Work

A phantom study to achieve comparable 124I PET recovery and address scanner variability for dosimetry purposes in (re)differentiated thyroid cancer

Year: 2026

Type: article

Abstract: Background Accurate quantification of iodine uptake is essential for performing pre-treatment dosimetry of 131 I therapy after redifferentiation of radioiodine-refractory thyroid cancer. Standardized procedures for 124 I PET/CT-based dosimetry are currently lacking. We aim to evaluate the relation between 18 F and 124 I imaging for two different PET/CT scanners, the effect of bias correction on recovery across scanners and investigate the impact of clinically-encountered background (BG)-to-lesion ratios on recovery correction. Methods Cylindrical and NEMA body phantoms were scanned following vendor-recommended 124 I acquisition using clinically representative activity concentrations (5.6–5.7 kBq/mL in cylindrical phantom, 45.1–59.2 kBq/mL in NEMA spheres) and BG-to-sphere ratios (∼1:125 to 1:infinity) using two digital PET/CT scanners (Philips Vereos and GE Healthcare Omni). Additionally, BG-to-sphere ratio ∼1:10 was acquired to compare 124 I to the EARL 18 F standards 1 (EARL1). Calibration accuracy and recovery coefficients (RC max , RC mean ) were compared between scanners with and without bias correction. Results 124 I recovery was ∼20% higher for the Omni compared to the Vereos, showing calibration accuracies of 1.12–1.15 vs. 0.94, and RC mean reaching 0.86 vs. 0.69. After bias correction, RC mean was comparable between scanners (<1%) but below the lower limits of EARL1. A single fit for recovery correction (R 2 = 0.97) was obtained for different BG-to-sphere ratios for both scanners as RC mean was comparable (p > 0.4). Conclusion Vendor-recommended 124 I acquisition and reconstruction leads to differences in quantification but can be compensated using a bias correction. Recovery correction is minimally affected by different BG-to-lesion ratios, suggesting that one RC curve is sufficient, simplifying 124 I calibration procedures in studies requiring 124 I quantification.

Source: Physica Medica

DOI: 10.1016/j.ejmp.2026.105772