Tracer uptake in mediastinal and paraaortal thoracic lymph nodes as a potential pitfall in image interpretation of PSMA ligand PET/CT

The Application of Radiolabeled Targeted Molecular Probes for the Diagnosis and Treatment of Prostate Cancer

Radiopharmaceuticals targeting prostate-specific membrane antigens (PSMA) are essential for the diagnosis, evaluation, and treatment of prostate cancer (PCa), particularly metastatic castration-resistant PCa, for which conventional treatment is ineffective. These molecular probes include [⁶⁸Ga]PSMA, [¹⁸F]PSMA, [Al¹⁸F]PSMA, [^99mTc]PSMA, and [⁸⁹Zr]PSMA, which are widely used for diagnosis, and [¹⁷⁷Lu]PSMA and [²²⁵Ac]PSMA, which are used for treatment. There are also new types of radiopharmaceuticals. Due to the differentiation and heterogeneity of tumor cells, a subtype of PCa with an extremely poor prognosis, referred to as neuroendocrine prostate cancer (NEPC), has emerged, and its diagnosis and treatment present great challenges. To improve the detection rate of NEPC and prolong patient survival, many researchers have investigated the use of relevant radiopharmaceuticals as targeted molecular probes for the detection and treatment of NEPC lesions, including DOTA-TOC and DOTA-TATE for somatostatin receptors, 4A06 for CUB domain-containing protein 1, and FDG. This review focused on the specific molecular targets and various radionuclides that have been developed for PCa in recent years, including those mentioned above and several others, and aimed to provide valuable up-to-date information and research ideas for future studies.

Combined forced diuresis and late acquisition on [68Ga]Ga-PSMA-11 PET/CT for biochemical recurrent prostate cancer: a clinical practice-oriented study

OBJECTIVES

Increased detection of prostate cancer (PCa) recurrences using [⁶⁸Ga]Ga-PSMA-11 PET/CT has been reported by adding forced diuresis or late-phase imaging to the standard protocol. However, the combination of these procedures in the clinical setting is still not standardized.

METHODS

One hundred prospectively recruited biochemical recurrent PCa patients were restaged with dual-phase [⁶⁸Ga]Ga-PSMA-11 PET/CT from September 2020 to October 2021. All patients received a standard scan (60 min), followed by diuretics (140 min) and a late-phase abdominopelvic scan (180 min). PET readers with low (n = 2), intermediate (n = 2), or high (n = 2) experience rated (i) standard and (ii) standard + forced diuresis late-phase images in a stepwise fashion according to E-PSMA guidelines, scoring their level of confidence. Study endpoints were (i) accuracy against a composite reference standard, (ii) reader's confidence level, and (iii) interobserver agreement.

RESULTS

Forced diuresis late-phase imaging increased the reader's confidence category for local and nodal restaging (both p < 0.0001), and the interobserver agreement in identifying nodal recurrences (from moderate to substantial, p < 0.01). However, it significantly increased diagnostic accuracy exclusively for local uptakes rated by low-experienced readers (from 76.5 to 84%, p = 0.05) and for nodal uptakes rated as uncertain at standard imaging (from 68.1 to 78.5%, p < 0.05). In this framework, SUVmax kinetics resulted in an independent predictor of PCa recurrence compared to standard metrics, potentially guiding the dual-phase PET/CT interpretation.

CONCLUSIONS

The present results do not support the systematic combination of forced diuresis and late-phase imaging in the clinical setting, but allow the identification of patients-, lesions-, and reader-based scenarios that might benefit from it.

KEY POINTS

• Increased detection of prostate cancer recurrences has been reported by adding diuretics administration or an additional late abdominopelvic scan to the standard [⁶⁸Ga]Ga-PSMA-11 PET/CT procedure. • We verified the added value of combined forced diuresis and delayed imaging, showing that this protocol only slightly increases the diagnostic accuracy of [⁶⁸Ga]Ga-PSMA-11 PET/CT, thus not justifying its systematic use in clinics. • However, it can be helpful in specific clinical scenarios, e.g., when PET/CT is reported by low-experienced readers. Moreover, it increased the reader's confidence and the agreement among observers.

