Magnetic resonance imaging at 3.0 T for submandibular gland sparing radiotherapy

Purpose: Besides sparing the parotid gland, sparing the submandibular gland is considered to be important in preventing xerostomia in head-and-neck cancer patients. Delineation of the submandibular gland at CT, and even on T1- and T2-weighted MR images, is difficult, due to low contrast with the surrounding tissues. MR sialography might be used for delineation. Methods and materials: Sixteen oropharyngeal cancer patients received a CT and MRI exam as part of the standard treatment imaging protocol. Patients were scanned in their five-point RT immobilization mask. The MRI exam included T1- and T2-weighted MRI scans and an MR sialography scan. Thirty submandibular glands were delineated on only CT, on the combined CT and T1- and T2-weighted MRI scans and on all MR images. A Wilcoxon signed-rank test was performed to test if the delineated volumes were significantly different. Results: The delineated volume of the submandibular gland was 7.3 mL in the CT-delineation, 7.1 mL in the CT/MRI-delineation and 8.1 mL in the MRI-delineation. The MRI-delineation was significantly larger than the other delineations (p < 0.001). The differences were mainly located in the cranial direction. Conclusion: The delineation of the submandibular gland was improved in the cranial direction by using T1- and T2-weighted MRI and MR sialography, compared to the other delineations.