I-131 SPECT/CT elucidates cryptic findings on planar whole-body scans and can reduce needless therapy with I-131 in post-thyroidectomy thyroid cancer patients

Current Advances in Radioactive Iodine-Refractory Differentiated Thyroid Cancer

BACKGROUND

Differentiated thyroid cancer (DTC) patients have an outstanding overall long-term survival rate, and certain subsets of DTC patients have a very high likelihood of disease recurrence. Radioactive iodine (RAI) therapy is a cornerstone in DTC management, but cancer cells can eventually develop resistance to RAI. Radioactive iodine-refractory DTC (RAIR-DTC) is a condition defined by ATA 2015 guidelines when DTC cannot concentrate RAI ab initio or loses RAI uptake ability after the initial therapy. The RAIR condition implies that RAI cannot reveal new met-astatic foci, so RAIR-DTC metabolic imaging needs new tracers. 18F-FDG PET/CT has been widely used and has demonstrated prognostic value, but 18F-FDG DTC avidity may remain low. Fibroblast activation protein inhibitors (FA-Pi)s, prostatic-specific membrane antigen (PSMA), and somatostatin receptor (SSTR) tracers have been proposed as theragnostic agents in experimental settings and Arg-Gly-Asp (RGD) peptides in the diagnostic trial field. Multi-targeted tyrosine kinase inhibitors are relatively new drugs approved in RAIR-DTC therapy. Despite the promising targeted setting, they relate to frequent adverse-event onset. Sorafenib and trametinib have been included in re-differentiation protocols aimed at re-inducing RAI accumulation in DTC cells. Results appear promising, but not excellent.

CONCLUSIONS

RAIR-DTC remains a challenging nosological entity. There are still controversies on RAIR-DTC definition and post-RAI therapy evaluation, with post-therapy whole-body scan (PT-WBS) the only validated criterion of response. The recent introduction of multiple diagnostic and therapeutic agents obliges physicians to pursue a multidisciplinary approach aiming to correct drug introduction and timing choice.

Clinical Implications of Adding SPECT/CT to Radioiodine Whole-Body Scan in Patients With Differentiated Thyroid Cancer: A Systematic Review and Meta-analysis

PURPOSE

This study aimed to determine the usefulness of adding SPECT/CT to radioiodine whole-body scans (WBSs) for the treatment of differentiated thyroid cancer (DTC).

PATIENTS AND METHODS

A systematic review and meta-analysis were performed following the PRISMA guidelines (PROSPERO registration: CRD42022341732) to compare the feasibility of conclusive readings and the frequency of changes in treatment plans in patients with DTC undergoing WBS + SPECT/CT versus WBS. MEDLINE, EMBASE, and Cochrane databases were searched to identify relevant articles concerning thyroid cancer, radioactive iodine, and SPECT/CT or SPECT, published before August 16, 2023. Studies not comparing WBS + SPECT/CT with WBS, those lacking target outcomes, and those not involving human subjects were excluded. The risk of bias was assessed using the RoBANS 2.0 (Risk of Bias Assessment Tool for Nonrandomized Studies) tool. The GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) system was used to evaluate the quality of evidence and strength of recommendations.

RESULTS

A total of 30 studies (prospective n = 9, retrospective n = 21) were included in the meta-analyses. Adding SPECT/CT to WBS was shown to increase conclusive readings for cervical lesions, extracervical lesions, and all regions. Lesion-based analyses showed improvements of 14%, 20%, and 18%, respectively, whereas scan-based analyses showed improvements of 27%, 9%, and 34%. The addition of SPECT/CT to WBS led to changes in 30% of treatment plans after diagnostic scans and 9% of treatment plans after posttherapeutic scans. The quality of evidence and strength of recommendations were low.

CONCLUSIONS

Compelling evidence demonstrates that the addition of SPECT/CT to WBS improves lesion localization, diagnostic performance, and therapy plan for patients with DTC.

False-Positive Radioiodine Uptake in the Cervix in a Patient with Thyroid Cancer

Radioactive iodine (RAI) accumulation is commonly used for the detection of metastatic disease posttotal thyroidectomy. However, false-positive results have been reported due to abnormal RAI accumulation in some benign pathologies apart from metastatic sites. Here, we present one such case where false-positive I-131 uptake in the pelvis which localized to the cervix and was attributed to menstruation.

