Clinical Significance of Diffuse Hepatic Uptake on Post-Therapeutic 131I- Whole Body Scan in Differentiated Thyroid Cancer

Background: Differentiated thyroid cancers (DTC) are among the most curable cancers, with a 10-year survival rate of 80.95%. These patients are treated by radio-iodine ablation (RAIA). Post-therapy whole body scan (Rx WBS) is done 5-7 days after RAIA. Diffuse hepatic uptake (DHU) in RxWBS after radioiodine remnant ablation might indicate metabolization of radioiodine-marked thyroglobulin fragments. Objective:  To analyze the diffuse hepatic uptake of 131I on a post-ablative 131I whole body scan by grading diffuse hepatic uptake and evaluating its clinical significance in the outcome of differentiated thyroid cancer (DTC). Patients and Methods: This is a prospective cohort study conducted in the thyroid division of the National Institute of Nuclear Medicine and Allied Sciences (NINMAS). A total of 67 low- and intermediate-risk groups of differentiated thyroid carcinoma (DTC) patients who were referred to the thyroid division for radio-iodine ablation after thyroidectomy were chosen for the study. Analysis of Rx WBS images was done. DTC patients were divided according to visually graded diffuse hepatic uptake or no hepatic uptake and followed up for one year. Follow-ups were done by measuring Tg and TgAb and doing high-resolution ultrasound (HRUS) of the neck. One year later, a diagnostic whole-body scan was done. Outcomes were disease-free (DF) conditions, persistent disease (PD), or recurrence. Results: Out of 67 patients, low-risk DTC was diagnosed in 32 and intermediate-risk in 35 patients. No high-risk group was included in this study. Two groups of patients were created: DHU and those with no hepatic uptake. Out of them, 48 patients had DHU. These findings and clinical data were compared and analyzed using SPSS, and a significant association (P = 0.40) was found between different doses of 131I administered for ablation and DHU. Age, histopathological type, lymph node involvement, ALT level, thyroid bed uptake, and fatty liver were found to be insignificant when compared with DHU. After 1 year of follow-up, 52 (76.6%) patients were disease-free (DF), and persistence disease (PD) and recurrence were present in 10 (14.9%) and 5 (7.5%) patients, respectively. Among DF patients, DHU was present in 79.2% of patients. The comparison of DHU and the outcome of the DTC showed an insignificant p value of 0.640. Conclusion: The ablative dose of 131I greater than 100 mCi had a positive relationship with DHU, which might be due to radiolabeled hormones. There was no significant association between DHU and the uptake in the thyroid bed, Tg values, age, stage of the disease, presence of local or distant metastases, recurrence, or survival. Bangladesh J. Nuclear Med. 26(2): 160-166, 2023