FAP imaging in rare cancer entities-first clinical experience in a broad spectrum of malignancies.

PURPOSE: 68 Ga-FAPI (fibroblast activation protein inhibitor) is a rapidly evolving and highly promising radiotracer for PET/CT imaging, presenting excellent results in a variety of tumor entities, particularly in epithelial carcinomas. This retrospective analysis sought to evaluate the potential and impact of FAPI-PET/CT in rare cancer diseases with respect to improvement in staging and therapy, based on tracer uptake in normal organs and tumors. MATERIAL AND METHODS: Fifty-five patients with rare tumor entities, defined by a prevalence of 1 person out of 2000 or less, received a 68 Ga-FAPI-PET/CT scan. Fourteen women and 41 men (median age 60) were included within the following subgroups: cancer of unknown primary (n = 10), head and neck cancer (n = 13), gastrointestinal and biliary-pancreatic cancer (n = 17), urinary tract cancer (n = 4), neuroendocrine cancer (n = 4), and others (n = 7). Tracer uptake was quantified by standardized uptake values SUVmax and SUVmean and the tumor-to-background ratio (TBR) was determined (SUVmax tumor/SUVmean organ). RESULTS: In 20 out of 55 patients, the primary tumor was identified and 31 patients presented metastases (n = 88), characterized by a high mean SUVmax in primary (10.1) and metastatic lesions (7.6). The highest uptake was observed in liver metastases (n = 6) with a mean SUVmax of 9.8 and a high TBR of 8.7, closely followed by peritoneal carcinomatosis (n = 16) presenting a mean SUVmax of 9.8 and an excellent TBR of 29.6. In terms of the included subgroups, the highest uptake regarding mean SUVmax was determined in gastrointestinal and biliary-pancreatic cancer with 9.8 followed closely by urinary tract cancer with 9.5 and head and neck cancer (9.1). CONCLUSION: Due to excellent tumor visualization and, thereby, sharp contrasts in terms of high TBRs in primary and metastatic lesions in different rare malignancies, 68 Ga-FAPI-PET/CT crystallizes as a powerful and valuable imaging tool, particularly with respect to epithelial carcinomas, and therefore an enhancement to standard diagnostics imaging methodologies. The realization of further and prospective studies is of large importance to confirm the potential of FAP imaging in oncology.

Pharmacokinetic studies of [68 Ga]Ga-PSMA-11 in patients with biochemical recurrence of prostate cancer: detection, differences in temporal distribution and kinetic modelling by tissue type.

PURPOSE: [68 Ga]Ga-PSMA-11 is a promising radiopharmaceutical for detecting tumour lesions in prostate cancer, but knowledge of the pharmacokinetics is limited. Dynamic PET-CT was performed to investigate the tumour detection and differences in temporal distribution, as well as in kinetic modelling of [68 Ga]Ga-PSMA-11 by tissue type. METHODS: Dynamic PET-CT over the lower abdomen and static whole-body PET-CT 80-90 min p.i. from 142 patients with biochemical recurrence were retrospectively analysed. Detection rates were compared to PSA levels. Average time-activity curves were calculated from tumour lesions and normal tissue. A three-compartment model and non-compartment model were used to calculate tumour kinetics. RESULTS: Overall detection rate was 70.42%, and in patients with PSA > 0.4 ng/mL 76.67%. All tumour lesions presented the steepest standardised uptake value (SUV) incline in the first 7-8 min before decreasing to different degrees. Normal tissue presented with a low uptake, except for the bladder, which accumulated activity the steepest 15-16 min. p.i.. While all tumour lesions continuously increased, bone metastases showed the steepest decline, resulting in a significantly lower SUV than lymph node metastases (60 and 80-90 min). Transport rate from the blood and tracer binding and internalisation rate were lower in bone metastases. Heterogeneity (fractal dimension) and vascular density were significantly lower in bone metastases. CONCLUSION: Even at low PSA between 0.51 and 0.99 ng/mL, detection rate was 57%. Dynamic imaging showed a time window in the first 10 min where tumour uptake is high, but no bladder activity is measured, aiding accuracy in distinction of local recurrence. Kinetic modelling provided additional information for tumour characterisation by tissue type.

Novel FAP ligands enable improved imaging contrast in sarcoma patients due to FAPI-PET/CT.

