RADIOTHERAPY FOR THE MANAGEMENT OF BONE METASTASES IN DIFFERENTIATED THYROID CANCER

Abstract

Purpose:

Bone metastases are observed in over 50% of patients with differentiated thyroid cancer (DTC) who develop metastatic disease. Local treatments including external beam radiation therapy (RT) may be used for radioactive iodine-refractory, progressive, or symptomatic disease. The purpose of this study was to evaluate the efficacy of radiotherapy doses and techniques for DTC bone metastases.

Materials and Methods:

This retrospective study included all patients with DTC who received RT for bone metastases. The primary outcome was treated metastasis control (TMC), calculated from the date of radiotherapy completion to the date of lesion progression, death, or last follow-up. The biological effective dose (BED, α/β=10) was used to compare radiotherapy regimens. The dose-response relationship was evaluated using BED₁₀ as a continuous variable in increments of 10. Subsequently, the group was divided into low dose radiation (BED₁₀<40) and high dose radiation (BED₁₀>=40). The cumulative incidence of TMC was estimated using the Aalen-Johansen method and compared between two BED groups using the Gray test. Univariate and multivariate models were performed to assess for predictors of TMC. A two-sided p-value of <0.05 was considered statistical significance.

Results:

In total, 107 patients with DTC were treated for 280 bone metastases between 2003 and 2023. Patients were stratified into two groups: high BED₁₀≥40 (n=35) and low BED₁₀<40 (n=72). Our results demonstrated that high BED treatment was associated with significantly lower cumulative incidence of progression (HR 0.50, p=0.003), with a median progression time of 3.3 years for low BED and not reached for high BED groups. In total 55/107 patients had molecular profiling, but no mutations were found to predict TMC.

Conclusions:

In this retrospective cohort study, a clear dose-response relationship was identified for patients with DTC bone metastases. When suitable, treatment of these patients should include a higher dose exceeding BED₁₀=40.