[Procedure Guideline for Prostate Cancer Imaging with PSMA-ligand PET/CT]

PSMA-PET/CT for imaging prostate cancer (PC) has spread worldwide since its clinical introduction in 2011. The majority of experiences have been collected for PSMA-PET-imaging of recurrent PC. Data for primary staging of high-risk PC are highly promising. Meanwhile, a plethora of PSMA-ligands are available for clinical use (e. g. ⁶⁸Ga-PSMA-11, ⁶⁸Ga-PSMA-I&T, ⁶⁸Ga-PSMA-617, ¹⁸F-DCFBC, ¹⁸F-DCFPyL, ¹⁸F-PSMA-1007, ¹⁸F-rhPSMA-7 and ¹⁸F-JK-PSMA-7). However, an official approval is available only for ⁶⁸Ga-PSMA-11 (approved by the US FDA in 2020) and ¹⁸F-DCFPyL (approved by the US FDA in 2021).Recommendations for acquisition times vary from 1-2 h p. i. It has been shown that for the majority of tumour lesions, the contrast in PSMA-PET/CT increases with time. Therefore, additional late imaging can help to clarify unclear findings. PSMA-PET/CT should be performed prior to commencing an androgen deprivation therapy (ADT) since (long term) ADT reduces the visibility of PC lesions. Following injection of PSMA-ligands, hydration and forced diuresis are recommended for PSMA-ligands with primarily excretion via the kidneys in order to increase the visibility of tumour lesions adjacent to the urinary bladder.PSMA-ligands are physiologically taken up in multiple normal organs. For some ¹⁸F-labelled PSMA-ligands, presence of unspecific focal bone uptake has been reported. When using these tracers, focal bone uptake without CT-correlate should be interpreted with great caution. Besides prostate cancer, practically all solid tumors express PSMA in their neovasculature thereby taking up PSMA-ligands, although usually at a lower extent compared to PC. Also multiple benign lesions and inflammatory processes (e. g. lymph nodes) take up PSMA-ligands, also usually at lower extent compared to PC.

Update of PSMA Theranostics in Prostate Cancer: Current Applications and Future Trends

There is now an increasing trend for targeting cancers to go beyond early diagnosis and actually improve Progression-Free Survival and Overall Survival. Identifying patients who might benefit from a particular targeted treatment is the main focus for Precision Medicine. Radiolabeled ligands can be used as predictive biomarkers which can confirm target expression by cancers using positron emission tomography (PET). The same ligand can subsequently be labeled with a therapeutic radionuclide for targeted radionuclide therapy. This combined approach is termed “Theranostics”. The prostate-specific membrane antigen (PSMA) has emerged as an attractive diagnostic and therapeutic target for small molecule ligands in prostate cancer. It can be labeled with either positron emitters for PET-based imaging or beta and alpha emitters for targeted radionuclide therapy. This review article summarizes the important concepts for Precision Medicine contributing to improved diagnosis and targeted therapy of patients with prostate cancer and we identify some key learning points and areas for further research.

Prostate Cancer Theranostics: From Target Description to Imaging

Prostate-specific membrane antigen-PET/computed tomography (PSMA-PET/CT) is the investigation of choice for imaging prostate cancer. Demonstrating high diagnostic accuracy, PSMA-PET/CT detects disease at very early stages of recurrence, where the chances of a definitive cure may be at their greatest. A number of PSMA-radioligands are in established clinical routine, and there are currently only limited data and no single tracer can clearly be advocated over the others at present. Further clinical trial data, comparing and contrasting radiotracers and reporting outcome-based data are necessary to further increase the implementation of this very promising imaging modality.

The influence of colour scale in lesion detection and patient-based sensitivity in [68Ga]Ga-PSMA-PET/CT

OBJECTIVE

To investigate the influence of colour scales on the interpretation of [68Ga]Ga-PSMA-11 PET/CT for the diagnosis of recurrent prostate cancer.

METHODS

50 consecutive patients who underwent [68Ga]Ga-PSMA-11 PET/CT for recurrent prostate cancer were selected for this retrospective study. The scans were randomised, anonymised and read by five different readers first in the visually nonlinear colour scale 'PET-rainbow'. Scans were then rerandomised and read in the visually linear colour scale 'hot-metal new'. For each scan in each colour scale the numbers of pathological, equivocal and benign lesions were noted. Scans where the majority of readers (≥3) reported at least one PET-positive lesion were recorded as 'pathological'. Patient-level sensitivity was obtained by composite standard with 14.8 ± 1.2 months of follow-up.

