Machine Learning CT-Based Automatic Nodal Segmentation and PET Semi-Quantification of Intraoperative 68Ga-PSMA-11 PET/CT Images in High-Risk Prostate Cancer: A Pilot Study

High-resolution intraoperative PET/CT specimen imaging, coupled with prostate-specific membrane antigen (PSMA) molecular targeting, holds great potential for the rapid ex vivo identification of disease localizations in high-risk prostate cancer patients undergoing surgery. However, the accurate analysis of radiotracer uptake would require time-consuming manual volumetric segmentation of 3D images. The aim of this study was to test the feasibility of using machine learning to perform automatic nodal segmentation of intraoperative 68Ga-PSMA-11 PET/CT specimen images. Six (n = 6) lymph-nodal specimens were imaged in the operating room after an e.v. injection of 2.1 MBq/kg of 68Ga-PSMA-11. A machine learning-based approach for automatic lymph-nodal segmentation was developed using only open-source Python libraries (Scikit-learn, SciPy, Scikit-image). The implementation of a k-means clustering algorithm (n = 3 clusters) allowed to identify lymph-nodal structures by leveraging differences in tissue density. Refinement of the segmentation masks was performed using morphological operations and 2D/3D-features filtering. Compared to manual segmentation (ITK-SNAP v4.0.1), the automatic segmentation model showed promising results in terms of weighted average precision (97-99%), recall (68-81%), Dice coefficient (80-88%) and Jaccard index (67-79%). Finally, the ML-based segmentation masks allowed to automatically compute semi-quantitative PET metrics (i.e., SUVmax), thus holding promise for facilitating the semi-quantitative analysis of PET/CT images in the operating room.

Identification of incidental brain tumors in prostate cancer patients via PSMA PET/CT

PURPOSE

Brain metastases are rare in patients with prostate cancer and portend poor outcome. Prostate-specific membrane antigen positron emission tomography (PSMA PET)/CT scans including the brain have identified incidental tumors. We sought to identify the incidental brain tumor detection rate of PSMA PET/CT performed at initial diagnosis or in the setting of biochemical recurrence.

METHODS

An institutional database was queried for patients who underwent 68Ga-PSMA-11 or 18F-DCFPyL (18F-piflufolastat) PET/CT imaging at an NCI-designated Comprehensive Cancer Center from 1/2018 to 12/2022. Imaging reports and clinical courses were reviewed to identify brain lesions and describe clinical and pathologic features.

RESULTS

Two-thousand seven hundred and sixty-three patients underwent 3363 PSMA PET/CT scans in the absence of neurologic symptoms. Forty-four brain lesions were identified, including 33 PSMA-avid lesions: 10 intraparenchymal metastases (30%), 4 dural-based metastases (12%), 16 meningiomas (48%), 2 pituitary macroadenomas (6%), and 1 epidermal inclusion cyst (3%) (incidences of 0.36, 0.14, 0.58, 0.07, and 0.04%). The mean parenchymal metastasis diameter and mean SUVmax were 1.99 cm (95%CI:1.25-2.73) and 4.49 (95%CI:2.41-6.57), respectively. At the time of parenchymal brain metastasis detection, 57% of patients had no concurrent extracranial disease, 14% had localized prostate disease only, and 29% had extracranial metastases. Seven of 8 patients with parenchymal brain metastases remain alive at a median 8.8 months follow-up.

CONCLUSION

Prostate cancer brain metastases are rare, especially in the absence of widespread metastatic disease. Nevertheless, incidentally detected brain foci of PSMA uptake may represent previously unknown prostate cancer metastases, even in small lesions and in the absence of systemic disease.

Eligibility for 177Lu-PSMA Therapy Depends on the Choice of Companion Diagnostic Tracer: A Comparison of 68Ga-PSMA-11 and 99mTc-MIP-1404 in Metastatic Castration-Resistant Prostate Cancer

¹⁷⁷Lu-prostate-specific membrane antigen-617 (¹⁷⁷Lu-PSMA-617) is an effective therapy for metastatic castration-resistant prostate cancer (mCRPC), with evidence of improved survival over standard care. The VISION trial inclusion criteria required a metastatic lesion-to-liver ratio of greater than 1 on ⁶⁸Ga-PSMA-11 PET scans. We aimed to determine whether an equivalent ratio is suitable for a SPECT tracer, ^99mTc-MIP-1404, and to compare lesion and lesion-to-normal-organ ratios between the 2 radiotracers. Methods: Two cohorts of patients with mCRPC matched for age, prostate-specific antigen level, and total Gleason score, with either ^99mTc-MIP-1404 SPECT/CT (n = 25) or ⁶⁸Ga-PSMA-11 PET/CT (n = 25) scans, were included for analysis. Up to 3 lesions in each site (prostate/prostate bed, lymph nodes, bone and soft-tissue metastases) as well as normal liver, parotid gland, spleen, and mediastinal blood-pool SUV_max were measured. Results: ^99mTc-MIP-1404 SPECT lesion SUV_max was not significantly different from ⁶⁸Ga-PSMA-11 PET (median, 18.2 vs. 17.3; P = 0.93). However, ^99mTc-MIP-1404 liver SUV_max was higher (median, 8.5 vs. 5.8; P = 0.002) and lesion-to-liver ratios were lower (median, 2.7 vs. 3.5; P = 0.009). There was no significant difference in parotid gland or splenic SUV_max or lesion-to-parotid gland ratios between the 2 tracers although there was a small difference in lesion-to-spleen ratios (P = 0.034). Conclusion: There are differences in biodistribution and, in particular, liver activity, between ⁶⁸Ga-PSMA-11 and ^99mTc-MIP-1404. Therefore, if ^99mTc-MIP-1404 is used to assess eligibility for ¹⁷⁷Lu-PSMA-617 therapy, a lower adjusted lesion-to-liver ratio should be used.

Comparison of the preparation of the radiopharmaceutical 68Ga-PSMA-11 at two Czech worksites

Radiopharmaceutical 68Ga-PSMA-11 is one of the newest positron radiopharmaceuticals available for nuclear medicine departments in the Czech Republic. The radiopharmaceutical preparation can be carried out manually or instrumentally using modules for synthesis. Despite the greater technological difficulty of preparation, the success of synthesis of this radiopharmaceutical by both methods is very high, and the evaluated quality parameters of the radiopharmaceutical are comparable by both manual and instrumental preparation methods. Also, regarding professional exposure, the preparation of 68Ga-PSMA-11 does not significantly affect the whole-body and finger dosimetry results.

Assessment of Prostate Carcinoma Aggressiveness: Relation to 68Ga-PSMA-11-PET/MRI and Gleason Score

BACKGROUND/AIM

To test the correlation of ⁶⁸Ga-PSMA-11 uptake and the expression of PSMA (prostatic specific membrane antigen) with the Gleason score, apparent diffusion coefficient (ADC) and pharmacokinetic parameters obtained from dynamic contrast agent-enhanced MRI/PET.

PATIENTS AND METHODS

Forty newly diagnosed, therapy naïve patients with prostatic carcinoma (PC) (mean age of 56.7, range=34-79), who were referred for ⁶⁸Ga-PSMA-11-PET/MRI for primary staging and had undergone radical prostatectomy (RAPE) were included in this prospective study. Their blood samples were tested for serum levels of prostate-specific antigen (PSA) and proPSA. The patients' prostates were evaluated using whole-mount sections, which helped determine the extent and grade of the tumor; tests were performed to determine immunohistochemical PSMA expression.

RESULTS

A correlation between PSMA expression and the accumulation of ⁶⁸Ga-PSMA-11 was found using the Spearman correlation coefficient (p=0.0011). A stronger correlation was found between Gleason patterns 3 or 4 and PSMA expression (p=0.06). Furthermore, the correlation of Gleason score with the overall ⁶⁸Ga-PSMA-11 accumulation within the tumor or non-tumor tissue was found to be significant (p=0.0157). A significant relation was found only with the K_ep elimination rate constant, which was stronger in Gleason pattern 4 than in Gleason pattern 3. A weaker correlation was found between the accumulation of ⁶⁸Ga-PSMA-11 and K^trans in Gleason pattern 4: the most significant relation being between ADC_min and Gleason pattern 3 and 4 (p=0.0074). The total size of the tumor correlated with levels of proPSA (p<0.0001), and its extra prostatic extension correlated with levels of proPSA (p<0.0001).

CONCLUSION

⁶⁸Ga-PSMA-11 correlates well with the expression of PSMA. Gleason pattern 3 and 4 had a higher correlation with ⁶⁸Ga-PSMA-11 levels than did Gleason pattern 5. Either no correlation, or a weak correlation, was established with pharmacokinetics.

PSMA-based 18F-DCFPyL PET: a better choice than multiparametric MRI for prostate cancer diagnosis?

Owing to the high tissue contrast, multiparametric MRI (mpMRI) has already been the most widely applied imaging method for prostate cancer. Recently, prostate-specific membrane antigen (PSMA) ligands for nuclear imaging are emerging as a promising modality in prostate cancer, especially since the 2 PET/CT agents (⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPy) approved by U.S. Food and Drug Administration (FDA). However, limited studies have performed the comparison of mpMRI versus recently approved ¹⁸F-DCFPyL PET/CT. In this issue of AJNMMI, Lu et al. compared the performance of ¹⁸F-DCFPyL PET/CT and pelvic mpMRI in intermediate-high risk and biochemical recurrent prostate cancer patients. The results demonstrated the two modalities have a good concordance rate for patient-based analysis, and ¹⁸F-DCFPyL PET/CT has a better diagnostic performance in detecting lymph node metastases and bone metastases for lesion-based analysis. The use of ¹⁸F-DCFPyL PET/CT provides more diagnostic confidence to better assess prostate cancer lesions.

