The added value of 18F-FDG PET/CT compared to 68Ga-PSMA PET/CT in patients with castration-resistant prostate cancer

Purpose: The 68Ga-PSMA PET/CT is a commonly used imaging modality in prostate cancers. However, few studies have compared the diagnostic efficiency between 68Ga-PSMA and 18F-FDG PET/CT and evaluated whether a heterogeneous metabolic phenotype (especially PSMA-FDG+ lesions) exists in patients with castration-resistant prostate cancer (CRPC). We determined the added value of 18F-FDG PET/CT compared to 68Ga-PSMA PET/CT in CRPC patients and identified CRPC patients who may benefit from additional 18F-FDG PET/CT. Methods: Data of 56 patients with CRPC who underwent both 68Ga-PSMA and 18F-FDG PET/CT from May 2018 to February 2021 were retrospectively analysed. Patients were classified into two groups with or without PSMA-FDG+ lesions. The differences in patient characteristics between the two groups and predictors of patients who having at least one PSMA-FDG+ lesion were analysed. Results: Although both the detection rate (75.0% vs. 51.8%, P = 0.004) and positive lesion number (135 vs. 95) of 68Ga-PSMA PET/CT were higher than 18F-FDG PET/CT, there were still 13/56 (23.2%) patients with at least one PSMA-FDG+ lesion. The prostate-specific antigen (PSA) and Gleason score were both higher in the patients with PSMA-FDG+ lesions than in those without PSMA-FDG+ lesions (P = 0.04 and P<0.001, respectively). Multivariate regression analysis showed that the Gleason score (≥8) and PSA (≥7.9 ng/mL) were associated with the detection rate of patients who had PSMA-FDG+ lesions (P = 0.01 and P = 0.04, respectively). The incidences of having PSMA-FDG+ lesions in low-probability (Gleason score<8 and PSA<7.9 ng/mL), medium-probability (Gleason score≥8 and PSA<7.9 ng/mL or Gleason score<8 and PSA≥7.9 ng/mL), and high-probability (Gleason score≥8 and PSA≥7.9 ng/mL) groups were 0%, 21.7%, and 61.5%, respectively (P<0.001). Conclusion: Gleason score and PSA are significant predictors for PSMA-FDG+ lesions, and CRPC patients with high Gleason score and PSA may benefit from additional 18F-FDG PET/CT.

The Heterogeneous Metabolic Patterns of Ganglia in 68Ga-PSMA, 11C-choline, and 18F-FDG PET/CT in Prostate Cancer Patients

PURPOSE

Studies have indicated that PSMA-positive ganglia represent a diagnostic pitfall for nuclear medicine physicians. No studies have described choline and FDG uptake in ganglia, which may be a source of misdiagnosis. Herein, we described the percentage and uptake pattern of 68Ga-PSMA, 11C-choline and 18F-FDG PET/CT in ganglia and evaluated the heterogeneous metabolic patterns of ganglia to differentiate from lymph node metastases (LNM).

METHODS

Thirty-nine patients who underwent 11C-choline PET/CT and 120 patients who underwent 68Ga-PSMA PET/CT and 18F-FDG PET/CT were retrospectively analyzed. The prevalence of PSMA-positive, choline-positive and FDG-positive ganglia was determined, the SUVmax of ganglia in different locations were measured, and the configuration was described. The SUVmax cutoff of PSMA-PET, choline-PET and FDG-PET was determined by ROC curve analysis to differentiate ganglia from LNM.

RESULTS

329 PSMA-positive ganglia were identified in 120 patients, 95 choline-positive ganglia were identified in 39 patients, and 39 FDG-positive ganglia were identified in 34 patients. PSMA-positive uptake was observed in 98.3%, 95.8%, and 80.0% of cervical, coeliac, and sacral ganglia, respectively. Choline-positive uptake was observed in 84.6%, 97.4%, and 61.5% of cervical, coeliac, and sacral ganglia, respectively. FDG-positive uptake was observed in 16.7%, 13.3%, and 2.5% of cervical, coeliac, and sacral ganglia, respectively. Cervical and coeliac ganglia had a higher rate of PSMA-positive uptake than sacral ganglia. Choline uptake was highest in coeliac ganglia followed by cervical and sacral ganglia. PSMA, choline or FDG uptake in LNM was all significantly higher than ganglia. ROC curve analysis revealed that at a 4.1 SUVmax cutoff of PSMA-PET, the sensitivity, specificity and accuracy of LNM identification was 88.4%, 97.9% and 96.2%, respectively. ROC curve analysis revealed that at a 2.35 SUVmax cutoff for choline-PET, the sensitivity, specificity, and accuracy of LNM identification was 95.0%, 92.6% and 93.0%, respectively. ROC curve analysis revealed that at a 2.55 SUVmax cutoff for FDG-PET, the sensitivity, specificity, and accuracy of LNM identification was 77.3%, 87.2%, and 81.9%, respectively. PSMA-, Choline- and FDG-positive ganglia are mainly band-shaped; most LNMs exhibited nodular and teardrop-shaped configuration.

CONCLUSION

68Ga-PSMA and 11C-choline uptake in ganglia was common, and FDG-positive ganglia were observed at lower frequency. Using 68Ga-PSMA, 11C-choline and 18F-FDG uptake and anatomic location and configuration, the differentiation of ganglia from adjacent LNM is feasible.