RESULTS

Increased numbers of lesions per patient were reported for all readers in PET-rainbow compared to hot-metal new (37.4 ± 15.2 vs. 33.9 ± 16.4, respectively, P = 0.0005). On a per-patient basis, 43 scans were rated pathological in PET-rainbow, compared to 39 in hot-metal new. Follow-up was available for 30 patients confirming 26 pathological scans with positive follow-up in PET-rainbow, and 23 in hot-metal new. Three pathological scans were missed in hot-metal new. Patient-level sensitivity was higher for PET-rainbow (0.96) compared to hot-metal new (0.85). Inter-reader reliability was higher for hot-metal new (Fleiss κ = 0.76) compared to PET-rainbow (Fleiss κ = 0.60).

CONCLUSION

Use of PET-rainbow was associated with improved lesion detection and sensitivity compared to hot-metal new, although at cost of reduced inter-rater agreement. Consequently, the use of PET-rainbow for clinical routine and future studies involving [68Ga]Ga-PSMA-11 is recommended.

The influence of digital PET/CT on diagnostic certainty and interrater reliability in [68Ga]Ga-PSMA-11 PET/CT for recurrent prostate cancer

Objective

To investigate the impact of digital PET/CT on diagnostic certainty, patient-based sensitivity and interrater reliability.

Methods

Four physicians retrospectively evaluated two matched cohorts of patients undergoing [⁶⁸Ga]Ga-PSMA-11 PET/CT on a digital (dPET/CT n = 65) or an analogue scanner (aPET/CT n = 65) for recurrent prostate cancer between 11/2018 and 03/2019. The number of equivocal and pathological lesions as well as the frequency of discrepant findings and the interrater reliability for the two scanners were compared.

Results

dPET/CT detected more lesions than aPET/CT (p < 0.001). A higher number of pathological scans were observed for dPET/CT (83% vs. 57%, p < 0.001). The true-positive rate at follow-up was 100% for dPET/CT compared to 84% for aPET/CT (p < 0.001). The proportion of lesions rated as non-pathological as a total of all PSMA-avid lesions detected for dPET/CT was comparable to aPET/CT (61.8% vs. 57.0%, p = 0.99). Neither a higher rate of diagnostically uncertain lesions (11.5% dPET/CT vs. 13.7% aPET/CT, p = 0.95) nor discrepant scans (where one or more readers differed in opinion as to whether the scan is pathological) were observed (18% dPET/CT vs. 17% aPET/CT, p = 0.76). Interrater reliability for pathological lesions was excellent for both scanner types (Cronbach’s α = 0.923 dPET/CT; α = 0.948 aPET/CT) and interrater agreement was substantial for dPET/CT (Krippendorf’s α = 0.701) and almost perfect in aPET/CT (α = 0.802).

Conclusions

A higher detection rate for pathological lesions for dPET/CT compared with aPET/CT in multiple readers was observed. This improved sensitivity was coupled with an improved true-positive rate and was not associated with increased diagnostic uncertainty, rate of non-specific lesions, or reduced interrater reliability.

Key Points

• New generation digital scanners detect more cancer lesions in men with prostate cancer.

• When using digital scanners, the doctors are able to diagnose prostate cancer lesions with better certainty

• When using digital scanners, the doctors do not disagree with each other more than with other scanner types.

Combination of Forced Diuresis with Additional Late Imaging in 68Ga-PSMA-11 PET/CT: Effects on Lesion Visibility and Radiotracer Uptake

