Anatomical changes in the pharyngeal constrictors after chemo-irradiation of head and neck cancer and their dose-effect relationships: MRI-based study

Purpose: Dysfunction of pharyngeal constrictors (PCs) after chemo-irradiation of head and neck (HN) cancer has been proposed as major cause of dysphagia. We conducted prospective MRI study to evaluate anatomical changes in the PCs after chemo-irradiation. to gaol insight of the mechanism of their dysfunction arid their dose-effect relationships. The PCs were compared to the stemucleidomastoid muscles (SCMs), which receive high doses but do riot relate to swallowing. Patients and methods: Twelve patients with stage III-IV HN cancer underwent MRI before arid 3 months after completing chemo-irradiation T1- arid T2-weighted signals and muscle thickness were evaluated for PCs (superior. middle, and inferior), and SCMs. Meats muscle doses were determined after registration with the planning CT. Results: T1-weighted signals decreased in both PCs arid SCMs receiving >50 Gy (p < 0 03). but not in muscles receiving lower doses. T2-weighted signals in the PCs increased significantly as the dose increased (R-2 = - 0 34, p - 0.01). The T2 signal changes in the PCs were significantly higher than the T2 changes in the SCMs (p < 0 001) Increased thickness was noted in all PCs, with muscles receiving >50 Gy gaining significantly more thickness than PCs receiving lesser closes (p=0.02). In contrast, the SCM thickness decreased post-therapy (p = 0.002) Conclusions. These MRI-based findings. notably the differences between PCs and SCMs, suggest that underlying causes of PC dysfunction are inflammation and edema, likely consequential to acute mucositis affecting the submucosa-lying PCs. These results support reducing mean PC doses to <50 Gy, as well as reducing acute mucositis, to improve long-term dysphagia. (C) 2009 Flsevier Ireland Ltd All rights reserved. Radiotherapy and Oncology 93 (2009) 510-515