Biograph 16hr

A Biograph 16 HR PET/CT scanner (Siemens Healthineers) was used in the single-center study. Briefly, patients were fasted for more than 6 h; and before imaging, their blood glucose levels needed to be less than 8 mmol/L. ¹⁸F-FDG (Sumitomo HM-12, pH 4–8, radioactive purity > 95%, radioactive concentration > 370 MBq/ml) was then intravenously injected at a dose of 3.7 MBq/kg; the image acquisition was started 1 h later. CT image scan was preformed (tube voltage 120 kV, tube current 50 mAs, rotational speed 0.5 s/r, FOV 812 mm × 812 mm, 512 × 512 matrix, slice thickness 4 mm) from the vertex to the proximal legs. Low-dose CT was used for attenuation correction, and a standard B19f soft-tissue reconstruction kernel was used for CT images. Consequently, PET image scans (8-bed positions at 2.5 min each, FOV 812 mm × 812 mm, 144 × 144 matrix, slice thickness 4 mm) were acquired from the vertex to the proximal legs with correction for dead time, scatter, and decay. PET images were iteratively reconstructed in 3D mode using ordered subset expectation maximization (2 iterations, 24 subsets, and Gaussian filtering). CT and PET images were reconstructed at a slice thickness of 2.0 mm and an increment of 1.0 mm.

Patients underwent PET/CT scans both before CRT (pre-CRT) and after receiving 20 fractions of radiation doses (mid-CRT). PET/CT scans were obtained with a BIOGRAPH 16HR (Siemens Molecular Imaging, Knoxville, TN) with an axial field of view of 16.2 cm. All images were composed of 128 × 128 pixels with voxel dimensions of 4 × 4 × 4 mm. Patients fasted for at least 6 h before the administration of 0.2 mCi/kg or 7.4 MBq/kg body weight of 18F-FDG, which was produced onsite using Siemens Cyclotron (Eclipse ST 111, Siemens/CTI, Knoxville, TN), and they then rested for approximately 60 (range, 55–75) minutes before the PET scan. The 16-slice CT process was performed for attenuation correction with an X-ray tube voltage and current peak of 120 kV and 120 mA, respectively, a slice thickness of 5 mm, and a spacing of 4 mm. The images were reconstructed using a three-dimensional ordered subset expectation maximization algorithm and attenuation correction derived from the CT data.

¹⁸F-FDG PET/CT (Biograph 16HR; Siemens, Germany) examinations were acquired after fasting for 6 h and 60–75 min after intravenous injection of ¹⁸F-FDG (3.70–5.55 MBq/kg weight). The blood glucose level was below 120 mg/dl in all included patients before tracer injection. All patients had normal tidal breathing during PET and CT scans. Patients underwent low-dose CT scans (120–140 kV, 65 mA and 5.0 mm slice), followed by PET scans with six to eight bed positions (2 min per bed positions) per patient based on the height. The PET images were reconstructed with attenuation corrected CT using the ordered subset expectation maximization (OSEM) algorithm. Then, all dates were transferred in DICOM format to the Beth Israel PET/CT viewer plugin for FIJI and displayed as axial, coronal, and sagittal images. The SUVmax, SUVmean, MTV, and TLG of all lesions were delineated semiautomatically by the Beth Israel PET/CT viewer plugin for FIJI (http://sourceforge.net/projects/bifijiplugins/) (ImageJ distribution) (13 (link)).

PET/CT scans were performed using a Biograph 16 HR (Siemens Healthineers, Erlangen, Germany) or a Biograph 64 system (Siemens Healthineers, Erlangen, Germany). All patients were inquired to fast and avoid strenuous exercise at least 6 h before ¹⁸F-FDG injection, and the level of fasting blood glucose was no more than 7.0 mmol/L. Images were acquired approximately 60 ± 5 min after intravenous injection of 3.7 MBq of ¹⁸F-FDG per kilogram of body weight. Six or seven-bed positions were imaged from the base of the skull to the mid-thigh. PET images were obtained for 2–3 min per bed position. All image reconstructions were performed with the ordered-subset expectation maximization algorithm, incorporating a CT-based transmission map. PET images were reconstructed at 200 × 200 pixels using a Gaussian filter of 5.0 mm full width at half maximum value.