Development and validation of 68Ga-PSMA-11 PET/CT-based radiomics model to detect primary prostate cancer

Background

This study aimed to develop a novel analytic approach based on a radiomics model derived from ⁶⁸Ga-prostate-specific membrane antigen (PSMA)-11 PET/CT for predicting intraprostatic lesions in patients with prostate cancer (PCa).

Methods

This retrospective study included consecutive patients with or without PCa who underwent surgery or biopsy after ⁶⁸Ga-PSMA-11 PET/CT. A total of 944 radiomics features were extracted from the images. A radiomics model was constructed using the least absolute shrinkage and selection operator (LASSO) algorithm with tenfold cross-validation in the training set. PET/CT images for the test set were reviewed by experienced nuclear medicine radiologists. The sensitivity, specificity, positive predictive value, negative predictive value, and area under the receiver operating characteristic curve (AUC) were calculated for the model and radiologists’ results. The AUCs were compared.

Results

The total of 125 patients (86 PCa, 39 benign prostate disease [BPD]) included 87 (61 PCa, 26 BPD) in the training set and 38 (61 PCa, 26 BPD) in the test set. Nine features were selected to construct the radiomics model. The model score differed between PCa and BPD in the training and test sets (both P < 0.001). In the test set, the radiomics model performed better than the radiologists’ assessment (AUC, 0.85 [95% confidence interval 0.73, 0.97] vs. 0.63 [0.47, 0.79]; P = 0.036) and showed higher sensitivity (model vs radiologists, 0.84 [0.63, 0.95] vs. 0.74 [0.53, 0.88]; P = 0.002).

Conclusion

Radiomics analysis based on ⁶⁸Ga-PSMA-11 PET may non-invasively predict intraprostatic lesions in patients with PCa.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00936-5.

Standardised Uptake Values as Determined on PSMA PET/CT is associated with Oncological Outcomes in Prostate Cancer Patients

Objectives

To investigate the association between intraprostatic, intratumoral maximum standardised uptake values (SUV_max) on prostate‐specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in patients with prostate cancer (PCa) prior to robot‐assisted radical prostatectomy (RARP) and pathology outcomes, including pathological International Society of Urological Pathology score (pISUP) and lymph node (LN) status (pN0/pN1).

Patients and Methods

A bi‐centric, secondary analysis of two previous, prospective cohort studies was performed in 318 patients with biopsy confirmed PCa and who were scheduled for RARP. Before surgery, patients received a PSMA PET/CT with either ⁶⁸Ga‐PSMA‐11 (59% of the patients) or ¹⁸F‐PSMA (DCFPyL; 41%) as radiotracer. PET/CT images were analysed both visually and semi‐quantitatively by measuring the SUV_max of the most intense suspect lesion in the prostate. The association between the SUV_max of the primary tumour and pre‐ and postoperative variables was analysed.

Results

The SUV_max was associated with clinical and biopsy preoperative variables, as well as with pISUP score and pathological tumour stage. Patients with a pISUP of ≤2 showed significantly lower SUV_max compared to patients with a pISUP of >2 for both tracers (SUV_max¹⁸F‐PSMA: median 5.1 vs 9.6, P = 0.002; SUV_max⁶⁸Ga‐PSMA‐11: 6.6 vs 8.6, P = 0.003). Moreover, patients with pN1 had significantly higher median SUV_max than those with pN0/pNx for both tracers (SUV_max¹⁸F‐PSMA: 7.9 vs 12.3, P = 0.04; SUV_max⁶⁸Ga‐PSMA‐11: 7.6 vs 12.0, P < 0.001). On multivariable logistic regression analysis, the intraprostatic SUV_max was an independent predictor of pN1 for both ⁶⁸Ga‐PSMA‐11 (per doubling: odds ratio [OR] 1.96, 95% confidence interval [CI] 1.27–3.01)) and ¹⁸F‐PSMA (per doubling: OR 1.79, 95% CI 1.06–3.03).

Conclusion

Intraprostatic, intratumoral PSMA intensity on PET/CT, as semi‐quantitatively expressed by SUV_max, may be a valuable innovative biomarker in patients with localised PCa, as it is highly associated with known conventional prognostic factors, such as pISUP and LN status.

Reduced Acquisition Time Per Bed Position for PET/MRI Using 68Ga-RM2 or 68Ga-PSMA11 in Patients With Prostate Cancer: A Retrospective Analysis

BACKGROUND. Growing clinical adoption of PET/MRI for prostate cancer (PC) evaluation has increased interest in reducing PET/MRI scanning times. Reducing acquisition time per bed position below current times of at least 5 minutes would allow shorter examination lengths. OBJECTIVE. The purpose of this study was to evaluate the effect of different reduced PET acquisition times in patients with PC who underwent ⁶⁸Ga-PSMA-11 or ⁶⁸Ga-RM2 PET/MRI using highly sensitive silicon photomultiplier-based PET detectors. METHODS. This study involved retrospective review of men with PC who underwent PET/MRI as part of one of two prospective trials. Fifty men (mean [± SD] age, 69.9 ± 6.8 years) who underwent ⁶⁸Ga-RM2 PET/MRI and 50 men (mean age, 66.6 ± 5.7 years) who underwent ⁶⁸Ga-PSMA-11 PET/MRI were included. PET/MRI used a time-of-flight-enabled system with silicon photomultiplier-based detectors. The acquisition time was 4 minutes per bed position. PET data were reconstructed using acquisition times of 30 seconds, 1 minute, 2 minutes, 3 minutes, and 4 minutes. Three readers independently assessed image quality for each reconstruction using a 5-point Likert scale (with 1 denoting nondiagnostic and 5 indicating excellent quality). One reader measured SUV_max for up to six lesions per patient. Two readers independently assessed lesion conspicuity using a a 3-point Likert scale (with 1 indicating that lesions were not visualized and 3 denoting that they were definitely visualized). RESULTS. Mean image quality across readers at 30 seconds, 1 minutes, 2 minutes, 3 minutes, and 4 minutes was, for ⁶⁸Ga-RM2 PET/MRI, from 1.0 ± 0.2 to 1.7 ± 0.7, 2.0 ± 0.3 to 2.6 ± 0.8, 3.1 ± 0.5 to 3.9 ± 0.8, 4.6 ± 0.6 to 4.7 ± 0.6, and 4.8 ± 0.4 to 4.8 ± 0.5, respectively, and for ⁶⁸Ga-PSMA-11 PET/MRI it was from 1.2 ± 0.4 to 1.8 ± 0.6, 2.2 ± 0.4 to 2.8 ± 0.7, 3.6 ± 0.6 to 4.1± 0.8, 4.8 ± 0.4 to 4.9 ± 0.4, and 4.9 ± 0.3 to 5.0 ± 0.2, respectively. The mean lesion SUV_max for ⁶⁸Ga-RM2 PET/MRI was 11.1 ± 12.4, 10.2 ± 11.7, 9.6 ± 11.3, 9.5 ± 11.6, and 9.4 ± 11.6, respectively, and for ⁶⁸Ga-PSMA-11 PET/MRI it was 14.7 ± 8.2, 12.9 ± 7.4, 12.1 ± 7.8, 11.7 ± 7.9, and 11.6 ± 7.9, respectively. Mean lesion conspicuity (reader 1/reader 2) was, for ⁶⁸Ga-RM2 PET/MRI, 2.4 ± 0.5/2.7 ± 0.5, 2.9 ± 0.3/2.9 ± 0.3, 3.0 ± 0.0/3.0 ± 0.0, 3.0 ± 0.0/3.0 ± 0.0, and 3.0 ± 0.0/3.0 ± 0.0, respectively, and for ⁶⁸Ga-PSMA-11 PET/MRI it was 2.6 ± 0.5/2.8 ± 0.4, 3.0 ± 0.2/2.9 ± 0.3, 3.0 ± 0.1/3.0 ± 0.2, 3.0 ± 0.0/3.0 ± 0.0, and 3.0 ± 0.0/3.0 ± 0.0, respectively. CONCLUSION. Our data support routine 3-minute acquisitions, which provided results very similar to those for 4-minute acquisitions. Two-minute acquisitions, although they lowered quality somewhat, provided acceptable performance and warrant consideration. CLINICAL IMPACT. When PC is evaluated using modern PET/MRI equipment, time per bed position may be reduced compared with historically used times. TRIAL REGISTRATION. ClinicalTrials.gov NCT02624518 and NCT02678351.

Biphasic GA 68-labeled prostate specific membrane antigen-11 positron emission tomography/computed tomography scans in the differential diagnosis and risk stratification of initial primary prostate cancer

Background

This study aimed to assess the value of biphasic GA 68-labeled prostate-specific membrane antigen-11 (⁶⁸Ga-PSMA-11) positron emission tomography/computed tomography (PET/CT) scan in the differential diagnosis and risk stratification of initial primary prostate cancer (PCa).

