Determination of effective half-life of 131I in thyroid cancer patients using remote dose-rate meter.

Background: Continuously monitored external dose-rate signals from remote dose-rate meters (DRMs) were analyzed to determine the effective half-life (T_eff) of ¹³¹I in differentiated thyroid cancer (DTC) patients. The aim is to gain novel understanding of the excretion of radioactive iodine (RAI) in DTC patients and to demonstrate that a remote DRM system can be reliably used for real-time monitoring of external dose-rates of DTC patients.

Methods: 110 DTC patients who received postoperative RAI therapy between September 2018 and February 2023 in Turku University Hospital were studied retrospectively. The external dose-rates of the patients were continuously monitored during their hospitalization with a remote DRM fixed in the ceiling of the isolation room. Generalized linear mixed model (GLMM) was used to analyse the association between logarithmical T_eff and patient characteristics.

Results: The median T_eff for all patients was 12.60 h (Q1: 10.35; Q3: 14.75 h). Longer T_effs were associated with higher BMI (p = 0.004), lower GFR (p < 0.001), and diabetes (p = 0.007). Our study also revealed that neither age nor subsequent RAI therapies have a significant impact on the whole body T_eff (p = 0.522 and p = 0.414, respectively).

Conclusion: Patients with higher BMI, decreased GFR, or diabetes have a longer whole-body T_eff of ¹³¹I. Ceiling-mounted remote DMRs can reliably be used to determine patient's T_eff. Since T_eff values vary among patients, ceiling-mounted meters can be used to optimize the length of radiation isolation period at the hospital while improving patient comfort and staff efficiency.