Epidermal Cyst Mimicking Thyroid Cancer Metastasis

ABSTRACT

A 26-year-old woman with pulmonary metastasis of thyroid cancer underwent a total thyroidectomy and cervical lymph node dissection followed by 2 courses of 131I therapy. The posttherapeutic whole-body scan after the second dose of 131I therapy showed diffuse tracer uptake in both lungs. Besides this, there is a local abnormal radiotracer uptake in the left axillary region. SPECT/CT images localized this abnormal radioactivity in a subcutaneous, oval-shaped, approximately 2.2-cm slightly hyperdense lesion, which was pathologically confirmed as an epidermal cyst.

Intramedullary Spinal Cord Metastases from Differentiated Thyroid Cancer, a Case Report

Intramedullary spinal cord metastases (ISCM) are uncommon metastases of the spinal cord. Magnetic resonance (MR) plays an important role in surgical planning when ISCM is suspected in the differential diagnosis. The incidence of ISCM is expected to increase due to the longer survival of cancer patients as well as the widespread use of MR in the diagnosis of neurological syndromes. The management of these patients is controversial because of the multiple clinical presentations and lack of controlled studies on the efficacy of different therapeutic approaches. Increased awareness of this rare entity may lead to an earlier diagnosis with novel imaging approaches at a stage when neurological deficits are reversible. A case of ISCM in a 49-year-old patient with differentiated thyroid cancer is reported.

An Unusual False-Positive Uptake of Radioiodine Caused by Breast Implants

ABSTRACT

A 40-year-old woman with a history of papillary thyroid cancer underwent ablative 131I therapy. Postablation whole-body 131I scintigraphy revealed not only increased activity in the thyroid bed but also in the anterior part of the chest. SPECT/CT images localized the activity in the bilateral breast implants.

Clinical applications of single-photon emission computed tomography/computed tomography in post-ablation 131iodine scintigraphy in children and young adults with differentiated thyroid carcinoma

BACKGROUND

The utility of integrated single-photon emission computed tomography/computed tomography (SPECT/CT) in children and young adults with differentiated thyroid carcinoma is incompletely studied.

OBJECTIVE

To determine the value of adding SPECT/CT to conventional whole-body scintigraphy in post-ablation iodine-131 (¹³¹I) scintigraphy for children and young adults with differentiated thyroid carcinoma.

MATERIALS AND METHODS

Planar scintigraphy and SPECT/CT were performed on 42 post-surgical children and young adults (32 female, 10 male; mean age 14.3±4.9 years, range 7-20 years) with differentiated thyroid carcinoma (39 papillary, 2 follicular, 1 mixed) 5 days after the therapeutic administration of 1.9-7.4 GBq of ¹³¹I. Planar and SPECT/CT images were interpreted independently, and sites of uptake were categorized as positive or equivocal with respect to thyroid bed, lymph node and distant metastasis uptake. An experienced thyroid endocrinologist used a combination of surgical histopathology and scintigraphic findings to determine whether the addition of SPECT/CT would change patient management.

RESULTS

Planar scintigraphy evidenced 88 radioiodine-avid foci and SPECT/CT confirmed all foci. No additional foci were disclosed by SPECT/CT. SPECT/CT correctly classified 16/88 (18%) foci that were unclear or wrongly classified at planar scintigraphy. Globally, SPECT/CT showed an incremental value over planar scintigraphy in 9 (21.4%) patients and changed therapeutic management in 3 (7.1%; 95% confidence interval, 2-20%) patients.

CONCLUSION

SPECT/CT improved localization and characterization of focal ¹³¹I uptake on post-ablation whole-body scintigraphy in children and young adults with differentiated thyroid carcinoma. Further prospective evaluation in a larger series is justified to prove the effect of post-ablation SPECT/CT-based management decisions.

Physiologic Uterine Uptake of Radioiodine During Menstruation Demonstrated by SPECT/CT

A 35-year-old woman with papillary thyroid cancer underwent I therapy after thyroidectomy. Post-therapy whole body scan revealed increased activity in the pelvis, in addition to the activity in the neck. On SPECT/CT images, the radioactivity in the pelvis was localized in the rectum and cervix. Further inquiry discovered that the patient was menstruating. We concluded that abnormal radioiodine uptake in menstrual uterus might be an exceptional finding mimicking a metastasis.

