Page 32 - Towards personalized therapy for metastatic prostate cancer: technical validation of [18F]fluoromethylcholine

Chapter 2
The radiochemical purity was > 99.5% and no chemical impurities were detected as assessed by analytical radio/ultra-violet-HPLC (UV-HPLC). Residual concentrations of dibromomethane (0-8 ppm) and 2-(dimethylamino)ethanol (95±40 ppm) were determined by flame ionization detector - gas chromatography (FID-GC). Absence of bacterial endotoxins in the product was confirmed by an Endosafe portable test system (PTS) reader (Charles River) and all samples were tested for sterility.
PET/CT Imaging
All studies were performed on a Gemini TF-64 PET/CT scanner (Philips Medical Systems, Best, the Netherlands) with an axial field per view of 18 cm. Low-dose CT (LD-CT) was collected using a beam current of 30 to 50 mAs at 120 keV. CT was reconstructed using an image matrix size of 512x512 resulting in voxel sizes of 1.17x1.17 mm and a slice thickness of 5 mm. For PET, data were reconstructed by means of a raw action ordered subset expectation maximization algorithm using default reconstruction parameters. Time of flight (TF) information was used during reconstruction. Reconstructed images had an image matrix size of 144x144, a voxel size of 4x4 mm and a slice thickness of 5 mm.
All patients underwent the standard [18F]FCH image acquisition protocol at our institution: following the LD-CT, ‘early’ PET image acquisition started 2 min after intravenous injection of 4 MBq/kg [18F]FCH, using a 35 cm scan trajectory over the pelvic region (2 min/bed position); patients were asked to void 20 min post injection (p.i.), and at 30 min p.i. a ‘late’ whole body PET sequence was started, from mid-thigh to the skull vertex, again using 2 min acquisitions/ bed position. Patient preparation was similar to that required for FDG PET [28].
PET/CT data analysis
PET/CT images were evaluated by an experienced nuclear medicine specialist who first identified all lymph nodes with enhanced FCH uptake versus their direct background (on early and/ or late scan time points) within the field of view of the early scan trajectory. Lymph node diameters were measured using the CT component of the PET/ CT scanner, and standard CT and MRI, where available.
PET and LD-CT images were converted to ECAT 7 format and regions of interest (ROIs) were semi-automatically drawn around every pelvic LN that met the inclusion criteria mentioned above, using in-house developed software, as previously described [29, 30].
30