Search

Neuroendocrine neoplasms (NEN) are rare and heterogeneous tumors, originating mostly from the gastro-entero-pancreatic (GEP) tract followed by the lungs. Multidisciplinary discussion is mandatory for optimal diagnostic and therapeutic management. Well-differentiated NEN (NET) present a high expression of somatostatin receptors (SSTR) and can be studied with [68Ga]-DOTA-peptides ([68Ga]Ga-DOTANOC, [68Ga]Ga-DOTATOC, [68Ga]Ga-DOTATATE) PET/CT to assess disease extension and the eligibility for peptide receptor radionuclide therapy (PRRT). SSTR-analogues labelled with 90Y or 177Lu have been used since mid-90s for NET therapy. PRRT is now considered an effective and safe treatment option for SSTR-expressing NET: following the approval of 177Lu-DOTATATE by FDA and EMA, PRRT is now part of the therapeutic algorithms of the main scientific societies. New strategies to improve PRRT efficacy and to reduce its toxicity are under evaluation (eg, personalization of treatment schemes, the selection of the most suitable patients, improvement of response assessment criteria, optimization of treatment sequencing, feasibility of PRRT-retreatment, combination of PRRT with other treatments options). Recently, several emerging radiopharmaceuticals showed encouraging results for both imaging and therapy (eg, SSTR-analogues labelled with 18F, SSTR-antagonists for both diagnosis and therapy, alpha-labelling for therapy, radiopharmaceuticals binding to new cellular targets). Aim of this review is to focus on current knowledge and to outline emerging perspectives for NEN's diagnosis and therapy., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Objectives: To assess how patients' dependent parameters may affect [68Ga]Ga-DOTANOC image quality and to propose a theoretical body mass index (BMI)-adjusted injected activity (IA) scheme, to improve imaging of high weight patients., Methods: Among patients prospectively enrolled (June-2019 and May-2020) in an Institutional Ethical Committee-approved electronic archive, we included those affected by primary gastro-entero-pancreatic (GEP) or lung neuroendocrine tumour and referred by our Institutional clinicians (excluding even minimal radiopharmaceutical extravasation, movement artefacts, renal insufficiency). All PET/CT images were acquired following EANM guidelines and rated for visual quality (1 = non-diagnostic, 2 = poor, 3 = moderate, 4 = good). Collected data included patient's body mass, height, BMI, age, IA (injected activity), IA/Kg (IAkg), IA/BMI (IABMI), liver SUVmean, liver SUVmax standard deviation, liver-signal-to-noise (LSNR), normalised&#95;LSNR (LSNR&#95;norm) and contrast-to-noise ratio (CNR) for positive scans and were compared to image rating (poor vs moderate/good)., Results: Overall, 77 patients were included. Rating concordance was high (agreement = 81.8%, Fleiss k score = 0.806). All patients' dependent parameters resulted significantly different between poor-rated and moderate/good-rated scans (IA: p = 0.006, IAkg: p =< 0.001, body weight: p =< 0.001, BMI: p =< 0.001, IABMI: p =< 0.001). Factors significantly associated with moderate/good rating were BMI ( p =< 0.001), body weight ( p =< 0.001), IABMI ( p =< 0.001), IAkg ( p = 0.001), IA ( p = 0.003), LSNR&#95;norm ( p = 0.01). The BMI-based model presented the best predictive efficiency (81.82%). IABMI performance to differentiate moderate/good from poor rating resulted statistically significant (IA-AUC = 0.78; 95% CI: 0.68-0.89; cut-off value of 4.17 MBq*m 2 /kg, sensitivity = 81.1%, specificity = 66.7%). If BMI-adjusted IA (=4.17*BMI) would have been applied in this population, the median IA would have slightly inferior (-4.8%), despite a different IA in each patient., Advances in Knowledge: BMI resulted the best predictor of image quality. The proposed theoretical BMI-adjusted IA scheme (4.17*BMI) should yield images of better quality (especially in high-BMI patients) maintaining practical scanning times (3 min/bed).

