Pretherapeutic 124I dosimetry reliably predicts intratherapeutic blood kinetics of 131I in patients with differentiated thyroid carcinoma receiving high therapeutic activities

Diagnostic performance of [124I]m-iodobenzylguanidine PET/CT in patients with pheochromocytoma

^123/131I-MIBG scintigraphy has shown a high specificity for imaging pheochromocytoma and paraganglioma however with low sensitivity due to low spatial resolution. ¹²⁴I-MIBG PET may overcome this limitation to improve the staging of patients with (suspected) pheochromocytoma. Methods: We analyzed the sensitivity, specificity, positive and negative predictive values (PPV, NPV) of ¹²⁴I-MIBG PET in 43 consecutive patients with suspected (recurrence of) pheochromocytoma using histopathological (n = 25) and clinical validation (n = 18) as standard of truth. Furthermore, we compared ¹²⁴I-MIBG PET versus contrast enhanced CT (CE-CT) per-patient and per-lesion detection rate of ¹²⁴I-MIBG PET in 13 additional patients with known metastatic malignant pheochromocytoma (MMP). Results: ¹²⁴I-MIBG PET/CT was positive in 19/43 (44%) patients with suspected pheochromocytoma. Presence of pheochromocytoma was confirmed in 22/43 (51%). ¹²⁴I-MIBG PET/CT sensitivity, specificity, PPV, NPV were 86%, 100%, 100%, 88%, respectively. ¹²⁴I-MIBG PET was positive in 11/13 (85%) MMP patients. Combined ¹²⁴I-MIBG PET and CE-CT detected 173 lesions, of which 166 (96%) and 118 (68%) were visible on ¹²⁴I-MIBG PET and CE-CT, respectively. Discussion: ¹²⁴I-MIBG PET detects pheochromocytoma with high accuracy at initial staging and high detection rate at re-staging. Superior diagnostic performance aids guidance of surgical and medical management including personalized ¹³¹I-MIBG therapy.

Radio-Iodide Treatment: From Molecular Aspects to the Clinical View

Simple Summary

This year marks the 80th commemoration of the first time that radio-iodide treatment (RAI) was used. RAI is one of the most effective targeted internal radiation anticancer therapies ever devised and it has been used for many decades, however, a thorough understanding of the underlying molecular mechanisms involved could greatly improve the success of this therapy. This is an in-depth innovative review focusing on the molecular mechanisms underlying radio-iodide therapy in thyroid cancer and how the alteration of these mechanisms affects the results in the clinic.

Abstract

Thyroid radio-iodide therapy (RAI) is one of the oldest known and used targeted therapies. In thyroid cancer, it has been used for more than eight decades and is still being used to improve thyroid tumor treatment to eliminate remnants after thyroid surgery, and tumor metastases. Knowledge at the molecular level of the genes/proteins involved in the process has led to improvements in therapy, both from the point of view of when, how much, and how to use the therapy according to tumor type. The effectiveness of this therapy has spread into other types of targeted therapies, and this has made sodium/iodide symporter (NIS) one of the favorite theragnostic tools. Here we focus on describing the molecular mechanisms involved in radio-iodide therapy and how the alteration of these mechanisms in thyroid tumor progression affects the diagnosis and results of therapy in the clinic. We analyze basic questions when facing treatment, such as: (1) how the incorporation of radioiodine in normal, tumor, and metastatic thyroid cells occurs and how it is regulated; (2) the pros and cons of thyroid hormonal deprivation vs. recombinant human Thyroid Stimulating Hormone (rhTSH) in radioiodine residence time, treatment efficacy, thyroglobulin levels and organification, and its influence on diagnostic imaging tests and metastasis treatment; and (3) the effect of stunning and the possible causes. We discuss the possible incorporation of massive sequencing data into clinical practice, and we conclude with a socioeconomical and clinical vision of the above aspects.

Thyroid stunning in radioiodine-131 therapy of benign thyroid diseases

PURPOSE

Existence and cause of thyroid stunning was controversially discussed for decades but the underlying mechanism remains unclear. Numerous studies describe thyroid stunning in radioiodine-131 therapy (RIT) of differentiated thyroid carcinoma. However, there are no studies evaluating thyroid stunning in benign thyroid diseases caused by the radioiodine uptake test (RIUT). Therefore, the influence of pre-therapeutic tracer radiation dose on therapeutic iodine-131 uptake was evaluated retrospectively.

METHODS

A total of 914 RIT patients were included. Exclusion criteria were anti-thyroid drugs, pre- and/or intra-therapeutic effective half-lives (EHL) beyond 8.04 days and externally performed RIUT or 24 h RIUT. All patients received RIUT 1 week before RIT. Thyroid volume was estimated via ultrasound. Tracer radiation dose to the thyroid was calculated retrospectively. The dependence of changes in the pre-therapeutic to the therapeutic extrapolated-maximum-¹³¹I-uptake (EMU) from the dose in RIUT was evaluated statistically.

RESULTS

EMU in RIUT ranged from 0.10 to 0.82 (median: 0.35) and EMU in RIT ranged from 0.10 to 0.74 (median: 0.33). Averaged over the whole cohort the therapeutic EMU decreased significantly (2.3% per Gray intra-thyroidal tracer radiation dose). A disease-specific evaluation showed dose-dependent thyroid stunning from 1.2% per Gray in solitary toxic nodules (n = 327) to 21% per Gray in goiters (n = 135) which was significant for the subgroups of disseminated autonomies (n = 114), multifocal autonomies (n = 178) and goiters (p < 0.05) but not for Graves' diseases (n = 160) and solitary toxic nodules (p > 0.05).

CONCLUSIONS

The presented data indicate for the first time a significant dependence of pre-therapeutic radiation dose on thyroid stunning in goiter and disseminated and multifocal autonomy. To achieve the desired intra-thyroidal radiation dose, RIT activity should be adapted depending on the dose in RIUT.