title: Low-activity (124)I-PET/low-dose CT versus (131)I probe measurements in pretherapy assessment of radioiodine uptake in benign thyroid diseases.
abstract: BACKGROUND
  Radioiodine therapy of benign thyroid diseases requires pretherapy assessment of radioactive iodine uptake (RAIU) for reliable therapy planning.
  
  
  OBJECTIVE
  Our objective was to assess RAIU by low-activity (124)I-positron emission tomography/low-dose computed tomography ((124)I-PET/CT) in comparison with standard (131)I probe measurements.
  
  
  METHODS
  This prospective comparative study was conducted at the Jena University Hospital, Jena, Germany, in a referral center setting.
  
  
  METHODS
  A total of 79 patients with benign thyroid diseases were screened, 40 of whom met the inclusion criteria (stable TSH, free T3 and free T4 levels; no thyroid-specific medication, no iodine contamination) and 24 of whom agreed to participate by signing an informed consent.
  
  
  METHODS
  All patients received the standard (131)I scintillation probe uptake test 30 hours after administration of 3 MBq (131)I. Seven days later, all patients were subjected to (124)I-PET/CT uptake measurement 30 hours after administration of 1 MBq (124)I.
  
  
  METHODS
  The decay-corrected uptake values of both techniques were compared. Additionally, 3 different volume-of-interest-based evaluation methods in PET/CT (whole neck [WN], automatic isocontour [IC], and manually contoured [MC]) were evaluated.
  
  
  RESULTS
  The (131)I probe measurement and (124)I-PET.WN method provided very similar mean RAIU (30.7% ± 10.3%; 31.7% ± 8.9%), resulting in a significant positive correlation (r = 0.93, P < .001). Compared with (124)I-PET.WN, the (124)I-PET.IC (29.8% ± 8.6%) and the (124)I-PET.MC (24.5% ± 7.1%) demonstrated lower uptake values.
  
  
  CONCLUSIONS
  Using activities as low as 1 MBq, the (124)I-PET.WN method shows a good correlation with conventional (131)I probe measurement. Thus, (124)I-PET/CT is a suitable alternative for pretherapy RAIU evaluations. This may offer potential additional benefits such as PET/ultrasound fusion imaging and CT volumetry.
authors.affiliation: Clinic of Nuclear Medicine (J.G.W., T.W., C.K., M.F.), Jena University Hospital, 07743 Jena, Germany and Ernst-Abbe-Fachhochschule Jena (C.K.), University of Applied Sciences, 07740 Jena, Germany.
authors.forename: Julian G
authors.initials: JG
authors.lastname: Westphal
authors.forename: Thomas
authors.initials: T
authors.lastname: Winkens
authors.forename: Christian
authors.initials: C
authors.lastname: Kühnel
authors.forename: Martin
authors.initials: M
authors.lastname: Freesmeyer
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D011829:Radiation Dosage; D011849:Radioactive Tracers; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D016606:Thyroid Nodule / Q000000981:diagnostic imaging* / Q000378:metabolism*; D014055:Tomography, Emission-Computed / Q000295:instrumentation / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes; D011849:Radioactive Tracers