# Recombinant TSH Performs as Well as Thyroid Hormone Withdrawal for Iodine-131 Therapy With Dosimetry for Thyroid Cancer

## TL;DR

This study shows that recombinant TSH is as effective as thyroid hormone withdrawal for preparing patients for iodine-131 therapy in thyroid cancer treatment.

## Contribution

The study demonstrates noninferiority of rhTSH compared to THW for I-131 dosimetry in metastatic thyroid cancer.

## Key findings

- rhTSH resulted in a lower calculated allowed I-131 dose compared to THW.
- The terminal effective half-life was longer in the rhTSH group.
- Thyroglobulin levels were higher during treatment in the rhTSH group.

## Abstract

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.