68Ga-PSMA-11 PET/CT Follow-Up of Patients with Prostate Cancer with Bone Metastases Who Had Reduced Bone Density after Androgen Deprivation Therapy

Bone metastases from prostate cancer (PCa) often show an increase in density on computed tomography (CT) after successful androgen deprivation therapy (ADT). Density may be reduced, however, as the disease progresses or, contrarily, when disease is no longer active. The current study investigated the role of 68Ga-PSMA-11 positron emission tomography/computed tomography (PET/CT) in differentiating between these two conditions. Methods: The study cohort included 15 PCa patients with sclerotic/blastic bone metastasis in whom reduction in bone density of metastasis was noted on follow-up 68Ga-PSMA-11 PET/CT after ADT. Each patient had two PET/CT scans. Prior to the first scan, six patients were castration naïve and nine patients were already treated. All patients had ADT between the two PET/CT scans. PET parameters (SUVmax and tumor-to-background ratio), and CT parameters (HUmax) were determined and compared for each lesion on both scans. Patient’s response was based on prostate-specific antigen (PSA) levels and appearance of new lesions. The Kolmogorov–Smirnov test was used to evaluate normal distribution of the continuous variables. Results: Post-ADT reduction in bone density was identified in 37 lesions. The mean HUmax was 883.9 ± 175.1 on the first scan and 395.6 ± 157.1 on the second scan (p < 0.001). Twenty-one of the 37 lesions showed no increased tracer uptake on the second PET/CT scan raising the likelihood of a response. The other 16 lesions were associated with increased uptake suggestive of an active resistant disease. Bone density was not different in lesions that no longer showed an increased uptake as compared with those that did. Seven of the study patients responded to therapy, and none of the 16 lesions found in these patients showed increased 68Ga-PSMA-11 uptake. In eight patients with progressive disease, all 12 lesions in five of them showed increased 68Ga-PSMA-11 uptake, there was mixed response in two patients (having two lesions with increased uptake and one without) and although all three lesions no longer showed an increased uptake, new lesions were detected in the eighth patient. Conclusion: A decrease in density of bone lesions may reflect clinical progression, or contrarily, a response to therapy in patients with PCa and skeletal involvement treated with ADT. Uptake of 68Ga-PSMA-11 may separate between these two vastly opposing conditions.

Diagnostic value of 18F-FDG PET/CT in patients with biochemical recurrent prostate cancer and negative 68Ga-PSMA PET/CT

PURPOSE

⁶⁸Ga-PSMA PET/CT has a high detection rate in prostate cancer patients with biochemical recurrence (BCR). However, few studies have reported other imaging methods for BCR with negative ⁶⁸Ga-PSMA PET/CT findings. We investigated the value of ¹⁸F-FDG compared with ⁶⁸Ga-PSMA and identified BCR patients with ⁶⁸Ga-PSMA-negative findings who are most likely to benefit from ¹⁸F-FDG PET/CT.

METHODS

Seventy-two BCR patients with negative ⁶⁸Ga-PSMA PET/CT findings were retrospectively identified from 510 patients who underwent concomitant ⁶⁸Ga-PSMA and ¹⁸F-FDG PET/CT between June 2018 and August 2020. Patients were categorised into groups with positive or negative ¹⁸F-FDG PET/CT findings. Differences in patients' characteristics between these two groups and predictors of positive ¹⁸F-FDG findings were analysed.

RESULTS

The detection rate of ¹⁸F-FDG PET/CT was 16.7% (12/72) in BCR patients with ⁶⁸Ga-PSMA-negative findings. PSA and Gleason score were significantly higher in the ¹⁸F-FDG-positive group than in the ¹⁸F-FDG-negative group (P < 0.001 and P < 0.001, respectively). A multivariate analysis indicated that PSA (PSA ≥2.3 ng/mL) and Gleason score (Gleason score ≥ 8) correlated with ¹⁸F-FDG-positive findings (P < 0.001 and P = 0.015, respectively). The probabilities of ¹⁸F-FDG-positive findings in the low-potential (PSA <2.3 ng/mL and Gleason score <8), moderate-potential (PSA <2.3 ng/mL and Gleason score ≥ 8 or PSA ≥2.3 ng/mL and Gleason score <8), and high-potential (PSA ≥2.3 ng/mL and Gleason score ≥ 8) groups were 0%, 11.5%, and 90.0%, respectively (P < 0.001).

CONCLUSION

PSA level and Gleason score are independent predictors of ¹⁸F-FDG-positive findings, and BCR patients with ⁶⁸Ga-PSMA-negative findings with high PSA and Gleason score are most likely to benefit from ¹⁸F-FDG PET/CT.

68Ga PSMA Uptake at Roux-en-Y Eso-jejunostomy Junction Mimicking the Recurrence of Gastric Carcinoma in PET/CT

A 67-year-old male patient had undergone total gastrectomy and Roux-en-Y eso-jejunostomy 3 years ago for the treatment of tubular adenocarcinoma located at the corpus of the stomach. The patient was diagnosed with Gleason score 8 (4+4) metastatic prostate cancer during the follow-up period and received hormone therapy. Owing to his elevated prostate-specific antigen levels (77 ng/mL), his clinician referred him gallium-68 (⁶⁸Ga) prostate-specific membrane antigen 11 (PSMA) positron emission tomography/computed tomography (PET/CT) for restaging. PET/CT showed multiple ⁶⁸Ga PSMA receptor-positive skeletal lesions and linear PSMA activity at the eso-jejunostomy junction. He was then referred to undergo ¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) PET/CT to screen for gastric carcinoma recurrence. PET/CT images demonstrated no ¹⁸F-FDG avid lesion. However, endoscopy and biopsy performed with samples from the eso-jejunostomy junction revealed superficial benign squamous epithelial fragments.

PSMA whole-body tumor burden in primary staging and biochemical recurrence of prostate cancer

PURPOSE

The objective of this study was to evaluate whether ⁶⁸Ga-PSMA PET/CT whole-body tumor burden (PSMAwbtb) is associated with clinical parameters and laboratory parameters in prostate cancer patients.

