Abstract: Background and purpose: Poorly differentiated thyroid carcinoma (PDTC) is a rare malignant tumor with high rates of invasion and distant metastasis, and there is no effective treatment. This study aimed to investigate the efficacy and adverse effects of intensity-modulated radiotherapy (IMRT) for locoregionally advanced and recurrent PDTC. Methods: From February 2011 to September 2014, eight patients with biopsy-proven T_4a-b PDTC who underwent IMRT at our center were enrolled. The prescribed dose was 60 Gy/30 F to high-risk areas for one patient with extracapsular invasion after radical surgery, and 66 Gy/33 F to primary lesion and positive lymph nodes for the rest patients who also received cisplatin-based chemotherapy. Results: After completion of treatment, 2 patients had complete response (CR) to the locoregional disease, 1 patient had partial response (PR) and 5 patients had stable disease (SD). By the last follow-up, the overall locoregional control rate was 87.5% (5 CR+1 PR+1 SD). Four patients (50%) finally died of locoregional disease progress (12.5%) and lung metastasis (37.5%). Most of the treatment-related toxicities were grade 1-2. Conclusion: IMRT-based therapy was effective and safe for locoregionally advanced and recurrent PDTC, with improved locoregional control and overall survival, as well as acceptable toxicities.

Key words: Intensity-modulated radiotherapy, Poorly differentiated thyroid carcinoma, Locoregional control