Aim/introduction: Digital PET/CT allows Q.Clear image reconstruction with different Beta (β) levels. However, no definitive standard β level for [68 Ga]Ga-DOTANOC PET/CT has been established yet. As patient's body mass index (BMI) can affect image quality, the aim of the study was to visually and semi-quantitatively assess different β levels compared to standard OSEM in overweight patients., Materials and Methods: Inclusion criteria: (1) patients with NEN included in a prospective CE-approved electronic archive; (2) [68 Ga]Ga-DOTANOC PET/CT performed on a digital tomograph between September2019/March2021; (3) BMI ≥ 25. Images were acquired following EANM guidelines and reconstructed with OSEM and Q.Clear with three β levels (800, 1000, 1600). Scans were independently reviewed by three expert readers, unaware of clinical data, who independently chose the preferred β level reconstruction for visual overall image quality. Semi-quantitative analysis was performed on each scan: SUVmax of the highest uptake lesion (SUVmax-T), liver background SUVmean (SUVmean-L), SUVmax-T/SUVmean-L, Signal-to-noise ratio for both liver (LSNR) and the highest uptake lesion (SNR-T), Contrast-to-noise ratio (CNR)., Results: Overall, 75 patients (median age: 63 years old [23-87]) were included: pre-obesity sub-group (25 ≤ BMI < 30, n = 50) and obesity sub-group (BMI ≥ 30, n = 25). PET/CT was positive for disease in 45/75 (60.0%) cases (14 obese and 31 pre-obese patients). Agreement among readers' visual rating was high (Fleiss κ = 0.88) and the β1600 was preferred in most cases (in 96% of obese patients and in 53.3% of pre-obese cases). OSEM was considered visually equal to β1600 in 44.7% of pre-obese cases and in 4% of obese patients. In a minority of pre-obese cases, OSEM was preferred (2%). In the whole population, CNR, SNR-T and LSNR were significantly different (p < 0.001) between OSEM and β1600, conversely to SUVmean-L (not significant). These results were also confirmed when calculated separately for the pre-obesity and obesity sub-groups β800 and β1000 were always rated inferior., Conclusions: Q.Clear is a new technology for PET/CT image reconstruction that can be used to increase CNR and SNR-T, to subsequently optimise overall image quality as compared to standard OSEM. Our preliminary data on [68 Ga]Ga-DOTANOC PET/CT demonstrate that in overweight NEN patients, β1600 is preferable over β800 and β1000. Further studies are warranted to validate these results in lesions of different anatomical region and size; moreover, currently employed interpretative PET positivity criteria should be adjusted to the new reconstruction method., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: The conventional imaging flowchart for prostate cancer (PCa) staging may fail in correctly detecting lymph node metastases (LNM). Pelvic lymph node dissection (PLND) represents the only reliable method, although invasive. A new amino acid PET compound, [ 18 F]-fluciclovine, was recently authorized in suspected PCa recurrence but not yet included in the standard staging work-up of primary PCa. A prospective monocentric study was designed to evaluate [ 18 F]-fluciclovine PET/CT diagnostic performance for preoperative LN staging in primary high-risk PCa., Methods: Consecutive patients (pts) with biopsy-proven PCa, standard staging (including [ 11 C]choline PET/CT), eligible for PLND, were enrolled to undergo an investigational [ 18 F]-fluciclovine PET/CT. Nodal uptake higher than surrounding background was reported by at least two readers (blinded to [ 11 C]choline) using a visual 5-point scale (1-2 probably negative; 4-5 probably positive; 3 equivocal); SUVmax, target-to-background (aorta-A; bone marrow-BM) ratios (TBRs), were also calculated. PET results were validated with PLND. [ 18 F]-fluciclovine PET/CT performance using visual score and semi-quantitative indexes was analyzed both per patient and per LN anatomical region, compared to conventional [ 11 C]choline and clinical predictive factors (to note that diagnostic performance of [ 18 F]-fluciclovine was explored for LNM but not examined for intrapelvic or extrapelvic M1 lesions)., Results: Overall, 94 pts underwent [ 18 F]-fluciclovine PET/CT; 72/94 (77%) high-risk pts were included in the final analyses (22 pts excluded: 8 limited PLND; 3 intermediate-risk; 2 treated with radiotherapy; 4 found to be M1; 5 neoadjuvant hormonal therapy). Median LNM risk by Briganti nomogram was 19%. LNM confirmed on histology was 25% (18/72 pts). Overall, 1671 LN were retrieved; 45/1671 (3%) LNM detected. Per pt, median no. of removed LN was 22 (mean 23 ± 10; range 8-51), of LNM was 2 (mean 3 ± 2; range 1-10). Median LNM size was 5 mm (mean 5 ± 2.5; range 2-10). On patient-based