16 slice brilliance big bore ct scanner

A Philips 16-slice Brilliance big-bore CT scanner (Philips Medical Systems, Amsterdam, The Netherlands) was used for imaging. The patients were immobilized with a thermoplastic mold in a supine position or immobilized with an abdominal pelvic fixator in a prone position. Scanning was performed from the upper border of the T2 vertebra to the middle of the femur with a slice thickness of 3 mm and a slice gap of 3 mm.

Patients with cervical cancer under postoperative IMRT and VMAT in authors’ hospital from January 2018 to September 2020 were retrospectively reviewed in this study. All the patients were immobilized by a thermoplastic abdominal fixation device in the supine position. CT simulation was scanned from the iliac crest to the ischial tuberosities with a 16‐slice Brilliance Big Bore CT scanner (Philips Healthcare, Cleveland, OH) at 3‐mm thickness. Intravenous contrast was injected during CT scan to enhance the contrast of target volumes. CT images were transferred using the Digital Imaging and Communications in Medicine format and reconstructed using a matrix size of 512 × 512.
Manual segmentations of the CTV and OARs were delineated and verified by two senior radiation oncologists with more than 10 years of clinical experience for cervical cancer and were taken as a ground truth for the evaluation of automatic segmentations. The target contour guideline of the Radiation Therapy Oncology Group (RTOG) 0418 and its atlas on the RTOG website was followed.²¹ After the delineation, central vaginal CTV and regional nodal CTV were interpolated into a combined CTV for the sake of easy modeling of automatic segmentation.

All CT and CBCT images were acquired as part of the patient's routine treatment course.
Original planning CT and re‐planning CT images were acquired on a Philips Brilliance Big Bore 16‐slice CT scanner (Philips Healthcare, Cleveland, OH). CT images were acquired with a full‐fan 120 kVp beam. The scanning parameters used to acquire each planning and re‐planning CT, can be found in Table S2 and S3, respectively. The CT images were reconstructed using the device's default filtered back‐projection algorithm, with a default slice thickness of 3 mm and slice size of 512 × 512. The voxel size varied between image sets as the CT operator would select the smallest field of view (FoV) required to cover the patient.14CBCT images were acquired with either a Varian Truebeam or Clinac iX On‐Board Imaging (OBI) system (Varian Medical Systems, Palo Alto, CA). CBCT scans were acquired with either a standard (20 mA) or low‐dose (10 mA) protocol using a full‐fan 100 kVp beam with a full bow‐tie filter. The scanning parameters used to acquire each CBCT can be found in Table S4. CBCT scans were reconstructed by the treatment unit's OBI software (v 2.0‐2.1) which uses a Feldkamp‐Davis‐Kress (FDK) reconstruction algorithm with a Ram‐Lak filter.15, 16 Image slices were 384 × 384 in size when acquired with the Clinac iX's system, and 512 × 512 when acquired with the Truebeam's system.

Our clinic utilizes a Phillips Brilliance Big Bore 16‐slice CT scanner for patient simulation. Using Gammex 467 tissue characterization plugs inside acrylic phantoms, we studied various CT acquisition settings and phantom sizes to establish imaging protocols and create a CT‐to‐density table from which the TPS estimates relative stopping power ratios for proton beam dose calculations.5, 13, 14 These protocols were tested in the TPS by comparing the mass densities determined by the protocols in patient CT datasets against reference ICRU 49 data for known human tissues.5Accurate dose calculation in proton therapy depends on proton relative stopping power ratios. RayStation uses an internal mass density to stopping power conversion during dose calculation. Individual CT voxels are assigned a known biological material based on mass density. The stopping power is then calculated on the fly using the density of the voxel, the properties of the known material (e.g., mean excitation potential and elemental composition) and the Bethe‐Bloch equation. A stoichiometric calibration was also independently performed by an external proton physicist to verify stopping powers calculated by RayStation.