Pictorial Review of False-Positive Results on Radioiodine Scintigrams of Patients with Differentiated Thyroid Cancer

Radioiodine has served an important role in the diagnostic workup and treatment of patients with differentiated thyroid cancer for more than 6 decades. The interpretation of radioiodine scintigraphic studies should be performed in conjunction with a comprehensive history, histopathologic correlation, and pertinent laboratory values, as well as correlation with available anatomic images and the findings from physical examination. A thorough understanding of the physiology and biodistribution of radioiodine is critical when interpreting radioiodine scintigraphic studies to avoid misinterpretation of physiologic and nonthyroid pathologic variants as thyroid cancer metastases. Differentiating a false-positive finding from a true metastasis on pretherapy radioiodine scintigrams is important to determine the appropriate radioiodine treatment dose. The correct interpretation of posttherapy radioiodine scintigraphic studies is also important to determine if repeat radioiodine treatment will be necessary and for the future clinical and imaging followup of the patient. A variety of different factors, such as the presence of the sodium-iodide symporter and the passive diffusion or retention of radioiodine in normal and pathologic structures, can result in false-positive results on radioiodine scintigrams. Numerous false-positive findings have been reported in the literature and are further demonstrated with the increasing availability of single photon emission computed tomography (SPECT) integrated with computed tomography (CT) as true dual-modality imaging (SPECT/CT). SPECT/CT has been documented to be of incremental value in the accurate anatomic localization and characterization of radioiodine uptake as false-positive findings, particularly in cases with discordant findings of a low serum thyroglobulin level but positive findings on radioiodine whole-body planar scintigrams. The objectives of this review are to describe the physiology and biodistribution of radioiodine and to provide examples of false-positive results on radioiodine scintigrams, with clinical and anatomic correlation, in the following categories of radioiodine uptake: functional uptake secondary to sodium-iodide symporter expression, radioiodine retention, nonthyroid neoplasms, inflammatory or infectious uptake, contamination, and other causes. ^©RSNA, 2017.

Controversies in the Management of Low-Risk Differentiated Thyroid Cancer

Controversy exists over optimal management of low-risk differentiated thyroid cancer. This controversy occurs in all aspects of management, including surgery, use of radioactive iodine for remnant ablation, thyroid hormone supplementation, and long-term surveillance. Limited and conflicting data, treatment paradigm shifts, and differences in physician perceptions contribute to the controversy. This lack of physician consensus results in wide variation in patient care, with some patients at risk for over- or undertreatment. To reduce patient harm and unnecessary worry, there is a need to design and implement studies to address current knowledge gaps.

Diagnostic Performance of 18F-FDG PET/CT in Papillary Thyroid Carcinoma with Negative 131I-WBS at first Postablation, Negative Tg and Progressively Increased TgAb Level

Differentiated thyroid cancer (DTC) patients with negative serum thyroglobulin (Tg), negative ¹³¹I whole–body scintigraphy (¹³¹I-WBS) at first post-ablation and progressively increased TgAb level are a relatively rare entity in the follow-up after total thyroidectomy and radioactive iodine therapy. The value of ¹⁸F-FDG PET/CT in detecting the recurrence of disease in these patients has only been reported in a small case series. The goal of this study was to investigate the diagnostic accuracy of ¹⁸F-FDG PET/CT in detecting recurrent disease in these specific PTC patients and to identify risk factors for patients with positive ¹⁸F-FDG PET/CT results. Eighty-two PTC patients who had ¹⁸F-FDG PET/CT scans with negative Tg, negative ¹³¹I-WBS at first post-ablation and progressively increased TgAb levels were included. We found that the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ¹⁸F-FDG PET/CT in this patient group were determined as 84%, 72%, 92%, 57% and 82%, respectively. ¹⁸F-FDG PET/CT scan had a good diagnostic performance and should be performed routinely in PTC patients with negative Tg, negative ¹³¹I-WBS at first postablation and progressively increased TgAb level, especially when span for progressively increased TgAb level ≥ 3 years and/or progressively increased TgAb value up to 150 IU/mL.

