{"title":"Estimation of effective half-life and lesion-specific kinetics in I-131 therapy for differentiated thyroid cancer using dual-timepoint imaging.","authors":"Yusuke Iizuka, Ryota Nakashima, Rihito Aizawa, Masaaki Kajisako, Maki Shioji, Katsuhiko Mitsumoto, Koji Itagaki, Shigeto Kawase, Takashi Mizowaki","doi":"10.1186/s40658-026-00916-x","DOIUrl":null,"url":null,"abstract":"<p><strong>Background: </strong>Accurate estimation of lesion-specific effective half-life (T<sub>eff</sub>) is essential for patient-specific dosimetry in radioiodine (I-131) therapy for differentiated thyroid cancer (DTC). Although conventional multi-timepoint imaging provides detailed kinetic information, it is often impractical for routine clinical implementation. This study prospectively evaluated a simplified dual-timepoint planar imaging protocol aimed at balancing quantitative reliability with clinical feasibility.</p><p><strong>Methods: </strong>Fifty patients with DTC undergoing I-131 therapy were prospectively analyzed. Whole-body planar images were acquired twice after administration: an early scan at 1.98-3.25 days (mean, 2.71 days) and a delayed scan at 8.97-17.16 days (interval between the two scans ranged from 6.18 to 14.28 days [mean, 12.35 days]). Lesion-specific T<sub>eff</sub> values were calculated assuming mono-exponential clearance between the two scans using a log-linear approximation of measured activity counts. Quantitative reproducibility was assessed by comparing activity-count calibration slopes derived from an internal reference I-131 capsule between independent imaging sessions.</p><p><strong>Results: </strong>The mean T<sub>eff</sub> was 2.16 ± 0.56 days and 3.11 ± 0.74 days for thyroid bed (n = 35) and metastatic (n = 19; p < 0.001) lesions, respectively. Among metastatic sites, bone and lung metastases showed numerically similar T<sub>eff</sub> values (3.22 ± 0.76 and 3.36 ± 0.80 days, respectively); however, this subgroup comparison was limited by the small sample size. Calibration slopes derived from the internal reference capsule demonstrated only 5.0% inter-session variability, indicating high quantitative reproducibility.</p><p><strong>Conclusions: </strong>Dual-timepoint planar imaging incorporating internal capsule calibration enables reproducible estimation of lesion-specific T<sub>eff</sub> in patients undergoing I-131 therapy for DTC. This approach achieves a practical balance between quantitative accuracy and clinical feasibility, enabling reliable characterization of iodine kinetics with minimal imaging burden and supporting individualized dosimetry in routine clinical practice.</p>","PeriodicalId":11559,"journal":{"name":"EJNMMI Physics","volume":" ","pages":""},"PeriodicalIF":3.5000,"publicationDate":"2026-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13574748/pdf/","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"EJNMMI Physics","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1186/s40658-026-00916-x","RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING","Score":null,"Total":0}
引用次数: 0
Abstract
Background: Accurate estimation of lesion-specific effective half-life (Teff) is essential for patient-specific dosimetry in radioiodine (I-131) therapy for differentiated thyroid cancer (DTC). Although conventional multi-timepoint imaging provides detailed kinetic information, it is often impractical for routine clinical implementation. This study prospectively evaluated a simplified dual-timepoint planar imaging protocol aimed at balancing quantitative reliability with clinical feasibility.
Methods: Fifty patients with DTC undergoing I-131 therapy were prospectively analyzed. Whole-body planar images were acquired twice after administration: an early scan at 1.98-3.25 days (mean, 2.71 days) and a delayed scan at 8.97-17.16 days (interval between the two scans ranged from 6.18 to 14.28 days [mean, 12.35 days]). Lesion-specific Teff values were calculated assuming mono-exponential clearance between the two scans using a log-linear approximation of measured activity counts. Quantitative reproducibility was assessed by comparing activity-count calibration slopes derived from an internal reference I-131 capsule between independent imaging sessions.
Results: The mean Teff was 2.16 ± 0.56 days and 3.11 ± 0.74 days for thyroid bed (n = 35) and metastatic (n = 19; p < 0.001) lesions, respectively. Among metastatic sites, bone and lung metastases showed numerically similar Teff values (3.22 ± 0.76 and 3.36 ± 0.80 days, respectively); however, this subgroup comparison was limited by the small sample size. Calibration slopes derived from the internal reference capsule demonstrated only 5.0% inter-session variability, indicating high quantitative reproducibility.
Conclusions: Dual-timepoint planar imaging incorporating internal capsule calibration enables reproducible estimation of lesion-specific Teff in patients undergoing I-131 therapy for DTC. This approach achieves a practical balance between quantitative accuracy and clinical feasibility, enabling reliable characterization of iodine kinetics with minimal imaging burden and supporting individualized dosimetry in routine clinical practice.
期刊介绍：
EJNMMI Physics is an international platform for scientists, users and adopters of nuclear medicine with a particular interest in physics matters. As a companion journal to the European Journal of Nuclear Medicine and Molecular Imaging, this journal has a multi-disciplinary approach and welcomes original materials and studies with a focus on applied physics and mathematics as well as imaging systems engineering and prototyping in nuclear medicine. This includes physics-driven approaches or algorithms supported by physics that foster early clinical adoption of nuclear medicine imaging and therapy.
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