Appropriate Use Criteria for Nuclear Medicine in the Evaluation and Treatment of Differentiated Thyroid Cancer

Update on iodine-refractory differentiated thyroid carcinoma

Radioiodine therapy represents a fundamental pillar in the routine adjuvant therapy of patients with high-risk differentiated thyroid carcinoma. However, a non-negligible percentage of these patients will develop iodine refractoriness, showing a worse prognosis, as well a lower survival, which demonstrates a clear need to explore different therapeutic approaches. Iodine refractory patient treatment continues to be a challenge, currently having different novel therapeutic options that should be known by the different specialties related to differentiated thyroid carcinoma (DTC). The aim of this work is to review iodine refractory thyroid carcinoma treatment, focusing especially on the definition of iodine refractoriness, highlighting its importance due to its high mortality, and introducing the different therapeutic options available for these patients.

Molecular Theranostics in Radioiodine-Refractory Differentiated Thyroid Cancer

Differentiated thyroid cancer (DTC) is the most common subtype of thyroid cancer and has an excellent overall prognosis. However, metastatic DTC in certain cases may have a poor prognosis as it becomes radioiodine-refractory. Molecular imaging is essential for disease evaluation and further management. The most commonly used tracers are [18F]FDG and isotopes of radioiodine. Several other radiopharmaceuticals may be used as well, with different diagnostic performances. This review article aims to summarize radiopharmaceuticals used in patients with radioiodine-refractory DTC (RAI-R DTC), focusing on their different molecular pathways. Additionally, it will demonstrate possible applications of the theranostics approach to this subgroup of metastatic DTC.

Role of 131I in low-risk differentiated thyroid cancer

Differentiated thyroid cancer (DTC) is the most frequent endocrine neoplasm, with an increase in recent decades. Papillary carcinoma is the most frequent histological subtype and a large number of cases are related to tumors of small size and with little clinical repercussion, detected incidentally or as a consequence of the availability of diagnostic techniques. The "good prognosis" of the majority of cases has maintained for years the controversy in the approach to these patients, especially in two basic aspects of the therapeutic protocol: surgery and the administration of radioiodine. While in metastatic and high-risk patients, the administration of ¹³¹I therapy is widely accepted, in intermediate-low risk patients its use is highly questioned. In this paper we review the available evidence on radioiodine therapy in low-risk patients.

The progress of radiomics in thyroid nodules

Due to the development of Artificial Intelligence (AI), Machine Learning (ML), and the improvement of medical imaging equipment, radiomics has become a popular research in recent years. Radiomics can obtain various quantitative features from medical images, highlighting the invisible image traits and significantly enhancing the ability of medical imaging identification and prediction. The literature indicates that radiomics has a high potential in identifying and predicting thyroid nodules. So in this article, we explain the development, definition, and workflow of radiomics. And then, we summarize the applications of various imaging techniques in identifying benign and malignant thyroid nodules, predicting invasiveness and metastasis of thyroid lymph nodes, forecasting the prognosis of thyroid malignancies, and some new advances in molecular level and deep learning. The shortcomings of this technique are also summarized, and future development prospects are provided.

Predictive Value of Clinical and Pathological Characteristics for Metastatic Radioactive Iodine-Refractory Differentiated Thyroid Carcinoma: A 16-year Retrospective Study

PURPOSE

To assess predictive value of clinical and pathological characteristics for metastatic radioactive iodine-refractory differentiated thyroid carcinoma (RAIR-DTC) in early stage retrospectively.

METHODS

We studied 199 metastatic DTC patients who were divided into two groups (TgAb negative and TgAb positive). The stimulated Tg (Sti-Tg) at the first and second radioiodine therapy (RIT) were defined as Sti-Tg1 and Sti-Tg2, the suppressed Tg (Sup-Tg) were designated as Sup-Tg1 and Sup-Tg2, while the TgAb were defined as TgAb1 and TgAb2, respectively. Univariate analysis and Logistic regression were used to investigate the effects of 13 observed factors to predict RAIR-DTC.

RESULTS

In TgAb negative group, ROC curve analysis showed that cut-off values of age, Sti-Tg2/Sti-Tg1 and Sup-Tg2/Sup-Tg1 to predict RAIR-DTC were 40 years old, 57.0% and 81.0%, respectively. Age, extrathyroid invasion, Sti-Tg2/Sti-Tg1, Sup-Tg2/Sup-Tg1 and BRAF gene mutation were proved to be independent factors predicting RAIR-DTC. In TgAb-positive group, ROC curve analysis showed that cut-off values of age, TgAb1 and TgAb2/TgAb1 to predict RAIR-DTC were 55 years old, 297 IU/ml (14.8 times higher than the upper limit) and 53.6%, respectively.