SPECT/CT in the Treatment of Differentiated Thyroid Cancer

Single-photon emission computed tomography with integrated computed tomography (SPECT/CT) systems has been applied in a wide range of clinical circumstances, and differentiated thyroid cancer (DTC) is one of the most important indications of SPECT/CT imaging. In the treatment of DTC, SPECT/CT images have been reported to have many advantages over conventional planar whole-body scintigraphy based on its precise localization and characterization of abnormal foci of radioactive iodine (RAI) accumulation, influencing the staging, risk stratification, and clinical management as well as reader confidence. On the other hand, SPECT/CT has limitations including additional radiation exposure from the CT component, additional imaging time, and cost-related issues. Each SPECT/CT image acquired at different time points throughout the management of DTC may have a different clinical meaning and significance. This review article addresses the clinical usefulness of RAI SPECT/CT images acquired during the pre-ablation period, post-therapy period, and long-term follow-up period, respectively.

Pediatric papillary thyroid cancer: current management challenges

Although with a standardized incidence of 0.54 cases per 100,000 persons, differentiated thyroid cancer (DTC) is a rare disease in children and adolescents, it nonetheless concerns ~1.4% of all pediatric malignancies. Furthermore, its incidence is rising. Due to the rarity and long survival of pediatric DTC patients, in most areas of treatment little evidence exists. Treatment of pediatric DTC is therefore littered with controversies, many questions therefore remain open regarding the optimal management of pediatric papillary thyroid cancer (PTC), and many challenges remain unsolved. In the present review, we aim to provide an overview of these challenging areas of patient and disease management in pediatric PTC patients. Data on diagnosis, surgery, radionuclide, and endocrine therapy are discussed, and the controversies therein are highlighted.

Variants and pitfalls on radioiodine scans in pediatric patients with differentiated thyroid carcinoma

BACKGROUND

Potentially false-positive findings on radioiodine scans in children with differentiated thyroid carcinoma can mimic functioning thyroid tissue and functioning thyroid carcinomatous tissue. Such false-positive findings comprise variants and pitfalls that can vary slightly in children as compared with adults.

OBJECTIVE

To determine the patterns and frequency of these potential false-positive findings on radioiodine scans in children with differentiated thyroid carcinoma.

MATERIALS AND METHODS

We reviewed a total of 223 radioiodine scans from 53 pediatric patients (mean age 13.3 years, 37 girls) with differentiated thyroid carcinoma. Focal or regional activity that likely did not represent functioning thyroid tissue or functioning thyroid carcinomatous tissue were categorized as variants or pitfalls. The final diagnosis was confirmed by reviewing the concurrent and follow-up clinical data, correlative ultrasonography, CT scanning, serum thyroglobulin and antithyroglobulin antibody levels. We calculated the frequency of these variants and pitfalls from diagnostic and post-therapy radioiodine scans.

RESULTS

The most common variant on the radioiodine scans was the thymic activity (24/223, 10.8%) followed by the cardiac activity (8/223, 3.6%). Salivary contamination and star artifact, caused by prominent thyroid remnant, were the most important observed pitfalls.

CONCLUSION

Variants and pitfalls that mimic functioning thyroid tissue or functioning thyroid carcinomatous tissue on radioiodine scan in children with differentiated thyroid carcinoma are not infrequent, but they decrease in frequency on successive radioiodine scans. Potential false-positive findings can be minimized with proper knowledge of the common variants and pitfalls in children and correlation with clinical, laboratory and imaging data.

Endocrine radionuclide scintigraphy with fusion single photon emission computed tomography/computed tomography

AIM: To review the benefits of single photon emission computed tomography (SPECT)/computed tomography (CT) hybrid imaging for diagnosis of various endocrine disorders.

METHODS: We performed MEDLINE and PubMed searches using the terms: “SPECT/CT”; “functional anatomic mapping”; “transmission emission tomography”; “parathyroid adenoma”; “thyroid cancer”; “neuroendocrine tumor”; “adrenal”; “pheochromocytoma”; “paraganglioma”; in order to identify relevant articles published in English during the years 2003 to 2015. Reference lists from the articles were reviewed to identify additional pertinent articles. Retrieved manuscripts (case reports, reviews, meta-analyses and abstracts) concerning the application of SPECT/CT to endocrine imaging were analyzed to provide a descriptive synthesis of the utility of this technology.