Renal excretion of some prostate-specific membrane antigen (PSMA) ligands and consequently increased bladder activity can obscure locally relapsing prostate cancer lesions in PSMA PET/CT. Furthermore, additional late imaging in PSMA PET/CT provides a useful method to clarify uncertain findings. The aim of this retrospective study was to investigate a modified imaging protocol combining late additional imaging with hydration and forced diuresis in individuals undergoing additional late scanning for uncertain lesions or low prostate-specific antigen. Methods: We compared an older protocol with a newer one. In the old protocol, patients undergoing ⁶⁸Ga-PSMA-11 PET/CT were examined at 90 min after injection, with 1 L of oral hydration beginning at 30 min after injection and 20 mg of furosemide given intravenously at 1 h after injection, followed by additional late imaging at 2.5 h after injection without further preparation. In the new protocol, a second group received the same procedure as before, with an additional 0.5 L of oral hydration and 10 mg of furosemide intravenously 30 min before the late imaging. We examined 132 patients (76 with the old protocol and 56 with the new one) with respect to urinary bladder activity (SUV_mean), prostate cancer lesion uptake (SUV_max), and lesion contrast (ratio of tumor SUV_max to bladder SUV_mean for local relapses and ratio of tumor SUV_max to gluteal-muscle SUV_mean for nonlocal prostate cancer lesions). Results: Bladder activity was significantly greater for the old protocol in the late scans than for the new protocol (ratio of bladder activity at 2.5 h to bladder activity at 1.5 h, 2.33 ± 1.17 vs. 1.37 ± 0.50, P < 0.0001). Increased tumor SUV_max and contrast were seen at 2.5 h compared with 1.5 h (P < 0.0001 for old protocol; P = 0.02 for new protocol). Increased bladder activity for the old protocol resulted in decreased lesion-to-bladder contrast, which was not the case for the new protocol. Tumor-to-background ratios increased at late imaging for both protocols, but the increase was significantly lower for the new protocol. For the old protocol, comparing the 1.5-h to the 2.5-h acquisitions, 4 lesions in 4 patients (4/76 = 5.2% of the cohort) were visible at the postdiuresis 1.5-h acquisition but not at 2.5 h, having been obscured as a result of the higher bladder activity. In the new protocol, 2 of 56 (3.6%) patients had lesions visible only at late imaging, and 2 patients had lesions that could be better discriminated at late imaging. Conclusion: Although the combination of diuretics and hydration can be a useful method to increase the visualization and detectability of locally recurrent prostate cancer in standard ⁶⁸Ga-PSMA-11 PET/CT, their effects do not sufficiently continue into additional late imaging. Additional diuresis and hydration are recommended to improve the visibility, detection, and diagnostic certainty of local recurrences.

Case series - 18F-DCFPyL-positron emission tomography/computed tomography (PET/CT) time of imaging

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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.

Factors Predicting Metastatic Disease in 68Ga-PSMA-11 PET-Positive Osseous Lesions in Prostate Cancer

Bone is the most common site of distant metastatic spread in prostate adenocarcinoma. Prostate-specific membrane antigen (PSMA) uptake has been described in both benign and malignant bone lesions, which can lead to false-positive findings on ⁶⁸Ga-PSMA-11 PET. The purpose of this study was to evaluate the diagnostic accuracy of ⁶⁸Ga-PSMA-11 PET for osseous prostate cancer metastases and improve bone uptake interpretation using semiquantitative metrics. Methods: Fifty-six prostate cancer patients (18 before prostatectomy and 38 with biochemical recurrence) who underwent ⁶⁸Ga-PSMA-11 PET/MRI or PET/CT examinations with osseous PSMA-ligand uptake were included in the study. Medical records were reviewed retrospectively by board-certified nuclear radiologists to determine true or false positivity based on a composite endpoint. For each avid osseous lesion, we measured biologic volume; size; PSMA Reporting and Data System (RADS) rating; SUV_max; and ratio of lesion SUV_max to liver, blood pool, and background bone SUV_max Differences between benign and malignant lesions were evaluated for statistical significance, and cutoffs for these parameters were determined to maximize diagnostic accuracy. Results: Among 56 participants, 13 (22.8%) had false-positive osseous ⁶⁸Ga-PSMA-11 findings and 43 (76.8%) had true-positive osseous ⁶⁸Ga-PSMA-11 findings. Twenty-two patients (39%) had 1 osseous lesion, 18 (32%) had 2-4 lesions, and 16 (29%) had 5 or more lesions. Cutoffs resulting in statistically significant (P < 0.005) differences between benign and malignant lesions were a PSMA RADS rating of at least 4, an SUV_max of at least 4.1, and SUV_max ratios of at least 2.11 for lesion to blood pool, at least 0.55 for lesion to liver, and at least 4.4 for lesion to bone. These measurements corresponded to a lesion-based ⁶⁸Ga-PSMA-11 PET lesion detection rate of 80%, 93%, 89%, 21%, and 89%, respectively, for malignancy, and a specificity of 73%, 73%, 73%, 93%, and 60%, respectively. Conclusion: PSMA RADS rating, SUV_max, and SUV_max ratio for lesion to blood pool can help differentiate benign from malignant lesions on ⁶⁸Ga-PSMA-11 PET. An SUV_max ratio of more than 2.2 for lesion to blood pool is a reasonable parameter to support image interpretation and presented a superior lesion detection rate and specificity when compared with visual interpretation by PSMA RADS. These parameters hold clinical value by improving diagnostic accuracy for metastatic prostate cancer on ⁶⁸Ga-PSMA-11 PET/MRI and PET/CT.

