Mr linac

Patients treated on MR-Linac underwent a planning CT scan (Philips, Big Bore CT) and MR simulation scan either on diagnostic MRI (Siemens, Aera 1.5T) or MR-Linac (Elekta Unity, 1.5 T). Bladder filling protocol on MR simulation required patients to empty bladder and drink 700 mls of water 1 h prior to scanning. Scanning was performed in treatment position, ideally with an empty rectum. If rectum ≥5 cm on initial planning scan patients were re-scanned following bowel preparation. Radiotherapy planning was performed on Monaco® v5.40.01 (Elekta AB, Stockholm, Sweden) for Phase 1 and Raystation® v10.0.1.52 (RaySearch Laboratories AB, Stockholm, Sweden) for Phase 2.

All cine-MRIs were performed on the Philips (Best, the Netherlands) 1.5 T MRI scanner, part of the MR-Linac with a standardized head and neck receiver coil (flip angle, 35°; echo time/repetition time, 2.298/4.577 ms; matrix, 120; bandwidth, 479 Hz; number of signal averages, 1; pixel spacing, 0.8 × 0.8 mm; frames per second, 4).
Cine-MRI captured motion in the axial (level of vocal cords), coronal (view of both cricoid and thyroid cartilages), and sagittal (between vocal cords) planes for 3 min. Consistency of scanning positions for each patient was achieved by providing radiographers with labeled printouts to aid localization. Each scan session consisted of 2 min of scanning at rest (where the patient was free to swallow at their natural rate) and 1 min of active swallowing every 10 to 15 s (to ensure that a minimum of 3 swallow events were captured).