Methods

A total of 51 patients with PCa (8 low- and intermediate-risk PCa patients and 43 high-risk PCa patients) and 36 patients with benign prostate lesions, who underwent standard whole-body imaging and delayed pelvic imaging of ⁶⁸Ga-PSMA-11 PET/CT, were enrolled in this prospective study. The PET parameters, such as maximum and mean standard uptake value (SUVmax and SUVmean), and maximum and mean standard retention index of PET images were calculated and compared in different prostate lesions. The diagnostic performances of the PET parameters were evaluated by receiver operating characteristic (ROC) curves.

Results

All the PET parameters of PCa participants were significantly higher than those of participants with benign prostate lesions (P<0.001). The SUVmean of delayed imaging had the best performance in the diagnosis of PCa with an area under the curve (AUC) of 0.918 (95% CI: 0.858 to 0.977), the sensitivity of 90.0%, and specificity of 83.3%. The SUVmax and SUVmean of high-risk PCa participants were significantly higher than those of low- and intermediate-risk PCa participants (P<0.005). The SUVmax of standard imaging had the best performance in predicting high-risk PCa with an AUC of 0.890 (95% CI: 0.799 to 0.980), a sensitivity of 76.7%, and a specificity of 100.0%.

Conclusions

The biphasic ⁶⁸Ga-PSMA-11 PET/CT scan had good performance in discriminating prostate cancer from benign prostate diseases. The SUVmean of the prostate lesion at delayed imaging of ⁶⁸Ga-PSMA-11 PET/CT had the best value in the differential diagnosis of PCa, and the SUVmax at standard imaging was most valuable in predicting the risk stratification of PCa.

Renal Cortical Scarring: 68Ga-PSMA-11 PET versus 99mTc-DMSA Scan in a Case with Pyelonephritis

We previously reported ⁶⁸Ga-prostate‑specific membrane antigen (PSMA)-11 and ^99mTcdimercaptosuccinic acid (DMSA) images of the 1st case of our prospective research comparing renal PSMA PET to DMSA scan in adult patients with pyelonephritis. Here, we present renal cortical PSMA PET and DMSA images of our 2nd patient with chronic recurring pyelonephritis which demonstrated renal parenchymal defects secondary to scarring in the kidney.

An 89Zr-labeled PSMA tracer for PET/CT imaging of prostate cancer patients

The short half-life of existing prostate-specific membrane antigen (PSMA) tracers limits their time for internalization into tumor cells after injection, which is an essential prerequisite for robust detection of tumor lesions with low PSMA expression on PET/CT scans. Due to its longer half-life, the ⁸⁹Zr-labeled ligand ⁸⁹Zr-PSMA-Df allows acquisition of PET scans up to 6 days after injection, thereby overcoming the above limitation. We investigated whether ⁸⁹Zr-PSMA-Df allowed more sensitive detection of weak PSMA-positive prostate cancer lesions. Methods: We selected 14 prostate cancer patients with biochemical recurrence who exhibited no PSMA-positive lesions on a PET scan acquired with existing PSMA tracers (⁶⁸Ga-PSMA-11, ¹⁸F-JK-PSMA-7). Within 5 weeks after the negative scan, we performed a second PSMA-PET scan using ⁸⁹Zr-PSMA-Df (117±16 MBq, PET acquisition within 6 days of injection). Results: ⁸⁹Zr-PSMA-Df detected 15 PSMA-positive lesions in 8/14 patients, who had a PET-negative reading of their initial PET scans with existing tracers. In these 8 patients, the new scans revealed localized recurrence of disease (3/8), metastases in lymph nodes (3/8), or lesions at distant sites (2/8). Based on these results, patients received lesion-targeted radiotherapies (5/8), androgen deprivation therapies (2/8), or no therapy (1/8). The plausibility of 14/15 lesions was supported by histology, clinical follow-up after radiotherapy or subsequent imaging. Furthermore, comparison of the 15 ⁸⁹Zr-PSMA-Df-positive lesions with their correlates on the original PET scan revealed that established tracers exhibited mild accumulation in 7/15 lesions but contrast-to-noise ratios (CNR) were too low for robust detection of these lesions (CNR 2.4±3.7 for established tracers vs. 10.2±8.5 for ⁸⁹Zr-PSMA-Df, P = 0.0014). The SUV_max of the 15 ⁸⁹Zr-PSMA-Df-positive lesions (11.5±5.8) was significantly higher than the SUV_max on the original PET scans (4.7±2.8, P = 0.0001). Kidneys were the most exposed organ with doses of 3.3±0.7 mGy/MBq. The effective dose was 0.15±0.04 mSv/MBq. Conclusion: In patients with weak PSMA expression, a longer period of time might be needed for ligand internalization than that offered by existing PSMA tracers to make lesions visible on PET/CT scans. Hence, ⁸⁹Zr-PSMA-Df might be of significant benefit to patients in whom the search for weak PSMA-positive lesions is challenging. Radiation exposure should be weighed against the potential benefit of metastasis-directed therapy or salvage radiotherapy, which we initiated in 36% (5/14) of our patients based on their ⁸⁹Zr-PSMA-Df PET scans.

Comparison of Early Imaging and Imaging 60 min Post-Injection after Forced Diuresis with Furosemide in the Assessment of Local Recurrence in Prostate Cancer Patients with Biochemical Recurrence Referred for 68Ga-PSMA-11 PET/CT

Background: 68Ga-PSMA-11 PET/CT is a promising method for the assessment of local recurrence (LR) in prostate cancer (PCa) patients. The aim of this study was to evaluate the diagnostic performance of early 68Ga-PSMA-11 PET imaging in comparison to 68Ga-PSMA-11 PET imaging 60 min post-injection (p.i.) in the detection of LR in patients with biochemical recurrence (BR) of prostate carcinoma. Materials and Methods: 190 image sets of patients with BR in PCa who underwent 68Ga-PSMA-11 PET/CT were assessed retrospectively (median prostate specific antigen (PSA) value, 0.70 ng/mL (range, 0.1–105.6 ng/mL)). Patients received an early static scan of the pelvic area (median, 248 s p.i. (range, 56–923 s)) and a whole-body scan 60 min p.i. (median, 64 min p.i. (range, 45–100 min)) with intravenous administration of 20 mg furosemide i.v. at the time of tracer application, followed by intravenous hydration with 500 mL of sodium chloride (NaCl 0.9%). Assessment was based on visual analysis and calculation of the maximum standardized uptake value (SUVmax) of the pathologic lesions present in the prostate fossa found in the early PET imaging and 60 min PET scans. The scans were characterized as negative, positive, or equivocal. The results were compared, and the combination of early and 60 min p.i. imaging was evaluated. Results: Image assessment resulted in 30 (15.8%) positive, 17 (8.9%) equivocal, and 143 (75.3%) negative findings in early scans, and 28 (14.7%) positive, 25 (13.2%) equivocal, and 137 (72.1%) negative findings of LR in 60 min p.i. images. For combined image analysis, 33 (17.4%) cases were positive and 20 (10.5%) were equivocal. There was no statistical significance between the number of positive (p = 0.815), negative (p = 0.327), and equivocal (p = 0.152) findings. Furthermore, the combination of both scans showed no statistically significant differences for the positive and negative findings (p = 0.063). The median SUVmax was 4.9 (range, 2.0–55.2) for positive lesions in the early scans and 8.0 (range, 2.1–139.9) in the scans 60 min p.i. The median SUVmax for bladder activity was 2.5 (range, 0.9–12.2) in the early scans and 8.2 (range, 1.8–27.6) in the scans 60 min p.i. Conclusion: Early static imaging additional to 68Ga-PSMA-11 PET images acquired 60 min p.i. has limited value in patients prepared with furosemide and hydration, and showed no statistically significant change in the detection rate (DR) of LR and the number of equivocal findings. Based on our results, in departments following a protocol with forced diuresis, including furosemide, additional early static imaging cannot be routinely recommended for the assessment of BR in PCa patients.

68Ga-PSMA-11 PET imaging in patients with ongoing androgen deprivation therapy for advanced prostate cancer

Purpose

Prostate-specific membrane antigen (PSMA) targeted positron emission tomography (PET) imaging significantly improved the detection of recurrent prostate cancer (PCa). However, the value of PSMA PET imaging in patients with advanced hormone-sensitive or hormone-resistant PCa is still largely unknown. The aim of this study was to analyze the detection rate and distribution of lesions using PSMA PET imaging in patients with advanced PCa and ongoing androgen deprivation therapy (ADT).

Methods

A total of 84 patients diagnosed with hormone-sensitive or hormone-resistant PCa who underwent ⁶⁸Ga-PSMA-11 PET/magnetic resonance imaging (MRI) or computer tomography (CT) under ongoing ADT were retrospectively analyzed. We assessed the detection of PSMA-positive lesions overall and for three PSA subgroups (0 to < 1 ng/mL, 1 to < 20 ng/mL and > 20 ng/mL). In addition, PSMA-positive findings were stratified by localization (prostatic fossa, pelvic, para-aortic, mediastinal/supraclavicular and axillary lymph nodes, bone lesions and visceral lesions) and hormone status (hormone-sensitive vs. hormone-resistant). Furthermore, we assessed how many patients would be classified as having oligometastatic disease (≤ 3 lesions) and theoretically qualify for metastasis-directed radiotherapy (MDRT) in a personalized patient management.