RESULTS: The emergence of hybrid SPECT/CT camera technology now allows simultaneous acquisition of combined multi-modality imaging, with seamless fusion of three-dimensional volume datasets. The usefulness of combining functional information to depict the bio-distribution of radiotracers that map cellular processes of the endocrine system and tumors of endocrine origin, with anatomy derived from CT, has improved the diagnostic capability of scintigraphy for a range of disorders of endocrine gland function. The literature describes benefits of SPECT/CT for ^99mTc-sestamibi parathyroid scintigraphy and ^99mTc-pertechnetate thyroid scintigraphy, ¹²³I- or ¹³¹I-radioiodine for staging of differentiated thyroid carcinoma, ¹¹¹In- and ^99mTc- labeled somatostatin receptor analogues for detection of neuroendocrine tumors, ¹³¹I-norcholesterol (NP-59) scans for assessment of adrenal cortical hyperfunction, and ¹²³I- or ¹³¹I-metaiodobenzylguanidine imaging for evaluation of pheochromocytoma and paraganglioma.

CONCLUSION: SPECT/CT exploits the synergism between the functional information from radiopharmaceutical imaging and anatomy from CT, translating to improved diagnostic accuracy and meaningful impact on patient care.

In Thyroidectomized Thyroid Cancer Patients, False-Positive I-131 Whole Body Scans Are Often Caused by Inflammation Rather Than Thyroid Cancer

Objective. To show that I-131 false-positive results on whole-body scans (WBSs) after thyroidectomy for thyroid cancer may be a result of inflammation unassociated with the cancer. Methods. We performed a retrospective image analysis of our database of thyroid cancer patients who underwent WBS from January 2008 to January 2012 to identify and stratify false positives. Results. A total of 564 patients underwent WBS during the study period; 96 patients were referred for 99 I-131 single-photon emission computed tomography (SPECT/CT) scans to better interpret cryptic findings. Among them, 73 scans were shown to be falsely positive; 40/73 or 54.7% of false-positive findings were a result of inflammation. Of the findings, 17 were in the head, 1 in the neck, 4 in the chest, 3 in the abdomen, and 14 in the pelvis; 1 had a knee abscess. Conclusions. In our series, inflammation caused the majority of false-positive WBSs. I-131 SPECT/CT is powerful in the differentiation of inflammation from thyroid cancer. By excluding metastatic disease, one can properly prognosticate outcome and avoid unnecessary, potentially harmful treatment of patients with thyroid cancer.

A low postoperative nonstimulated serum thyroglobulin level excludes the presence of persistent disease in low-risk papillary thyroid cancer patients: implication for radioiodine indication

OBJECTIVE

To evaluate the presence of persistent disease, including on post-therapy whole-body scan (RxWBS), in low-risk patients with papillary thyroid carcinoma (PTC) >1 cm who have low nonstimulated thyroglobulin (Tg) (measured with a sensitive assay), negative anti-Tg antibodies (TgAb) and neck ultrasound (US) showing no metastases after total thyroidectomy.

PATIENTS

We studied 154 patients with PTC >1 cm classified as low risk, who had US without metastases, negative TgAb, nonstimulated Tg ≤ 0·25 ng/ml and TSH ≤ 2 mIU/l about 3 months after total thyroidectomy.

RESULTS

Tg measured immediately before (131) I was ≤ 1 ng/ml in 89·5% of the patients and >1 ng/ml in 10·5%. None of the patients showed ectopic uptake on RxWBS. Uptake in the thyroid bed was observed in 146 (94·8%) patients and was ≤ 2% in all of them. In the control assessment 9-12 months after ablation, stimulated Tg (sTg) ≤ 1 ng/ml was achieved in 150 patients (97·4%). Only one patient had sTg >2 ng/ml (2·5 ng/ml) and none of the patients had apparent disease detected by imaging methods. During further short-term follow-up after control assessment (median of 24 months), none of the patients had tumour recurrence.

CONCLUSIONS

The combination of nonstimulated Tg ≤0·25 ng/ml, negative TgAb and US without metastases after thyroidectomy rules out the presence of persistent disease (including on RxWBS) in low-risk patients with PTC >1 cm. This demonstration weakens the indication of ablation with (131) I in these cases.

Rare renal metastases from differentiated thyroid carcinoma: early clinical detection and treatment based on radioiodine

OBJECTIVE

The aim of this study was to explore the clinical characteristics of renal metastatic cancer, the methods for its detection by radioiodine (131)I, and the response to (131)I treatment in fourteen patients with renal metastases from differentiated thyroid carcinoma (DTC).