analyses (n = 72), diagnostic performance for LNM resulted significant with [ 18 F]-fluciclovine (AUC 0.66, p 0.04; 50% sensitivity, 81% specificity, 47% PPV, 83% NPV, 74% accuracy), but not with [ 11 C]choline (AUC 0.60, p 0.2; 50%, 70%, 36%, 81%, and 65% respectively). Briganti nomogram (OR = 1.03, p = 0.04) and [ 18 F]-fluciclovine visual score (≥ 4) (OR = 4.27, p = 0.02) resulted independent predictors of LNM at multivariable analyses. On region-based semi-quantitative analyses (n = 576), PET/CT performed better using TBR parameters (TBR-A similar to TBR-BM; TBR-A fluciclovine AUC 0.61, p 0.35, vs choline AUC 0.57 p 0.54; TBR-BM fluciclovine AUC 0.61, p 0.36, vs choline AUC 0.58, p 0.52) rather than using absolute LN SUVmax (fluciclovine AUC 0.51, p 0.91, vs choline AUC 0.51, p 0.94). However, in all cases, diagnostic performance was not statistically significant for LNM detection, although slightly in favor of the experimental tracer [ 18 F]-fluciclovine for each parameter. On the contrary, visual interpretation significantly outperformed PET semi-quantitative parameters (choline and fluciclovine: AUC 0.65 and 0.64 respectively; p 0.03) and represents an independent predictive factor of LNM with both tracers, in particular [ 18 F]-fluciclovine (OR = 8.70, p 0.002, vs OR = 3.98, p = 0.03)., Conclusion: In high-risk primary PCa, [ 18 F]-fluciclovine demonstrates some advantages compared with [ 11 C]choline but sensitivity for metastatic LN detection is still inadequate compared to PLND. Visual (combined morphological and functional), compared to semi-quantitative assessment, is promising but relies mainly on readers' experience rather than on unquestionable LN avidity., Trial Registration: EudraCT number: 2014-003,165-15., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

2-deoxy-2-[ 18 F]fluorodeoxyglucose (FDG) positron emission tomography (PET) gained an impressive role in the diagnostic management of many oncological diseases, even though its use in imaging prostate cancer (PC) is limited to selected cases, mostly advanced stage of PC and selection for prostate specific antigen membrane (PSMA) radioligand therapy (RLT). In the past years, several PET tracers have been developed for both staging and restaging PC. The three most employed PET molecules in daily practice are [ 11 C] or [ 18 F]F-Choline, [ 18 F]F-Fluciclovine (Anti-1- amino-3-[18F]Fluorocyclobutane-1-Carboxylic Acid, also known as (Anti-[ 18 F]FACBC), [ 68 Ga]Ga-PSMA and recently FDA approved the first Fluorinated PSMA-based named [ 18 F]F-DCFPyl. Each one has its own physiological and peculiarity which are worth exploring. Moreover, an increasing number of case reports and studies have reported tracers' variants, pitfalls, or even non-prostatic diseases (benign and malignant) incidentally detected. In prostate oncology, PET can be performed with several indications in different stages of disease, as highlighted in the EAU Guidelines on PC. A correct scan interpretation depends on the knowledge of both the physiological distribution of the tracers and the uptake of possible variants and pitfalls. The aim of this critical review is to provide a comprehensive knowledge of physiological distribution of these three tracers, as well as an updated overview of variants and pitfalls., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Imaging in hematological diseases has evolved extensively over the past several decades. Positron emission tomography/computed tomography (PET/CT) with of 2-[18 F]-fluoro-2-deoxy-d-glucose ([18 F] FDG) is currently essential for accurate staging and for early and late therapy response assessment for all FDG-avid lymphoproliferative histologies. The widely adopted visual Deauville 5-point scale and Lugano Classification recommendations have recently standardized PET scans interpretation and improved lymphoma patient management. In addition [18 F] FDG-PET is routinely recommended for initial evaluation and treatment response assessment of Multiple Myeloma (MM) with significant contribution in risk-stratification and prognostication, although magnetic resonance imaging remains the Gold Standard for the assessment of bone marrow involvement. In this review, an overview of the role of [18 F] FDG-PET, in hematological malignancies is provided, particularly focusing on Hodgkin lymphoma (HL) and Diffuse Large B Cell Lymphoma (DLBCL), both in adult and pediatric populations, and MM, at each point of patient management. Potential alternative molecular imaging applications in this field, such as non-[18 F] FDG-tracers, whole body magnetic resonance imaging (WB-MRI), hybrid PET/MRI and emerging radiomics research are briefly presented., (Copyright © 2021. Published by Elsevier B.V.)