Results

We detected PSMA-positive lesions in 94.0% (79 of 84) of all patients. In the three PSA subgroups detection rates of 85.2% (0 to < 1 ng/mL, n = 27), 97.3% (1 to < 20 ng/mL, n = 37) and 100% (> 20 ng/mL, n = 20) were observed, respectively. PSMA-positive visceral metastases were observed only in patients with a PSA > 1 ng/mL. Detection of PSMA-positive lesions did not significantly differ between patients with hormone-sensitive and hormone-resistant PCa. Oligometastatic PCa was detected in 19 of 84 patients (22.6%). Almost all patients, 94.7% (n = 18) would have been eligible for MDRT.

Conclusions

In this study, we observed an overall very high detection rate of 94% using PSMA PET imaging in patients with advanced PCa and ongoing ADT. Even in a majority of patients with very low PSA values < 1 ng/ml PSMA-positive lesions were found.

Use of 68Ga-PSMA-11 and 18F-FDG PET-CT Dual-Tracer to Differentiate Between Lymph Node Metastases and Ganglia

Purpose

Differentiating lymph node metastases (LNM) from peripheral ganglia by physiological prostate-specific membrane antigen (PSMA) uptake is challenging. Two tracers (⁶⁸Ga-PSMA-11 and ¹⁸F-fluorodeoxyglucose [FDG]) metabolic uptake patterns were evaluated by positron emission tomography-computed tomography (PET-CT), searching for differences that could tell ganglia from LNM.

Methods

Dual ⁶⁸Ga-PSMA-11 and ¹⁸F-FDG PET-CT data of 138 prostate cancer patients acquired from June 2018 to December 2019 were retrospectively evaluated. Ganglia and LNM with PSMA-11 uptake above local background were analyzed by the location and PSMA-11-PET and FDG-PET maximum standardized uptake value (SUVmax).

Results

PSMA-11-positive ganglia (n = 381) and LNM (n = 83) were identified in 138 and 58 patients, respectively. The LNM SUVmax of PSMA-11-PET (16.4 ± 14.8 vs 2.3 ± 0.7, P < 0.001) and FDG-PET (3.3 ± 3.2 vs 1.5 ± 0.5, P < 0.001) were higher than in ganglia. The probabilities of being an LNM in the low-potential (PSMA-11-PET SUVmax of <4.1 and FDG-PET SUVmax of <2.05), moderate-potential (PSMA-11-PET SUVmax of >4.1 and FDG-PET SUVmax of <2.05, or PSMA-11-PET SUVmax of <4.1 and FDG-PET SUVmax of >2.05), and high-potential (PSMA-11-PET SUVmax of >4.1 and FDG-PET SUVmax of >2.05) groups were 0.9% (3/334), 44.6% (37/83), and 91.5% (43/47), respectively (P < 0.001). The cervical and coeliac ganglia had higher PSMA-11 and FDG uptake than the sacral ganglia (P < 0.001 for all). LNM PSMA-11 and FDG uptake was similar in these three locations.

Conclusion

The FDG-PET and PSMA-11-PET SUVmax, especially when combined, could well differentiate LNM from ganglia. The tracers uptake differed between cervical/coeliac and sacral ganglia, so the lesion location should be considered during image assessment.

Head-to-Head Comparison of 68Ga-NOTA (68Ga-NGUL) and 68Ga-PSMA-11 in Patients with Metastatic Prostate Cancer: A Prospective Study

⁶⁸Ga-NOTA Glu-Urea-Lys (NGUL) is a novel prostate-specific membrane antigen (PSMA)-targeting tracer used for PET/CT imaging. This study aimed to compare performance in the detection of primary and metastatic lesions and to compare biodistribution between ⁶⁸Ga-NGUL and ⁶⁸Ga-PSMA-11 in the same patients with prostate cancer. Methods: Eleven patients with metastatic prostate cancer were prospectively recruited. The quantitative tracer uptake was determined in normal organs and in primary and metastatic lesions. Results: ⁶⁸Ga-NGUL showed significantly lower normal-organ uptake and rapid urinary clearance. The number and sites of detected PSMA-positive primary and metastatic lesions were identical, and no significant quantitative uptake difference was observed. ⁶⁸Ga-NGUL showed a relatively lower tumor-to-background ratio than ⁶⁸Ga-PSMA-11. Conclusion: In a head-to-head comparison with ⁶⁸Ga-PSMA-11, ⁶⁸Ga-NGUL showed lower uptake in normal organs and similar performance in detecting PSMA-avid primary and metastatic lesions. ⁶⁸Ga-NGUL could be a valuable option for PSMA imaging.

Dual-phase 68Ga-PSMA-11 PET/CT may increase the rate of detected lesions in prostate cancer patients

BACKGROUND

This study was conducted to compare the early static (3-6 min post-injection (p.i.)) and standard whole body (1 h, p.i.) 68Ga-PSMA-11 PET/CT imaging for detection of lesions in prostate cancer (PC) patients.

MATERIALS AND METHODS

In this study, PC patients suspected of recurrence underwent 68Ga-PSMA-11 PET/CT. Early static images were acquired from the pelvis and the lower abdomen 3-5 minutes after radiotracer injection and, a routine whole body scan was performed from the skull to the mid-thigh 1 h after injection. Quantitative analysis (SUVmax) was evaluated in suspicious lesions.

RESULTS

Of 19 evaluated PC patients with a median age of 72 ± 1.66 years (range: 55-85 years) and prostate-specific antigen (PSA) of 1.72 ± 6.11 ng/ml (range: 0.1-100 ng/ml) (median ± SE), 16 showed positive in the whole body PET/CT. All of the patients with positive whole body scans due to pelvic involvement had positive early scan results. Totally, 22 lesions were detected in both early and delay scans in the pelvic which 16 were related to prostate involvement, 4 were related to lymph node involvement, and 2 were related to bone involvement. Moreover, in addition to the mentioned 22 lesions, early PET imaging successfully detected local recurrence in a patient who was negative on WB PET/ CT; this lesion was masked in the delay scan due to bladder activity. The median SUVmax values of the early and delay scans were 3.69 ± 1.07 (median ± SE) (range: 1.2-14.5) and 5.85 ± 1.69 (range: 3.1-23.4), respectively. (p = 0.005).

CONCLUSION

Early static 68Ga-PSMA-11 PET/CT imaging might discriminate metastases from urinary bladder activity. Therefore, early static imaging in combination with whole body 60-min p.i. imaging can improve the detection of local involvement pelvic disease.

2020 FDA TIDES (Peptides and Oligonucleotides) Harvest

2020 has been an extremely difficult and challenging year as a result of the coronavirus disease 2019 (COVID-19) pandemic and one in which most efforts have been channeled into tackling the global health crisis. The US Food and Drug Administration (FDA) has approved 53 new drug entities, six of which fall in the peptides and oligonucleotides (TIDES) category. The number of authorizations for these kinds of drugs has been similar to that of previous years, thereby reflecting the consolidation of the TIDES market. Here, the TIDES approved in 2020 are analyzed in terms of chemical structure, medical target, mode of action, and adverse effects.

Survey by the French Medicine Agency (ANSM) of the imaging protocol, detection rate, and safety of 68Ga-PSMA-11 PET/CT in the biochemical recurrence of prostate cancer in case of negative or equivocal 18F-fluorocholine PET/CT: 1084 examinations

Introduction

Despite growing evidence of a superior diagnostic performance of ⁶⁸Ga-PSMA-11 over ¹⁸F-fluorocholine (FCH) PET/CT, the number of PET/CT centres able to label on site with gallium-68 is still currently limited. Therefore, patients with biochemical recurrence (BCR) of prostate cancer frequently undergo FCH as the 1st-line PET/CT. Actually, the positivity rate (PR) of a second-line PSMA-11 PET/CT in case of negative FCH PET/CT has only been reported in few short series, in a total of 185 patients. Our aims were to check (1) whether the excellent PR reported with PSMA-11 is also obtained in BCR patients whose recent FCH PET/CT was negative or equivocal; (2) in which biochemical and clinical context a high PSMA-11 PET/CT PR may be expected in those patients, in particular revealing an oligometastatic pattern; (3) whether among the various imaging protocols for PSMA-11 PET/CT used in France, one yields a significantly highest PR; (4) the tolerance of PSMA-11.

Patients and methods

Six centres performed ⁶⁸Ga-PSMA-11 PET/CTs during the first 3 years of its use in France. Prior to each PET/CT, the patient’s data were submitted prospectively for authorisation to ANSM, the French Medicine Agency. The on-site readings of 1084 PSMA-11 PET/CTs in BCR patients whose recent FCH PET/CTs resulted negative or equivocal were pooled and analysed.

Results

(1) The overall PR was 68%; for a median serum PSA level (sPSA) of 1.7 ng/mL, an oligometastatic pattern (1–3 foci) was observed in 31% of the cases overall; (2) PR was significantly related to sPSA (from 41% if < 0.2 ng/mL to 81% if ≥ 2 ng/mL), to patients’ age, to initial therapy (64% if prostatectomy vs. 85% without prostatectomy due to frequent foci in the prostate fossa), to whether FCH PET/CT was negative or equivocal (PR = 62% vs. 82%), and to previous BCR (PR = 63% for 1st BCR vs. 72% in case of previous BCR); (3) no significant difference in PR was found according to the imaging protocol: injected activity, administration of a contrast agent and/or of furosemide, dose length product, one single or multiple time points of image acquisition; (4) no adverse event was reported after PSMA-11 injection, even associated with a contrast agent and/or furosemide.