PURPOSE: A high expression of fibroblast activation protein (FAP) was observed in multiple sarcomas, indicating an enormous potential for PET/CT using 68Ga-radiolabeled inhibitors of FAP (FAPI). Therefore, this retrospective study aimed to evaluate the role of the novel hybrid imaging probe for sarcomas as a first clinical evaluation. METHODS: A cohort of 15 patients underwent 68Ga-FAPI-PET/CT for staging or restaging. The acquisition of PET scans was performed 60 min after administration of 127 to 308 MBq of the tracer. The uptake of 68Ga-FAPI in malignant tissue as well as in healthy organs was quantified by standardized uptake values SUVmean and SUVmax. RESULTS: Excellent tumor-to-background ratios (> 7) could be achieved due to low background activity and high SUVmax in primary tumors (median 7.16), local relapses (median 11.47), and metastases (median 6.29). The highest uptake was found for liposarcomas and high-grade disease (range 18.86-33.61). A high SUVmax (> 10) was observed for clinically more aggressive disease. CONCLUSION: These preliminary findings suggest a high potential for the clinical use of 68Ga-FAPI-PET/CT for patients diagnosed with sarcoma.

18F-PSMA-1007 multiparametric, dynamic PET/CT in biochemical relapse and progression of prostate cancer.

OBJECTIVES: Aim of the present analysis is to investigate the biodistribution and pharmacokinetics of the recently clinically introduced radioligand 18F-PSMA-1007 in patients with biochemical recurrence or progression of prostate cancer (PC) by means of multiparametric (dynamic and whole-body) PET/CT. METHODS: Twenty-five (25) patients with PC biochemical relapse or progression (median age = 66.0 years) were enrolled in the analysis. The median PSA value was 1.2 ng/mL (range = 0.1-237.3 ng/mL) and the median Gleason score was 7 (range = 6-10). All patients underwent dynamic PET/CT (dPET/CT) scanning (60 min) of the pelvis and lower abdomen as well as whole-body PET/CT with 18F-PSMA-1007. PET/CT assessment was based on qualitative evaluation, SUV calculation, and quantitative analysis based on a two-tissue compartment model and fractal analysis. RESULTS: 15/25 patients were PET-positive. Plasma PSA values in the 18F-PSMA-1007 positive group were higher (median = 3.6 ng/mL; range = 0.2-237.3 ng/mL) than in the 18F-PSMA-1007 negative group (median value = 0.7 ng/mL; range = 0.1-3.0 ng/mL). Semi-quantitative analysis in the PC lesions demonstrated a mean SUVaverage = 25.1 (median = 15.4; range = 3.5-119.2) and a mean SUVmax = 41.5 (median = 25.7; range = 3.8-213.2). Time-activity curves derived from dPET/CT revealed an increasing tracer accumulation during the 60 min of dynamic PET acquisition into the PC lesions, higher than in the urinary bladder and the colon. Significant correlations were observed between 18F-PSMA-1007 uptake (SUV), influx, and fractal dimension (FD). CONCLUSIONS: 18F-PSMA-1007 PET/CT could detect PC lesions in 60% of the patients of a mixed population, including also patients with very low PSA values. Higher PSA values were associated with a higher detection rate. Dynamic PET analysis revealed an increasing tracer uptake during the dynamic PET acquisition as well as high binding and internalization of the radiofluorinated PSMA ligand in the PC lesions.

Fibroblast activation protein inhibitor (FAPI) PET for diagnostics and advanced targeted radiotherapy in head and neck cancers.

PURPOSE: Cancer-associated fibroblasts (CAFs) expressing fibroblast activation protein (FAP) have been associated with the aggressive nature of head and neck cancers (HNCs). These tumours grow diffusely, leading to extremely challenging differentiation between tumour and healthy tissue. This analysis aims to introduce a novel approach of tumour detection, contouring and targeted radiotherapy of HNCs using visualisation of CAFs: PET-CT with 68Ga-radiolabeled inhibitors of FAP (FAPI). METHODS: FAPI PET-CT was performed without complications prior to radiotherapy in addition to contrast enhanced CT (CE-CT) and MRI on 14 patients with HNC. First, for tissue biodistribution analysis, volumes of interest were defined to quantify SUVmean and SUVmax in tumour and healthy parenchyma. Secondly, using four thresholds of three-, five-, seven- and tenfold increase of FAPI enhancement in the tumour as compared with normal tissue, four different gross tumour volumes (FAPI-GTV) were created automatically. These were compared with GTVs created conventionally with CE-CT and MRI (CT-GTV). RESULTS: The biodistribution analysis revealed high FAPI avidity within tumorous lesions (e.g. primary tumours, SUVmax 14.62 ± 4.44; SUVmean 7.41 ± 2.39). In contrast, low background uptake was measured in healthy tissues of the head and neck region (e.g. salivary glands: SUVmax 1.76 ± 0.31; SUVmean 1.23 ± 0.28). Considering radiation planning, CT-GTV was of 27.3 ml, whereas contouring with FAPI resulted in significantly different GTVs of 67.7 ml (FAPI × 3, p = 0.0134), 22.1 ml (FAPI × 5, p = 0.0419), 7.6 ml (FAPI × 7, p = 0.0001) and 2.3 ml (FAPI × 10, p = 0.0001). Taking these significant disparities between the GTVs into consideration, we merged FAPI-GTVs with CT-GTVs. This resulted in median volumes, that were, as compared to CT-GTVs, significantly larger with FAPI × 3 (54.7 ml, + 200.5% relative increase, p = 0.0005) and FAPI × 5 (15.0 ml, + 54.9%, p = 0.0122). Furthermore, FAPI-GTVs were not covered by CE-CT-based planning target volumes (CT-PTVs) in several cases. CONCLUSION: We present first evidence of diagnostic and therapeutic potential of FAPI ligands in head and neck cancer. Larger studies with histopathological correlation are required to validate our findings.

