PET/CT evaluation of prostate cancer patients with Al^sup 18^F-PSMA-HBED-CC: a head-to-head comparison with ^sup 68^Ga-PSMA-HBED-CC

Objectives: PSMA-targeting PET tracers have become available for imaging due to the over expression of PSMA in prostate cancer (PC) lesions. 68Ga-PSMA-HBED-CC (68Ga-PSMA-611, ABX) PET/CT represents a clinically relevant and commonly used technique for the evaluation of these patients. 68Ga labeled compounds are produced with generators providing limited activity per synthesis (1 to 4 patients per batch). 18F-labelled tracers, like Al18F-PSMA-HBED-CC (Al18F-PSMA-611, ABX), can be produced in larger scale with a lower positron energy that potentially offers higher image quality as well as the possibility to acquire late images. To test this hypothesis, we compared on a head-to-head basis the image quality and detection performance of both radiopharmaceuticals in a sample of PC patients. We analyzed 15 patients (median age: 66, range: 52-78 years) who underwent both 68Ga-PSMA and Al18F-PSMA PET/CT scanning within a time window of 1-2 weeks, 60 minutes after the i.v. administration of 2.0 and 4.0 MBq/kg, respectively. Studies were performed with a 64-slice PET/CT scan with TOF correction. Fourteen patients had high-risk biopsy proven PC prior therapy (Gleason > 7, PSA: 7.6-83 ng/mL). The remaining patient was imaged prior to 177Lu-PSMA therapy and had hormone-resistant metastatic disease (PSA: 21 ng/mL). The study was approved by the institutional Ethics Committee. We measured the SUVmax in all abnormal foci as well as the SUVmax ratio (SR) in all coincident lesions, defined as SUVmax lesion/SUVmax background. Gluteal musculature was selected as background. Al18F-PSMA PET/CT demonstrated abnormal findings in all patients with images of high visual quality. Besides, 7/14 patients submitted for initial staging had evidence of metastatic disease. Abnormal foci (n=60) were seen in the following sites: prostate gland (n=17), lymph nodes (n=6), bone (n=36) and lung (n=1). Thirteen bone lesions were positive only with this tracer (22%), whereas the remaining 47 (78%) were also abnormal for 68Ga-PSMA. For concordant lesions (n=47), we found a significantly higher SR for Al18F-PSMA compared to 68Ga-PSMA: 10.7 (2.7-37.4) and 6.0 (1.7-32.3), median (range), for each tracer, respectively (P=0.0003). Furthermore, a significant correlation was found between the SUVmax of both radiopharmaceuticals (r=0.43, P=0.02). Al18F-PSMA PET/CT is a promising imaging technique for the evaluation of PC patients. Further studies are needed to confirm these preliminary results.