Purpose/Objective(s): Anaplastic thyroid carcinoma is a rare cancer and has a poor prognosis. Several radiation protocols have been reported, but the results were not satisfactory. The aim of this study was to determine the effect of hypofractionated radiotherapy.

Materials/Methods: Thirty-three patients (21 male patients and 12 female patients) who received radiotherapy for ATC between 2000 and 2014 in our institution were included in this study.

Results: Nineteen patients were treated with ≥ 5 Gy per fraction (Gy/fr), and 18 of those patients received 5 Gy/fr. Twenty-eight patients died, and 27 of those patients died from ATC. Sixteen patients died from distance metastasis and 6 patients died from local recurrence. In the ≥ 5 Gy/fr group, local recurrence occurred in 5 patients and 1 of them died from active bleeding from a local tumor. There was local recurrence in 7 patients who received the other protocol, and 5 of them died from asphyxiation, active bleeding or uncontrollable growth of a local tumor on the neck. The median overall survival (OS) period in all patients was 5 months. In multivariate analysis, patients who received an equivalent dose in 2 Gy fractions (EQD₂) ≥ 50 Gy had significantly better OS (p = 0.016). In univariate analysis, patients who received ≥ 5 Gy/fr did not have significantly better OS (p = 0.872) or LC (p = 0.090). The chi-squared test showed that significantly fewer patients died from local recurrence in the ≥ 5 Gy/fr group (p = 0.025).

Conclusion: Multivariate analysis showed that EQD₂ ≥ 50 Gy resulted in better OS, and ≥ 5 Gy/fr decreased the rate of mortality from local recurrence.

Multivariate analysis for OS.
	HR	95 % CI	p value
Male vs female	2.14	0.96-5.13	0.064
EQD2 (≥ 50 Gy vs < 50 Gy)	0.26	0.097-0.76	0.016
Note: OS = overall survival, HR = Hazard ratio, CI = confidence interval, EQD2 = equivalent dose in 2 Gy fractions. Factors with p < 0.01 in univariate analysis were included in multivariate analysis.