Anatomical changes in the pharyngeal constrictors after chemo-irradiation of head and neck cancer and their dose-effect relationships: MRI-based study.
OBJECTIVE
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 gain insight of the mechanism of their dysfunction and their dose-effect relationships. The PCs were compared to the sternocleidomastoid muscles (SCMs), which receive high doses but do not relate to swallowing.


METHODS
Twelve patients with stage III-IV HN cancer underwent MRI before and 3 months after completing chemo-irradiation. T1- and T2-weighted signals and muscle thickness were evaluated for PCs (superior, middle, and inferior), and SCMs. Mean muscle doses were determined after registration with the planning CT.


RESULTS
T1-weighted signals decreased in both PCs and 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 doses (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.
Popovtzer
Aron
A
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA.
Cao
Yue
Y
Feng
Felix Y
FY
Eisbruch
Avraham
A
D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000532:radiotherapy*; D003131:Combined Modality Therapy; D004307:Dose-Response Relationship, Radiation; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009334:Neck Muscles / Q000473:pathology / Q000528:radiation effects; D010609:Pharyngeal Muscles / Q000473:pathology / Q000528:radiation effects*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000175:diagnosis