Influence of localization of PSMA-positive oligo-metastases on efficacy of metastasis-directed external-beam radiotherapy-a multicenter retrospective study

PURPOSE

Approximately 40-70% of biochemically persistent or recurrent prostate cancer (PCa) patients after radical prostatectomy (RPE) are oligo-metastatic in ⁶⁸gallium-prostate-specific membrane antigen positron emission tomography (⁶⁸Ga-PSMA PET). Those lesions are frequently located outside the prostate bed, and therefore not cured by the current standards of care like external-beam radiotherapy (EBRT) of the prostatic fossa. This retrospective study analyzes the influence of oligo-metastases' site on outcome after metastasis-directed radiotherapy (MDR).

METHODS

Retrospectively, 359 patients with PET-positive PCa recurrences after RPE were analyzed. Biochemical recurrence-free survival (BRFS) (prostate-specific antigen (PSA) < post-radiotherapy nadir + 0.2 ng/mL) was assessed using Kaplan-Meier survival and Cox regression analysis.

RESULTS

All patients were initially clinically without distant metastases (cM0). Seventy-five patients had local recurrence within the prostatic fossa, 32 patients had pelvic nodal plus local recurrence, 117 patients had pelvic nodal recurrence, 51 patients had paraaortic lymph node metastases with/without locoregional recurrence, and 84 patients had bone or visceral metastases with/without locoregional recurrence. Median PSA before MDR was 1.2 ng/mL (range, 0.04-47.5). Additive androgen deprivation therapy (ADT) was given in 35% (125/359) of patients. Median PSA nadir after MDR was 0.23 ng/mL (range, < 0.03-18.30). After a median follow-up of 16 months (1-57), 239/351 (68%) patients had no biochemical recurrence. Patients with distant lymph node and/or distant metastases, the so-called oligo-body cohort, had an overall in-field control of 90/98 (91%) but at the same time, an ex-field progress of 44/96 (46%). In comparison, an ex-field progress was detected in 28/154 (18%) patients with local and/or pelvic nodal recurrence (oligo-pelvis group). Compared with the oligo-pelvis group, there was a significantly lower BRFS in oligo-body patients at the last follow-up.

CONCLUSION

Overall, BRFS was dependent on patterns of metastatic disease. Thus, MDR of PSMA PET-positive oligo-metastases can be offered considering that about one-third of the patients progressed within a median follow-up of 16 months.

The role of additional late PSMA-ligand PET/CT in the differentiation between lymph node metastases and ganglia

PURPOSE

Differentiating between prostate cancer (PC) lesions and benign structures which exhibit radiotracer uptake in PSMA-ligand PET/CT can be challenging. Additional late imaging has been shown to be a powerful method for the discrimination between PC and non-PC lesions, owing to the increasing tracer uptake of the former. Nevertheless, there are no pre-existing studies which describe the dynamic tracer uptake for ganglia, which this present study aims to address.

METHODS

Fifty consecutive patients with PC who received standard and late ⁶⁸Ga-PSMA-11-PET/CT (by local protocol at 1.5 h "standard" and 2.5 h p.i. "late") underwent retrospective evaluation. All lesions with a tracer uptake above local background indicative for ganglia as well as PC lesions were analysed with regard to their maximum standardised uptake values (SUVmax) and localisation.

RESULTS

Overall, 86 PSMA-positive ganglia were identified in 70% (n = 35) of the patients. Five ganglia exhibited PSMA avidity at late imaging only, and three at standard imaging only. A total of 66 lesions suggestive for PC were detected in 44 patients (88%), of which 45% (n = 30) were morphologically identified as lymph nodes (LN), the remainder being locally recurrent lesions or bone metastases. No solid organ metastases were present in our cohort. At late scanning, 73% of the LN exhibited an increase in SUVmax, whereas 65% of the ganglia exhibited a decreasing or stable SUVmax.

CONCLUSION

Whereas the presence of increasing tracer uptake in potential PC lesions can provide additional data about the likelihood of malignancy, increasing SUVmax alone does not reliably differentiate between ganglia and PC lesions and is a potential diagnostic pitfall. We therefore recommend high-resolution CT to enable morphological characterisation of ganglia.

