Anupam Kotwal, Abbey Fingeret, Jarod Hamsa, Dana Awad, Craig Johnson, Frank Rutar, Carrie Carson, Anery Patel, Whitney Goldner
Journal of the Endocrine Society, Volume 9, Issue 5, May 2025, bvaf050
https://doi.org/10.1210/jendso/bvaf050
Dosimetry helps calculate the optimal iodine-131 (I-131) dose for treating metastatic differentiated thyroid cancer (DTC). We aimed to evaluate if recombinant human TSH (rhTSH) and thyroid hormone withdrawal (THW) are equivalent methods of preparation for dosimetry-guided I-131 therapy in metastatic DTC.
We performed a retrospective cohort study of 51 adults with metastatic DTC who received I-131 with dosimetry from 2010 through 2022. Gamma camera and blood activity measurements were taken following the pretherapeutic I-131 dose. Statistical analysis compared rhTSH and THW groups; P < .05 was considered significant.
Fifty-one adults undergoing 55 I-131 dosimetry-guided treatments were included: 22 by rhTSH and 33 by THW. The median age was lower (P = .0008), and the proportion of stage IV (P = .009) was higher in rhTSH compared to the THW group. The terminal effective half-life at 24 to 48 hours in the whole body was longer in rhTSH compared to THW group (21.9 vs 17.1 hours; P = .014), but this difference was less significant when limited to the n = 37 metastatic cases (P = .046) and not different for red marrow effective half-life. The calculated allowed I-131 dose was lower in rhTSH compared to THW group (187.5 mCi vs 259.9 mCi; P = .0000). Thyroglobulin was higher during treatment in the rhTSH group (P = .031), whereas its reduction at 3 months was not different after adjusting for age and stage.
rhTSH is noninferior to THW in preparation for I-131 dosimetry. Compared to THW, rhTSH results in lower calculated allowed I-131 dose after dosimetry, which could translate to fewer side effects or impact on quality of life.
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