06.17 Utilization of External Beam Radiation in Differentiated Thyroid Cancer

Posted on January 25, 2017

C. M. Kiernan1, A. A. Parikh1, C. C. Solorzano1  1Vanderbilt University Medical Center,Nashville, TN, USA

Introduction: External beam radiation (EBRT) for differentiated thyroid cancer (DTC) is recommended in patients >45 years old, with locally advanced unresectable or metastatic disease. This study describes the patterns of EBRT utilization and overall survival of patients with DTC who received EBRT.

Methods:
A total of 46,095 patients diagnosed with DTC between 2003-2006 were identified using the National Cancer Database.  Patients with anaplastic thyroid cancer and patients with more than one cancer diagnosis were excluded. The use of EBRT was documented. Descriptive statistics, Kaplan Meier estimator of overall survival and multivariate cox-proportional hazards regressions were used.

Results:
A total of 546 (1.2%) patients received EBRT.  Patients in the EBRT cohort were on average older (60 vs. 48 years, p<0.001) and presented with larger tumors (4.2 vs. 3.5cm).  They were also more likely to have extrathyroidal extension (46% vs. 11%, p<0.001), positive lymph nodes (65% vs. 34%, p<0.001), positive margins (41% vs. 9%, p<0.001), and distant metastases (34% vs. 1%, p<0.001). The majority of patients in the EBRT group (60%) had stage IV disease at presentation. The 5-year overall survival (OS) was lower in the EBRT group (53% vs. 95%, p<0.001).  On subgroup analysis of patients >45 years of age who underwent total thyroidectomy and had gross extrathyroidal extension EBRT was also associated with decreased OS (84% vs. 42%, p<0.001).  Stage for stage, the 5-year OS was lower in the EBRT group: stage II (96% vs. 81%, p=0.001), stage III (92% vs. 75%, p<0.001) and stage IV (72% vs. 33%, p<0.001).  By cox-proportional hazards regression controlling for multiple patient and tumor factors, EBRT was associated with increased all-cause mortality (HR 2.76, CI 2.01-3.79, p<0.001).

Conclusion:
EBRT is used infrequently in DTC. Patients who receive EBRT are older with more advanced disease. In this large population database study, the utilization of EBRT was associated with decreased overall survival by multivariable analysis. Further study regarding the impact of EBRT on the quality of life of patients with DTC is needed.