Deep neural network for automatic characterization of lesions on 68Ga-PSMA-11 PET/CT

PURPOSE

This study proposes an automated prostate cancer (PC) lesion characterization method based on the deep neural network to determine tumor burden on ⁶⁸Ga-PSMA-11 PET/CT to potentially facilitate the optimization of PSMA-directed radionuclide therapy.

METHODS

We collected ⁶⁸Ga-PSMA-11 PET/CT images from 193 patients with metastatic PC at three medical centers. For proof-of-concept, we focused on the detection of pelvis bone and lymph node lesions. A deep neural network (triple-combining 2.5D U-Net) was developed for the automated characterization of these lesions. The proposed method simultaneously extracts features from axial, coronal, and sagittal planes, which mimics the workflow of physicians and reduces computational and memory requirements.

RESULTS

Among all the labeled lesions, the network achieved 99% precision, 99% recall, and an F1 score of 99% on bone lesion detection and 94%, precision 89% recall, and an F1 score of 92% on lymph node lesion detection. The segmentation accuracy is lower than the detection. The performance of the network was correlated with the amount of training data.

CONCLUSION

We developed a deep neural network to characterize automatically the PC lesions on ⁶⁸Ga-PSMA-11 PET/CT. The preliminary test within the pelvic area confirms the potential of deep learning methods. Increasing the amount of training data should further enhance the performance of the proposed method and may ultimately allow whole-body assessments.

Digital versus analogue PET in [68Ga]Ga-PSMA-11 PET/CT for recurrent prostate cancer: a matched-pair comparison

PURPOSE

Digital PET/CT scanners represent a significant step forward in molecular imaging. We report here the clinical impact of digital PET in PSMA-PET/CT.

METHODS

In this retrospective study, 88 consecutive patients who underwent [⁶⁸Ga]Ga-PSMA-11 PET/CT on a digital PET/CT (dPET/CT) scanner for recurrent prostate cancer (PC) were included in a first cohort. In a second step, 88 individuals who underwent an analogue [⁶⁸Ga]Ga-PSMA-11 PET/CT (aPET/CT) were selected after they were matched to the first cohort for clinical parameters. Following consensus read by two nuclear medicine physicians, the number and type of PC lesions as well as benign, PSMA-positive lesions were recorded. The results were complemented by extensive [⁶⁸Ga]Ga phantom measurements to determine imaging characteristics of both scanners.

RESULTS

dPET/CT revealed a greater number of PC lesions compared to aPET/CT (326 versus 142) as well as a proportional increase in benign causes of tracer-uptake (144 versus 65). A greater number of scans were noted as pathological for PC on dPET/CT (74/88) compared to aPET/CT (64/88, p < 0.05). The PSMA positivity rate for PC was significantly higher in dPET/CT for the lowest PSA values (PSA < 2.0 ng/ml, p < 0.05).

CONCLUSION

dPET/CT detected more PC lesions compared to aPET/CT. A significantly higher rate of pathological PET/CTs was noted in the group with the lowest PSA values. A higher number of benign PSMA-positive lesions were also noted in dPET/CT. The differences could be plausibly explained by the measured imaging characteristics of the scanners.

Dynamic patterns of [68Ga]Ga-PSMA-11 uptake in recurrent prostate cancer lesions

PURPOSE

Dual-time point PET/CT scanning with [⁶⁸Ga]Ga-PSMA-11 in the diagnosis of prostate cancer (PC) has been advanced as a method to increase detection of PC lesions, particularly at early stages of biochemical recurrence and as a potential means to aid the discrimination between benign and pathological prostate-specific membrane antigen (PSMA) uptake. However, the assumption that all PC lesions uniformly exhibit increasing tracer uptake at delayed imaging has not yet been investigated, which this present study aims to address.

METHODS

One hundred consecutive patients with biochemically recurrent PC who received standard and late [⁶⁸Ga]Ga-PSMA-11 PET/CT (by local protocol at 1.5 h "standard" and 2.5 h p.i. "late") underwent retrospective evaluation. All lesions with a tracer uptake above local background were analysed with regard to their maximum standardised uptake values at standard and late images (SUVmax) and characterised according to their morphological characteristics.

RESULTS

Seventy-nine of 100 patients had PSMA-positive scans, in whom a total of 185 individual PSMA-positive lesions were identified. These were morphologically characterised as bone lesions (n = 48), solid organ lesions (n = 3), lymph node (LN) lesions (n = 78) and locally recurrent lesions in the prostatic fossa or seminal vesicles (n = 56). The relative uptake between standard and late imaging was considered; all lesions classified as local recurrence presented with increasing (86%) or stable patterns of tracer uptake (14%). In contrast, only 58% of bone lesions exhibited increasing tracer uptake, with 21% exhibiting a stable pattern and 21% exhibiting a decreasing tracer uptake at late imaging.