SUBJECTS AND METHODS

DTC patients (n = 2,955) that received treatment with (131)I were retrospectively analyzed. Scans ((131)I-WBS, (31)I-SPECT/CT and/or (18)F-FDG-PET/CT) were performed after an oral therapeutic dose of (131)I. Therapeutic efficacy was evaluated based on changes in Tg and anatomical imaging changes at renal lesions.

RESULTS

Among these 14 patients, 11 had avidity for (131)I, but three patients did not accumulate (131)I after (131)I treatment. In the 11 (131)I-positive renal lesions, 10 cases were detected by (131)I-SPECT/CT combined with another imaging modality and one case by (131)I-WBS combined with ultrasonography (US). In the three (131)I-negative renal lesions, two cases were detected by 18F-FDG-PET/CT and one case by computed tomography (CT). In 11 patients with (131)I-avid renal metastases, Serum Tg levels in 81.82% (9/11) patients showed a gradual decline, and 18.18% (2/11) of the patients showed a significant elevation. There was no marked difference in serum Tg before the last (131)I treatment (Z = 0.157; p = 0.875). Only one patient presented partial response, eight patients exhibited stable disease, and renal metastases progressed in two patients showing progressive disease. No patients reached complete response.

CONCLUSION

(131)I-SPECT/CT, combined with another imaging modality after (131)I-WBS, can contribute to the early detection of renal metastases of DTC. (131)I therapy is a feasible and effective treatment for most DTC renal metastases with avidity for (131)I.

Endocrine scintigraphy with hybrid SPECT/CT

Nuclear medicine imaging of endocrine disorders takes advantage of unique cellular properties of endocrine organs and tissues that can be depicted by targeted radiopharmaceuticals. Detailed functional maps of biodistributions of radiopharmaceutical uptake can be displayed in three-dimensional tomographic formats, using single photon emission computed tomography (CT) that can now be directly combined with simultaneously acquired cross-sectional anatomic maps derived from CT. The integration of function depicted by scintigraphy and anatomy with CT has synergistically improved the efficacy of nuclear medicine imaging across a broad spectrum of clinical applications, which include some of the oldest imaging studies of endocrine dysfunction.

Differentiated thyroid cancer-personalized therapies to prevent overtreatment

The concept of individualized therapy is rapidly gaining recognition in the management of patients with differentiated thyroid cancer (DTC). This Review provides an overview of the most important elements of this paradigm shift in DTC management and discusses the implications for clinical practice. In the majority of patients with DTC who have an inherently good prognosis, the extent of surgery, the dosage of (131)I therapy and the use of levothyroxine therapy are all aspects suitable for individualization, on the basis of both the stage of disease and the response to treatment. In individuals with advanced disease, newer imaging techniques, advances in (131)I therapy and the use of targeted molecular therapies (such as multitargeted kinase inhibitors) have provided new options for the personalized care of patients, for whom until recently no effective therapies were available. Individualized therapies could reduce adverse effects, including the sometimes debilitating hypothyroidism that used to be required before initiation of (131)I treatment, and major salivary gland damage, a common and unpleasant side effect of (131)I therapy. Highly individualized interdisciplinary treatment of patients with DTC might lead to improved outcomes with reduced severity and frequency of complications and adverse effects. However, in spite of ongoing research, personalized therapies remain in their infancy.

Is empirical radioactive iodine therapy still a valid approach to patients with thyroid cancer and elevated thyroglobulin?

BACKGROUND

At present, empirical radioactive iodine therapy is recommended for patients with thyroid cancer and elevated thyroglobulin (Tg) after initial therapy when neck ultrasonography (US), chest computed tomography (CT), and 18-fluorodeoxyglucose positron emission tomography (FDG-PET) do not reveal metastases. The objective of this study was to determine whether empirical (131)I therapy is indeed useful in these patients.

METHODS

Patients with papillary thyroid cancer submitted to total thyroidectomy followed by remnant ablation with (131)I in whom whole-body scanning at the time of ablation (WBS-ablation) did not reveal metastases and who had elevated Tg after initial therapy were selected. Included in the study were patients with basal Tg >2 ng/mL or Tg >5 ng/mL after stimulation with recombinant human thyrotropin or Tg >10 ng/mL after levothyroxine withdrawal for 4 weeks. All patients were first investigated by neck US and chest CT. FDG-PET/CT was performed in patients with negative US and CT. The final sample of this study consisted of patients with negative US, CT, and FDG-PET/CT. These patients received an activity of 100 mCi (131)I and were submitted to posttherapy WBS (RxWBS).