68Ga-PSMA PET/CT in the evaluation of bone metastases in prostate cancer.

PURPOSE: The aims of this retrospective analysis were to compare 68Ga-PSMA PET findings and low-dose CT findings (120 kV, 30 mA), and to obtain semiquantitative and quantitative 68Ga-PSMA PET data in patients with prostate cancer (PC) bone metastases. METHODS: In total, 152 PET/CT scans from 140 patients were evaluated. Of these patients, 30 had previously untreated primary PC, and 110 had biochemical relapse after treatment of primary PC. All patients underwent dynamic PET/CT scanning of the pelvis and lower abdomen as well as whole-body PET/CT with 68Ga-PSMA-11. The PET/CT scans were analysed qualitatively (visually), semiquantitatively (SUV), and quantitatively based on a two-tissue compartment model and a noncompartmental approach leading to the extraction of the fractal dimension. Differences were considered significant for p values <0.05. RESULTS: In total, 168 68Ga-PSMA-positive and 113 CT-positive skeletal lesions were detected in 37 patients (8 with primary PC, 29 with biochemical recurrence). Of these 168 lesions, 103 were both 68Ga-PSMA PET-positive and CT-positive, 65 were only 68Ga-PSMA-positive, and 10 were only CT-positive. The Yang test showed that there were significantly more 68Ga-PSMA PET-positive lesions than CT-positive lesions. Association analysis showed that PSA plasma levels were significantly correlated with several 68Ga-PSMA-11-associated parameters in bone metastases, including the degree of tracer uptake (SUVaverage and SUVmax), its transport rate from plasma to the interstitial/intracellular compartment (K1), its rate of binding to the PSMA receptor and its internalization (k3), its influx rate (Ki), and its distribution heterogeneity. CONCLUSION: 68Ga-PSMA PET/CT is a useful diagnostic tool in the detection of bone metastases in PC. 68Ga-PSMA PET visualizes more bone metastases than low-dose CT. PSA plasma levels are significantly correlated with several 68Ga-PSMA PET parameters.

Treatment response evaluation with 18F-FDG PET/CT and 18F-NaF PET/CT in multiple myeloma patients undergoing high-dose chemotherapy and autologous stem cell transplantation.

AIM: The aim of this study was to assess the combined use of the radiotracers 18F-FDG and 18F-NaF in treatment response evaluation of a group of multiple myeloma (MM) patients undergoing high-dose chemotherapy (HDT) followed by autologous stem cell transplantation (ASCT) by means of static (whole-body) and dynamic PET/CT (dPET/CT). PATIENTS AND METHODS: Thirty-four patients with primary, previously untreated MM scheduled for treatment with HDT followed by ASCT were enrolled in the study. All patients underwent PET/CT scanning with 18F-FDG and 18F-NaF before and after therapy. Treatment response by means of PET/CT was assessed according to the European Organization for Research and Treatment of Cancer (EORTC) 1999 criteria. The evaluation of dPET/CT studies was based on qualitative evaluation, semi-quantitative (SUV) calculation, and quantitative analysis based on two-tissue compartment modelling and a non-compartmental approach leading to the extraction of fractal dimension (FD). RESULTS: An analysis was possible in 29 patients: three with clinical complete response (CR) and 26 with non-CR (13 patients near complete response-nCR, four patients very good partial response-VGPR, nine patients partial response-PR). After treatment, 18F-FDG PET/CT was negative in 14/29 patients and positive in 15/29 patients, showing a sensitivity of 57.5 % and a specificity of 100 %. According to the EORTC 1999 criteria, 18F-FDG PET/CT-based treatment response revealed CR in 14 patients (18F-FDG PET/CT CR), PR in 11 patients (18F-FDG PET/CT PR) and progressive disease in four patients (18F-FDG PET/CT PD). In terms of 18F-NaF PET/CT, 4/29 patients (13.8 %) had a negative baseline scan, thus failed to depict MM. Regarding the patients for which a direct lesion-to-lesion comparison was feasible, 18F-NaF PET/CT depicted 56 of the 129 18F-FDG positive lesions (43 %). Follow-up 18F-NaF PET/CT showed persistence of 81.5 % of the baseline 18F-NaF positive MM lesions after treatment, despite the fact that 64.7 % of them had turned to 18F-FDG negative. Treatment response according to 18F-NaF PET/CT revealed CR in one patient (18F-NaF PET/CT CR), PR in five patients (18F-NaF PET/CT PR), SD in 12 patients (18F-NaF PET/CT SD), and PD in seven patients (18F-NaF PET/CT PD). Dynamic 18F-FDG and 18F-NaF PET/CT studies showed that SUVaverage, SUVmax, as well as the kinetic parameters K1, influx and FD from reference bone marrow and skeleton responded to therapy with a significant decrease (p < 0.001). CONCLUSION: F-FDG PET/CT demonstrated a sensitivity of 57.7 % and a specificity of 100 % in treatment response evaluation of MM. Despite its limited sensitivity, the performance of 18F-FDG PET/CT was satisfactory, given that 6/9 false negative patients in follow-up scans (66.7 %) were clinically characterized as nCR, a disease stage with very low tumor mass. On the other hand, 18F-NaF PET/CT does not seem to add significantly to 18F-FDG PET/CT in treatment response evaluation of MM patients undergoing HDT and ASCT, at least shortly after therapy.

