External Beam Radiotherapy in the Management of Differentiated Thyroid Cancer: A Single Institution Retrospective Cohort Review.
Abstract
Purpose
The role of external beam radiotherapy (EBRT) in differentiated thyroid cancer (DTC) remains debated and is largely guided by retrospective data, much of which predates modern radiotherapy techniques. In this retrospective cohort study, we evaluate outcomes of patients with advanced DTC treated in the modern radiotherapy era.
Materials And Methods
A retrospective cohort review was conducted of 232 DTC patients treated at a single institution between 2004 and 2020. Patients with clinical or pathological T4 disease, gross residual disease after thyroidectomy, unresectable disease, multiple neck recurrences poorly controlled with radioactive iodine, were included. The radiotherapy cohort (n=133) received EBRT with IMRT/VMAT. Patients treated with palliative doses were excluded. The comparator cohort (n=99) did not receive EBRT. Data collection included patient demographics, disease characteristics, disease management, and patient outcomes/ toxicity. Kaplan-Meier methods and Cox regression analyses were used for statistical analysis.
Results
The EBRT group presented with more adverse factors (older age, male predominance). Locoregional relapse free survival (lrRFS) was significantly improved in the EBRT group (HR 0.41, p=0.0028), with a significantly longer time to first locoregional recurrence or death (median 6.6 years versus 3.2 years, p<0.001). Multivariable analysis confirmed EBRT was associated with improved lrRFS. Overall survival was not significantly different. EBRT was well-tolerated from an esophageal and laryngeal toxicity perspective.
Conclusions
Adjuvant neck EBRT with modern radiation techniques, such as IMRT and VMAT, appears to improve locoregional RFS in DTC patients. Review of our failure patterns following neck EBRT does not demonstrate significant marginal failures, indicating the efficacy of conformal planning. These findings support consideration of EBRT in patients at high-risk of locoregional recurrence. Future research is warranted to refine patient selection criteria and to investigate the long-term impact of neck VMAT/IMRT on disease control and patient recorded outcomes in DTC.