Objective：To investigate the clinical effect and toxic and side effects of external beam radiotherapy in patients with recur－rent and metastatic thyroid carcinoma. Methods：A total of 29 patients with metastatic thyroid carcinoma and 35 patients with recurrent thyroid carcinoma，who were admitted to Department of Radiology in Peking Union Medical College Hospital from January 2008 to January 2018，were enrolled. Three-dimensional conformal radiotherapy，intensity-modulated radiotherapy，or stereotactic radiotherapy was applied as the external beam radiotherapy. Patients’ survival，clinical outcome，and adverse reactions were evaluated. The Verbal Rating Scale and Response Evaluation Criteria in Solid Tumors（RECIST1.1） were used for outcome evaluation. The Kaplan-Meier method was used to calculate survival rate，and the Cox proportional hazards model was used to analyze prognostic factors. Results：The median follow-up time was 38 months. The 2- and 3-year overall survival rates were 67.2%（95% confidence interval[CI]：0.556-0.787） and 51.6%（95%CI：0.394-0.638），respectively. Pathological type was a prognostic factor for overall survival rate（hazard ratio=0.32，95%CI：0.163-0.629，P=0.001）. As for the 40 patients with measurable lesions，disease control rates after one month and two years of external beam radiotherapy were 92.5% and 60.94%，respectively. No RTOG grade 3 or above toxic and side effects were observed. Conclusion：In patients with recurrent and metastatic thyroid carcinoma，external beam radiotherapy can significantly improve symp－toms and control local lesions.