F-18 labelled PSMA-1007: biodistribution, radiation dosimetry and histopathological validation of tumor lesions in prostate cancer patients.

PURPOSE: The prostate-specific membrane antigen (PSMA) targeted positron-emitting-tomography (PET) tracer 68Ga-PSMA-11 shows great promise in the detection of prostate cancer. However, 68Ga has several shortcomings as a radiolabel including short half-life and non-ideal energies, and this has motivated consideration of 18F-labelled analogs. 18F-PSMA-1007 was selected among several 18F-PSMA-ligand candidate compounds because it demonstrated high labelling yields, outstanding tumor uptake and fast, non-urinary background clearance. Here, we describe the properties of 18F-PSMA-1007 in human volunteers and patients. METHODS: Radiation dosimetry of 18F-PSMA-1007 was determined in three healthy volunteers who underwent whole-body PET-scans and concomitant blood and urine sampling. Following this, ten patients with high-risk prostate cancer underwent 18F-PSMA-1007 PET/CT (1 h and 3 h p.i.) and normal organ biodistribution and tumor uptakes were examined. Eight patients underwent prostatectomy with extended pelvic lymphadenectomy. Uptake in intra-prostatic lesions and lymph node metastases were correlated with final histopathology, including PSMA immunostaining. RESULTS: With an effective dose of approximately 4.4-5.5 mSv per 200-250 MBq examination, 18F-PSMA-1007 behaves similar to other PSMA-PET agents as well as to other 18F-labelled PET-tracers. In comparison to other PSMA-targeting PET-tracers, 18F-PSMA-1007 has reduced urinary clearance enabling excellent assessment of the prostate. Similar to 18F-DCFPyL and with slightly slower clearance kinetics than PSMA-11, favorable tumor-to-background ratios are observed 2-3 h after injection. In eight patients, diagnostic findings were successfully validated by histopathology. 18F-PSMA-1007 PET/CT detected 18 of 19 lymph node metastases in the pelvis, including nodes as small as 1 mm in diameter. CONCLUSION: 18F-PSMA-1007 performs at least comparably to 68Ga-PSMA-11, but its longer half-life combined with its superior energy characteristics and non-urinary excretion overcomes some practical limitations of 68Ga-labelled PSMA-targeted tracers.

Novel Bispecific PSMA/GRPr Targeting Radioligands with Optimized Pharmacokinetics for Improved PET Imaging of Prostate Cancer.

A new series of bispecific radioligands (BRLs) targeting prostate-specific membrane antigen (PSMA) and gastrin releasing peptide receptor (GRPr), both expressed on prostate cancer cells, was developed. Their design was based on the bombesin (BN) analogue, H2N-PEG2-[D-Tyr(6),ß-Ala(11),Thi(13),Nle(14)]BN(6-14), which binds to GRPr with high affinity and specificity, and the peptidomimetic urea-based pseudoirreversible inhibitor of PSMA, Glu-ureido-Lys. The two pharmacophores were coupled through copper(I)-catalyzed azide-alkyne cycloaddition to the bis(tetrafluorophenyl) ester of the chelating agent HBED-CC via amino acid linkers made of positively charged His (H) and negatively charged Glu (E): -(HE)n- (n = 0-3). The BRLs were labeled with (68)Ga, and their preliminary pharmacological properties were evaluated in vitro (competitive and time kinetic binding assays) on prostate cancer (PC-3, LNCaP) and rat pancreatic (AR42J) cell lines and in vivo by biodistribution and small animal PET imaging studies in both normal and tumor-bearing mice. The IC50/Ki values determined for all BRLs essentially matched those of the respective monomers. The maximal cellular uptake of the BLRs was observed between 20 and 30 min. The BRLs showed a synergistic ability in vivo by targeting both PSMA (LNCaP) and GRPr (PC-3) positive tumors, whereas the charged -(HE)n- (n = 1-3) linkers significantly reduced the kidney and spleen uptake. The bispecific (PSMA and GRPr) targeting ability and optimized pharmacokinetics of the compounds developed in this study could lead to their future application in clinical practice as more sensitive radiotracers for noninvasive imaging of prostate cancer (PCa) by PET/CT and PET/MRI.