CONCLUSIONS

For TgAb-negative DTC, age over 40, extraglandular invasion, mutated BRAF gene, Sti-Tg decreased less than 43%, and Sup-Tg decreased less than 19% after the first two courses of RIT were independent predictors for RAIR-DTC. For TgAb-positive DTC, age over 55, extraglandular invasion, mutated BRAF gene, distant metastasis before RIT, TgAb level 14.8 times higher than the upper limit, TgAb dropped less than 46.4% after two courses of RIT were influencing factors.

Peptide Receptor Radionuclide Therapy in Thyroid Cancer

The treatment options that are currently available for management of metastatic, progressive radioactive iodine (RAI)-refractory differentiated thyroid cancers (DTCs), and medullary thyroid cancers (MTCs) are limited. While there are several systemic targeted therapies, such as tyrosine kinase inhibitors, that are being evaluated and implemented in the treatment of these cancers, such therapies are associated with serious, sometimes life-threatening, adverse events. Peptide receptor radionuclide therapy (PRRT) has the potential to be an effective and safe modality for treating patients with somatostatin receptor (SSTR)+ RAI-refractory DTCs and MTCs. MTCs and certain sub-types of RAI-refractory DTCs, such as Hürthle cell cancers which are less responsive to conventional modalities of treatment, have demonstrated a favorable response to treatment with PRRT. While the current literature offers hope for utilization of PRRT in thyroid cancer, several areas of this field remain to be investigated further, especially head-to-head comparisons with other systemic targeted therapies. In this review, we provide a comprehensive outlook on the current translational and clinical data on the use of various PRRTs, including diagnostic utility of somatostatin analogs, theranostic properties of PRRT, and the potential areas for future research.

The Diagnostic Usefulness of 131I-SPECT/CT at Both Radioiodine Ablation and during Long-Term Follow-Up in Patients Thyroidectomized for Differentiated Thyroid Carcinoma: Analysis of Tissue Risk Factors Ascertained at Surgery and Correlated with Metastasis Appearance

¹³¹I Single-photon emission computerized tomography/computerized tomography (SPECT/CT) in the management of patients thyroidectomized for differentiated thyroid carcinoma (DTC) was further investigated. Retrospectively, 106 consecutive DTC patients were enrolled at the first radioiodine ablation, 24 at high risk (H), 61 at low risk (L) and 21 at very low risk (VL). ¹³¹I whole-body scan (WBS) and SPECT/CT were performed after therapeutic doses using a hybrid dual-head gamma camera. At ablation, SPECT/CT correctly classified 49 metastases in 17/106 patients with a significantly (p < 0.001) more elevated number than WBS which evidenced 32/49 foci in 13/17 cases. In this case, 86/106 patients could be monitored in the follow-up including 13/17 cases with metastases already at post-therapeutic scans. SPECT/CT after radioiodine diagnostic doses more correctly than WBS ascertained disease progression in 4/13 patients, stable disease in other 4/13 cases and disease improvement in the remaining 5/13 cases. Further 13/86 patients with only residues at post-therapeutic scans showed at SPECT/CT 16 neck lymph node (LN) metastases, three unclear and 13 occult at WBS. Significant involvement of some tissue risk factors with metastasis appearance was observed, such as minimal extrathyroid tumor extension and neck LN metastases. These risk factors should be carefully considered in DTC patient follow-up where ¹³¹I-SPECT/CT routinely use is suggested as a support tool of WBS.

Preablation Diagnostic Whole-Body Scan vs Empiric Radioactive Iodine Ablation in Differentiated Thyroid Cancer: Cost-effectiveness Analysis

OBJECTIVE

To perform a comparative analysis of postthyroidectomy radioactive iodine ablation dosing with or without the implementation of a diagnostic whole-body scan in patients with well-differentiated thyroid cancer.

STUDY DESIGN

Decision analysis model.

SETTING

Hospital or ambulatory center.

METHODS

A decision tree model was created to determine the cost-effectiveness of radioactive iodine ablation dosed with diagnostic whole-body scans versus empiric radioactive iodine ablation in patients with differentiated thyroid cancer undergoing postthyroidectomy ablation. The decision tree was populated with values from the published literature. Costs were represented by 2020 Medicare reimbursement rates (US dollars), and morbidity and survival data were used to calculate quality-adjusted life-years. The incremental cost-effectiveness ratio was the primary outcome.

RESULTS

Empiric radioactive iodine dosing was the dominant economic strategy, producing 0.94 more quality-adjusted life-years while costing $1250.07 less than management with a diagnostic whole-body scan. Sensitivity analyses upheld these results except in cases involving a large discrepancy in successful ablation rates between the diagnostic and empiric treatment arms.

CONCLUSION

For patients with differentiated thyroid cancer requiring postthyroidectomy ablation, it is more cost-effective to administer radioactive iodine empirically.