%0 Journal Article %A Arthur Braat %A Bastiaan van Nierop %A Hugo de Jong %A Marnix Lam %A Gerard Krijger %A Bart de Keizer %T The effect of 68Ga-PSMA-11 (HBED-CC) activity concentration reduction on image quality and detection of prostate cancer metastases %D 2017 %J Journal of Nuclear Medicine %P 391-391 %V 58 %N supplement 1 %X 391Objectives: 68Ga-PSMA-11-PET/CT is increasingly used in clinical practice for primary staging or detecting recurrent prostate cancer. A reduction of the administered radioactivity will reduce patient radiation dose. Moreover, as the 68Ga-yield decreases in an older 68Ge/68Ga generator less patient doses can be prepared per eluate when upholding the current prevailing dose in the Netherlands (2 MBq/kg). Therefore, a reduction of the administered activity could also help to meet the high clinical demands and help to cut costs for the expensive generators. The goal of this study was to investigate if 68Ga-PSMA-11 activity concentration could be reduced while maintaining diagnostic quality.Methods: Twenty-five males with prostate cancer referred to our center for a 68Ga-PSMA-11-PET/CT were prospectively included after informed consent was obtained. After standard PET/CT (2.0 MBq/kg) an additional list-mode scan was acquired between the kidney and bladder and reconstructed to simulate 0.5, 1.0, 1.5 and 2.0 MBq/kg scans (Fig. 1), resulting in a total of 100 datasets. During a consensus reading two nuclear medicine physicians identified all metastases on the standard PET/CT, as baseline assessment for comparison to the blinded list-mode datasets. At least one week later, all blinded datasets were independently assessed in a random order by both physicians on image quality (3-point scale: unacceptable, acceptable, good) and the presence of metastases (2-point scale: yes or no). If metastases were present, the number of metastases and location were described.Results: A total of 55 metastases were present in the datasets FOV. Five patients had lymph node metastases, two patients had lymph node + bone metastases, and 18 patients had no metastases. Smallest metastasis was a 3-mm lymph node. Image quality of the datasets was deemed acceptable to good by observer 1 at 2.0 and 1.5 MBq/kg in 100% and 82%, respectively, while it was evidently decreased in the 1.0 and 0.5 MBq/kg datasets to 40% and 4%, respectively. Observer 2 deemed image quality acceptable to good at 2.0, 1.5 and 1.0 MBq/kg in 100%, 96% and 84%, respectively, while it was evidently decreased at 0.5 MBq/kg datasets to 48%. In patient based analysis the number of lymph node metastases in the 0.5, 1.0, 1.5, and 2.0 MBq/kg reconstructions was correctly identified by observer 1 in 84%, 80%, 84% and 84%, respectively, whereas observer 2 correctly identified 72%, 68%, 72% and 72%, respectively. Bone metastases were all correctly identified by observer 1 and 2, however observer 2 also identified one additional bone lesion in one patient in the 1.0, 1.5 and 2.0 MBq/kg reconstruction.Conclusion: These results suggest 68Ga-PSMA-11 activity concentration can be reduced to 1.5 MBq/kg with subjective acceptable loss of image quality and without compromising detection of metastases. Research Support: None %U