(68)Ga-PSMA-11 dynamic PET/CT imaging in biochemical relapse of prostate cancer.

OBJECTIVES: We aim to investigate the pharmacokinetics and distribution of the recently clinically introduced radioligand (68)Ga-PSMA-11 in men with recurrent prostate cancer (PC) by means of dynamic and whole-body PET/CT. The correlation between PSA levels and (68)Ga-PSMA-11 PET parameters is also investigated. METHODS: 31 patients with biochemical failure after primary PC treatment with curative intent (median age 71.0 years) were enrolled in the analysis. The median PSA value was 2.0 ng/mL (range = 0.1 - 130.0 ng/mL) and the median Gleason score was 7 (range = 5 - 9). 8/31 (25.8 %) of the included patients had a PSA value < 0.5 ng/ml. All patients underwent dynamic PET/CT (dPET/CT) scanning (60 min) of the pelvis and lower abdomen as well as whole-body PET/CT with (68)Ga-PSMA-11. dPET/CT assessment was based on qualitative evaluation, SUV calculation, and quantitative analysis based on a two-tissue compartment model and a non-compartmental approach leading to the extraction of fractal dimension (FD). RESULTS: 22/31 patients (71.0 %) were (68)Ga-PSMA-11-positive, while 9/31 (29.0 %) patients were (68)Ga-PSMA-11-negative. The median PSA value in the (68)Ga-PSMA-11-positive group was significantly higher (median = 2.35 ng/mL; range = 0.19 - 130.0 ng/mL) than in the (68)Ga-PSMA-11-negative group (median value: 0.34 ng/mL; range = 0.10 - 4.20 ng/mL). A total of 76 lesions were semi-quantitatively evaluated. PC recurrence-associated lesions demonstrated a mean SUVaverage = 12.4 (median = 9.0; range = 2.2 - 84.5) and mean SUVmax = 18.8 (median = 14.1; range = 3.1 - 120.3). Dynamic PET/CT studies of the pelvis revealed the following mean values for the PC recurrence-suspicious lesions: K1 = 0.26, k3 = 0.30, influx = 0.14 and FD = 1.24. Time-activity curves derived from PC-recurrence indicative lesions revealed an increasing (68)Ga-PSMA-11 accumulation during dynamic PET acquisition. Correlation analysis revealed a moderate, but significant, correlation between PSA levels and the number of lesions detected on (68)Ga-PSMA-11 PET/CT (r = 0.54) and between PSA levels and SUVaverage (r = 0.48) or SUVmax (r = 0.44). CONCLUSIONS: Ga-PSMA-11 PET/CT demonstrated an overall detection rate of 71.0 % 60 min p.i. of the radiotracer in a mixed patient population with respect to PSA levels and including patients with very low PSA values. Higher PSA values were associated with a higher detection rate. The tracer uptake in PC-recurrence-indicative lesions is increasing during the 60 minutes of dynamic PET acquisition.

Intra-individual comparison of (68)Ga-PSMA-11-PET/CT and multi-parametric MR for imaging of primary prostate cancer.

PURPOSE: Multi-parametric magnetic resonance imaging (MP-MRI) is currently the most comprehensive work up for non-invasive primary tumor staging of prostate cancer (PCa). Prostate-specific membrane antigen (PSMA)-Positron emission tomography-computed tomography (PET/CT) is presented to be a highly promising new technique for N- and M-staging in recurrent PCa-patients. The actual investigation analyses the potential of (68)Ga-PSMA11-PET/CT to assess the extent of primary prostate cancer by intra-individual comparison to MP-MRI. METHODS: In a retrospective study, ten patients with primary PCa underwent MP-MRI and PSMA-PET/CT for initial staging. All tumors were proven histopathological by biopsy. Image analysis was done in a quantitative (SUVmax) and qualitative (blinded read) fashion based on PI-RADS. The PI-RADS schema was then translated into a 3D-matrix and the euclidian distance of this coordinate system was used to quantify the extend of agreement. RESULTS: Both MP-MRI and PSMA-PET/CT presented a good allocation of the PCa, which was also in concordance to the tumor location validated in eight-segment resolution by biopsy. An Isocontour of 50 % SUVmax in PSMA-PET resulted in visually concordant tumor extension in comparison to MP-MRI (T2w and DWI). For 89.4 % of sections containing a tumor according to MP-MRI, the tumor was also identified in total or near-total agreement (euclidian distance ≤1) by PSMA-PET. Vice versa for 96.8 % of the sections identified as tumor bearing by PSMA-PET the tumor was also found in total or near-total agreement by MP-MRI. CONCLUSIONS: PSMA-PET/CT and MP-MRI correlated well with regard to tumor allocation in patients with a high pre-test probability for large tumors. Further research will be needed to evaluate its value in challenging situation such as prostatitis or after repeated negative biopsies.

