patients had a negative Indium-111-Octreotide result revealing a sensitivity of 80%.

CONCLUSION

Our findings demonstrate the diagnostic value of Indium-111-Octreotide in differentiated thyroid cancer that fails to respond to I-131 treatment. It opens the possibility for additional treatment with high doses of Indium-111-Octreotide or its analogs in a majority of the patients.

Isotope imaging for metastatic thyroid cancer

Many isotopes are available for imaging patients with suspected thyroid cancer recurrence and metastases. TSH-stimulated low-dose 131I whole-body scanning with serum thyroglobulin either by standard LT4 withdrawal or rhTSH stimulation is the preferred test for monitoring patients without palpable disease or elevated serum thyroglobulin on LT4 therapy (Fig. 5). This approach has the advantage of finding disease that may be amenable to 131I therapy, although low-dose 131I scans are less sensitive than are scans with other imaging agents. 123I has better imaging characteristics than 131I and has been shown to be equivalent or superior to low-dose 131I in recent studies. As the availability of 123I increases and the cost decreases, this agent may replace 131I in imaging for recurrent or metastatic thyroid cancer. Patients who have an elevated serum thyroglobulin on LT4 therapy or after TSH stimulation but have a negative low-dose 131I scan require other imaging procedures to find the suspected disease. The authors currently perform a sensitive neck ultrasound to look for surgically remediable disease and consider a noncontrast CT scan of the chest to look for small pulmonary metastases that poorly concentrate low doses of 131I (Fig. 5). Fluoro-18-deoxyglucose PET, 99mTc MIBI, 201Tl, and 99mTc tetrofosmin are primarily useful in the setting of a negative whole-body 131I scan and elevated serum thyroglobulin. 18FDG-PET seems to have the highest sensitivity in this setting and would be the preferred imaging agent, but availability and cost are major issues (Fig. 5). Although some researchers have advocated these radiopharmaceuticals as first-line agents replacing 131I, there is little support for this position. This approach to imaging is not cost-effective because positive scans in these patients would most likely require 131I scintigraphy to determine whether the lesions are amenable to radioiodine therapy. 99mTc pertechnetate, 99mTc furifosmin, and somatostatin receptor scintigraphy have a limited role in imaging for recurrent or metastatic differentiated thyroid carcinoma. In choosing among 99mTc MIBI, 201Tl, and 99mTc tetrofosmin, the technetium label of sestamibi and tetrofosmin results in better image quality and faster imaging than 201Tl. Although 99mTc sestamibi and 99mTc tetrofosmin have not been compared in a large series, the higher tumor-to-background ratio and consistently high sensitivities of 99mTc tetrofosmin suggest that it could potentially have additional value over 99mTc sestamibi, but there is still limited experience with 99mTc tetrofosmin.

Nuclear medicine imaging procedures in differentiated thyroid carcinoma patients with negative iodine scan

Radioiodine treatment following surgery is an effective therapy in differentiated thyroid carcinoma (DTC) patients. However, in DTC patients with metastases characterized by very low or absent iodine uptake, total thyroidectomy and radical loco-regional lymphoadenectomy is the only effective therapeutic approach. In the present article, we have discussed the most recently available nuclear medicine techniques utilized for the detection of DTC metastases that have lost the capacity to trap radioiodine. A review of the data published in the literature has been presented, and a comparative analysis made of the results obtained by other imaging modalities such as high resolution neck ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI). In our experience, the most sensitive and accurate imaging procedure is represented by the combination of neck US and whole body 99mTc-methoxy-isobutylisonitrile (99mTc-MIBI) scintigraphy; this combination might be proposed as a first-line diagnostic approach in DTC patients with increased serum thyroglobulin (Tg) levels and negative high dose 131I scans.

Evaluation of indium-111 pentetreotide somatostatin receptor scintigraphy to detect recurrent thyroid carcinoma in patients with negative radioiodine scintigraphy

