Optima 640

We conducted our simulations with SIMIND. While SIMIND has been validated for multiple SPECT studies [33 (link)], [42 ], we further validated the accuracy of our simulation approach in the context of α-RPT SPECT. For this purpose, we compared the projection data obtained with our simulation approach to that obtained on an actual scanner. More specifically, we considered a NEMA phantom that was scanned on a GE Optima 640 SPECT system with the HEGP collimator using the procedure as described in more detail in Section III-D. We then modeled this acquisition using our simulation approach. For our simulation, the activity map was designed to simulate the known ²²³Ra activity concentrations filled in the physical phantom and the attenuation map of the NEMA phantom was derived from the CT scans. Then, we generated the simulated projections using SIMIND, modeling the same acquisition process as described later in Section III-D1. The profiles of the projection data at four angular positions spaced uniformly over 360° obtained with the scanner and that with the simulation approach were compared directly, without any normalization. The match of these profiles, as we see later in the results section, provided evidence of the accuracy of our simulations.

Clinical data were acquired at the Royal Surrey NHS Foundation Trust in Guildford, UK, using the GE Optima 640 SPECT/CT system for 5 patients who were treated with SIRT with ${}^{90}$ Y resin microspheres (SIR-Spheres). The patient data involved in this study were anonymised. The injected activity was in the range between 1.5 and 2.2 GBq and the SPECT acquisitions lasted 40 min, with 120 20 s projections. The energy window was set between 75 and 225 keV. A medium energy general purpose parallel-hole MEGP collimator was used. The CT image was acquired for attenuation estimation and was used as anatomical image in the HKEM and FHKEM.

To evaluate vendor, collimator, and device-specific effects on low activity ⍺-emitter SPECT acquisition, we evaluated three dual-head SPECT/CT cameras: a Discovery 670 and an Optima 640 SPECT/CT from GE and a Symbia T6 from Siemens. All the cameras were equipped with their specific set of collimators: MEGP (medium energy general purpose) for GE or MELP (medium energy low-penetration) for Siemens and HEGP (high-energy general purpose) for both vendors. Enclosed in Table 2 and Table 3 are the camera system and collimator characteristics of each unit, respectively.