Objectives: Visceral leishmaniasis (VL) is the most severe manifestation of the infection caused by the protozoan Leishmania, recently on increase in Italy and Spain. The aim of the study was to describe FDG uptake patterns in VL patients (pts) who underwent 18F-FDG PET/CT., Methods: A retrospective monocentric study of pts who underwent FDG PET/CT between 2008 and 2017 and later diagnosed with VL was performed. Semi-quantitative parameters were calculated in FDG-positive lesions: SUVmax, SUVmax spleen/SUVmax liver ratio (SLR), SUVmax focal/diffuse spleen ratio (FDR)., Results: Overall, 23 pts were included. PET/CT was negative in 2 immunocompromised pts, positive in 21/23 (91%) [6 spleen only, 2 spleen + nodes, 7 spleen + bone marrow (BM), 4 spleen + BM + nodes, 1 spleen + BM + lung, 1 BM only + nodes, 2 nodes only]. Splenic involvement was demonstrated in 20/23 (87%) pts. Two different splenic patterns were observed: diffuse (13/20 pts, mean spleen SUVmax = 7.3 ± 4.2 [4.0-14.1], mean SLR = 2.2 ± 1.6 [1.3-6.7]) and focal over diffuse (7/20 pts, mean SUVmax = 12.6 ± 4.5 [9.5-20.5], mean SLR = 2.8 ± 0.8 [2.1-4.4], mean FDR = 2.1 ± 0.8 [1.2-3.6]). Extra-splenic FDG-avid findings were detected in 15/21 pts (65%): bone marrow in 13/15 (mean SUVmax = 4.0 ± 1.3 [2.8-6.0]), nodes in 67/15 and lung in 1/15., Conclusions: PET/CT demonstrated splenic FDG uptake in all immunocompetent VL pts; two splenic patterns (diffuse/focal over diffuse) were observed and indistinguishable from splenic involvement by other disorders. The most frequent extra-splenic FDG-positive sites were BM and lymph nodes. Considering the potential disease aggressiveness and recent outbreaks in north-eastern Italy, VL should be considered in the differential diagnosis of FDG-positive splenic findings in pts from endemic areas or reporting travels to endemic countries.

Purpose: To evaluate the role of F-18-Fluorothymidine (FLT) PET/CT in lymphoma patients with suspected recurrent or residual disease., Methods: Adult lymphoma patients presenting with positive or equivocal F-18-FDG PET/CT at end-treatment or follow-up were prospectively addressed to an additional F-18-FLT-PET/CT. SUV max and tumour-to-background ratios (TBRs) were recorded for the most avid lesion. Biopsy or, when not available, clinical or imaging assessment were employed as standard of reference., Results: Overall 52 patients were recruited. Histology was available in 20/52 patients (38%), proliferation-index (Ki-67) in 14/20. Disease was excluded in 13/52 patients (25%) (one reactive follicular hyperplasia, five reactive-inflammatory tissues, four reactive nodes, two nodal sarcoid-like and one non-specific peri-caecal finding). FDG and FLT scans were concordant in disease restaging in 34/52 patients (65%), whereas in 18/52 cases (35%) relevant discrepancies were recorded. SUV max and TBR were significantly higher in the disease versus the disease-free group, with both tracers (p = 0.0231 and 0.0219 for FDG; p = 0.0008 and 0.0016 for FLT). FLT-SUVmax demonstrated slightly better performance in discriminating benign from malignant lesions (ROC-AUC: 0.8116 and 0.7949 for FLT-SUV max and TBR; 0.7120 and 0.7140 for FDG). Optimal FLT-SUV max cut-offs were searched: three would lead to 95% sensitivity, 81% accuracy, and 39% specificity, whereas seven led to 100%, 41%, and 56% respectively. No statistically significant correlation was observed between the two FLT indices and Ki-67., Conclusions: According to our results in a clinical setting of recurrent or residual lymphoma, FLT is not significantly superior to FDG and it is unlikely that it will be employed independently. FLT may be restricted to a few specific cases, as complementary to standard FDG imaging, to confirm a diagnosis or to define a better target to biopsy. However, due to FLT suboptimal performance, many findings would remain inconclusive, requiring further diagnostic procedures and reducing the effectiveness of performing an additional FLT scan.