The follow-up of patients who underwent thyroidectomy for differentiated thyroid carcinoma is based on the combination of serum thyroglobulin (Tg) measurement and radioiodine total-body scan (ITBS). The diagnostic strategy to be used in patients with elevated serum Tg level but negative ITBS remains debatable. Somatostatin receptor scintigraphy (SRS) has been proposed. Our objective was to compare the results of SRS and conventional radiological imaging (CRI) for the diagnosis of recurrent disease and/or metastases in 15 patients who had had thyroidectomy for differentiated carcinoma (14 papillary, 1 Hurthle cell carcinoma) and who displayed elevated Tg levels (10 to 65000 ng/mL) together with negative ITBS performed after 100 mCi. All patients underwent SRS and CRI within 3 months, allowing comparison of the 2 approaches for the identification of thyroid carcinoma metastases. CRI first included a chest x-ray and ultrasonography of the neck. It was followed by computed tomography (CT) scanning and/or magnetic resonance imaging (MRI) of the neck, chest and occasionally abdomen, and 99mTc bone scintigraphy in case of negative results. In 6 patients with Tg levels ranging from 65 to 65000 ng/mL, CRI detected 12 histologically proven metastases among 9 organs. Among these patients, SRS identified only 6 metastases. SRS identified 1 case of mediastinal recurrence that was not detected by CRI. In another patient with a Tg level of 51 ng/mL, a cervical node was identified using both SRS and CRI but proved to be a false-positive (inflammatory cervical node). In the other 8 patients with Tg levels ranging from 10 to 580 ng/mL, SRS and CRI were negative, and the source of Tg secretion remains unknown. The results of SRS did not correlate with serum Tg level. In conclusion, the diagnostic accuracy of SRS in this study was disappointing and clearly lower than that of CRI. Our results do not support the use of SRS as a guide conventional imaging modalities in patients operated on for differentiated thyroid carcinoma who display elevated Tg levels together with negative ITBS.

Visualisation of a paraganglioma by technetium-99m-sestamibi scintigraphy

A 68-yr-old woman presented to our observation with multinodular goiter and a contiguous right laterocervical mass. In spite of ultrasound, technetium and iodine scan, CT and fine-needle biopsy, the precise origin of the mass remained uncertain. On additional multi-phase sestamibi scan, the neck region showed an early high uptake rapidly decreasing over time in the laterocervical mass, and a persistent inhomogeneous distribution in the thyroid gland. This behavior suggested that the laterocervical mass could derive from an anatomical structure other than the thyroid. Surgical exploration established the extrathyroid nature of the laterocervical mass and the histological examination confirmed that it was a typical paraganglioma. This finding is in keeping with a recent report of positive sestamibi uptake in a cervical paraganglioma, although our case showed a more rapid kinetic. This tumor should be therefore taken into consideration in the differential interpretation of focal sestamibi uptake.

Diagnostic value of technetium-99m methoxyisobutyl isonitrile (99mTc-MIBI) scintigraphy in detecting thyroid cancer metastases: a critical evaluation

Technetium-99m methoxyisobutyl isonitrile (99mTc-MIBI) scintigraphy has recently been used in clinical application for detecting thyroid cancer metastases, its role being considered supplementary to serum thyroglobulin (Tg) measurements and radioactive iodine (131I) whole-body scans (WBS). The present retrospective study was designed to elucidate the role of 99mTc-MIBI scans in localizing metastatic lesions by assessing sensitivity and specificity of the scan results obtained in a group of 68 thyroidectomized thyroid cancer patients. Presence or absence of thyroid cancer was judged with other diagnostic modes including serum Tg measurements, 131I WBS, bone scans, chest x-rays, computed tomography (CT), ultrasonography, histopathology, and evolution of disease during follow-up. All scans were read on lesion basis for detecting neck, lung, and bone metastases and also on region basis, namely head-neck, chest, and abdomen-pelvis-extremities (ab-p-ex) areas. The sensitivity of detection was 94.4% (17/18) for neck, 78.4% (40/51) for lung, and 92.8% (64/69) for skeletal lesions. Positive predictive value (PPV) and negative predictive value (NPV) were 96.3% (26/27) and 97.7% (43/44) for head-neck; 94.7% (71/75) and 50.0% (12/24) for chest; 100.0% (25/25) and 93.1% (54/58) for ab-p-ex regions, respectively. For all scan sites taken together, PPV and NPV were 96.1% (122/127) and 86.5% (109/126), respectively. In conclusion, the present study reveals that 99mTc-MIBI can be proposed as a first-line diagnostic agent for the follow-up protocol of thyroid cancer patients, although the ability to detect small lung metastases is somewhat limited.

Comparison of 18FDG-PET with 131iodine and 99mTc-sestamibi scintigraphy in differentiated thyroid cancer