METHODS

We retrospectively evaluated prostate cancer patients submitted to PSMA PET/CT for primary staging purposes or due to biochemical recurrence (BR). PSMAwbtb metrics (total volume of PSMA-avid tumor (PSMA-TV)) and total uptake of PSMA-avid lesions (PSMA-TL) were calculated semi-automatically. Spearman's rank correlations between PSMAwbtb metrics and clinical, laboratory parameters (age, time-to-BR, years of diagnosis of prostate cancer, free and total serum PSA levels, and the Gleason score) and with the highest SUVmax of a lesion (hSUVmax) were analyzed.

RESULTS

Among the 257 PSMA PET/CT studies, there were 46 scans (17.9%) performed for primary staging and 211 (82.1%) for BR. PSMA-TV and PSMA-TL were calculated for the 157 positive scans (58.8%), which were 43 patients (93.5%) in the primary staging group and 114 patients (54.0%) in the BR group. In the primary staging group, we observed a significant correlation between PSMA-TL and hSUVmax (p = 0.0021). In the BR group, there was a significant direct correlation between PSMA-TL and the variables age (p = 0.0031), total serum PSA values (p = < 0.0001), free serum PSA values (p = < 0.0001), and the hSUVmax (p = < 0.0001). Similar results were obtained for PSMA-TV.

CONCLUSION

PSMAwbtb has a direct and positive correlation with serum PSA values and age in prostate cancer patients with BR.

Impact of 68 Gallium prostate-specific membrane antigen tracers on the management of patients with prostate cancer who experience biochemical recurrence

OBJECTIVE

To investigate the impact of ⁶⁸ Gallium prostate-specific membrane antigen (⁶⁸ Ga-PSMA) tracers on the management of prostate cancer (PCa) patients with biochemical recurrence (BCR) by conducting a systematical review and meta-analysis.

MATERIALS AND METHODS

We performed a literature search of the PubMed, Embase and Web of Science databases up to 29 October 2019. We included studies that reported the proportion of patients whose management changed after ⁶⁸ Ga-PSMA tracers were used in patients with BCR. We used the Quality Assessment of Diagnostic Accuracy Studies-2 tool to evaluate the quality of the included studies. The proportion of patients with management changes were pooled using a random-effects model. Subgroup analyses and meta-regression analyses were performed to explore the source of heterogeneity. A Sankey diagram was used to show treatment change from before to after the use of ⁶⁸ Ga-PSMA tracers.

RESULTS

We included 20 eligible studies (2026 patients). The pooled proportion of patients with management change was 53% (95% confidence interval [CI] 46-60) in patients with BCR and 51% (95% CI, 34-67) in patients with early BCR (prostate-specific antigen [PSA] <0.5 ng/mL). The pooled positron-emission tomography-positive rate in patients with BCR was 68% (95% CI 59-78). Fourteen studies reported management change, with most changes being intermodal in nature (42%, vs 17% intramodal change).

CONCLUSIONS

The use of ⁶⁸ Ga-PSMA tracers altered the management of more than half of PCa patients with BCR, including those with early BCR. ⁶⁸ Ga-PSMA tracers might be used to guide individualized treatment in patients with BCR, particularly those with early BCR.

Comparative Findings Between 68Ga-PSMA and 18F-FDG PET/CT for Hepatocellular Carcinoma

We have reported here the case of a 69-year-old man who presented with spinal cord compression due to bone metastases as the first manifestation of hepatocellular carcinoma (HCC). For the initial staging, the patient underwent ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computerized tomography (PET/CT) imaging, which demonstrated mild ¹⁸F-FDG uptake in the multiple expansile osteolytic bone lesions, but no remarkable atypical ¹⁸F-FDG uptake in the liver lesion on low-doses CT. An additional PET/CT scan was performed to evaluate the prostate-specific membrane antigen (PSMA) expression, which has recently been reported to be a potential biological marker in a variety of tumors including HCC. High PSMA uptake was recorded in both the metastatic bone lesions and the primary liver lesion/tumor by the ⁶⁸Ga-PSMA PET/CT.

Renal Cortical 68Ga-PSMA-11 PET and 99mTc-DMSA Images

⁶⁸Ga-prostate-specific membrane antigen (PSMA) ligands are novel PET radiotracers for prostate cancer. These radiotracers also localize in the normal renal cortex to a high degree and can demonstrate parenchymal defects. We recently started a prospective research study to compare ⁶⁸Ga-PSMA-11 PET/CT with ^99mTc-dimercaptosuccinic acid (DMSA) scan in adults with pyelonephritis. Here, we present a side-by-side comparison of renal cortical PSMA PET/CT and DMSA images of an adult patient with chronic recurring pyelonephritis. Methods: Our prospective study was approved by the Ethical Committees. DMSA images (multiple planar and SPECT) were obtained 3 h after intravenous injection of 111 MBq (3 mCi) of ^99mTc-DMSA. On a separate day, we obtained PET/CT images of the kidneys 60 min after intravenous injection of 74 MBq (2 mCi) of ⁶⁸Ga-PSMA-11 after the patient provided written informed consent. Results: The patient was a 46-y-old woman with history of chronic recurring pyelonephritis. Both DMSA scan and PSMA PET/CT demonstrated slight cortical thinning with mildly reduced uptake in the upper pole of the right kidney, with no significant cortical defects. There was an excellent distribution of activity in the renal cortex and better image resolution with PSMA PET than with DMSA scan. Non-attenuation-corrected PSMA PET images also showed the same findings, with reasonable image quality. Conclusion: In our first case, ⁶⁸Ga-PSMA-11 PET imaging provided promising results in an adult patient with pyelonephritis. The results of our prospective study on a larger number of adult patients will provide a more accurate comparison of ⁶⁸Ga-PSMA-11 PET to ^99mTc-DMSA scanning in pyelonephritis.

