Main Session
Sep 29
PQA 07 - Head and Neck Cancer, Lung Cancer/Thoracic Malignancies, and Nursing and Supportive Care

3540 - Local Control and Dose-Response of Radiation Therapy for Bone Metastases in Differentiated Thyroid Cancer

03:45pm - 05:00pm ET
Poster Hall - Exhibit Hall A
Screen: 16
POSTER

Presenter(s)

Qian Liu, MD Headshot
Qian Liu, MD - Mayo Clinic Rochester, Rochester, MN

Q. Liu1,2, D. J. Ma1, M. Ryder3, J. E. Hallanger Johnson3, D. K. Ebner1, T. D. Malouff4, D. M. Routman1, J. M. Wilson3, M. Neben Wittich1, S. C. Lester1, Y. Garces1, and R. J. Brisson1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Radiation Oncology, Cancer Hospital, Chinese Academy of Medical Science, Peking Union Medical College, Beijing, China, 3Mayo Clinic, Rochester, MN, 4Creighton University Medical Center, Omaha, NE

Purpose/Objective(s):

Radiation therapy (RT) is frequently used for bone metastases in patients with differentiated thyroid cancer (DTC), yet optimal dosing and the durability of lesion control remain uncertain. We evaluated lesion-level local control and dose-response relationships using competing-risk methods.

Materials/Methods:

We retrospectively analyzed 179 bone metastases from 81 DTC patients treated with RT between 2013 and 2025. Median follow-up was 33 months. Treatments ranged from 1–10 fractions (median BED10: 60 Gy), most commonly 24 Gy ×1, 20 Gy ×5, and 30 Gy ×3. Local control was assessed using Kaplan-Meier (KM), and in a competing-risk analysis, the cumulative incidence function, treating death without prior local failure as a competing event. Predictors of failure were assessed using Fine–Gray regression. Restricted cubic spline modeling was used to assess dose-response patterns. Post-RT fracture was recorded as a treatment-related outcome.

Results:

KM lesion-level local control at 1, 2, and 3 years was 97.0%, 93.3%, and 91.1%, respectively. In competing risk analysis, corresponding local control rates were 97.2%, 93.9%, 92.2%. Death without prior local failure represented a substantial competing event, with a 3-year cumulative incidence of 25.5%. Increasing BED10, independently reduced failure hazard (HR 0.97 per Gy, 95% CI 0.96–0.99, p=0.004). Spline modeling demonstrated a nonlinear dose–response relationship, with elevated risk at lower BED10, a plateau near 40–60 Gy, and a clear decline in hazard emerging beyond 75 Gy. Lesions treated with BED =75 Gy had significantly lower failure risk (Gray’s p=0.041); 83% of them received 24 Gy in 1 fraction. Post-RT fracture occurred in 9.5% of lesions, with a median time to fracture of 23.8 months (IQR 19.5 – 39.5) and no increase observed in higher-dose treatments (7.4% vs 10.4% for BED10 <75 Gy).

Conclusion:

RT provides durable local control for DTC bone metastases, with competing mortality more common than local failure. When anatomically feasible, delivery of BED10 =75 Gy, most commonly 24 Gy ×1 in our cohort, should be considered to maximize long-term control, particularly in the setting of low fracture risk.