RESULTS

Among the 24 patients receiving empirical (131)I therapy, no ectopic uptake was seen in 23 and mild uptake in the thyroid bed (<0.5%) in 15. Only one patient presented pulmonary metastases detected by RxWBS. Disease was observed in two other patients during short-term follow-up (mean 22 months), one with lymph node metastases diagnosed by a repeat US and one with bone metastases diagnosed by CT and FDG-PET scans.

CONCLUSIONS

We conclude that RxWBS rarely reveals disease in patients with elevated Tg after ablation, but with negative findings on WBS-ablation, US, CT, and FDG-PET. In this situation, empirical (131)I therapy should be restricted to patients with documented progression of serum Tg.

SPECT/CT evaluation of unusual physiologic radioiodine biodistributions: pearls and pitfalls in image interpretation

Radioiodine imaging has a well-established role in depicting metastatic disease after thyroidectomy in patients with well-differentiated thyroid cancer. Uptake of radioiodine in thyroid metastases depends on expression of sodium-iodide symporter (NIS) by tumor tissues. However, because radioiodine may also accumulate in normal structures and tissues, it is important to distinguish physiologic radioiodine activity from metastatic disease. Furthermore, secretions that contain radioiodine may also simulate pathologic uptake. A spectrum of physiologic distributions, normal variants, and benign mimics of disease have been described in the literature; yet, even when armed with a comprehensive knowledge of these patterns, interpreting radiologists and nuclear physicians may still encounter diagnostic uncertainty. Single-photon emission computed tomography (SPECT) with integrated computed tomography (CT) is a novel technology that, when applied to diagnostic iodine 123 or iodine 131 ((131)I) radioiodine scintigraphy, may accurately localize and help distinguish benign mimics of disease, with the potential to alter the management plan. SPECT/CT is increasingly being used with radioiodine scintigraphy to evaluate patients with thyroid cancer and shows promise for improving imaging specificity and reducing false-positive results.

SPECT/CT and tumour imaging

Scintigraphic techniques are sensitive imaging modalities in the diagnosis and follow-up of cancer patients providing the functional and metabolic activity characteristics of the tumour. Hybrid SPECT/CT improves the diagnostic accuracy of these well-established imaging techniques by precise anatomical localization and characterization of morphological findings, differentiation between foci of physiological and pathological tracer uptake, resulting in a significant impact on patient management and more definitive interpretations. The use of SPECT/CT has been studied in a variety of applications in tumour imaging which are reviewed in this article. By combining functional and anatomical information in a single imaging session, SPECT/CT has become a one-stop cancer imaging modality.

SPECT-CT in routine clinical practice: increase in patient radiation dose compared with SPECT alone

OBJECTIVE

To assess the patient radiation dose during routine clinical single-photon emission computed tomography-computed tomography (SPECT-CT) and measure the increase as compared with SPECT alone.

MATERIALS AND METHODS

Data pertaining to 357 consecutive patients who had undergone radioisotope imaging along with SPECT-CT of a selected volume were retrospectively evaluated. Dose of the injected radiopharmaceutical (MBq) was noted, and the effective dose (mSv) was calculated as per International Commission on Radiological Protection (ICRP) guidelines. The volume-weighted computed tomography dose index (CTDIvol) and dose length product of the CT were also assessed using standard phantoms. The effective dose (mSv) due to CT was calculated as the product of dose length product and a conversion factor depending on the region of investigation, using ICRP guidelines. The dose due to CT was compared among different investigations. The increase in effective dose was calculated as CT dose expressed as a percentage of radiopharmaceutical dose.

RESULTS

The per-patient CT effective dose for different studies varied between 0.06 and 11.9 mSv. The mean CT effective dose was lowest for 99mTc-ethylene cysteine dimer brain SPECT-CT (0.9 ± 0.7) and highest for 99mTc-methylene diphosphonate bone SPECT-CT (4.2 ± 2.8). The increase in radiation dose (SPECT-CT vs. SPECT) varied widely (2.3-666.4% for 99mTc-tracers and 0.02-96.2% for 131I-tracers). However, the effective dose of CT in SPECT-CT was less than the values reported for conventional CT examinations of the same regions.

