Time efficient 124I-PET volumetry in benign thyroid disorders by automatic isocontour procedures: mathematic adjustment using manual contoured measurements in low-dose CT

Abstract

Benign thyroid diseases are widely common in western societies. However, the volumetry of the thyroid gland, especially when enlarged or abnormally formed, proves to be a challenge in clinical routine. The aim of this study was to develop a simple and rapid threshold-based isocontour extraction method for thyroid volumetry from ¹²⁴I-PET/CT data in patients scheduled for radioactive iodine therapy. PET/CT data from 45 patients were analysed 30 h after 1 MBq ¹²⁴I administration. Anatomical reference volume was calculated using manually contoured data from low-dose CT images of the neck (MC). In addition, we applied an automatic isocontour extraction method (IC_0.2/1.0), with two different threshold values (0.2 and 1.0 kBq/ml), for volumetry of the PET data-set. IC_0.2/1.0 shape data that showed significant variation from MC data were excluded. Subsequently, a mathematical correlation using a model of linear regression with multiple variables and step-wise elimination (mIC_0.2/1.0), between IC_0.2/1.0 and MC, was established. Data from 41 patients (IC_0.2), and 32 patients (IC_1.0) were analysed. The mathematically calculated volume, mIC, showed a median deviation from the reference (MC), of ±9 % (1–54 %) for mIC_0.2 and of ±8.2 % (1–50 %) for mIC_1.0 Contour extraction with both, mIC_1.0 and mIC_0.2 gave rapid and reliable results. However, mIC_0.2 can be applied to significantly more patients (>90 %) and is, therefore, deemed to be more suitable for clinical routine, keeping in mind the potential advantages of using ¹²⁴I-PET/CT for the preparation of patients scheduled for radioactive iodine therapy.