Page 52 - 89Zr-Immuno-PET:Towards a Clinical Tool to Guide Antibody-based Therapy in Cancer

Chapter 3
two iterations and 16 subsets followed by postsmoothing of the reconstructed image using a 5-mm FWHM Gaussian filter. Because images with attenuation correction showed high noise levels due to the low amount of radioactivity administered to the patients (for radiation exposure reasons), OSEM reconstructions without attenuation correction were done as well. Reconstructions without attenuation correction provided images with a quality similar to that of the diagnostic FDG scans (next paragraph). Interpretation of the scans was therefore performed using these non-attenuation-corrected images and was based on asymmetry and retention of activity, especially on late images.
In case of FDG-PET scanning, all patients fasted overnight before the PET study. Whole body scans were made using approximately seven bed positions from the base of the skull to the pelvis. At each bed position, a 7-minutes emission scan in two-dimensional mode was made. Scanning started ~ 60 minutes after i.v. injection of 370 MBq 18FDG (Cyclotron BV, Amsterdam, the Netherlands). All scans were corrected as described above for the 89Zr scans; however, no attenuation correction was done. The PET images were evaluated visually using standard ECAT (CTI/Siemens) software: foci with increased uptake versus background were considered abnormal, taking physiological biodistribution of FDG into account.
CT and MRI were scored by one experienced radiologist (J.A. Castelijns), FDG-PET by one experienced nuclear physician (E.F.I. Comans), whereas immuno-PET examinations were scored by consensus of two experienced nuclear physicians (E.F.I. Comans and J.C. Roos). CT/MRI and nuclear imaging examinations were performed in an independent and blinded way, without knowledge of the pathologic outcome. Observers were not informed about the sites of tumor involvement. All patients had neck dissections performed 6 to 8 days after the administration of the radio-immunoconjugate. After fixation, all palpable and visible lymph nodes were dissected from the surgical specimen and cut into 2- to 4-mm-thick slices for microscopic examinations. The different slices of one lymph node were examined by a pathologist and the percentage tumor involvement was estimated. The outcome of the histopathologic examination of the neck dissection specimen was used as the gold standard.
For topographical examination, the findings were recorded per side as well as per lymph node level according to the classification of the American Academy of Otorhinolaryngology and Head and Neck Surgery (15). Patients underwent either CT or MRI or both. For evaluation of overall anatomic imaging results, the
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