PSMA PET/CT with Glu-urea-Lys-(Ahx)-[68Ga(HBED-CC)] versus 3D CT volumetric lymph node assessment in recurrent prostate cancer.

PURPOSE: PET/CT with the PSMA ligand is a powerful new method for the early detection of nodal metastases in patients with biochemical relapse. The purpose of this retrospective investigation was to evaluate the volume and dimensions of nodes identified by Glu-urea-Lys-(Ahx)-[(68)Ga(HBED-CC)] ((68)Ga-PSMA-11) in the setting of recurrent prostate cancer. METHODS: All PET/CT images were acquired 60 ± 10 min after intravenous injection of (68)Ga-PSMA-11 (mean dose 176 MBq). In 21 patients with recurrent prostate cancer and rising PSA, 49 PSMA-positive lymph nodes were identified. Using semiautomated lymph node segmentation software, node volume and short-axis and long-axis dimensions were measured and compared with the maximum standardized uptake values (SUVmax). Round nodes greater than or equal to 8 mm were considered positive by morphological criteria alone. The percentage of nodes identified by elevated SUVmax but not by conventional morphological criteria was determined. RESULTS: The mean volume of (68)Ga-PSMA-11-positive nodes was 0.5 ml (range 0.2 - 2.3 ml), and the mean short-axis diameter was 5.8 mm (range 2.4 - 13.3 mm). In 7 patients (33.3 %) with 31 PSMA-positive nodes only 11 (36 %) were morphologically positive based on diameters >8 mm on CT. In the remaining 14 patients (66.7 %), 18 (37 %) of PSMA positive lymph nodes had short-axis diameters <8 mm with a mean short-axis diameter of 5.0 mm (range 2.4 - 7.9 mm). Thus, in this population, (68)Ga-PSMA-11 PET/CT detected nodal recurrence in two-thirds of patients who would have been missed using conventional morphological criteria. CONCLUSION: (68)Ga-PSMA-11 PET/CT is more sensitive than CT based 3D volumetric lymph node evaluation in determining the node status of patients with recurrent prostate cancer, and is a promising method of restaging prostate cancers in this setting.

Comparison of PET/CT and PET/MRI hybrid systems using a 68Ga-labelled PSMA ligand for the diagnosis of recurrent prostate cancer: initial experience.

PURPOSE: (68)Ga-labelled HBED-CC-PSMA is a highly promising tracer for imaging recurrent prostate cancer (PCa). The intention of this study was to evaluate the feasibility of PET/MRI with this tracer. METHODS: Twenty patients underwent PET/CT 1 h after injection of the (68)Ga-PSMA ligand followed by PET/MRI 3 h after injection. Data from the two investigations were first analysed separately and then compared with respect to tumour detection rate and radiotracer uptake in various tissues. To evaluate the quantification accuracy of the PET/MRI system, differences in SUVs between PET/CT and corresponding PET/MRI were compared with differences in SUVs between PET/CT 1 h and 3 h after injection in another patient cohort. This cohort was investigated using the same PET/CT system. RESULTS: With PET/MRI, different diagnostic sequences, higher contrast of lesions and higher resolution of MRI enabled a subjectively easier evaluation of the images. In addition, four unclear findings on PET/CT could be clarified as characteristic of PCa metastases by PET/MRI. However, in PET images of the PET/MRI, a reduced signal was observed at the level of the kidneys (in 11 patients) and around the urinary bladder (in 15 patients). This led to reduced SUVs in six lesions. SUVmean values provided by the PET/MRI system were different in muscles, blood pool, liver and spleen. CONCLUSION: PCa was detected more easily and more accurately with Ga-PSMA PET/MRI than with PET/CT and with lower radiation exposure. Consequently, this new technique could clarify unclear findings on PET/CT. However, scatter correction was challenging when the specific (68)Ga-PSMA ligand was used. Moreover, direct comparison of SUVs from PET/CT and PET/MR needs to be conducted carefully.

²¹³Bi-DOTATOC receptor-targeted alpha-radionuclide therapy induces remission in neuroendocrine tumours refractory to beta radiation: a first-in-human experience.

