Hispeed dx i spiral

A helical CT scanner (GE HiSpeed DX/i Spiral) was used for simulation CT imaging acquisition (slice thickness was 2.5 mm). Patients were scanned in supine position on a flat table-top, without specific bowel preparation and following a bladder filling protocol. No intravenous contrast has been used.

Each patient, underwent a 0.35 T MRI simulation (ViewRay Inc., Mountain View, CA, USA) subsequently (within 20 minutes) to a CT simulation (GE, Optima CT580 W, HiSpeed DX/I Spiral), both acquired with the same immobilization and positioning devices.
Patients were immobilized in supine position with both arms above their head, using a dedicated MR compatible modular immobilization device (Fluxboard™, Macromedics®, The Netherlands).
Additionally, during the MRI simulation, a cine MRI was acquired to evaluate patient’s compliance to properly maintain deep inspiration breath hold (DIBH) to decide if breath-hold treatment was suitable. Two parameters were set to quantitatively evaluate DIBH patient’s compliance: boundary and ROI%. Boundary is a defined margin from CTV, taking target intra-fraction maximum allowed motion into account. ROI% is the maximum allowed percentage of the target volume outside the defined boundary to keep the delivery going: if this threshold exceeds, the beam delivery is interrupted. Usually, ROI% for LAPC OA MRgRT was set to 5%, boundary to 3 mm. DIBH evaluation was performed only during the MRI simulation and consequentially the CT simulation was acquired accordingly, avoiding extra CT scan acquisition, in particular 4D CT.