Aim: During our daily clinical practice using 11C-Choline PET/CT for restaging patients affected by relapsing prostate cancer (rPCa) we noticed an unusual but significant occurrence of hypodense hepatic lesions with a different tracer uptake. Thus, we decided to evaluate the possible correlation between rPCa and these lesions as possible hepatic metastases., Materials and Methods: We retrospectively enrolled 542 patients diagnosed with rPCa in biochemical relapse after a radical treatment (surgery and/or radiotherapy). Among these, patients with a second tumor or other benign hepatic diseases were excluded. All patients underwent 11C-Choline PET/CT during the standard restaging workup of their disease. We analyzed CT images to evaluate the presence of hypodense lesions and PET images to identify the relative tracer uptake. In accordance to the subsequent oncological history, five clinical scenarios were recognized [Table 1]: normal low dose CT (ldCT) and normal tracer distribution (Group A); evidence of previously unknown hepatic round hypodense areas at ldCT with normal rim uptake (Group B); evidence of previously known hepatic round hypodense areas at ldCT stable over time and with normal rim uptake (Group C); evidence of previously known hepatic round hypodense areas at ldCT, in a previous PET/CT scan, with or without rim uptake and significantly changing over time in terms of size and/or uptake (Group D); evidence of hepatic round hypodense areas at ldCT with or without rim uptake confirmed as prostate liver metastases by histopathology, triple phase ceCT, ce-ultra sound (CEUS) and clinical/biochemical evaluation (Group E). We evaluated the correlation with PSA level at time of scan, rim SUVmax and association with local relapse or non-hepatic metastases (lymph nodes, bone, other parenchyma)., Results: Five hundred and forty-two consecutive patients were retrospectively enrolled. In 140 of the 542 patients more than one 11C-choline PET/CT had been performed. A total of 742 11C-Choline PET/CT scans were analyzed. Of the 542 patients enrolled, 456 (84.1%) had a normal appearance of the liver both at ldCT and PET (Group A). 19/542 (3,5%) belonged to Group B, 13/542 (2.4%) to Group C, 37/542 (6.8%) to Group D and 18/542 (3.3%) to Group E. Mean SUVmax of the rim was: 4.5 for Group B; 4.2 for Group C; 4.8 for Group D; 5.9 for Group E. Mean PSA level was 5.27 for Group A, 7.9 for Group B, 10.04 for Group C, 10.01 for Group D, 9.36 for Group E. Presence of positive findings at 11C-Choline PET/CT in any further anatomical area (local relapse, lymph node, bone, other extra hepatic sites) correlated with an higher PSA (p = 0.0285). In both the univariate and multivariate binary logistic regression analyses. PSA, SUVmax of the rim, local relapse, positive nodes were not associated to liver mets (Groups D-E) (p > 0.05). On the contrary, a significant correlation was found between the presence of liver metG (group D-E) and bone lesions (p= 0.00193)., Conclusion: Our results indicate that liver metastases in relapsing prostate cancer may occur frequently. The real incidence evaluation needs more investigations. In this case and despite technical limitations, Choline PET/CT shows alterations of tracer distribution within the liver that could eventually be mistaken for simple cysts but can be suspected when associated to high trigger PSA, concomitant bone lesions or modification over time. In this clinical setting an accurate analysis of liver tracer distribution (increased or decreased uptake) by the nuclear medicine physician is, therefore, mandatory.

A significant number of patients radically treated for prostate cancer (PCa) will develop prostate-specific antigen recurrence (27-53%). Localizing the anatomical site of relapse is critical, in order to achieve the optimal treatment management. To date the diagnostic accuracy of standard imaging is low. Several desirable features have been identified for the amino-acid-based PET agent, fluciclovine ( 18 F) including: long 18 F half-life which allows more practical use in centers without a cyclotron onsite; acting as a substrate for amino acid transporters upregulated in PCa or associated with malignant phenotype; lacking of incorporation into protein; and limited urinary excretion. Fluciclovine ( 18 F) is currently approved both in USA and Europe with specific indication in adult men with suspected recurrent PCa based on elevated prostate-specific antigen following prior treatment.

A patient multiple endocrine neoplasia type 1 presenting with radiological suspicion of pancreatic neuroendocrine tumor relapse after surgical and somatostatin analog treatment underwent restaging Ga-DOTANOC PET/CT. Standard and delayed images detected an area of focal intense uptake moving from the left para-aortic to the paracaval region. The lesion was identified at previous imaging in different abdominal locations (eg, adjacent to the duodenal wall at presurgical PET and in the aortocaval region at restaging contrast-enhanced CT). Dual time-point Ga-DOTANOC PET/CT was crucial to accurately diagnose the wandering mesenteric lymph node, a potential interpretation pitfall especially when found far from the initial position.

