(124)I PET/CT in Patients with Differentiated Thyroid Cancer: Clinical and Quantitative Image Analysis

Thyroid. 2016 Mar;26(3):441-8. doi: 10.1089/thy.2015.0482.


Background: Although radioactive iodine (RAI) imaging/therapy is one of the earliest applications of theranostics, there remain a number of unresolved clinical questions as to the optimization of diagnostic techniques/protocols and improvements in patient-specific treatment planning strategies. The objectives of this study were to determine the imaging characteristics and clinical feasibility of (124)I positron emission tomography/computed tomography (PET/CT) for the determination of extent of disease and evaluation of RAI kinetics in its physiologic and neoplastic distribution in patients with differentiated thyroid cancer (DTC).

Methods: The study was designed as a prospective phase II diagnostic trial of patients with confirmed DTC. Following adequate preparation, patients received 2 mCi (124)I in liquid form and sequential whole-body PET/CT imaging was performed at five time points (2-4 h, 24 ± 6 h, 48 ± 6 h, 72 ± 6 h, and 96 ± 6 h post-administration). All patients who had (124)I imaging subsequently underwent RAI treatment with (131)I, with administered activities ranging from 100 to 300 mCi. Post-treatment scans were obtained 5-7 days after RAI treatment. A by-patient and by-lesion analysis of the (124)I images was performed and compared with the post-treatment (131)I scans as well as F-18 FDG PET/CT images. Quantitative image analysis was also performed to determine the total functional volume (mL), activity per functional volume (μCi/mL), and cumulated activity (μCi/h) for remnants, salivary glands, and nodal metastases.

Results: Fifteen patients (6 women; Mage = 57 years; range 29-91 years) were enrolled into the study. Forty-six distinct lesions were identified in these 15 patients on (124)I PET/CT images, with a sensitivity of 92.5%. In addition, (124)I identified 22.5% more foci of RAI-avid lesions compared with the planar (131)I post-treatment scans. This study demonstrates different kinetic profiles for normal thyroid remnants (peaked at 24 h with mono-exponential clearance), salivary glands (peaked at 4 h with bi-exponential clearance), and metastatic lesions (protracted retention), as well as individual variations in functional volumes and thus cumulated activities.

Conclusions: (124)I PET/CT is a valuable clinical imaging tool/agent, both in determining the extent of disease in the setting of metastatic DTC and in the functional volumetric and kinetic evaluation of target lesions.

Publication types

  • Clinical Trial, Phase II
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Cell Differentiation*
  • Feasibility Studies
  • Female
  • Humans
  • Iodine Radioisotopes / administration & dosage
  • Iodine Radioisotopes / pharmacokinetics*
  • Male
  • Middle Aged
  • Neoplasm Metastasis
  • Positron Emission Tomography Computed Tomography*
  • Predictive Value of Tests
  • Prognosis
  • Prospective Studies
  • Radiopharmaceuticals / administration & dosage
  • Radiopharmaceuticals / pharmacokinetics*
  • Sodium Iodide / administration & dosage
  • Sodium Iodide / pharmacokinetics*
  • Thyroid Neoplasms / diagnostic imaging*
  • Thyroid Neoplasms / metabolism
  • Thyroid Neoplasms / pathology
  • Tissue Distribution


  • Iodine Radioisotopes
  • Radiopharmaceuticals
  • Sodium Iodide