CONCLUSION

Addition of CT to nuclear medicine imaging in the form of SPECT-CT increases the radiation dose to the patient, with the effective dose due to CT exceeding the effective dose of RP in many instances. Hence, appropriate utilization and optimization of the protocols of SPECT-CT is needed to maximize benefit to patients.

Role of SPECT/CT in differentiated thyroid cancer

Radioiodine scintigraphy and therapy has played a major role in the treatment and follow-up of thyroid cancer patients for decades. Single-photon emission computed tomography/computed tomography in this setting is emerging as a useful tool in accurately localizing sites of pathological uptake and physiological mimics of disease, thus providing more accurate staging prognostic information for risk stratification, which in turn tailors management and follow-up regimes. This review presents the current evidence and potential indications of single-photon emission computed tomography/computed tomography in thyroid cancer.

Postradioiodine treatment whole-body scan in the era of 18-fluorodeoxyglucose positron emission tomography for differentiated thyroid carcinoma with elevated serum thyroglobulin levels

BACKGROUND

Patients with differentiated thyroid cancer (DTC) who have a suspicious recurrent or persistent disease based on an elevated serum thyroglobulin (Tg) or Tg antibodies (TgAb) are usually referred for empiric radioiodine ((131)I) administration to localize and treat the disease. The aim of this retrospective monocentric study was to assess the sensitivity of postempiric (131)I whole-body scan (WBS) compared to 18-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in such patients who had an initial normal postablation WBS.

METHODS

Among 47 consecutive patients with DTC who had a normal postablation WBS and were referred for empiric (131)I administration, 34 patients (12M, 22F; mean age 53 years) underwent FDG PET/CT and form the basis of this report: 23 patients had persistently elevated serum Tg levels, 10 had elevated Tg levels observed during follow-up after they initially became under 1 ng/mL, and 1 had appearance of TgAb during follow-up. Postempiric (131)I WBS and FDG PET/CT were analyzed by independent readers.

RESULTS

A total of 75 lesions were found in 23 patients, distributed in 36 organs. Lesions were located in the neck (30), lungs (28), mediastinum (11), and bones (6). The sensitivities for the detection of individual lesions and for the diagnosis of metastatic organs were 88% and 97% for PET/CT and 16% and 22% for WBS, respectively (p<0.01). PET/CT was abnormal in 22 patients, among which 5 also had an abnormal postempiric (131)I WBS. There was only one patient with an abnormal postempiric (131)I WBS and a normal FDG PET/CT. This patient underwent two further (131)I administrations, with the last WBS being normal and the last stimulated Tg level being undetectable. Other patients were either treated with surgery, or classified as radioactive iodine refractory and treated with levothyroxine suppressive therapy or tyrosine kinase inhibitors.

CONCLUSION

In patients with suspicious recurrence based on the Tg level after a normal postablation WBS, FDG PET/CT is the preferred scintigraphic method to localize disease rather than postempiric (131)I WBS. Empiric (131)I administration may be used only in patients who do not have a significant FDG uptake.

Advances in the follow-up of differentiated or medullary thyroid cancer

The long-term survival of patients with thyroid cancer and the possibility of tumour recurrence up to 30-40 years after the achievement of a disease-free status illustrate the importance of lifelong follow-up in these individuals. This Review discusses the most innovative aspects of follow-up protocols for patients with differentiated thyroid cancer, that is, of papillary or follicular hystotype, and those with medullary thyroid cancer. Particular focus is placed on the relevance of new ultrasensitive assays for thyroglobulin measurement and the option of using recombinant human TSH to stimulate thyroglobulin secretion. Methods to compensate for the loss of diagnostic significance of serum thyroglobulin levels in patients with differentiated thyroid cancer and circulating anti-thyroglobulin antibodies are highlighted, as well as the role of the postoperative calcitonin stimulation test and the clinical relevance of determining the doubling time of calcitonin and carcinoembryonic antigen in patients with medullary thyroid cancer. Moreover, this Review gives some insights into the role of molecular thyroid cancer testing, both for prognostic and for therapeutic purposes. Finally, a general overview of traditional imaging procedures, such as neck ultrasonography, CT, MRI and bone scintigraphy, is provided alongside a comparison with new nuclear imaging tests such as PET.