CONCLUSION

A heterogeneous pattern of dynamic tracer uptake was observed, with a largely increasing pattern observed for locally recurrent lesions and lymph nodes and a significant proportion of bone lesions exhibiting decreasing tracer uptake. The results are of significance not only in the imaging and identification of PC lesions, but they also have implications for PSMA-directed ligand therapy.

Does lymph node localization affect prostate-specific membrane antigen uptake?

OBJECTIVE

To investigate the relationship between lymph node (LN) size and localization and prostate-specific membrane antigen (PSMA) uptake in patients with prostate cancer.

PATIENTS AND METHODS

Between February 2015 and February 2017, a total of 178 patients diagnosed with prostate adenocarcinoma by gallium-68 PSMA PET/computed tomography were evaluated. Seventy-eight patients with LN PSMA uptake were included in the study.The short-axis diameter and maximum and mean standardized uptake values (SUV) were measured from axial images of LNs with PSMA uptake. LN conglomerates were considered a single lesion. Patients were divided into two groups according to the presence (group 1) or absence (group 2) of bone uptake in addition to the LN uptake; subgroups were constituted according to the short-axis diameter and PSMA-positive LN region for each group. LNs were classified according to their localization as pelvic, abdominal, or cervical/thoracic.

RESULTS

In both groups, the SUV were significantly higher in LNs with short-axis diameters more than 8 mm than those with diameters up to 8 mm (P < 0.001 and < 0.001, respectively). Also, both groups showed a moderate correlation between the LN size and SUV.When the analysis was carried out according to the localization, but after excluding the LN conglomerates, the correlation between the pelvic and abdominal LNs was higher in the second group.

CONCLUSION

The highest significant positive correlation between LN size and SUV was in patients with pelvic and abdominal LN metastases without bone involvement according to the gallium-68 PSMA PET/computed tomography images in our study.

Minimal residual disease in prostate cancer patients after primary treatment: theoretical considerations, evidence and possible use in clinical management

Minimal residual disease is that not detected by conventional imaging studies and clinically the patient remains disease free. However, with time these dormant cells will awaken and disease progression occurs, resulting in clinically and radiological detectable metastatic disease. This review addresses the concept of tumor cell dissemination from the primary tumor, the micrometastatic niche and tumor cell survival and finally the clinical utility of detecting and characterizing these tumor cells in order to guide management decisions in treating patients with prostate cancer.

PSMA Ligand PET/MRI for Primary Prostate Cancer: Staging Performance and Clinical Impact

PURPOSE

Primary staging of prostate cancer relies on modalities, which are limited. We evaluate simultaneous [⁶⁸Ga]Ga-PSMA-11 PET (PSMA-PET)/MRI as a new diagnostic method for primary tumor-node-metastasis staging compared with histology and its impact on therapeutic decisions.

EXPERIMENTAL DESIGN

We investigated 122 patients with PSMA-PET/MRI prior to planned radical prostatectomy (RP). Primary endpoint was the accuracy of PSMA-PET/MRI in tumor staging as compared with staging-relevant histology. In addition, a multidisciplinary team reassessed the initial therapeutic approach to evaluate its impact on the therapeutic management.

RESULTS

PSMA-PET/MRI correctly identified prostate cancer in 119 of 122 patients (97.5%). Eighty-one patients were treated with RP and pelvic lymphadenectomy. The accuracy for T staging was 82.5% [95% confidence interval (CI), 73-90; P < 0.001], for T2 stage was 85% (95% CI, 71-94; P < 0.001), for T3a stage was 79% (95% CI, 43-85; P < 0.001), for T3b stage was 94% (95% CI, 73-100; P < 0.001), and for N1 stage was 93% (95% CI, 84-98; P < 0.001). PSMA-PET/MRI changed the therapeutic strategy in 28.7% of the patients with either the onset of systemic therapy/radiotherapy (n = 16) or active surveillance (n = 19).

CONCLUSIONS

PSMA-PET/MRI can provide an accurate staging of newly diagnosed prostate cancer. In addition, treatment strategies were changed in almost a third of the patients due to the information of this hybrid imaging technique.