68Ga-PSMA PET/CT in the evaluation of locally advanced and metastatic breast cancer, a single center experience

Current research indicates that prostate-specific membrane antigen (PSMA) is related to angiogenesis of many solid tumors including breast cancer (BC), our objective is evaluating PSMA expression in primary tumor and metastatic BC by Positron emission tomography/computed tomography (PET/CT). In this retrospective study twenty-one patients with BC included all molecular subtypes, was evaluated with 18F-FDG-PET/CT imaging as stratification and 68Ga-PSMA-PET/CT. Primary sites of BC was identifying in all patients with 18F-FDG-PET/CT. We identified lymph node metastases in 17 patients (81%) and metastatic disease in 15 patients (71%). A total 127 lesions were detected by 18F-FDG-PET/CT, 30 of which were in the breast, 31 axillary lymph-node metastases, 25 mediastinal lymph-node metastases, 15 distant non-bone metastases and 26 bone metastases. 68Ga-PSMA-11-PET/CT showed lower detection-rate (DRs) than did 18F-FDG-PET/CT in all patients with LUM-A and LUM-B HER2. All 18F-FDG PET/CT positive lesions in patients TPN (local, lymph nodes, and metastatic lesions) showed 68Ga-PSMA-PET/CT uptake (P<0.05). Sensitivities and specificities of 99.2% and 93.6% for 18F-FDG-PET/CT and for 68Ga-PSMA-11-PET/CT of 84% and 91.8% (P<0.05). Accuracy measured as AUC was 0.86-0.95 in 18F-FDG-PET/CT and 0.74-0.94 for 68Ga-PSMA-PET/CT (P<0.05). In Patient-Based analysis we found that patients triple-negative subtype (TPN) evaluated with 68Ga-PSMA-PET/CT identified a higher number of positive patients than did LUM A. We conclude that a significate DRs to imaging with 68Ga-PSMA-PET/CT in the staging of locally advanced and metastatic BC with high rates in patients TPN, LUM B HER2+ and HER2 overexpression. We believe that concept of theranostics it may be considered as a potential diagnostic and therapeutic target.

Topical Sensor for the Assessment of PET Dose Administration: Metric Performance with an Autoinjector

Extravasation or partial extravasation of the radiopharmaceutical dose in PET can undermine SUV and image quality. A topical sensor has been validated using several metrics to characterize injection quality after manual injection. The performance of these metrics for autoinjector administration has been assessed. Methods: A single PET/CT scanner at a single site was used to characterize injections using an autoinjector with standardized apparatus, flush volume, and infusion rate (1-min infusion followed by 2 syringe flushes) for ¹⁸F-FDG, ⁶⁸Ga-prostate-specific membrane antigen, and ⁶⁸Ga-DOTATATE. In total, 296 patients with topical application of sensors were retrospectively analyzed using conventional statistical analysis and an artificial neural network. Results: Partial extravasation was noted in 1.3% of studies, with 9.1% (inclusive of partial extravasation) identified to have an injection anomaly (e.g., venous retention). Extravasation was independently predicted by the time that elapsed as the counts recorded by the injection sensor fell from the maximum value to within 200% of the reference sensor counts greater than 1,200 s; as the difference in counts for injection and reference sensors, normalized by dose, from 4 min after injection greater than 25; and as the ratio of the average counts per second recorded by the injection sensor at the end of a monitoring period to those of the reference sensor greater than 2. Conclusion: Extravasation and partial extravasation of PET doses are readily detected and differentiated using time-activity curve metrics. The metrics can provide the insight that could inform image quality or SUV accuracy issues. Further validation of key metrics is recommended in a larger and more diverse cohort.

68Ga-PSMA PET/CT for Primary Lymph Node and Distant Metastasis NM Staging of High-Risk Prostate Cancer

With the largest high-risk prostate cancer (PCa) cohort to date undergoing ⁶⁸Ga-prostate-specific membrane antigen (PSMA) PET/CT primary staging, we aimed to, first, characterize the metastatic spread of PCa in relation to tumor ⁶⁸Ga-PSMA uptake and the D'Amico classification and, second, compare ⁶⁸Ga-PSMA PET/CT findings with radical prostatectomy and pelvic lymph node dissection (PLND) histopathology findings. Methods: The study included 691 consecutive newly diagnosed, biopsy-proven, treatment-naïve, D'Amico high-risk PCa patients primary-staged by ⁶⁸Ga-PSMA PET/CT. PSMA SUV_max and metastatic findings were compared with prostate-specific antigen level, International Society of Urological Pathology (ISUP) grade, and clinical stage as traditional risk stratification parameters. Moreover, ⁶⁸Ga-PSMA PET/CT findings were compared with histology findings in radical prostatectomy patients undergoing PLND. Undetected lymph node metastases (LNMs) underwent immunohistochemical PSMA staining. Results: Advanced disease (N1/M1) was observed in 35.3% of patients (244/691) and was associated with increasing prostate-specific antigen level, ISUP grade, and clinical stage. LNMs (N1/M1a) were detected in 31.4% (217/691) and bone metastases (M1b) in 16.8% (116/691). Advanced disease frequencies in patients with ISUP grades 2 and 3 were 10.8% (11/102) and 37.1% (33/89), respectively. Risk of advanced disease for cT2a, cT2b, and cT2c tumors was almost equal (24.2%, 27.9%, and 22.4%, respectively). We observed a weak correlation between SUV_max and biopsy ISUP grade (ρ = 0.21; P < 0.001) and a modest correlation between SUV_max and postprostatectomy ISUP grade (ρ = 0.38; P < 0.001). Sensitivity, specificity, positive and negative predictive value, and accuracy for LNM detection on ⁶⁸Ga-PSMA PET/CT in the PLND cohort were 30.6%, 96.5%, 68.8%, 84.5%, and 83.1%, respectively. Undetected LNMs either were micrometastases located in the lymph node border or were without PSMA expression. Conclusion: In this high-risk PCa cohort, we identified advanced disease in about one third at diagnosis. ISUP grade was the superior predictor for advanced disease at diagnosis. We found a significant difference in frequency of advanced disease between ISUP grades 2 and 3, as supports the Gleason score 7 subdivision. Interestingly, we observed no significant differences in risk of advanced disease when comparing the different cT2 stages. The undetected LNMs were either PSMA-negative or micrometastases.