Purpose: Sensitive detection of cancer foci in men experiencing biochemical recurrence following initial treatment of prostate cancer is of great clinical significance with a possible impact on subsequent treatment choice. We describe a multisite experience of the efficacy and safety of the positron emission tomography/computerized tomography agent fluciclovine ( 18 F) after biochemical recurrence., Materials and Methods: A total of 596 patients underwent fluciclovine ( 18 F) positron emission tomography/computerized tomography at 4 clinical sites. Detection rate determinations were stratified by the baseline prostate specific antigen value. Diagnostic performance was assessed against a histological reference standard in 143 scans., Results: The subject level fluciclovine ( 18 F) positron emission tomography/computer tomography detection rate was 67.7% (403 of 595 scans). Positive findings were detected in the prostate/bed and pelvic lymph node regions in 38.7% (232 of 599) and 32.6% of scans (194 of 596), respectively. Metastatic involvement outside the pelvis was detected in 26.2% of scans (155 of 591). The subject level detection rate in patients in the lowest quartile for baseline prostate specific antigen (0.79 ng/ml or less) was 41.4% (53 of 128). Of these patients 13 had involvement in the prostate/bed only, 16 had pelvic lymph node involvement without distant disease and 24 had distant metastases. The positive predictive value of fluciclovine ( 18 F) positron emission tomography/computerized tomography scanning for all sampled lesions was 62.2%, and it was 92.3% and 71.8% for extraprostatic and prostate/bed involvement, respectively. Fluciclovine ( 18 F) was well tolerated and the safety profile was not altered following repeat administration., Conclusions: Fluciclovine ( 18 F) is well tolerated and able to detect local and distant prostate cancer recurrence across a wide range of prostate specific antigen values., (Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Purpose: To compare the accuracy of (18)F-FACBC and (11)C-choline PET/CT in patients radically treated for prostate cancer presenting with biochemical relapse., Methods: This prospective study enrolled 100 consecutive patients radically treated for prostate cancer and presenting with rising PSA. Of these 100 patients, 89 were included in the analysis. All had biochemical relapse after radical prostatectomy (at least 3 months previously), had (11)C-choline and (18)F-FACBC PET/CT performed within 1 week and were off hormonal therapy at the time of the scans. The two tracers were compared directly in terms of overall positivity/negativity on both a per-patient basis and a per-site basis. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy were calculated for both the tracers; follow-up at 1 year (including correlative imaging, PSA trend and pathology when available) was considered as the standard of reference., Results: In 51 patients the results were negative and in 25 patients positive with both the tracers, in eight patients the results were positive with (18)F-FACBC but negative with (11)C-choline, and in five patients the results were positive with (11)C-choline but negative with (18)F-FACBC. Overall in 49 patients the results were false-negative (FN), in two true-negative, in 24 true-positive (TP) and in none false-positive (FP) with both tracers. In terms of discordances between the tracers: (1) in one patient, the result was FN with (11)C-choline but FP with (18)F-FACBC (lymph node), (2) in seven, FN with (11)C-choline but TP with (18)F-FACBC (lymph node in five, bone in one, local relapse in one), (3) in one, FP with (11)C-choline (lymph node) but TP with (18)F-FACBC (local relapse), (4) in two, FP with (11)C-choline (lymph nodes in one, local relapse in one) but FN with (18)F-FACBC, and (5) in three, TP with (11)C-choline (lymph nodes in two, bone in one) but FN with (18)F-FACBC. With (11)C-choline and (18)F-FACBC, sensitivities were 32 % and 37 %, specificities 40 % and 67 %, accuracies 32 % and 38 %, PPVs 90 % and 97 %, and NPVs 3 % and 4 %, respectively. Categorizing patients by PSA level (<1 ng/ml 28 patients, 1 - <2 ng/ml 28 patients, 2 - <3 ng/ml 11 patients, ≥3 ng/ml 22 patients), the number (percent) of patients with TP findings were generally higher with (18)F-FACBC than with (11)C-choline: six patients (21 %) and four patients (14 %), eight patients (29 %) and eight patients (29 %), five patients (45 %) and four patients (36 %), and 13 patients (59 %) and 11 patients (50 %), respectively., Conclusion: (18)F-FACBC can be considered an alternative tracer superior to (11)C-choline in the setting of patients with biochemical relapse after radical prostatectomy.