18Fluorine-fluorodeoxyglucose (FDG) positron-emission tomography (PET) has emerged as a useful method in various fields of oncology. The aim of the present study was to evaluate the clinical significance of this technique in differentiated thyroid carcinoma and to compare the results with other imaging modalities, particularly with whole-body 131iodine scintigraphy (WBS) and hexakis (2-methoxyisobutylisonitrile) (99m)technetium (I) scintigraphy (MIBI). Whole-body PET imaging using FDG was performed in 54 patients. There were 39 patients with papillary tumors and 15 patients with follicular tumors (including 3 Hürthle-cell carcinomas). Primary tumor stage (pT) was pT1 in 5 cases, pT2 in 19 cases, pT3 in 2 cases, pT4 in 24 cases, and unknown in 4 cases, respectively. Finally, for each case an overall clinical evaluation was done including histology, cytology, thyroglobulin level, sonography, computed tomography, magnetic resonance imaging, and subsequent clinical course, to allow a comparison with functional imaging results. Compared with WBS, FDG-PET gave different results in the majority of cases with recurrence/metastases (11 FDG-true-positive/WBS-negative tumor sites and 8 WBS-true-positive/FDG-negative tumor sites). In 7 patients with recurrence/metastases, FDG-PET and WBS gave corresponding results (10 sites). In 28 patients, FDG-PET and WBS were normal (including 2 false-negative cases). MIBI was performed in 44 cases. FDG-PET was better correlated to MIBI (congruent positive results in 13 tumor sites) than to WBS. Compared with MIBI, FDG-PET was superior in 5 cases (including 3 patients with distant metastases). Two FDG-negative/MIBI-positive tumors were observed. Different tracer uptake mechanisms have to be considered regarding "nonspecific" tumor imaging with FDG-PET or MIBI. Nevertheless, since spatial resolution with respect to tomographic imaging is inferior with single photon emission computer tomography (SPECT) using MIBI, the observed higher sensitivity of PET might be due to the higher spatial resolution of this method. As far as grading could be obtained, FDG-PET seemed to be more sensitive than WBS in high-grade tumors, whereas WBS was positive predominantly in low-grade carcinomas, although statistical significance could not be reached. The results prove the clinical usefulness of FDG-PET and MIBI for detection of 131iodine-negative tumor tissue in differentiated thyroid cancer.

Selection of the optimal scanning agent for thyroid cancer

Physical and biologic principles, availability, and experience in use determine which radiopharmaceuticals will be the optimal agents to portray scintigraphically thyroid cancers. However, clinical reasoning must dictate which scanning procedure to use and when. To identify functioning thyroid nodules, and thereby exclude malignancy and also disclose the source of excess thyroid hormone, technetium Tc 99m pertechnetate is the agent of choice. To evaluate patients with metastatic differentiated thyroid cancer (DTC) for possible radiopharmaceutical therapy, low doses (no more than and probably less than 74 MBq or 2 mCi) of 131I iodide are preferred. 131I is especially necessary if dosimetry is undertaken to help prescribe the optimal therapeutic dose of 131I. For less well differentiated tumors that do not concentrate 131I, most experience has been with thallium 201, which enables depiction of most metastases, but, in time, newer agents may be found to produce superior scans. The goal of imaging of the less well differentiated cancers must be to direct additional therapy such as external beam radiation of surgical excision. It is unlikely that any scanning procedure that depends on the physiologic and biochemical activities of DTC will have as much sensitivity for locating tumors in the euthyroid as in the hypothyroid patient. A majority of medullary carcinomas of the thyroid (MCT) have been portrayed by indium 111 octreotide and by 99mTc pentavalent dimercaptosuccinic acid; other agents have concentrated to lesser levels in the tumors or have not been investigated as extensively. As of now, metastatic MCT defies therapy, and, therefore, scanning to detect the tumors has little clinical utility.

The changing role of radioiodine in the management of differentiated thyroid cancer

This article discusses several aspects of the evaluation and management of differentiated thyroid carcinoma that are changing or may change in the near future. Although conventional treatment of this disease is highly effective, some modification may improve the welfare of patients and the overall results. Because the symptoms of hypothyroidism are vexing, there has been great interest in using recombinant human thyroid-stimulating hormone (rhTSH) to prepare patients for iodine 131 imaging. rhTSH has been about as effective as thyroid hormone withdrawal for diagnostic imaging so that approval for this use is expected. Another topic of interest is the administration of 131I therapy to patients whose serum thyroglobulin levels are abnormal but whose diagnostic 131I scans are negative. Because the 131I scans after therapy are often abnormal in these patients and a reduction of serum thyroglobulin can occur, this approach seems effective. The long-term impact of this therapy on recurrence and survival, however, is unknown. A third issue that is currently under review is the amount of 131I that should be used for diagnostic scanning. Although past opinion favored larger doses, "stunning" of thyroid remnant and tumor can occur with diagnostic 131I imaging. Substituting iodine 123 is an alternative for postthyroidectomy scanning, but when administered as 300 uCi it is less accurate than 131I for recurrent disease or distant metastases. Related to these issues, two other topics are reviewed: the use of other radiopharmaceuticals for imaging patients with thyroid cancer, and 131I dosimetry.

