Low-activity 124I-PET/Low-Dose CT versus 131I probe measurements in pretherapy assessment of radioiodine uptake in benign thyroid diseases

Abstract

Context: 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 124I- positron emission tomography/lowdose computed tomography (124I-PET/ CT) in comparison with standard 131I probe measurements. Design/Setting: This prospective comparative study was conducted at the Jena University Hospital, Jena, Germany, in a referral center setting. Patients: 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. Interventions: All patients received the standard 131I scintillation probe uptake test 30 hours after administration of 3 MBq 131I. Seven days later, all patients were subjected to 124I-PET/CT uptake measurement 30 hours after administration of 1 MBq 124I. Main Outcome Measures: 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 131I probe measurement and 124I-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