[en] Purpose: To study the usefulness of dynamic magnetic resonance imaging in the evaluation of head and neck cancers treated with radiation therapy. Methods and Materials: Seventy-six patients (58 males and 18 females; ages 20-82) with head and neck cancers (10 nasopharyngeal carcinomas, 22 mesopharyngeal carcinomas, 10 hypopharyngeal carcinomas, 16 oral cavity carcinomas, 11 lingual carcinomas, and 7 laryngeal carcinomas) were treated by radiation therapy combined with concomitant low-dose cisplatinum. Magnetic resonance imaging (MRI) was performed before and 2 weeks after the irradiation in all cases. After bolus administration of gadopentetate dimeglumine (Gd-DTPA) (0.1 mmol/kg), images were obtained every 30 s (repetition time 200 ms, echo time 16 ms) using a 1.5 or 0.5-T superconductive unit. Biopsy or surgery was performed after radiation therapy and the histologic findings were correlated with the MRI findings (T₁, T₂, dynamic, and enhanced T₁). Results: Complete remission, partial response, and no response were obtained in 18, 36, and 7 cases, respectively. Dynamic MRI correctly diagnosed 17 of the 18 complete remission cases, 33 of the 36 partial response cases, and all of the 7 no-response cases. The accuracy of dynamic MRI, T₁-weighted image, T₂-weighted image, and Gd-enhanced T₁-weighted image was 94.4%, 68%, 82%, and 86%, respectively. Conclusion: Dynamic MRI proved to be useful in the evaluation of the radiation therapy of head and neck cancers