Accuracy of 68Ga-PSMA-11 PET/CT and multiparametric MRI for the detection of local tumor and lymph node metastases in early biochemical recurrence of prostate cancer

Anatomical and functional imaging plays a decisive role for detection and staging, of prostate cancer both primarily and post-treatment. While multiparametric MRI offers anatomic imaging with excellent soft tissue contrast, hybrid imaging based on positron emission tomography in combination with computed tomography (PET/CT) contributes functional imaging capacities. Since 68Ga-PSMA-11 was expected to be more efficient than the prior Choline-based PET radiotracers, it was the aim of the study to evaluate the diagnostic performance of the 68Ga-PSMA-11 PET/CT and multiparametric MRI in patients with recurrent prostate cancer and low PSA levels. 32 out of a cohort of 128 prostate cancer patients with biochemical relapse were referred for 68Ga-PSMA-11 PET/CT, MRI and bone scintigraphy. According to the histopathologically or clinically defined reference standard all results were classified as true positive, false positive, true negative or false negative. Local recurrence was present in 11/32 patients, lymph node metastases - in 13/32 patients and, bone metastases - in 6/32 patients. Against the standard of reference, sensitivity, specificity and accuracy for local recurrence of PET/CT were 63.6 %; 73.7%; 77.8%, respectively. MRI reached 90.9%; 94.7%; 92.3%, respectively. For local lymph node metastases PET/CT - 83.3%; 80.0% and 90.6%, respectively. MRI - 41.7%; 94.4%; 72.0%, respectively. For evaluation of bone metastases in PET/CT - 83.3%; 92.0%; 71.0%, respectively. Bone scintigraphy - 50.0%; 84.0%; 77.4%, respectively. In conclusion, mpMRI offered the better diagnostic accuracy in the detection of local recurrence and while PSMA PET/CT was superior in the detection of distant and lymph node metastases.

Optimization of injected 68Ga-PSMA activity based on list-mode phantom data and clinical validation

Optimization of injected gallium-68 (⁶⁸Ga) activity for ⁶⁸Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic point of view. However, no clear guidelines are available for ⁶⁸Ga-PSMA studies. Therefore, a phantom study is performed to determine the highest coefficient of variation (COV) acceptable for reliable image interpretation and quantification.

To evaluate image interpretation, the relationship of COV and contrast-to-noise ratio (CNR) was studied. The CNR should remain larger than five, according to the Rose criterion. To evaluate image quantification, the effect of COV on the percentage difference (PD) between quantification results of two studies was analyzed. Comparison was done by calculating the PD of the SUV_max. The maximum allowable PD_SUVmax was set at 20%. The highest COV at which both criteria are still met is defined as COV_max. Of the NEMA Image Quality phantom, a 20 min/bed (2 bed positions) scan was acquired in list-mode PET (Philips Gemini TF PET/CT). The spheres to background activity ratio was approximately 9:1. To obtain images with different COV, lower activity was mimicked by reconstructions with acquisition times of 10 min/bed to 5 s/bed. Pairs of images were obtained by reconstruction of two non-overlapping parts of list-mode data.

For the 10-mm diameter sphere, a COV of 25% still meets the criteria of CNR_SUVmean ≥ 5 and PD_SUVmax ≤ 20%. This phantom scan was acquired with an acquisition time of 116 s and a background activity concentration of 0.71 MBq/kg. Translation to a clinical protocol results in a clinical activity regimen of 3.5 MBq/kg min at injection. To verify this activity regimen, 15 patients (6 MBq/kg min) with a total of 22 lesions are included. Additional reconstructions were made to mimic the proposed activity regimen. Based on the CNR_SUVmax, no lesions were missed with this proposed activity regimen.

For our institution, a clinical activity regimen of 3.5 MBq/kg min at injection is acceptable, which indicates that activity can be reduced by almost 50% compared with the current code of practice. Our proposed method could be used to obtain an objective activity regimen for other PET/CT systems and tracers.

Optimal Timing of Prostate Specific Membrane Antigen Positron Emission Tomography/Computerized Tomography for Biochemical Recurrence after Radical Prostatectomy

PURPOSE

We developed a model predicting the probability of detecting prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography in patients with biochemical recurrence after radical prostatectomy.

MATERIALS AND METHODS

We retrospectively included 419 consecutive patients with biochemical recurrence (prostate specific antigen less than 2.0 ng/ml) after radical prostatectomy who underwent ⁶⁸Ga-prostate specific membrane antigen-11 positron emission tomography/computerized tomography to guide salvage therapy. Patients receiving androgen deprivation therapy between radical prostatectomy and prostate specific membrane antigen positron emission tomography/computerized tomography were excluded from the study. We used multivariable logistic regression to assess predictors for the detection of prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography. We minimized overfitting of the model and used decision curve analysis to determine clinical utility.