Tc-99m MIBI scintigraphy in patients with lung cancer. Comparison with CT and fluorine-18 FDG PET imaging

Tc-99m MIBI imaging has been used to evaluate patients with different neoplastic disorders, but its role in nuclear oncology has not been definitely established. In this study, we compared the results of Tc-99m MIBI (planar and SPECT imaging) with those of F-18 FDG PET radionuclide studies in 19 patients who had proven lung cancer. One patient was studied in follow-up. All patients underwent chest CT scans. MIBI and FDG images were qualitatively and quantitatively analyzed using region of interest analysis. Quantitative evaluation of MIBI and FDG activities in lung-tumor lesions was performed calculating tumor/nontumor ratios. On CT, 18 lung tumors were detected, while one patient was disease free. For lung lesions, the diagnostic sensitivity of planar MIBI imaging was 83%, while those of MIBI SPECT and FDG PET were both 100%. The quantitative analysis of lung-tumor MIBI and FDG activities showed that FDG uptake was significantly (P < 0.001) higher compared with MIBI uptake (5.5 +/- 3.1 vs 2.1 +/- 0.6); concordant MIBI and FDG images were found in 4 lesions in terms of central activity defect showing central necrotic tumor tissue. For lymph node abnormalities, planar MIBI scan only detected 3 lesions in 3 patients, whereas MIBI SPECT identified 9 lesions in 5 patients. FDG PET showed 13 lymph node abnormalities in 5 patients. This study shows similar results of Tc-99m MIBI SPECT and F-18 FDG PET in the diagnostic evaluation of patients with lung tumors. However, FDG lung tumor uptake was significantly higher compared with MIBI accumulation, suggesting a high glucose tumor metabolism. Thus, MIBI SPECT imaging may be useful to evaluate such patients and may be considered an alternative when PET is not available.

Technetium-99m tetrofosmin imaging in thyroid diseases: comparison with Tc-99m-pertechnetate, thallium-201 and Tc-99m-methoxyisobutylisonitrile scans

Technetium-99m tetrofosmin is a lipophilic phosphine used for myocardial perfusion imaging. Biodistribution studies have shown significant thyroid uptake of tetrofosmin and preliminary reports have suggested that tetrofosmin imaging may be of value in patients with thyroid cancer. In this study, tetrofosmin whole-body scintigraphy was performed in 35 patients with evidence of thyroid diseases. All patients underwent laboratory evaluation of thyroid function as well as 99mTc pertechnetate scan, thallium-201 (n=16) 99mTc-methoxyisobutylisonitrile (MIBI) (n=19) whole-body studies. Thyroid images were semi-quantitatively analysed by a 4-point score: 0=no significant uptake; 1=uptake increased as compared to background activity, but inferior to normal thyroid tissue; 2=uptake equal to normal thyroid tissue; 3=uptake superior to normal thyroid tissue. Pathology examinations were obtained. A total of 41 thyroid nodules were detected, of which 15 were goitre nodules, 13 adenomas and 13 malignant lesions. In goitre nodules, concordant results of tetrofosmin and pertechnetate uptake (score 1 or 0) were observed in the majority of lesions (87%). In function adenomas (n=10), both tetrofosmin uptake and pertechnetate uptake were score 3. In non-function adenomas (n=3), tetrofosmin uptake was score 3, while pertechnetate uptake was score 0. In six malignant lesions, tetrofosmin uptake was score 3, while pertechnetate uptake was score 0; in the other seven lesions, where a prevalence of goitre abnormalities was observed, results of tetrofosmin and pertechnetate uptake were similar (score 0 or 1). In seven (70%) of the ten patients with malignant nodules, whole-body tetrofosmin images showed increased abnormal uptake in a total of 28 extra-thyroid tumour sites, as subsequently confirmed by other techniques. When tetrofosmin images were compared to 201Tl and 99mTc-MIBI scans, concordant results were observed in all cases. In conclusion, tetrofosmin imaging may be particularly useful to characterize and stage patients with malignant thyroid nodules; it shows similar results to thallium but provides better image quality. Comparable findings were observed between tetrofosmin and MIBI studies. Thus, tetrofosmin may be an alternative to thallium and MIBI in the aforementioned patients.

Nuclear imaging in the management of thyroid carcinoma

The avidity of differentiated thyroid carcinoma for iodine is the basis for the use of radioiodine (131I) both for the detection and the treatment of recurrent thyroid cancer in patients following initial surgical treatment (thyroidectomy). Because recurrence of this type of cancer may be delayed for many years, long-term follow-up is needed. Nowadays such surveillance involves clinical assessment, monitoring of serum thyroglubulin, and, when indicated, whole-body imaging with 131I. Sensitivity of 131I imaging depends on proper preparation of the patient and careful attention to imaging technique. Interpretation of images requires knowledge of physiologic sites of radioiodine concentration and causes of artifacts. Because of the potential suppressive effect of the radiation from a diagnostic administration of 131I on the uptake of a subsequent therapeutic administration (so-called stunning of thyroid tissue) many centers limit the amount given for scanning to 2-3 mCi (74-111 MBq). Several tumor-seeking radioisotopic agents other than radioiodine have shown promise for improving the detection of metastases, and some of these agents offer a useful adjunct to 131I in the management of selected patients, particularly in those with suspected metastatic disease and negative 131I scans.