Treatment intensity and control rates in combining external-beam radiotherapy and radioactive iodine therapy for metastatic or recurrent differentiated thyroid cancer.

Abstract

To evaluate the treatment outcomes of external-beam radiotherapy (EBRT) with or without radioactive iodine therapy (RAIT) for metastatic or recurrent lesions of differentiated thyroid cancer (DTC). Between August 1997 and March 2018, 73 lesions (distant metastases, 50; regional lymph-node metastases, 17; postoperative tumor-bed recurrences, 6) in 36 patients that had received EBRT with or without RAIT were reviewed. Doses of EBRT were 8-70Gy (median 40Gy). Seventeen patients received RAIT after EBRT. Median follow-up time of imaging studies was 14months (range 1-110months). Two-year overall survival rates and control rates of EBRT sites were 71% and 62%, respectively. Two-year control rates for EBRT of < 30Gy (n = 7), 30Gy (n = 13), 31-49Gy (n = 25), 50Gy (n = 20), and > 50Gy (n = 8) were 0%, 56%, 53%, 79%, and 100%, respectively. There were statistically significant differences in control rates between < 30Gy and 30Gy (p = 0.003), and between 50Gy and > 50Gy (p = 0.037). Control rates of > 50Gy were significantly better compared to ≤ 50Gy (p = 0.021). Two-year control rates with (n = 28) and without (n = 45) post-EBRT RAIT were 89% and 45%, respectively (p = 0.009). In multivariate analysis, EBRT of > 50Gy and post-EBRT RAIT were significant independent factors for favorable control of EBRT sites (hazard ratio [HR], 5.72; 95% confidence interval [CI], 1.21-27.1; p = 0.028 and HR, 2.98; 95% CI, 1.28-6.98; p = 0.012, respectively). EBRT of > 50Gy and post-EBRT RAIT appeared to be useful for long-term control of EBRT sites for metastatic or recurrent lesions of DTC.