PURPOSE: Radiopeptide therapy using a somatostatin analogue labelled with a beta emitter such as (90)Y/(177)Lu-DOTATOC is a new therapeutic option in neuroendocrine cancer. Alternative treatments for patients with refractory disease are rare. Here we report the first-in-human experience with (213)Bi-DOTATOC targeted alpha therapy (TAT) in patients pretreated with beta emitters. METHODS: Seven patients with progressive advanced neuroendocrine liver metastases refractory to treatment with (90)Y/(177)Lu-DOTATOC were treated with an intraarterial infusion of (213)Bi-DOTATOC, and one patient with bone marrow carcinosis was treated with a systemic infusion of (213)Bi-DOTATOC. Haematological, kidney and endocrine toxicities were assessed according to CTCAE criteria. Radiological response was assessed with contrast-enhanced MRI and (68)Ga-DOTATOC-PET/CT. More than 2 years of follow-up were available in seven patients. RESULTS: The biodistribution of (213)Bi-DOTATOC was evaluable with 440 keV gamma emission scans, and demonstrated specific tumour binding. Enduring responses were observed in all treated patients. Chronic kidney toxicity was moderate. Acute haematotoxicity was even less pronounced than with the preceding beta therapies. CONCLUSION: TAT can induce remission of tumours refractory to beta radiation with favourable acute and mid-term toxicity at therapeutic effective doses.

[Importance of nuclear medicine diagnostics in CUP syndrome]. / Stellenwert der nuklearmedizinischen Diagnostik bei CUP-Syndrom.

CLINICAL/METHODICAL ISSUE: The diagnostic work-up in patients with carcinoma of unknown primary (CUP) syndrome is extensive, highly time-consuming and cost-intensive and ultimately often fails to detect a primary site. STANDARD RADIOLOGICAL METHODS: In this context chest X-ray and computed tomography (CT) have been used as standard imaging modalities in CUP syndrome. METHODOLOGICAL INNOVATIONS: Since the introduction of positron emission tomography (PET) evaluation of tumor vitality has become possible. Furthermore, PET-CT hybrid scanners allow the combination of functional and morphological imaging. PERFORMANCE: Several meta-analyses have reported an additional overall detection rate between 24.5 % and 44 % by either PET or PET-CT. Metastatic localization (cervical versus extracervical) did not influence the performance. The sensitivity was usually high (> 80 %) but specificity was moderate ranging from 68 % to 88 % at best. If mentioned, the results obtained by fluorodeoxyglucose (FDG)-PET significantly changed the clinical management in approximately one third of the patients studied. In a direct comparison with PET alone, PET-CT did not depict significantly more primary tumors but was able to reduce false positive findings. ACHIEVEMENTS: To determine the real additional value of PET-CT in the diagnosis of CUP syndrome large prospective studies with more uniform inclusion criteria are needed. Despite the capabilities of FDG-PET-CT there is as yet no evidence that a potentially improved diagnostic algorithm is translated into a better patient outcome. PRACTICAL RECOMMENDATIONS: Nevertheless, FDG-PET-CT should be performed in all CUP patients where conventional imaging failed to detect a primary site or the results are equivocal. In CUP patients with cervical lymph node metastases PET-CT should be carried out prior to panendoscopy to reduce the number of false negative biopsies.

PET imaging with a [68Ga]gallium-labelled PSMA ligand for the diagnosis of prostate cancer: biodistribution in humans and first evaluation of tumour lesions.

PURPOSE: Prostate-specific membrane antigen (PSMA) is a cell surface protein with high expression in prostate carcinoma (PC) cells. Recently, procedures have been developed to label PSMA ligands with (68)Ga, (99m)Tc and (123/124/131)I. Our initial experience with Glu-NH-CO-NH-Lys-(Ahx)-[(68)Ga(HBED-CC)]((68)Ga-PSMA) suggests that this novel tracer can detect PC relapses and metastases with high contrast. The aim of this study was to investigate its biodistribution in normal tissues and tumour lesions. METHODS: A total of 37 patients with PC and rising prostate-specific antigen (PSA) levels were subjected to (68)Ga-PSMA positron emission tomography (PET)/CT. Quantitative assessment of tracer uptake was performed 1 and 3 h post-injection (p.i.) by analysis of mean and maximum standardized uptake values (SUVmean/max) of several organs and 65 tumour lesions. Subsequently, tumour to background ratios were calculated. RESULTS: The PET/CT images showed intense tracer uptake in both kidneys and salivary glands. Moderate uptake was seen in lacrimal glands, liver, spleen and in small and large bowel. Quantitative assessment revealed excellent contrast between tumour lesions and most normal tissues. Of 37 patients, 31 (83.8 %) showed at least one lesion suspicious for cancer at a detection rate of 60 % at PSA <2.2 ng/ml and 100 % at PSA >2.2 ng/ml. Median tumour to background ratios were 18.8 (2.4-158.3) in early images and 28.3 (2.9-224.0) in late images. CONCLUSION: The biodistribution of the novel (68)Ga-PSMA tracer and its ability to detect PC lesions was analysed in 37 patients. Within healthy organs, kidneys and salivary glands demonstrated the highest radiotracer uptake. Lesions suspicious for PC presented with excellent contrast as early as 1 h p.i. with high detection rates even at low PSA levels.

