(CSEMP059) REAL-WORLD APPLICATION OF AMERICAN THYROID ASSOCIATION RISK-ADAPTED DOSING FOR POSTOPERATIVE RADIOACTIVE IODINE IN DIFFERENTIATED THYROID CANCER PATIENTS

Abstract:

Background: The 2015 American Thyroid Association (ATA) guidelines recommend a risk-adapted approach to postoperative radioactive iodine (RAI) dosing for differentiated thyroid cancer (DTC). This requires integration of pre-, intra-, and postoperative clinicopathological factors and determination of intent of RAI therapy as either remnant ablation, adjuvant treatment, or treatment of known disease. This study seeks to evaluate the performance of the thyroid cancer triage group at one tertiary care referral centre, in terms of adherence to a guideline-based and risk-adapted approach to RAI dosing recommendations.

Methods: We retrospectively analyzed the demographic and clinicopathological data of 1420 adult (18 years) patients diagnosed with DTC between 2016-2022 after thyroid surgery who were reviewed at an institutional thyroid cancer triage rounds and issued a recommendation for postoperative RAI dosing.

Results: Among 1420 patients, the median age at diagnosis was 47 years (range = 18-93 years) and median tumor size was 1.7cm (range 0.05-16.5cm). ATA risk of recurrence (ROR) was as follows: low 725 (51.1%), intermediate 470 (33.1%), and high 225 (15.8%).

The recommended RAI dose in the low risk group was: 0 mCi in 682 (94.1%) patients, 0-30 mCi in 15 (2.1%) patients, 30 mCi in 24 (3.3%) patients, and 30-100 mCi in 4 (0.6%) patients. The recommended RAI dose in the intermediate risk group was: 0 mCi in 53 (11.3%) patients, 0-30 mCi in 22 (4.7%) patients, 30 mCi in 329 (70.0%) patients, 30-100 mCi in 29 (6.2%) patients, 100 mCi in 36 (7.7%) patients, and 100-150 mCi in 1 (0.2%) patient. The recommended RAI dose in the high risk group was: 30 mCi in 11 (4.9%) patients, 30-100 mCi in 17 (7.6%) patients, 100 mCi in 156 (69.3%) patients, 100-150 mCi in 4 (1.8%) patients, 150 mCi in 34 (15.1%) patients, 150-200 mCi in 2 (0.9%) patients, and 200 mCi in 1 (0.4%) patient.

Discussion: In general, our centre followed the ATA risk-adapted approach to RAI dosing. As expected, the vast majority of low risk patients were not recommended postoperative RAI, and all high risk patients were recommended postoperative RAI (median dose = 100 mCi). There was significant variability in the recommended RAI dose among ATA intermediate risk patients (median dose = 30 mCi, range = 0-150 mCi), reflecting the heterogeneity in ROR among this cohort. At times, the triage group recommended an RAI dose range in order to incorporate postoperative thyroglobulin values, postoperative staging imaging, or patient values/preferences.