Background68Ga-PSMA PET/CT has an important role in assessment of prostate cancer patients with biochemical recurrence and is evolving in staging high- and intermediate risk disease. The aim of present study was to describe the metastatic patterns and frequency of involved sites of prostate cancer and to assess the incidence of benign Ga68-PSMA avid PET/CT findings in a large patient population.Methods68Ga-PSMA PET/CT studies performed in two tertiary medical centers over a period of 24 months were retrospectively reviewed. The incidence and location of pathological 68Ga-PSMA avid foci, suspicious to represent malignancy, as well as those of unexpected benign foci of increased 68Ga-PSMA activity were documented and analyzed.ResultsThere were 445 68Ga-PSMA studies in 438 men (mean age 72.4, range 51–92 years) with prostate cancer referred for biochemical failure (n = 270, 61%), staging high-risk disease (n = 112, 25%), response assessment (n = 30, 7%), follow-up (n = 22, 5%) and suspected bone metastases (n = 11, 2%). 68Ga-PSMA avid disease sites were observed in 319 studies (72%), in 181 studies (67%) for biochemical recurrence, 94 studies for staging (84%) (p < 0.05), in 22 studies for response assessment (73%), 10 follow up studies (45%) and in five patients with suspected bone metastases (45%). 68Ga-PSMA avid lesions were most commonly detected in the prostate (n = 193, 43%), loco-regional spread (n = 51, 11%), abdomino-pelvic nodes (n = 129, 29%) and distant metastases (n = 158, 36%), including bone metastases (n = 11, 25%), distant lymphadenopathy (n = 29, 7%) and other organs (n = 18, 4%). Distant 68Ga-PSMA-avid metastases were commonly seen in patients with biochemical recurrence (14/21 lesions), but were not seen in patient referred for staging (p < 0.013). There were 96 non-malignant 68Ga-PSMA avid foci in 81 studies, most common in reactive lymph nodes (n = 36, 38%), nonmalignant bone lesions (n = 21, 22%), thyroid nodules (n = 9, 9%), ganglions (n = 9, 9%) and lung findings (n = 8, 8%).ConclusionThe distribution of 68Ga-PSMA avid metastatic lesions is similar to data previously reported mainly from autopsy with comparable detection rates, indicating 68Ga-PSMA PET/CT is an accurate detection tool in patients with metastatic prostate cancer. If confirmed by further prospective studies 68Ga-PSMA PET/CT should be included in the guidelines to evaluate disease extent in these patients.

The accuracy of lutetium-177 ( 177 Lu) radiotracer concentration measurements using quantitative clinical software was determined by comparing in vivo results for a digital solid-state cadmium-zinc-telluride SPECT/CT (single photon emission computed tomography / x-ray computed tomography) system to in vitro sampling. First, image acquisition parameters were assessed for an International Electrotechnical Commission body phantom emulating clinical count rates loaded with a "lung" insert and 6 hot spheres with a 12:1 target-to-background ratio of 177 Lu solution. Then, the data of 28 whole-body SPECT/CT scans of 7 patients who underwent 177 Lu prostate membrane antigen ( 177 Lu-PSMA) radioligand therapy was retrospectively analyzed. Three users analyzed SPECT/CT images for in vivo urinary bladder radiotracer uptake using quantitative software (Q.Metrix, GE Healthcare). In vitro radiopharmaceutical concentrations were calculated using urine sampling obtained immediately after each scan, scaled to standardized uptake values (SUVs). Any in vivo/in vitro identity relations were determined by linear regression (ideally slope=1, intercept=0), within a 95 % confidence interval (CI).Phantom results demonstrated lower quantitative error for acquisitions using the 113 keV 177 Lu energy peak rather than including the 208 keV peak, given that only low-energy collimation was available in this camera configuration. In the clinical study, 24 in vivo/in vitro pairs were eligible for further analysis, having rejected 4 as outliers (via Cook's distance calculations). All linear regressions (R 2 ≥ 0.92, P<0.0001) provided identity in vivo/in vitro relations (95 % CI), with SUV averages from all users giving a slope of 1.03±0.09, an intercept of −0.25±0.64 g/mL, and an average residual difference of 20.4 %.Acquiring with the lower energy 177 Lu energy peak, solid-state SPECT/CT imaging 3 provides an accuracy to within ~20 % for in vivo urinary bladder radiotracer concentrations. This non-invasive in vivo quantitation method can potentially improve diagnosis, improve patient management and treatment response assessment, and provide data essential to 177 Lu dosimetry.

68Ga-PSMA-11, the radiotracer of choice for imaging of prostate cancer (PCa), may be produced with several radiolabeling techniques. Current study aimed to analyze various imaging parameters of the cold kit methodology produced 68Ga-PSMA-11 (68Ga-isoPROtrace-11) and to compare the results to available data in literature. Eighty 68Ga-PSMA-11 positron emission tomography/ computed tomography (PET/CT) scans were evaluated. 68Ga-isoPROtrace-11 for all the studies was produced by the room temperature cold kit methodology using a lyophilized ready-to-use vial. Normal biodistribution of the tracer was recorded by measuring mean standardized uptake value (SUVmean) and compared to the available published data. Pathological tracer uptake was measured using SUVmax in prostate gland (48 patients), lymph nodes (22 patients), bones (20 patients) and soft tissues (6 patients). Average tumour-to-background and tumour-to-liver contrast ratios were calculated. The data of 80 68Ga-PSMA-11 PET/CT scans were analyzed. Radiochemical purity of the tracer was 91% or more. The highest normal tissue uptake value of 68Ga-isoPROtrace-11 was found in the kidneys (average SUVmean 41.7), followed by the parotid (average SUVmean 14.5) and submandibular glands (average SUVmean 13.02). Normal prostate tissue showed low tracer uptake (average SUVmean 2.4). The biodistribution of 68Ga-isoPROtrace-11 in normal tissues was found to be similar to other published results. Pathological uptake (average SUVmax ± standard deviation) in prostate gland was 11.3 ± 7.5, in lymph node metastases 14.6 ± 13.7, in bones 15.9 ± 15.9 and 24.2 ± 16.4 in soft tissues. Average tumour uptake of 68Ga-isoPROtrace-11 in prostate was 11.3, in lymph node metastases 14.6, in bone metastases 15.9 and in soft tissue metastases 24.2. Average tumour-to-liver and tumour-to-mediastinal blood pool ratios were 2.7 and 13.54 respectively. This study presents biodistribution data of 68Ga-isoPROtrace-11 in a large PCa patient subset, showing clinical applicability of the tracer. Using cold kit technology may enable a high quality and easy labeling process. Prostate cancer (PCa) is the second most frequent malignancy (after lung cancer) in men worldwide 1. The most common diagnostic procedures for diagnosing PCa for over 30 years have been physical examination (i.e., the digital rectal examination), serum prostate specific antigen (PSA) levels, imaging tests and biopsy, either trans-rectal, trans-perineal, blind or image-directed. According to guidelines, imaging should be performed for the detection and characterization of disease in order to select treatment or guide patient management. Different anatomic and functional imaging tests are recommended depending on the patient's risk group 2. One of the major developments, occurred in molecular imaging in recent years, involves detection of prostate-specific membrane antigen (PSMA) with positron emission tomography/computed tomography imaging technique (PET/CT). PSMA is a cell surface transmembrane protein that is over-expressed in most P...

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