Determination of optimal 68Ga-PSMA PET/CT imaging time in prostate cancers by total-body dynamic PET/CT.

Abstract

68Ga-PSMA PET/CT has been widely used in patients with prostate cancer. Due to the limited axial field of view of conventional PET scanners, whole-body dynamic 68Ga-PSMA PET/CT has not been performed. We investigated the time-activity curves (TACs) of prostate cancer pathological lesions and physiologic bladder activity to determine the optimal 68Ga-PSMA PET/CT imaging time by total-body (TB) PET/CT. Dynamic TB-PET performed on 11 patients with prostate cancer was analyzed. TACs were obtained by drawing regions of interest in normal organs and pathological lesions (primary prostate lesions and lymph nodes and bone metastases). We evaluated the 68Ga-PSMA uptake pattern of normal organs, urinary bladder, and pathological lesions. The urinary bladder TAC increased slowly between 180 and 330s post-injection and then rapidly between 5.5 and 60.0min post-injection. The pathological lesion uptake increased rapidly during the first 5min post-injection and then slowly through the remaining 55min. Six minutes post-injection was the optimal time with the highest pathological lesion SUVmean values still higher than the urinary bladder activity value. However, these prostate lesion, lymph node metastasis, and bone metastasis SUVmean values were one-third, one-half, and one-half the corresponding values 60min post-injection, suggesting that early imaging might miss low PSMA uptake lesions. A minimum of 35min post-injection was required for the pathological lesions to have SUVmean values similar to the corresponding values at 60min post-injection (all P > 0.05), even though the pathological lesion SUVmean values showed a continuous upward trend through the 60min. Combining early dynamic 68Ga-PSMA PET (75-360s) and conventional static imaging 60min post-injection could avoid the urinary bladder activity interference to better detect pathological lesions and lesions with relatively low PSMA uptake. The pathological lesion SUVmean values at 35-59min and 60min post-injection were similar, so 68Ga-PSMA PET imaging could also be made at 35-59min post-injection.