Optima ct580w

Computed tomography (CT) imaging in treatment planning was performed using Optima CT580W (General Electric Medical Systems, Waukesha, WI, United States). Linear accelerator TrueBeam (Varian Medical Systems, Palo Alto, CA, United States) with an X-ray energy of 6 MV was used for radiation therapy. The treatment planning system used was Eclipse version 16.1 (Varian Medical Systems, Palo Alto, CA, United States), and PlanIQ version 2.2 (Sun Nuclear) was used for treatment plan evaluation. In PlanIQ, FDVH (a dose reduction estimation tool for OARs) was used.

All patients underwent image acquisition using the Standard Wing Board MTWB09 (CIVCO Radiotherapy, Orange City, IA, USA) with both arms raised, and a treatment-planning CT simulator (Optima CT580W; General Electric Medical Systems, Waukesha, WI, USA) was also used. A breathing monitoring system, Abches III (APEX medical, Tokyo, Japan), was used to monitor breath-holding. The respiratory control protocol instructed the patients to hold their breath at the end-expiratory stage and moved the mark to a position where the Abches III accessory pointer could be held reproducibly (Fig. 1). The patient can visually see the pointer and mark positions according to the respiratory level by wearing a special mirror. The fulcrum was adjusted so that the operating range of the pointer was appropriate. For image acquisition by a CT simulator, the field of view was 500 mm and the slice thickness was 2.5 mm. The image acquisition was performed in helical mode and the scan time was ~10 s per scan. The patient held their breath for several times only when the area that could be imaged was narrowed in 10 s. The imaging range was set such that multiple breath-holdings was avoided in the area where the tumor was located. The time necessary to enter and exit the CT simulator room was ~1 h and the time provided for patients to practice holding their breath was ~30 min.

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.