Conclusion

Compared with the performance of PSMA-11 PET/CT in BCR reported independently of FCH PET/CT in 6 large published series (n > 200), the selection based on FCH PET/CT resulted in no difference of PSMA-11 PR for sPSA < 1 ng/mL but in a slightly lower PR for sPSA ≥ 1 ng/mL, probably because FCH performs rather well at this sPSA and very occult BCR was over-represented in our cohort. An oligometastatic pattern paving the way to targeted therapy was observed in one fourth to one third of the cases, according to the clinico-biochemical context of the BCR. Systematic dual or triple acquisition time points or administration of a contrast agent and/or furosemide did not bring a significant added value for PSMA-11 PET/CT positivity and should be decided on individual bases.

Matched-Pair Comparison of 68Ga-PSMA-11 and 18F-rhPSMA-7 PET/CT in Patients with Primary and Biochemical Recurrence of Prostate Cancer: Frequency of Non-Tumor-Related Uptake and Tumor Positivity

Radiohybrid prostate-specific membrane antigen (rhPSMA) ligands are a new class of prostate cancer theranostic agents. ¹⁸F-rhPSMA-7 offers the advantages of ¹⁸F labeling and low urinary excretion compared with ⁶⁸Ga-PSMA-11. Here, we compare the frequency of non-tumor-related uptake and tumor positivity with ⁶⁸Ga-PSMA-11 and ¹⁸F-rhPSMA-7 in patients with primary or recurrent prostate cancer. Methods: This retrospective matched-pair comparison matched 160 ¹⁸F-rhPSMA-7 with 160 ⁶⁸Ga-PSMA-11 PET/CT studies for primary staging (n = 33) and biochemical recurrence (n = 127) according to clinical characteristics. Two nuclear medicine physicians reviewed all scans, first identifying all PET-positive lesions and then differentiating lesions suggestive of prostate cancer from those that were benign, on the basis of known pitfalls and ancillary information from CT. For each region, the SUV_max of the lesion with the highest PSMA ligand uptake was noted. Tumor positivity rates were determined, and SUV_max was compared separately for each tracer. Results: ¹⁸F-rhPSMA-7 and ⁶⁸Ga-PSMA-11 PET revealed 566 and 289 PSMA ligand-positive lesions, respectively. Of these, 379 and 100 lesions, equaling 67.0% and 34.6%, respectively, of all PSMA-positive lesions, were considered benign. The distribution of their etiology was similar (42%, 24%, and 25% with ¹⁸F-rhPSMA-7 vs. 32%, 24%, and 38% with ⁶⁸Ga-PSMA-11 for ganglia, bone, and unspecific lymph nodes, respectively). All primary tumors were positive with both agents (n = 33 each), whereas slightly more metastatic lesions were observed with ⁶⁸Ga-PSMA-11 in both disease stages (113 for ¹⁸F-rhPSMA-7 and 124 for ⁶⁸Ga-PSMA-11). The SUV_max of ¹⁸F-rhPSMA-7 and ⁶⁸Ga-PSMA-11 did not differ (P > 0.05) in local recurrence or primary prostate cancer; however, the tumor-to-bladder ratio was significantly higher with ¹⁸F-rhPSMA-7 (4.9 ± 5.3 vs. 2.2 ± 3.7, P = 0.02, for local recurrence; 9.8 ± 9.7 vs. 2.3 ± 2.6, P < 0.001, for primary prostate cancer). Conclusion: The tumor positivity rate was consistently high for ⁶⁸Ga-PSMA-11 and ¹⁸F-rhPSMA-7. Both tracers revealed a considerable number of areas of uptake that were reliably identified as benign by trained physicians making use of corresponding morphologic imaging and known PSMA pitfalls. These were more frequent with ¹⁸F-rhPSMA-7. However, the matched-pair comparison could have introduced a source of bias. Adequate reader training can allow physicians to differentiate benign uptake from disease and be able to benefit from the logistical and clinical advantages of ¹⁸F-rhPSMA-7.

Dynamic 68Ga-PSMA-11 PET/CT for the Primary Evaluation of Localized Renal Mass: A Prospective Study

The potential role of prostate-specific membrane antigen (PSMA) PET/CT in non-prostate cancer tumors has shown promising results. We examined the performance of dynamic ⁶⁸Ga-PSMA-11 PET/CT (DPSMA) for the evaluation of localized renal mass. Methods: A prospective case series of patients with a newly diagnosed renal mass who were referred for surgery was examined. DPSMA was performed in a standardized manner before surgery. The final surgical histology served as the standard of reference. PSMA expression in the tumor vasculature was assessed and staining intensity was scored. Tracer uptake and PSMA expression were compared between benign and malignant tissue. Results: Of 29 enhancing renal masses evaluated in 27 patients, 24 (83%) were malignant lesions. The median SUV_mean of benign and malignant lesions was 2.3 (interquartile range [IQR], 2.2-2.7) and 6.8 (IQR, 4.2-10.1), respectively (P = 0.009). Median SUV_max of benign and malignant lesions was 3.8 (IQR, 3.3-4.5) and 9.4 (IQR, 5.4-15.8), respectively (P = 0.015). The median washout coefficient (K ₂) was significantly lower in malignant lesions than in benign lesions (0.17 vs. 0.70, P = 0.02). Positive PSMA staining was found in 20 of 24 malignant lesions and in 2 of 5 benign lesions (P = 0.04). Conclusion: This pilot study demonstrated DPSMA uptake and kinetics in localized renal masses. Increased ⁶⁸Ga-PSMA-11 tracer uptake and intratumoral retention correlate with PSMA expression in malignant renal tumors compared with benign renal masses, supporting further assessment of DPSMA as a potential tool for evaluating localized renal masses.

Disparities in PET Imaging for Prostate Cancer at a Tertiary Academic Medical Center

The purpose of this study was to evaluate differences between patients receiving ¹⁸F-fluciclovine and ⁶⁸Ga-prostate-specific membrane antigen (⁶⁸Ga-PSMA-11) for biochemically recurrent prostate cancer at a tertiary medical center. Methods: All ¹⁸F-fluciclovine and ⁶⁸Ga-PSMA-11 PET studies performed at the University of California San Francisco from October 2015 to January 2020 were reviewed. Age, race/ethnicity, primary language, body mass index, insurance type, and home address were obtained through the electronic medical record. A logistic regression model was used to evaluate the predictor variables. Results: In total, 1,502 patients received ⁶⁸Ga-PSMA-11 and 254 patients received ¹⁸F-fluciclovine. Black patients had increased odds of receiving imaging with ¹⁸F-fluciclovine versus ⁶⁸Ga-PSMA-11 compared with non-Hispanic White patients (odds ratio, 3.88; 95% CI, 1.90-7.91). There were no other statistically significant differences. Conclusion: In patients receiving molecular imaging for prostate cancer at a single U.S. tertiary medical center, access to ⁶⁸Ga-PSMA-11 for Black patients was limited, compared with non-Hispanic White patients, by a factor of nearly 4.

The 68Ga/177Lu-theragnostic concept in PSMA-targeting of metastatic castration-resistant prostate cancer: impact of post-therapeutic whole-body scintigraphy in the follow-up

INTRODUCTION

A new therapeutic option for metastatic castration-resistant prostate cancer (mCRPC) of heavily pre-treated patients lies in ¹⁷⁷Lu-PSMA-617 radioligand therapy.

METHODS

On the basis of PSMA-targeted ⁶⁸Ga-PSMA-11 PET/CT, 32 consecutive mCRPC patients were selected for ¹⁷⁷Lu-PSMA-617 therapy (6 GBq/cycle, 2 to 6 cycles, 6-10 weeks apart) and followed until death. Post-therapy whole-body (WB) dosimetry and ⁶⁸Ga-PSMA-11 PET/CT data were compared and related to progression free and overall survival.

RESULTS

¹⁷⁷Lu-PSMA-617 dosimetry after the first cycle indicated high tumor doses for skeletal (4.01 ± 2.64; range 1.10-13.00 Gy/GBq), lymph node (3.12 ± 2.07; range 0.70-8.70 Gy/GBq), and liver (2.97 ± 1.38; range 0.76-5.00 Gy/GBq) metastases whereas the dose for tissues/organs was acceptable in all patients for an intention-to-treat activity of 24 GBq. Any PSA decrease after the first cycle was found in 23/32 (72%), after the second cycle in 22/32 (69%), after the third cycle in 16/28 (57%), and after the fourth cycle in 8/18 (44%) patients. Post-therapy 24 h WB scintigraphy showed decreased tumor-to-background ratios in 24/32 (75%) after the first therapy cycle, after the second cycle in 17/29 (59%), and after the third cycle in 13/21 (62%) patients. The median PFS was 7 months and the median OS 12 months. In the group of PSA responders (n = 22) the median OS was 17 months versus 11 months in the group of non-responders (n = 10), p < 0.05. Decreasing SUV_max values were found for parotid (15.93 ± 6.23 versus 12.33 ± 4.07) and submandibular glands (17.65 ± 7.34 versus 13.12 ± 4.62) following treatment, along with transient (n = 6) or permanent (n = 2) xerostomia in 8/32 (25%) patients. In 3/32 patients, nephrotoxicity changed from Grade 2 to 3, whereas neither Grade 4 nephrotoxicity nor hematotoxicity was found. In most patients a good agreement was observed for the visual interpretation of the tracer accumulation between 24 h WB and PET/CT scans. However, no significance could be calculated for baseline-absorbed tumor doses and SUV_max values of tumor lesions. 5/32 (16%) patients showed a mixed response pattern, which resulted in disease progression over time.

