Objective: The aim of this study was to identify radiotherapy (RT) induced changes of masticatory muscles and parotid glands
on magnetic resonance imaging (MRI) in patients with nasopharyngeal carcinoma (NPC).
Patients and Methods: Thirty-one patients treated with RT for NPC between 2009-2016 in our instution were included in
the study. MRI examinations performed before and after RT were reviewed retrospectively. Transverse diameters and signal
intensities of masticatory muscles and parotid glands were evaluated on T2 weighted axial MR images. Normal (hypointense)
signal was scored as 0, mild hyperintensity as 1 and severe hyperintensity as 2.
Results:The mean interval between pre-RT MRI and last control MRI was 44 months (12-84 months). Reductions of
transverse diameters were; right masseter (RM):2.32mm (15%), left masseter (LM):2.42mm (15.4%), right medial pterygoid
(RMP):1.26mm (8.7%), left medial pterygoid (LMP):1.71mm (12%), right lateral pterygoid (RLP):1.35mm (9.6%), left lateral
pterygoid (LLP):1.32mm (9.4%), right parotid gland (RP):8.22mm (26%), left parotid gland (LP):8.87mm (28%). T2 signal
changes were; RM: mild 8 cases (26%), LM: mild 5 cases (16%), RMP: mild 5 cases (16%), severe 1 case (3.5%), LMP: mild 4 cases
(13%), severe 2 cases (6.5%), RLP and LLP: mild 8 cases (26%), severe 3 cases (9.7%), RP: mild 10 cases (32%), severe 18 cases
(58%), LP: mild 10 cases (32%), severe 17 cases (55%).
Conclusion: Volume loss and hyperintensity were mostly seen in parotid glands. Masseter was the muscle with highest rate of
volume loss and lateral pyterygoid showed the highest rate of hyperintensity in masticatory muscles.
Key words: Magnetic resonance imaging, masticatory muscle, nasopharyngeal carcinoma, parotid gland, radiotherapy.