The role of 18F-Choline (FCH) PET/CT in detecting prostate cancer (PC) lesions, both during staging and restaging procedures, has been established in several studies. In some papers a dual-time acquisition protocol is suggested, with a dynamic acquisition of the pelvic region just after tracer injection. FCH, in fact, undergoes renal elimination and the detection of local or regional metastatic disease may be negatively influenced by the presence of physiological activity in the urinary tract in late acquisitions. Aim of the study was to evaluate the incremental diagnostic value of the dual-time acquisition protocol in a series of PC patients undergone FCH PET/CT in our department.
104 PET/CT scans in 94 consecutive patients, performed between February 2011 and October 2014, were considered in the retrospective analysis. The inclusion criteria were: 1) initial staging (18 studies): histologically-proven high-risk PC (Gleason score > 7 and/or PSA > 20 ng/ml); 2) recurrent disease (86 studies): biochemical relapse after primary treatment with curative intent. All scans were acquired using an integrated PET/CT camera (equipped with a full-ring dedicated PET scanner and a sixteen-slices CT scanner) in dual-time modality, with a dynamic acquisition (60 seconds x 10 frames) of the pelvic region just after tracer injection (3,5 MBq/Kg of 18F-fluoromethylcholine) followed by a whole-body acquisition 60 minutes post injection, from vertex to mid-thigh. A protocol with low-dose CT scan and 3D acquisition of PET data (7-8 bed positions, 2min/bed) was used. PET/CT images were visually analyzed by two nuclear medicine physicians: findings of dynamic frames and whole-body scans were evaluated and compared with the results of endorectal ultrasound, MRI and/or CT of the pelvis.
37 out of 104 studies were negative (both dynamic and whole-body images). Out of 60 positive scans, 12 showed lesions only outside the field-of-view of the dynamic acquisition, while 48 had pathological uptakes also in pelvic region. Among these latter ones, 45 showed a feeble uptake of the tracer in early images, confirmed and incremented in late images; in two cases pathological uptake was seen only in late images and in one case only in early dynamic images (bladder wall). 6 scans were ambiguous both in early and late images (4 lesions confirmed with further examinations), while one was negative in early images and ambiguous in late ones (right femoral head: no lesions found in a following CT scan).
In our series of PC patients, the use of an early dynamic acquisition of the pelvic region in FCH PET/CT scans led to a better diagnostic performance in just two cases out of 104 (2/55 considering only positive or ambiguous studies with lesions inside the field-of-view of the dynamic images). In 45 positive cases, findings of early images were comparable with those of late scans, with a theoretical increased diagnostic confidence. In the other 57 studies, early images were completely useless. The results of our analysis call into question the real usefulness of the dual-time acquisition protocol in FCH PET/CT scans performed during staging or restaging of PC patients.

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