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A phantom study to achieve comparable 124I PET recovery and address scanner variability for dosimetry purposes in (re)differentiated thyroid cancer
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DOI：10.1016/j.ejmp.2026.105772.png)
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Abstract
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Background Accurate quantification of iodine uptake is essential for performing pre-treatment dosimetry of I-131 therapy after redifferentiation of radioiodine-refractory thyroid cancer. Standardized procedures for I-124 PET/CT-based dosimetry are currently lacking. We aim to evaluate the relation between F-18 and I-124 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 I-124 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 (similar to 1:125 to 1:infinity) using two digital PET/CT scanners (Philips Vereos and GE Healthcare Omni). Additionally, BG-to-sphere ratio similar to 1:10 was acquired to compare I-124 to the EARL F-18 standards 1 (EARL1). Calibration accuracy and recovery coefficients (RCmax, RCmean) were compared between scanners with and without bias correction. Results I-124 recovery was similar to 20% higher for the Omni compared to the Vereos, showing calibration accuracies of 1.12-1.15 vs. 0.94, and RCmean reaching 0.86 vs. 0.69. After bias correction, RCmean 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 RCmean was comparable (p > 0.4). Conclusion Vendor-recommended I-124 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 I-124 calibration procedures in studies requiring I-124 quantification.
Keywords:
Quantification
Phantom study
Dosimetry
Recovery correction
Thyroid cancer
PET/CT
I-124
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