[Imaging diagnostics of hyperparathyroidism]. / Bildgebende Diagnostik des Hyperparathyreoidismus.

Primary hyperparathyroidism is diagnosed by the presence of hypercalcemia, hypercalciuria and elevated serum levels of parathyroid hormone and is treated surgically by removal of the enlarged gland. Both ultrasound and 99m-Tc-MIBI scintigraphy are used to localize enlarged parathyroid glands. With sonography, enlarged parathyroid glands are hypoechoic and are most frequently found dorsally or caudally to the thyroid and medially to the carotid arteries. Ectopic parathyroid glands in the mediastinum can be detected by scintigraphy only. Computed tomography and magnetic resonance imaging are not primarily indicated. The sensitivity of ultrasound is 90% at best. Causes for false negative ultrasound examinations are ectopic glands in the mediastinum, small glands weighing less than 200 mg and large goiters which make assessment of the retrothyroid space difficult. Ultrasound and scintigraphy in combination can achieve a sensitivity of more than 90%. A combination of both is indicated prior to minimally invasive resection and in cases of recurrence or persistence of hyperparathyroidism after resection.

Distinguishing Benign and Malignant Findings on [68 Ga]-FAPI PET/CT Based on Quantitative SUV Measurements.

AIM/PURPOSE: Fibroblast activation protein (FAP) is overexpressed by cancer-associated fibroblasts. However, activated fibroblasts have been shown to play a significant role also in certain benign conditions such as wound healing or chronic inflammation. Therefore, the current study aimed to identify whether FAPI uptake might differ between malignant lesions and benign conditions. MATERIAL AND METHODS: We retrospectively analyzed 155 patients with various cancer types who received [68 Ga]-FAPI-04/02-PET/CT between July 2017 and March 2020. SUVmax, SUVmean, and lesion-to-background ratios (LBR) of FAPI uptake were measured in benign processes compared to malignant lesions (primary and/or 2 exemplary metastases). In addition, receiver operating characteristic (ROC) curve analysis was conducted to compare the predictive capabilities of semiquantitative PET/CT parameters. Furthermore, the sensitivity, specificity, optimal cutoff value, and 95% confidence interval (CI) were determined for each parameter. RESULTS: Benign lesions exhibited significantly lower FAPI uptake compared to malignant lesions (mean SUVmax benign vs. malignant: 4.2 vs. 10.6; p < 0.001). In ROC analysis, cutoff values of these lesions (benign vs. malignant) were established based on SUVmax, SUVmean, and LBR. The SUVmax cutoff value for all lesions was 5.5 and the corresponding sensitivity, specificity, accuracy, and AUC were 78.8%, 85.1%, 82.0%, and 0.89%, respectively. CONCLUSION: Our aim was to systematically analyze the pattern of FAPI uptake in benign and malignant processes. This investigation demonstrates that FAPI uptake might be useful to differentiate malignant and benign findings due to different patho-physiological origins.

Detecting and Locating the Site of Local Relapse Using 18F-PSMA-1007 Imaging After Primary Treatment of 135 Prostate Cancer Patients-Potential Impact on PSMA-Guided Radiation Therapy.

PURPOSE: Due to limited imaging options, the visualization of a local relapse of prostate cancer used to pose a considerable challenge. However, since the integration of 18F-PSMA-1007-PET/CT into the clinic, a relapsed tumor can now easily be detected by hybrid imaging. The present study aimed to evaluate and map the allocate relapse in a large cohort of prostate cancer patients focusing on individual patient management conclusions for radiation therapy. PROCEDURES: The current study included 135 men with prostate cancer after primary treatment who underwent 18F-PSMA-1007-PET/CT due to biochemical relapse detecting a local relapse. Imaging data were reassessed and analyzed with regard to relapse locations. For the correlation of tumor foci with clinical data, we used binary logistic regression models as well as the Kruskal-Wallis test and Mann-Whitney test. RESULTS: In total, 69.6% of all patients (mean age: 65 years) underwent prostatectomy while 30.4% underwent radiation therapy. PET imaging detected most frequently a unifocal relapse (72.6%). There was a statistically significantly higher rate of ipsilateral cases among the relapsed tumors. Comparing both treatment approaches, tumors relapsed most commonly within the posterior region after surgery and transition/peripheral zone after radiation therapy, respectively. CONCLUSIONS: The present study confirms that 18F-PSMA-1007-PET/CT is highly suitable for the localization and allocation of a local relapse in patients with prostate cancer. The data enable further optimizing dose prescriptions and target volume delineations of radiation therapy in the future.