CONCLUSION

Serial PSA measurements and post-therapy 24 h WB scintigraphy seems to allow a sufficiently accurate follow-up of ¹⁷⁷Lu-PSMA-617-treated mCRPC patients whereas ⁶⁸Ga-PSMA-11 PET/CT should be performed for patient selection and final response assessment.

68Ga-PSMA-11 dose reduction for dedicated pelvic imaging with simultaneous PET/MR using TOF BSREM reconstructions

OBJECTIVES

When increasing the PET acquisition time to match the longer MRI protocol in simultaneous PET/MR, the injected PET tracer dose can possibly be lowered to reduce radiation exposure. Moreover, applying new commercially available time-of-flight (TOF) block sequential regularized expectation maximization (BSREM)-based reconstruction algorithms could allow for further dose reductions. The purpose of this study was to find the minimal dose of the tracer targeting the prostate specific membrane antigen (⁶⁸Ga-PSMA-11) for a dedicated 15-min pelvic PET/MR scan that still matches the image quality of a reference 3-min scan at 100% (150 MBq) dose.

METHODS

In this retrospective analysis, 25 patients were included. PET emission datasets were edited to simulate stepwise reductions of injected tracer dose. Reference TOF ordered subset expectation maximum (OSEM) and new TOF BSREM reconstructions were performed and differences in the resulting PET images were visually and quantitatively assessed.

RESULTS

Visually, TOF BSREM reconstructions with relatively high regularization parameter (β) values are preferred. Quantitatively, however, high β-values result in lower lesion maximum standardized uptake values (SUV_max) compared to the reference. A β-value of 550 was considered the optimal compromise for the lowest possible 10% dose reconstructions, resulting in comparable visual assessment and lesion SUV_max.

CONCLUSIONS

This study indicates that the injected ⁶⁸Ga-PSMA-11 tracer dose for a standard 3-min PET scan can be reduced to approximately 10% (15 MBq) when the PET acquisition time is matched to the 15-min pelvic MRI protocol, and when reconstructed with TOF BSREM using β = 550. This decreases the effective dose from 3.54 to 0.35 mSv.

KEY POINTS

• Low-dose dedicated pelvic⁶⁸Ga-PSMA-11 PET/MR reduces radiation exposure for patients. • Retrospective study investigating the minimal dose needed for adequate image quality for 15-min PET frames over the pelvis showed using quantitative and qualitative analysis that a substantial dose reduction is possible without significant loss of image quality when using the TOF BSREM reconstruction algorithm. • With the introduction of low-dose pelvic⁶⁸Ga-PSMA-11 PET/MR, new potential applications of⁶⁸Ga-PSMA-11 PET for local staging or investigation of equivocal MRI findings could become applicable, even for patients without confirmed prostate cancer.

68Ga-PSMA-11 PET/CT in patients with recurrent prostate cancer-a modified protocol compared with the common protocol

PURPOSE

⁶⁸Ga-PSMA-11 PET/CT is commonly performed at 1 h post injection (p.i.). However, various publications have demonstrated that most prostate cancer (PC) lesions exhibit higher contrast at later imaging. The aim of this study was to compare the "common" protocol of ⁶⁸Ga-PSMA-11 PET/CT with a modified protocol.

METHODS

In 2017, we used the following scanning protocol for ⁶⁸Ga-PSMA-11 PET/CT in patients with recurrent PC: acquisition at 1 h p.i. without further preparations. From 2018, all scans were conducted at 1.5 h p.i. In addition, patients were orally hydrated with 1 L of water 0.5 h p.i. and were injected with 20 mg of furosemide 1 h p.i. Both protocols including 112 patients (2017) and 156 (modified protocol in 2018) were retrospectively compared. Rates of pathologic scans, maximum standardized uptake values (SUVmax), and tumor contrast (ratio lesion-SUVmax/background-SUVmean) as well as average standardized uptake values (SUVmean) of urinary bladder were analyzed.

RESULTS

Both tumor contrast and tracer uptake were significantly (p < 0.001) higher in the novel protocol. Although statistically not significant, the rates of pathologic scans were also higher in the modified protocol: 76.3% vs. 68.8% for all PSA values including 38.9% vs. 25.0% for PSA < 0.5 ng/ml and 60.0% vs. 56.7% for PSA > 0.5-≤ 2.0 ng/ml. Average SUVmean of the urinary bladder was significantly (p < 0.001) lower with the modified protocol.

CONCLUSIONS

The modified protocol, which includes a combination of delayed image acquisition at 1.5 h p.i., hydration, and furosemide resulted in higher tumor contrast and seems to have the potential to increase the rates of pathological scans, especially at low PSA levels.

Detection Rate and Localization of Prostate Cancer Recurrence Using 68Ga-PSMA-11 PET/MRI in Patients with Low PSA Values ≤ 0.5 ng/mL

A first analysis of simultaneous ⁶⁸Ga-prostate-specific membrane antigen (PSMA)-11 PET/MRI showed some improvement in the detection of recurrent disease at low serum prostate specific antigen (PSA) values below 0.5 ng/mL compared with the already high detection rate of ⁶⁸Ga-PSMA-11 PET/CT. We therefore focused on all patients with biochemical recurrence and PSA values no higher than 0.5 ng/mL to assess the detection rate for ⁶⁸Ga-PSMA-11 PET/MRI. Methods: We retrospectively analyzed a cohort of 66 consecutive patients who underwent ⁶⁸Ga-PSMA-11 PET/MRI for biochemical recurrence with a PSA value no higher than 0.5 ng/mL at our institution. Median PSA level was 0.23 ng/mL (range, 0.03-0.5 ng/mL). Detection of PSMA-positive lesions within the prostate fossa, local and distant lymph nodes, bones, or visceral organs was recorded. In addition, all scans with ⁶⁸Ga-PSMA-11 PET/MRI-positive lesions were retrospectively assessed to analyze if lesions were detected inside or outside a standard salvage radiotherapy volume. Results: Overall, in 36 of 66 patients (54.5%) PSMA-positive lesions were detected; in 26 of 40 (65%) patients with a PSA level between 0.2 and 0.5 ng/mL and in 10 of 26 (38.5%) patients with a PSA level less than 0.2 ng/mL. Even at those low PSA values, only 8 of 66 (12.1%) patients had exclusive local recurrence. Lymph nodes were detected in 23 patients and bone metastases in 5 on ⁶⁸Ga-PSMA-11 PET/MRI. In 26 of 66 patients (39.4%), PSMA-positive lesions were located outside a standard salvage radiotherapy volume. Conclusion: Our data confirm that ⁶⁸Ga-PSMA-11 PET/MRI has a high detection rate for recurrent prostate cancer, even at low PSA levels no higher than 0.5 ng/mL. In addition, we show that ⁶⁸Ga-PSMA-11 PET/MRI detected PSMA-positive lesions outside a standard salvage radiotherapy volume in 39.4% of all patients.

68Ga-PSMA-11 PET/CT in newly diagnosed prostate cancer: diagnostic sensitivity and interobserver agreement

PURPOSE

To determine the diagnostic sensitivity and interobserver agreement of Gallium 68-prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA-11 PET/CT) imaging for diagnosis and staging of patients with newly diagnosed prostate cancer (PC).

MATERIALS AND METHODS

One hundred and seventy-three men (mean age, 68 ± 7.7 years; range 46-84 years) with newly diagnosed, untreated PC were enrolled in this prospective study between January 2017 and August 2018. All patients underwent a ⁶⁸Ga-PSMA-11 PET/CT examination. For each patient, we determined the disease stage, the Gleason score, and the maximum standardized uptake value (SUVmax) for primary prostatic tumor and extraprostatic metastases. The diagnostic sensitivity and interobserver agreement of ⁶⁸Ga-PSMA-11 PET/CT for diagnosis and staging of PC were established by histopathology as the reference standard.

RESULTS

⁶⁸Ga-PSMA-11 PET/CT examinations were interpreted as positive for PC in 166 of 173 patients (101 patients had primary prostatic tumor only, two patients had extraprostatic metastases only and 63 patients had combined lesions). The sensitivity of ⁶⁸Ga-PSMA-11 PET/CT examination in the diagnosis of PC was 96%. ⁶⁸Ga-PSMA-11 PET/CT produced a significant change of stage in 28.6% patients with an upstage in 17.9% patients and a downstage in 10.7% patients. The interobserver agreements were almost good to perfect (k = 0.63-0.89) for visual image interpretation, SUVmax measurement, and tumor staging.

CONCLUSION

⁶⁸Ga-PSMA-11 PET/CT is a valuable tool with high diagnostic sensitivity (96%) and high reproducibility for diagnosis and staging of patients with newly diagnosed PC.