RESULTS

Median prostate specific antigen at scanning was 0.40 ng/ml (IQR 0.30-0.70). Overall 174 (42%) patients had prostate cancer recurrence outside the prostatic fossa. Prostate specific antigen at time of scanning, and grade group, N stage and surgical margin status at radical prostatectomy specimen were significant predictors for detecting prostate cancer recurrence outside the prostatic fossa. The bootstrapped AUC of this model was 0.75 (IQR 0.73-0.77). The decision curve analysis showed a net benefit by a model based probability from 16%. Limitations include the retrospective design and the missing histological correlation of positive lesions.

CONCLUSIONS

Next to the prostate specific antigen at time of scanning, grade group, N stage and surgical margin status at radical prostatectomy specimen are significant predictors for detecting prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography. The presented model is implemented in a dashboard to assist clinicians in determining the optimal time to perform ⁶⁸Ga-prostate specific membrane antigen-11 positron emission tomography/computerized tomography in patients with biochemical recurrence after radical prostatectomy.

68Ga/64Cu PSMA Bio-Distribution in Prostate Cancer Patients: Potential Pitfalls for Different Tracers

BACKGROUND

68Ga-PSMA is a widely useful PET/CT tracer for prostate cancer imaging. Being a transmembrane protein acting as a glutamate carboxypeptidase enzyme, PSMA is highly expressed in prostate cancer cells. PSMA can also be labeled with 64Cu, offering a longer half-life and different resolution imaging. Several studies documented bio-distribution and pitfalls of 68Ga-PSMA as well as of 64Cu- PSMA. No data are reported on differences between these two variants of PSMA. Our aim was to evaluate physiological distribution of these two tracers and to analyze false positive cases.

METHODS

We examined tracer bio-distribution in prostate cancer patients with negative 68Ga-PSMA PET/CT (n=20) and negative 64Ga-PSMA PET/CT (n=10). A diagnostic pitfall for each tracer was documented.

RESULT

Bio-distribution of both tracers was similar, with some differences due to renal excretion of 68Ga- PSMA and biliary excretion of 64Cu-PSMA. 68Ga-PSMA uptake was observed in sarcoidosis while 64Cu- PSMA uptake was recorded in pneumonitis.

DISCUSSION

Both tracers may present similar bio-distribution in the human body, with similar uptake in exocrine glands and high intestinal uptake. Similarly to other tracers, false positive cases cannot be excluded in clinical practice.

CONCLUSION

The knowledge of difference in bio-distribution between two tracers may help in interpretation of PET data. Diagnostic pitfalls can be documented, due to the possibility of PSMA uptake in inflammation. Our results are preliminary to future studies comparing diagnostic accuracies of 68Ga-PSMA and 64Cu-PSMA.

Topical Sensor for the Assessment of Injection Quality for 18F-FDG, 68Ga-PSMA and 68Ga-DOTATATE Positron Emission Tomography

INTRODUCTION

Calculation of the standard uptake value (SUV) and image quality in positron emission tomography (PET) hinges on accurate dose delivery. Extravasation or partial extravasation of the radiopharmaceutical dose can undermine SUV and image quality, and contribute to unnecessary imaging (time and CT dose). Topical sensor characterisation of injections has been reported, with extravasation rates ranging from 9% to 23% for 18F-FDG after manual injection.

METHOD

A single site, single PET/CT scanner was used to characterise injections using an autoinjector with standardised apparatus, flush volume and infusion rate using 18F-FDG, 68Ga-PSMA and 68Ga-DOTATATE; more reflective of Australian PET facilities. 296 patients with topical application of LARA sensors were retrospectively analysed.

RESULTS

Only 1.1% of studies showed evidence of partial dose extravasation. In total, 9.1% were identified to have an injection anomaly (including venous retention). No statistically significant differences were noted across the radiopharmaceuticals for demographic data. Although not demonstrating a statistically significant correlation, there was more extravasated doses associated with female patients (P = .334), right side (P = .372), and hand injections (P = .539). Extravasation was independent of dose administered (P = .495), the radiopharmaceutical (P = .887), who injected the dose (P = .343), height (P = .438), weight (P = .607) or age (P = .716). Extravasation was associated with higher glucose levels (P < .001), higher t-half (P = .019) and higher aUCR10, tc50, aUCR1 and c1 (all P < .001).

CONCLUSION

Topical monitoring and characterisation of PET dose administration is possible and practical with the LARA device. Extravasation and partial extravasation of PET doses are not only readily detected but they are also preventable. The LARA device can provide the insights into variables that could eliminate extravasation as a cause of image quality or SUV accuracy issues.

68Ga-PSMA: a One-stop Shop in Radioactive Iodine Refractory Thyroid Cancer?

We report a case of a 47-year-old female known with metastatic papillary thyroid cancer. Her treatment history included total thyroidectomy and 3 previous radio ablations with a cumulative dose of 950 mCi of ¹³¹I. On follow-up, her thyroglobulin levels had demonstrated a rising trend (from 3789.0 to 4240.0 ug/L) despite a ¹²³I whole-body scan demonstrating a reduction in tracer avid lesions. She was suspected of having radio-resistant disease. The patient underwent both ¹⁸F-FDG and ⁶⁸Ga-PSMA PET/CT imaging with both scans demonstrating congruent lesions however with far greater intensity on the ⁶⁸Ga-PSMA study.

The "question-mark" MR anatomy of the cervico-thoracic ganglia complex: can it help to avoid mistaking it for a malignant lesion on 68Ga-PSMA-11 PET/MR?

Background

Detectable uptake of ⁶⁸Ga-PSMA-ligands in sympathetic ganglia may potentially lead to mistaking them for malignant lesions. Our aim was to investigate the anatomy of cervico-thoracic-ganglia-complex (CTG-C) in the MR part of multimodal ⁶⁸Ga-PSMA-11 PET/MR imaging, in view of PET factors hindering its proper identification.

