8675 Dosing of Radioactive Iodine for Papillary Thyroid Cancer in Advanced Chronic Kidney Disease

Abstract Disclosure: C. Cheatham: None. D. Beckman: None. INTRO Radioactive Iodine (RAI) ablation is an important treatment for patients diagnosed with papillary thyroid carcinoma. Most studies completed on RAI in renal dysfunction were focused on End Stage Renal Disease (ESRD) patients on dialysis to establish protocols on timing of dialysis to allow desired clinical response to RAI without increased risks and minimizing exposure of dialysis staff to radiation dose. The ideal RAI dosing and monitoring of patients with advanced chronic kidney disease (CKD) stage 4 or 5 not requiring dialysis has not been systematically reviewed. CASE 26 year-old female with CKD stage 4/5 secondary to chronic hydronephrosis from vesicoureteral reflux with baseline eGFR 15-20 mL/min/1.73 m2 was diagnosed with papillary thyroid cancer. She underwent total thyroidectomy with central and left lateral neck dissection, resulting in pathologic stage I, pT2 N1b M0 disease, high risk for recurrence according to the 2015 American Thyroid Association guidelines due to 17 positive lymph nodes from left level II-IV and VI, multiple with extranodal extension, as well as 1 vessel angioinvasion. She was referred for adjuvant RAI ablation after withdrawal from thyroid hormone. Decision was made to proceed with a 50% dose reduction and close monitoring of radioactivity clearance as an inpatient given decrease of eGFR to 10-12 mL/min/1.73 m2. She was cleared for discharge 4 days after RAI dose of 74.8mCi when activity level dropped to 2mR/hr. Post-ablation whole body scan showed activity in the thyroid bed and parasternal notch without evidence of metastatic disease. Post-treatment non-stimulated thyroglobulin 6 weeks later was 0.4 ng/mL down from 269.7 ng/mL. DISCUSSION Given RAI is predominately renally cleared, decreased renal function affects clearance rates and associated exposure to radiation. Risks with decreased RAI clearance include bone marrow toxicity and prolonged isolation requirements. In a 2017 retrospective review, patients with eGFR 30 mL/min/1.73 m2 had delayed clearance leading to a mean proportional reduction of exposure rate at 48 hours of -67.2% compared to -94.3% in healthy controls. While protocols exist for patients on hemodialysis, no such protocols have been established for patients with advanced CKD not requiring dialysis. For this patient, after multidisciplinary discussion with nuclear medicine, health physics, and nephrology in setting of further eGFR reduction during hormone withdrawal, decision was made to reduce the intended dose by 50% with inpatient monitoring and backup to dialyze if no significant decrease in radiation activity level was seen or if she were to progress to anuric or oliguric renal failure. This case highlights the need for established protocols and long-term studies to evaluate risk and treatment response in relation to dosing of RAI in this population, but a 50% dose reduction appears to be effective without adverse event. Presentation: 6/2/2024