2736 - Prophylactic Levothyroxine for Patients Receiving Radiotherapy for Mediastinal and Neck Lymphomas
Presenter(s)
K. M. Frechette1, S. Kern2, R. Guenzel3, M. M. Christensen4, B. S. Hoppe5, J. L. Peterson6, R. Tao7, W. G. Rule7, K. Aziz4, W. Breen8, and S. C. Lester8; 1Department of Radiation Oncology, Mayo Clinic Rochester, Rochester, MN, 2Mayo Clinic, Rochester, MN, 3Mayo Clinic, Eau Claire, WI, United States, 4Mayo Clinic Radiation Oncology, Rochester, MN, 5Mayo Clinic, Department of Radiation Oncology, Jacksonville, FL, 6Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, 7Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ, 8Department of Radiation Oncology, Mayo Clinic, Rochester, MN
Purpose/Objective(s): Lymphoma patients who have thyroid exposure to radiation (RT) are susceptible to long-term hypothyroidism. Data suggests suppression of thyroid stimulating hormone (TSH) in euthyroid pediatric Hodgkin lymphoma (HL) patients may have protective effects on long term thyroid function. We initiated a practice of prophylactic levothyroxine (LT4) for patients with curable lymphoma receiving mediastinal and/or neck RT and aimed to assess the feasibility and tolerability of this approach.
Materials/Methods: Adult lymphoma patients who were prescribed LT4 to take prior to and concurrent with upper mediastinal and/or neck proton RT at our institution between 2021-2025 were included. Thyroid dosimetry, thyroid function results, and toxicities were assessed.
Results: A total of 27 patients received prophylactic LT4 and were included. Patients had either HL (n=22) or primary mediastinal B cell lymphoma (n=5). The median age was 31 years (range 20-61). Median follow up was 16 months (IQR 1-26). Seventy-eight percent of patients had mediastinal involvement, and 85% had cervical neck involvement. The median dose of LT4 was 50 mcg (mode 50, range 50-125). Median time from LT4 initiation to RT was 12 days (range 1-27). Nineteen patients (70%) had a baseline TSH draw within 1 year of starting LT4 and all (100%) were within normal (0.3-4.2 mlU/L) limits (range 0.5-3.5). Five (19%) patients with a baseline TSH had an additional TSH draw pre-RT, and of these, all had a stable or decreased TSH (range of change 0-0.8 mlU/L). No patients had confirmation of a suppressed (<0.3) TSH at the time of RT start. Eleven patients (41%) had a TSH draw post-RT. Median time to first TSH check after RT was 2 months (range 0.1-17 months). Of these, all had a normal TSH (range 0.9-3.9). The compliance rate of LT4 at the end of RT was 100%. No toxicities related to LT4 were documented. No hospitalizations occurred during or within 30 days of RT. One patient (4%) was diagnosed with hypothyroidism 9 months after RT and was started on maintenance LT4. This patient was on 50 mcg LT4 during RT, and received a mean thyroid dose of 2726 cGy. Median RT dose for all patients was 3000 cGy (IQR 3000-3060). Mean thyroid dose across the cohort was 1507 cGy (IQR 1059-1867). Six (22%) and one (4%) patient had mean thyroid doses greater than 2000 cGy and 3000 cGy, respectively.
Conclusion: Prophylactic LT4 appears safe and well tolerated in patients receiving collateral radiation to the thyroid when undergoing treatment of lymphoma. Follow-up is needed to determine the protective effect of LT4 on thyroid function, and the ideal LT4 dosage needed for adequate suppression.