Patients and methods

In 106 patients, 212 sites of the CTG-C were retrospectively reviewed to assess the radiotracer uptake (SUV_max), size, shape, position, symmetry of location and visual uptake intensity. Asymmetry of PSMA-ligand uptake and increased uptake were regarded as risk factors of malignancy.

Results

In 66.0% left (L) and 53.8% right (R) CTG-C we noticed configurations, resembling the shape of an exclamation-mark, a question-mark, or its part (called “typical”). Tumor-like CTG-C shapes (oval, binodular or longitudinal) were detected in 28.3% L-CTG-C and in 40.6% R-CTG-C. When visual assessment of PET suggested malignancy, the recognition of “typical” shape of underlying CTG-C on MR generated a rise in the accuracy of their proper identification (from 34.4% to 75%, χ2(1) = 70.4; p < 0.001). Recognizing the shape of the CTG-C as “typical” in MR allowed us to classify as “not-suspicious” 61.9% of all CTG-C which were treated as “suspicious” after sole PET assessment.

Conclusions

The characteristic shape of cervico-thoracic-ganglia-complex (resembling a question-mark, or its part) helps in proper recognition of CTG-C on multimodal whole-body ⁶⁸Ga-PSMA-ligand PET/MR imaging, when detectable uptake might lead to considering pathology.

Preliminary results of a 68 Ga-PSMA PET/CT prospective study in prostate cancer patients with occult recurrence: Diagnostic performance and impact on therapeutic decision-making

BACKGROUND

In this prospective study (NCT03443609), we investigated the impact of 68Ga-PSMA-11 PET-CT on the treatment plan and therapeutic response obtained for patients with prostate cancer (PCa) presenting a recurrence with a low rising PSA.

METHODS

One hundred thirty hormone-naive (PSA < 1.5 ng/mL) patients were enrolled. All patients received radical treatment. PET images were recorded 1 and 2  hours after injection of tracer and interpreted by two independent nuclear physicians. Six months after treatment ended, a PSA assay was requested to evaluate the therapeutic efficacy of the treatment based on PSMA results.

RESULTS

Data analysis for the first 52 included patients has been completed. 68Ga-PSMA-11-positive lesions were detected in 38/52 (73.1%) patients. Ninety-four lesions were detected as follows, 53/94 in lymph nodes (56.4%), 25/94 in bone (26.6%), and 12/94 into the prostate bed (12.7%). Detection rates were 58%, 81%, and 82% for serum PSA levels lower than 0.25 ng/mL, between 0.25 to ≤ 0.69  ng/mL and 0.70  ng/mL, respectively. As a result of the PSMA PET-CT, therapeutic management changed in 38/52 patients (73.1%). Patients had undetectable serum PSA levels after treatment guided by 68Ga-PSMA-11 PET-CT results in 10/52 (19.2%) cases and with a PSA decrease of over 60% in 18/52 (34.6%) patients.

CONCLUSION

Whilst our patient population presented a very low PSA level, preliminary results of the 68Ga-PSMA PET-CT study showed recurrence localization in more than half of the patients and this had a major clinical impact, as it resulted in treatment change in more than half of the patients and a significant decrease in PSA levels in a third of patients.

Clinicopathological predictors of positive 68Ga-PSMA-11 PET/CT in PSA-only recurrence of localized prostate cancer following definitive therapy

OBJECTIVE

To demonstrate the effect of clinicopathological factors on ⁶⁸Ga-PSMA-11 PET/CT positivity at the time of biochemical recurrence (BCR) of localized prostate cancer (PCa) following definitive therapy.

METHODS

We retrospectively reviewed our institutional database for PCa patients who had BCR and subsequently underwent ⁶⁸Ga-PSMA-11 PET/CT between April 2014 and February 2018. A total of 51 patients who were metastasis-free before PSMA imaging and previously treated with definitive therapy (radical prostatectomy or external beam radiotherapy) for localized disease (pT1c-T3b pN0-1 cM0) were included.

RESULTS

37 out of 51 patients (72.5%) had positive ⁶⁸Ga-PSMA-11 PET/CT scans. Age at diagnosis, Gleason score (GS), D'Amico risk status of PCa, initial PSA level before treatment and PSA doubling time were not associated with PSMA positivity. Pre-scan PSA levels of > 0.2 ng/ml and PSA velocity of ≥ 1 ng/ml/year were significantly associated with increased PSMA positivity, whereas history of androgen deprivation therapy showed a trend towards significance. The optimal cutoffs for distinguishing between positive and negative scans were ≥ 0.71 ng/ml for pre-scan PSA and ≥ 1.22 ng/ml/yr for PSA velocity. In multivariable analysis, log pre-scan PSA and pre-scan PSA level > 0.2 ng/ml remained significant predictors for PSMA positivity, whereas the association of PSA velocity and of ADT was lost.

CONCLUSIONS

In BCR of localized PCa following definitive therapy, pre-scan PSA was strongly associated with positive ⁶⁸Ga-PSMA-11 scan, even at PSA levels ranging from 0.2 to 1.0 ng/ml. Therefore, clinical and pathological predictors of positive ⁶⁸Ga-PSMA-11 PET/CT in PSA-only recurrence of localized prostate cancer need to be further elucidated.

68Ga-PSMA PET/CT in prostate cancer patients - patterns of disease, benign findings and pitfalls

Background

68Ga-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.

Methods

68Ga-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.

Results

There 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%).

Conclusion

The 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.

Role of textural heterogeneity parameters in patient selection for 177Lu-PSMA therapy via response prediction

Purpose

Prostate cancer is most common tumor in men causing significant patient mortality and morbidity. In newer diagnostic/therapeutic agents PSMA linked ones are specifically important. Analysis of textural heterogeneity parameters is associated with determination of innately aggressive and therapy resistant cell lines thus emphasizing their importance in therapy planning. The objective of current study was to assess predictive ability of tumor textural heterogeneity parameters from baseline ⁶⁸Ga-PSMA PET prior to ¹⁷⁷Lu-PSMA therapy.

