Table 5.

Different demands of MRI acquired for diagnostic and radiotherapy purposes in cervix and rectal cancer

	MRI for diagnosis	MRI for radiotherapy
Couch	Soft, often concave Maximized for patient comfort	Needs to be flat, the same as in RT delivery
Patient positioning	Comfortable Supine	As for RT delivery Supine
Immobilization devices	None	Combifix knee support to stabilize pelvis
Bowel artefact management	IM Buscopan Anterior abdominal wall compression Saturation bands	IM Buscopan may be used in MRI simulation but may not be acceptable during daily treatment within MRI treatment workflow
Bladder status	Empty	Full
Coil placement	Pelvic coil centred on tumour	Anterior coil supports prevent distortion of external body contour Customized MR simulators may incorporate posterior coils into a flat couch
Field strength	Increasing strength improves signal to noise, but is more expensive and requires more room	Increasing field strength increases geometric distortion
Coverage	High resolution FOV limited to tumour	High resolution FOV must encompass entire tumour target Sequences including external body contour required for dose calculation
Preferred sequence	2d T 2W high resolution at tumour with ≤3 mm slice thickness, and voxel size <1 mm Imaging plane perpendicular to the rectum or cervical canal	T 2W 3d < 1 mm isotropic voxel size for target delineation Imaging plane true axial acquired perpendicular to the system
Geometric accuracy	Less important	Essential to localize the target
Electron density/ material composition information	Not required	Not required in a CT/ MRI combined workflow, but essential in MR-only simulation and MR treatment workflow

FOV, field of view;RT, radiotherapy.