Bright speed 16

Patients in our cohort were scanned for treatment planning using Bright Speed 16 (GE Healthcare, Milwaukee, WI, USA) or SOMATOM Definition Flash AS (Siemens Healthcare, Erlangen, Germany) with a pixel size of <1.0 mm and a slice thickness of <2.5 mm.
We used either an analytical anisotropic algorithm or an Acuros XB dose calculation algorithm equipped in an Eclipse treatment planning system (TPS; Varian Medical Systems, Palo Alto, CA, USA) with a calculation grid of 2 mm. The number of patients treated with the Varian CL2100, CLINAC iX, and TrueBeam STx were 41, 109, and 3, respectively. The dose to normal lung was constrained within V5Gy < 65%, V20Gy < 35%, and MLD < 20 Gy, considering the RTOG0617 protocol [13 (link)] and while maintaining an adequate target volume coverage at the time the treatment plans were created.
Both cDVH and dDVH were computed from a dose–volume curve calculated using CT images, a structure set, and calculated dose exported from the Eclipse TPS in-house using MATLAB (MathWorks, Natick, MA, USA). cDVH features, including cV_5Gy and cV_10Gy–cV_60Gy (in 10-Gy increments), and MLD, were also computed. Each dDVH feature was calculated between 5 and 60 Gy with dose bins of 2–8 Gy in 2-Gy increments (resulting in four patterns).

Whole lung volumetric CT scanning was performed using a 16-row multi-detector CT scanner (BrightSpeed 16; General Electric Healthcare, Milwaukee, USA). Scanning was performed from lung apices to the diaphragm during a single breath-hold at deep inspiration, using the following parameters: tube voltage 120 kVp; automatic tube-current modulation; gantry rotation speed of 0.5 s; and beam collimation of 16 × 0.625 mm. Thin-section CT data were reconstructed at 0.625 mm thickness using standard filtered back-projection algorithm; iterative reconstruction algorithms were not used.

All unenhanced and contrast-enhanced CT images from the two institutions were obtained using multislice spiral CT scanners (uCT 530; United Imaging, Shanghai, China; Discovery CT750 HD or BrightSpeed 16; GE Healthcare, Chicago, IL, USA). The imaging protocols are described in the Appendix. The image was reconstructed to 2.5-mm, or 5-mm thickness using a standard algorithm and was then uploaded to the image archiving and communication system (PACS).

To study the distribution of Ho inside the tumor and evaluate the development of tumor size over time, CT acquisitions were periodically performed. A CT scanner (GE BrightSpeed 16) was used at Voxcan to perform CT acquisitions. The imaging characteristics and CT acquisition protocol before and following the U87 cells implantation was described in previous studies (17 (link), 19 (link)).
Pre- and post-operative CT imaging was performed on the day of Ho suspension injection (D14) to assess tumor positioning and verify the distribution and location of injected Ho, respectively. After the treatment, the evolution of injected Ho suspension and the therapeutic effect of this radiation therapy were studied in group 1 (radioactive) and 2 (non-radioactive) by performing the first post-injection CT scan, 5 days after the intervention and then every ten days. For all minipigs, a manual segmentation of the tumor was performed after each post-operative CT acquisition. In this fashion, the changes of tumor size could be studied over time.

The study cohort dataset (Italy) was acquired with 2 CT scanners, a LightSpeed Pro 16, and a BrightSpeed 16 (both GE Healthcare). The CT examinations were performed in supine position in sustained deep inspiration. In case of more than two CT examinations per patient, each pair of consecutive CT scans was included. Therefore, an individual patient could have 1–4 pairs of scans. For the replication cohort, data was acquired with a Siemens Sensation Cardiac 64 scanner in supine position with deep inspiration. Each patient had 2 scans, one at the time of the diagnosis and another one at the last seen examination.

All examinations were performed with a dedicated hybrid SPECT-CT (Discovery NM/CT 670, GE Healthcare, Milwaukee, USA). The integrated CT component is identical in construction to a 16-slice-CT used in diagnostic CT imaging (model: Bright Speed 16, GE Healthcare, Milwaukee, USA). The standard CT reconstruction was performed by filtered back projection (FBP). Additionally, the system includes an iterative CT reconstruction algorithm (ASIR, Adaptive Statistical Iterative Reconstruction, GE Healthcare, Milwaukee, USA) established in diagnostic CT imaging [14 (link),20 (link)–22 (link)]. ASIR uses the images reconstructed by FBP as starting information. The parameter ASIR-level (from 0% to 100% selectable in increments of 10%) defined the merging of the iterative reconstruction and the FBP reconstruction. The imaging protocol was chosen in accordance with the basic scan protocol for LD-CT in SPECT-CT imaging in routine clinical practice. Imaging and reconstruction protocols are defined below.