Regularized reconstruction of digital time-of-flight 68Ga-PSMA-11 PET/CT for the detection of recurrent disease in prostate cancer patients

Accurate localization of recurrent prostate cancer (PCa) is critical, especially if curative therapy is intended. With the aim to optimize target-to-background uptake ratio in ⁶⁸Ga-PSMA-11 PET, we investigated the image quality and quantitative measures of regularized reconstruction by block-sequential regularized expectation maximization (BSREM).

Methods: The study encompassed retrospective reconstruction and analysis of 20 digital time-of-flight (TOF) PET/CT examinations acquired 60 min post injection of 2 MBq/kg of ⁶⁸Ga-PSMA-11 in PCa patients with biochemical relapse after primary treatment. Reconstruction by ordered-subsets expectation maximization (OSEM; 3 iterations, 16 subsets, 5 mm gaussian postprocessing filter) and BSREM (β-values of 100-1600) were used, both including TOF and point spread function (PSF) recovery. Background variability (BV) was measured by placing a spherical volume of interest in the right liver lobe and defined as the standard deviation divided by the mean standardized uptake value (SUV). The image quality was evaluated in terms of signal-to-noise ratio (SNR) and signal-to-background ratio (SBR), using SUV_max of the lesions. A visual assessment was performed by four observers.

Results: OSEM reconstruction produced images with a BV of 15%, whereas BSREM with a β-value above 300 resulted in lower BVs than OSEM (36% with β 100, 8% with β 1300). Decreasing the acquisition duration from 2 to 1 and 0.5 min per bed position increased BV for both reconstruction methods, although BSREM with β-values equal to or higher than 800 and 1200, respectively, kept the BV below 15%. In comparison of BSREM with OSEM, the mean SNR improved by 25 to 66% with an increasing β-value in the range of 200-1300, whereas the mean SBR decreased with an increasing β-value, ranging from 0 to 125% with a β-value of 100 and 900, respectively. Decreased acquisition duration resulted in β-values of 800 to 1000 and 1200 to 1400 for 1 and 0.5 min per bed position, respectively, producing improved image quality measures compared with OSEM at a full acquisition duration of 2 min per bed position. The observer study showed a slight overall preference for BSREM β 900 although the interobserver variability was high.

Conclusion: BSREM image reconstruction with β-values in the range of 400-900 resulted in lower BV and similar or improved SNR and SBR in comparison with OSEM.

Intra-individual comparison of 68Ga-PSMA-11 and 18F-DCFPyL normal-organ biodistribution

Purpose

Detailed data comparing the biodistribution of PSMA radioligands is still scarce, raising concerns regarding the comparability of different compounds. We investigated differences in normal-organ biodistribution and uptake variability between the two most commonly PSMA tracers in clinical use, ⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPyL.

Methods

This retrospective analysis included 34 patients with low tumor burden referred for PET/CT imaging with ⁶⁸Ga-PSMA-11 and subsequently ¹⁸F-DCFPyL. Images were acquired with 4 cross-calibrated PET/CT systems. Volumes of interest were placed on major salivary and lacrimal glands, liver, spleen, duodenum, kidneys, bladder, blood-pool and muscle. Normal-organ biodistribution of both tracers was then quantified as SUV_peak and compared using paired tests, linear regression and Bland-Altman analysis. Between-patient variability was also assessed. Clinical and protocol variables were investigated for possible interference.

Results

For both tracers the highest uptake was found in the kidneys and bladder and low background activity was noted across all scans. In the quantitative analysis there was significantly higher uptake of ⁶⁸Ga-PSMA-11 in the kidneys, spleen and major salivary glands (p <  0.001), while the liver exhibited slightly higher ¹⁸F-DCFPyL uptake (p = 0.001, mean bias 0.79 ± 1.30). The lowest solid-organ uptake variability was found in the liver (COV 21.9% for ⁶⁸Ga-PSMA-11, 22.5% for ¹⁸F-DCFPyL). There was a weak correlation between ¹⁸F-DCFPyL uptake time and liver SUV_peak (r = 0.488, p = 0.003) and, accordingly, patients scanned at later time-points had a larger mean bias between the two tracers’ liver uptake values (0.05 vs 1.46, p = 0.001).

Conclusion

Normal tissue biodistribution patterns of ⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPyL were similar, despite subtle differences in quantitative values. Liver uptake showed an acceptable intra-patient agreement and low inter-patient variability between the two tracers, allowing its use as a reference organ for thresholding scans in the qualitative comparison of PSMA expression using these different tracers.

Electronic supplementary material

The online version of this article (10.1186/s40644-019-0211-y) contains supplementary material, which is available to authorized users.

First Clinicopathologic Evidence of a Non-PSMA-Related Uptake Mechanism for 68Ga-PSMA-11 in Salivary Glands

The intense accumulation of prostate-specific membrane antigen (PSMA) radioligands in salivary glands is still not well understood. It is of concern for therapeutic applications of PSMA radioligands, because therapeutic radiation will damage these glands. A better understanding of the uptake mechanism is, therefore, crucial to find solutions to reduce toxicity. The aim of this study was to investigate whether the accumulation of PSMA-targeting radioligands in submandibular glands (SMGs) can be explained with PSMA expression levels using autoradiography (ARG) and immunohistochemistry (IHC). Methods: All patients gave written informed consent for further utility of the biologic material. The SMG of 9 patients, pancreatic tissue of 4 patients, and prostate cancer (PCA) lesions of 9 patients were analyzed. Tissue specimens were analyzed by means of PSMA-IHC (using an anti-PSMA-antibody and an immunoreactivity score system [IRS]) and ARG using ¹⁷⁷Lu-PSMA-617 (with quantification of the relative signal intensity compared with a PSMA-positive standard). The SUV_max in salivary glands, pancreas, and PCA tissues were quantified in 60 clinical ⁶⁸Ga-PSMA-11 PET scans for recurrent disease as well as the 9 primary tumors selected for ARG and IHC. Results: PCA tissue samples revealed a wide range of PSMA staining intensity on IHC (IRS = 70-300) as well as in ARG (1.3%-22% of standard). This variability on PCA tissue could also be observed in ⁶⁸Ga-PSMA-11 PET (SUV_max, 4.4-16) with a significant correlation between ARG and SUV_max (P < 0.001, R ² = 0.897). On IHC, ARG, and ⁶⁸Ga-PSMA-11 PET, the pancreatic tissue was negative (IRS = 0, ARG = 0.1% ± 0.05%, SUV_max of 3.1 ± 1.1). The SMG tissue displayed only focal expression of PSMA limited to the intercalated ducts on IHC (IRS = 10-15) and a minimal signal on ARG (1.3% ± 0.9%). In contrast, all SMG showed a high ⁶⁸Ga-PSMA-11 accumulation on PET scans (SUV_max 23.5 ± 5.2). Conclusion: Our results indicate that the high accumulation of PSMA radioligands in salivary glands does not correspond to high PSMA expression levels determined using ARG and IHC. These findings provide evidence, that the significant accumulation of PSMA radioligands in SMG is not primarily a result of PSMA-mediated uptake.

Monosodium Glutamate Reduces 68Ga-PSMA-11 Uptake in Salivary Glands and Kidneys in a Preclinical Prostate Cancer Model

We evaluated the ability of monosodium glutamate (MSG) to reduce salivary and kidney uptake of a prostate-specific membrane antigen (PSMA) radioligand without affecting tumor uptake. Methods: LNCaP tumor-bearing mice were intraperitoneally injected with MSG (657, 329, or 164 mg/kg) or phosphate-buffered saline (PBS). Fifteen minutes later, the mice were intravenously administered 68Ga-PSMA-11. PET/CT imaging and biodistribution studies were performed 1 h after administration. Results: Tumor uptake (percentage injected dose per gram [%ID]) was not statistically different between groups, at 8.42 ± 1.40 %ID in the 657 mg/kg group, 7.19 ± 0.86 %ID in the 329 mg/kg group, 8.20 ± 2.44 %ID in the 164 mg/kg group, and 8.67 ± 1.97 %ID in the PBS group. Kidney uptake was significantly lower in the 657 mg/kg group (85.8 ± 24.2 %ID) than in the 329 mg/kg (159 ± 26.2 %ID), 164 mg/kg (211 ± 27.4 %ID), and PBS groups (182 ± 33.5 %ID) (P < 0.001). Salivary gland uptake was lower in the 657 mg/kg (3.72 ± 2.12 %ID) and 329 mg/kg (5.74 ± 0.62 %ID) groups than in the PBS group (10.04 ± 2.52 %ID) (P < 0.01). Conclusion: MSG decreased salivary and kidney uptake of 68Ga-PSMA-11 in a dose-dependent manner, whereas tumor uptake was unaffected.

Impact of long-term androgen deprivation therapy on PSMA ligand PET/CT in patients with castration-sensitive prostate cancer

Purpose

Since the introduction of PSMA PET/CT with ⁶⁸Ga-PSMA-11, this modality for imaging prostate cancer (PC) has spread worldwide. Preclinical studies have demonstrated that short-term androgen deprivation therapy (ADT) can significantly increase PSMA expression on PC cells. Additionally, retrospective clinical data in large patient cohorts suggest a positive association between ongoing ADT and a pathological PSMA PET/CT scan. The present evaluation was conducted to further analyse the influence of long-term ADT on PSMA PET/CT findings.

