Abstract
2087
Objectives For an adequate staging of patients with differentiated thyroid cancer (DTC), the correct assignment of thyroid remnants (TRs) and lymph node metastases (LMs) is of importance. However, using only non-quantitative imaging information such as localization criteria, this tissue assignment is frequently impaired. The aim of this retrospective study was to investigate, whether kinetic (or quantitative) parameters can help improving LM assignment using serial I-124-PET/CT data.
Methods Patients (n=168) with a total of 351 lesions (TR: n=285; LM: n=66) received pretherapeutic I-124-PET/CT lesion dosimetry. After administration of ~25 MBq 124I, the PET scans acquired scanned at 24 h and one at a later imaging time point (>96 h) p.a. were analyzed. For each lesion, maximum activity concentration (MAC) at 24 h and effective half-life (EHL) were determined. Moreover, the product of MAC and EHL, which is proportional to the cumulated activity, was also investigated as a parameter (CAQ = cumulated activity proportional quantity). These kinetic parameters were evaluated in regard to their properties distinguish between TR and LM.
Results The median MAC, EHL, and CAQ values in TR were significantly higher than in LM (Table 1). In comparison, the TR and LM could be separated best by using the CAQ as compared to MAC or EHL. However, with a cut-off value of 4.9 h*MBq/ml a sensitivity 49% and specificity of 94% for TR was reached.
Conclusions Kinetic assessments using I-124-PET in patients prior to thyreoablative radioiodine therapy can be helpful to distinguish between TR and LM. A high CAQ value is highly predictive for TR