Results

Entropy showed a negative correlation (r_s = −0.327, p = 0.006, AUC = 0.695) and homogeneity showed a positive correlation (r_s = 0.315, p = 0.008, AUC = 0.683) with change in pre and post therapy PSA levels.

Conclusions

Study showed potential for response prediction through baseline PET scan using textural features. It suggested that increase in heterogeneity of PSMA expression seems to be associated with an increased response to PSMA radionuclide therapy.

Materials and Methods

Retrospective analysis of 70 patients was performed. All patients had metastatic prostate cancer and were planned to undergo ¹⁷⁷Lu-PSMA therapy. Pre-therapeutic ⁶⁸Ga- PSMA PET scans were used for analysis. 3D volumes (VOIs) of 3 lesions each in bones and lymph nodes were manually delineated in static PET images. Five PET based textural heterogeneity parameters (COV, entropy, homogeneity, contrast, size variation) were determined. Results obtained were then compared with clinical parameters including pre and post therapy PSA, alkaline phosphate, bone specific alkaline phosphate levels and ECOG criteria. Spearman correlation was used to determine statistical dependence among variables. ROC analysis was performed to estimate the optimal cutoff value and AUC.

PET/CT With 68Ga-PSMA in Prostate Cancer: Radiopharmaceutical Background and Clinical Implications

BACKGROUND AND OBJECTIVE

In the last twenty years, positron emission tomography / computed tomography (PET/CT) with radiolabeled choline, represented the most powerful imaging modality for prostate cancer (PCa). However, the low positive detection rate of the technique for PSA < 1 ng/ml prompted the development of other tracers for imaging PCa.

METHODS

We performed a critical review of 68Ga-PSMA, a receptor ligand tracer, which has been identified as the most promising radiopharmaceutical for imaging PCa.

RESULTS

The most promising feature of this radiopharmaceutical is the high positive detection rate for prostate specific antigen (PSA) levels < 1 ng/ml or less (i.e., PSA < 0.5 ng/ml). 68Ga-PSMA detection rate is also sensitive to PSA kinetics, expressed either as PSA doubling time or PSA velocity. There are initial results indicating that 68Ga-PSMA may significantly affect the clinical management of PCa patients, even though the additional advantages in comparison to radiolabeled choline need to be further supported in future perspective studies. Other clinical implications, such as whether 68Ga-PSMA PET/CT predicts PCa-specific survival, have not yet been investigated. Numerous clinical studies have been published, some of them with histopathological verification so that despite the recent introduction in the clinical field reliable estimation of sensitivity and specificity of 68Ga-PSMA PET/CT have been obtained through meta-analyses. Most clinical studies with PET/CT with 68Ga-PSMA are retrospective, single-institutional studies and in many cases include heterogeneous patient cohorts. Thus, multidisciplinary, well-throughout prospective trials are needed to better define the clinical implications of 68Ga- PSMA PET/CT in PCa patients. The increasing availability of positron emission tomography / magnetic resonance (PET/MR) hybrid devices promotes the use of this radiopharmaceutical especially at initial staging when identification of tumor localization and of extra-prostatic disease represent clinically relevant questions. PSMA cold ligands can also be labeled with beta emitters with good chemical stability so that 68Ga-PSMA PET/CT can be used to guide radiometabolic therapy of advanced metastatic PCa patients through 177Lu-labeled PSMA ligands.

CONCLUSION

PSMA labeled ligands appear very promising for diagnosis and treatment of PCa.

Quantitative performance and optimal regularization parameter in block sequential regularized expectation maximization reconstructions in clinical 68Ga-PSMA PET/MR

BACKGROUND

In contrast to ordered subset expectation maximization (OSEM), block sequential regularized expectation maximization (BSREM) positron emission tomography (PET) reconstruction algorithms can run until full convergence while controlling image quality and noise. Recent studies with BSREM and 18F-FDG PET reported higher signal-to-noise ratios and higher standardized uptake values (SUV). In this study, we investigate the optimal regularization parameter (β) for clinical 68Ga-PSMA PET/MR reconstructions in the pelvic region applying time-of-flight (TOF) BSREM in comparison to TOF OSEM. Two-minute emission data from the pelvic region of 25 patients who underwent 68Ga-PSMA PET/MR were retrospectively reconstructed. Reference OSEM reconstructions had 28 subsets and 2 iterations. BSREM reconstructions were performed with 15 β values between 150 and 1200. Regions of interest (ROIs) were drawn around lesions and in uniform background. Background SUVmean (average) and SUVstd (standard deviation), and lesion SUVmax (average of 5 hottest voxels) were calculated. Differences were analyzed using the Wilcoxon matched pairs signed-rank test.

RESULTS

A total of 40 lesions were identified in the pelvic region. Background noise (SUVstd) and lesions SUVmax decreased with increasing β. Image reconstructions with β values lower than 400 have higher (p < 0.01) background noise, compared to the reference OSEM reconstructions, and are therefore less useful. Lesions with low activity on images reconstructed with β values higher than 600 have a lower (p < 0.05) SUVmax compared to the reference. These reconstructions are likely visually appealing due to the lower background noise, but the lower SUVmax could possibly render small low-uptake lesions invisible.

CONCLUSIONS

In our study, we showed that PET images reconstructed with TOF BSREM in combination with the 68Ga-PSMA tracer result in lower background noise and higher SUVmax values in lesions compared to TOF OSEM. Our study indicates that a β value between 400 and 550 might be the optimal compromise between high SUVmax and low background noise.