Methods

A retrospective analysis was performed of all 1,704 patients who underwent a ⁶⁸Ga-PSMA-11 PET/CT scan at our institution from 2011 to 2017 to detect PC. Of 306 patients scanned at least twice, 10 had started and continued ADT with a continuous clinical response between the two PSMA PET/CT scans. These ten patients were included in the current analysis which compared the tracer uptake intensity and volume of PC lesions on PSMA PET/CT before and during ongoing ADT.

Results

Overall, 31 PC lesions were visible in all ten patients before initiation of ADT. However, during ongoing ADT (duration 42–369 days, median 230 days), only 14 lesions were visible in eight of the ten patients. The average tracer uptake values decreased in 71% and increased in 12.9% of the PC lesions. Of all lesions, 33.3% were still visible in six patients with a complete PSA response (≤0.1 ng/ml).

Conclusion

Continuous long-term ADT significantly reduces the visibility of castration-sensitive PC on PSMA PET/CT. If the objective is visualization of the maximum possible extent of disease, we recommend referring patients for PSMA PET/CT before starting ADT.

Simultaneous whole-body 18F-PSMA-1007-PET/MRI with integrated high-resolution multiparametric imaging of the prostatic fossa for comprehensive oncological staging of patients with prostate cancer: a pilot study

INTRODUCTION

The aim of the present study was to explore the clinical feasibility and reproducibility of a comprehensive whole-body ¹⁸F-PSMA-1007-PET/MRI protocol for imaging prostate cancer (PC) patients.

METHODS

Eight patients with high-risk biopsy-proven PC underwent a whole-body PET/MRI (3 h p.i.) including a multi-parametric prostate MRI after ¹⁸F-PSMA-1007-PET/CT (1 h p.i.) which served as reference. Seven patients presented with non-treated PC, whereas one patient presented with biochemical recurrence. SUV_mean-quantification was performed using a 3D-isocontour volume-of-interest. Imaging data was consulted for TNM-staging and compared with histopathology. PC was confirmed in 4/7 patients additionally by histopathology after surgery. PET-artifacts, co-registration of pelvic PET/MRI and MRI-data were assessed (PI-RADS 2.0).

RESULTS

The examinations were well accepted by patients and comprised 1 h. SUV_mean-values between PET/CT (1 h p.i.) and PET/MRI (3 h p.i.) were significantly correlated (p < 0.0001, respectively) and similar to literature of ¹⁸F-PSMA-1007-PET/CT 1 h vs 3 h p.i. The dominant intraprostatic lesion could be detected in all seven patients in both PET and MRI. T2c, T3a, T3b and T4 features were detected complimentarily by PET and MRI in five patients. PET/MRI demonstrated moderate photopenic PET-artifacts surrounding liver and kidneys representing high-contrast areas, no PET-artifacts were observed for PET/CT. Simultaneous PET-readout during prostate MRI achieved optimal co-registration results.

CONCLUSIONS

The presented ¹⁸F-PSMA-1007-PET/MRI protocol combines efficient whole-body assessment with high-resolution co-registered PET/MRI of the prostatic fossa for comprehensive oncological staging of patients with PC.

Clinical performance of 68Ga-PSMA-11 PET/MRI for the detection of recurrent prostate cancer following radical prostatectomy

PURPOSE

Sensitive visualization of recurrent prostate cancer foci is a challenge in patients with early biochemical recurrence (EBR). The recently established ⁶⁸Ga-PSMA-11 PET/CT has significantly improved the detection rate with published values of up to 55% for patients with a serum PSA concentration between 0.2-0.5 ng/mL. The increased soft tissue contrast in the pelvis using simultaneous ⁶⁸Ga-PSMA-11 PET/MRI might further improve the detection rate in patients with EBR and low PSA values over PET/CT.

METHODS

We retrospectively analyzed a cohort of 56 consecutive patients who underwent a ⁶⁸Ga-PSMA-11 PET/MRI for biochemical recurrence in our institution between April and December 2016 with three readers. Median PSA level was 0.99 ng/mL (interquartile range: 3.1 ng/mL). Detection of PSMA-positive lesions within the prostate fossa, local and distant lymph nodes, bones, or visceral organs was recorded. Agreement among observers was evaluated with Fleiss's kappa (k).

RESULTS

Overall, in 44 of 56 patients (78.6%) PSMA-positive lesions were detected. In four of nine patients (44.4%) with a PSA < 0.2 ng/mL, suspicious lesions were detected (two pelvic and one paraaortic lymph nodes, and two bone metastases). In eight of 11 patients (72.7%) with a PSA between 0.2 and < 0.5 ng/mL, suspicious lesions were detected (two local recurrences, six lymph nodes, and one bone metastasis). Five out of 20 patients with a PSA < 0.5 ng/mL had extrapelvic disease. In 12 of 15 patients (80.0%) with a PSA between 0.5 and < 2.0 ng/mL, suspicious lesions were detected (four local recurrences, nine lymph nodes, and four bone metastases). In 20 of 21 patients (95.2%) with a PSA >2.0 ng/mL, suspicious lesions were detected. The overall interreader agreement for cancer detection was excellent (κ = 0.796, CI 0.645-0.947).

CONCLUSIONS

Our data show that ⁶⁸Ga-PSMA-11 PET/MRI has a high detection rate for recurrent prostate cancer even at very low PSA levels <0.5 ng/mL. Furthermore, even at those low levels extrapelvic disease can be localized in 25% of the cases and local recurrence alone is seen only in 10%.

Performance of 68Ga-PSMA PET/CT for Prostate Cancer Management at Initial Staging and Time of Biochemical Recurrence

PURPOSE OF THE REVIEW

Recently introduced Gallium-68 labeled PSMA-ligands such as HBED-CC (⁶⁸Ga-PSMA) have shown promise for unmet diagnostic needs in prostate cancer.

RECENT FINDINGS

⁶⁸Ga-PSMA has demonstrated improved detection rates and specificity for prostate cancer compared to standard imaging approaches. In the setting of primary disease, ⁶⁸Ga-PSMA appears to preferentially identify treatment-relevant intermediate and high-risk prostate cancer. There is also a growing evidence that ⁶⁸Ga-PSMA positron emission tomography (PET) outperforms alternative conventional imaging methods including choline-based radiotracers for the localization of disease sites at biochemical recurrence, particularly at lower prostate-specific antigen (PSA) levels (< 1 ng/mL). However, the majority of published work lacks rigorous verification of imaging results. ⁶⁸Ga-PSMA offers significant promise for both, primary disease and biochemically recurrent prostate cancer. The evidence base to support ⁶⁸Ga-PSMA is however still underdeveloped, and more rigorous studies substantiating efficacy are needed.

Local recurrence of prostate cancer after radical prostatectomy is at risk to be missed in 68Ga-PSMA-11-PET of PET/CT and PET/MRI: comparison with mpMRI integrated in simultaneous PET/MRI. Eur J Nucl Med Mol Imaging. 2017;44:776-787. [PMID: 27988802 DOI: 10.1007/s00259-016-3594-z]

PURPOSE

The positron emission tomography (PET) tracer ⁶⁸Ga-PSMA-11, targeting the prostate-specific membrane antigen (PSMA), is rapidly excreted into the urinary tract. This leads to significant radioactivity in the bladder, which may limit the PET-detection of local recurrence (LR) of prostate cancer (PC) after radical prostatectomy (RP), developing in close proximity to the bladder. Here, we analyze if there is additional value of multi-parametric magnetic resonance imaging (mpMRI) compared to the ⁶⁸Ga-PSMA-11-PET-component of PET/CT or PET/MRI to detect LR.

METHODS

One hundred and nineteen patients with biochemical recurrence after prior RP underwent both hybrid ⁶⁸Ga-PSMA-11-PET/CT_low-dose (1 h p.i.) and -PET/MRI (2-3 h p.i.) including a mpMRI protocol of the prostatic bed. The comparison of both methods was restricted to the abdomen with focus on LR (McNemar). Bladder-LR distance and recurrence size were measured in axial T2w-TSE. A logistic regression was performed to determine the influence of these variables on detectability in ⁶⁸Ga-PSMA-11-PET. Standardized-uptake-value (SUV_mean) quantification of LR was performed.

RESULTS

There were 93/119 patients that had at least one pathologic finding. In addition, 18/119 Patients (15.1%) were diagnosed with a LR in mpMRI of PET/MRI but only nine were PET-positive in PET/CT and PET/MRI. This mismatch was statistically significant (p = 0.004). Detection of LR using the PET-component was significantly influenced by proximity to the bladder (p = 0.028). The PET-pattern of LR-uptake was classified into three types (1): separated from bladder; (2): fuses with bladder, and (3): obliterated by bladder). The size of LRs did not affect PET-detectability (p = 0.84), mean size was 1.7 ± 0.69 cm long axis, 1.2 ± 0.46 cm short-axis. SUV_mean in nine men was 8.7 ± 3.7 (PET/CT) and 7.0 ± 4.2 (PET/MRI) but could not be quantified in the remaining nine cases (obliterated by bladder).

CONCLUSION

The present study demonstrates additional value of hybrid ⁶⁸Ga-PSMA-11-PET/MRI by gaining complementary diagnostic information compared to ^{the 68}Ga-PSMA-11-PET/CT_low-dose for patients with LR of PC.