# High-Dose Radioiodine Therapy Did Not Result in Better Thyroglobulin Decline in Patients with Extra-Thyroid Tumor Extension of Papillary Thyroid Cancer

## TL;DR

This study found that higher doses of radioiodine therapy do not improve outcomes for patients with thyroid cancer that has spread beyond the thyroid.

## Contribution

The study shows that high-dose radioiodine therapy is not more effective than lower doses for reducing thyroglobulin in patients with extra-thyroid tumor extension.

## Key findings

- Higher radioiodine doses (200-250 mCi) did not significantly reduce thyroglobulin levels compared to lower doses.
- Nonmetastatic patients treated with less than 200 mCi had better thyroglobulin reduction than metastatic patients with higher doses.
- Macroscopic invasion did not affect thyroglobulin decrease after treatment.

## Abstract

In this study, the response to treatment in patients with extra-thyroid extension (ETE) of papillary thyroid cancer (PTC) was compared between different radioiodine treatment doses.

In this retrospective cross-sectional study, patients with pathology-proven ETE who were hospitalized for radioiodine therapy from December 2015 to May 2018 at a referral university hospital were identified. Demographic data, radioiodine doses, and off-levothyroxine thyroglobulin and antithyroglobulin levels, before and after treatment, were collected. Alterations in thyroglobulin levels before and after treatment were compared between patients receiving different doses of radioiodine.

Sixty patients were analyzed (mean age: 44.1 ± 14.4 years; 61.7% females). On average, the thyroglobulin levels were 59.1 ± 92.0 and 45.7 ± 81.5 ng/mL at baseline and after treatment, respectively. The thyroglobulin levels decreased from 6.2 ± 6.3 to 1.7 ± 0.2 ng/mL (
p
 = 0.510), 55.8 ± 101.3 to 11.5 ± 17.2 ng/mL (
p
 = 0.07), and 62.8 ± 91 to 60.9 ± 93.1 ng/mL (
p
 = 0.83) in the 100- to 149-, 150- to 199-, and 200- to 250-mCi iodine therapy groups, respectively. Treatment with doses of less than 200 mCi were significantly more effective in reducing posttreatment thyroglobulin levels compared with higher doses (
p
 = 0.05). In the subgroup analysis, nonmetastatic cases treated with less than 200 mCi iodine had significantly greater thyroglobulin reduction compared with metastatic patients treated with ≥200 mCi iodine (
p
 = 0.05). Macroscopic (vs. microscopic) invasion into adjacent tissues had no impact on thyroglobulin decrease.

The administration of higher radioiodine doses for the treatment of PTC patients with ETE does not yield additional therapeutic benefits in terms of posttreatment thyroglobulin reduction.