Comparison of 68Ga-HBED-CC PSMA-PET/CT and multiparametric MRI for gross tumour volume detection in patients with primary prostate cancer based on slice by slice comparison with histopathology

X-change symposium: status and future of modern radiation oncology-from technology to biology

Future radiation oncology encompasses a broad spectrum of topics ranging from modern clinical trial design to treatment and imaging technology and biology. In more detail, the application of hybrid MRI devices in modern image-guided radiotherapy; the emerging field of radiomics; the role of molecular imaging using positron emission tomography and its integration into clinical routine; radiation biology with its future perspectives, the role of molecular signatures in prognostic modelling; as well as special treatment modalities such as brachytherapy or proton beam therapy are areas of rapid development. More clinically, radiation oncology will certainly find an important role in the management of oligometastasis. The treatment spectrum will also be widened by the rational integration of modern systemic targeted or immune therapies into multimodal treatment strategies. All these developments will require a concise rethinking of clinical trial design. This article reviews the current status and the potential developments in the field of radiation oncology as discussed by a panel of European and international experts sharing their vision during the "X-Change" symposium, held in July 2019 in Munich (Germany).

Lesion-to-background ratio threshold value of SUVmax of simultaneous [68Ga]Ga-PSMA-11 PET/MRI imaging in patients with prostate cancer

Purpose

This study aimed to calculate an applicable relative ratio threshold value instead of the absolute threshold value for simultaneous ⁶⁸Ga prostate-specific membrane antigen/positron emission tomography ([⁶⁸Ga]Ga-PSMA-11 PET) in patients with prostate cancer (PCa).

Materials and methods

Our study evaluated thirty-two patients and 170 focal prostate lesions. Lesions are classified into groups according to Prostate Imaging Reporting and Data System (PI-RADS). Standardized uptake values maximum (SUVmax), corresponding lesion-to-background ratios (LBRs) of SUVmax, and LBR distributions of each group were measured based on regions of interest (ROI). We examined LBR with receiver operating characteristic analysis to determine threshold values for differentiation between multiparametric magnetic resonance imaging (mpMRI)-positive and mpMRI-negative lesions.

Results

We analyzed a total of 170 focal prostate lesions. Lesions number of PI-RADS 2 to 5 was 70, 16, 46, and 38. LBR of SUVmax of each PI-RADS scores was 1.5 (0.9, 2.4), 2.5 (1.6, 3.4), 3.7 (2.6, 4.8), and 6.7 (3.5, 12.7). Based on an optimal threshold ratio of 2.5 to be exceeded, lesions could be classified into MRI-positive lesion on [⁶⁸Ga]Ga-PSMA PET with a sensitivity of 85.2%, a specificity of 72.0%, with the corresponding area under the receiver operating characteristic curve (AUC) of 0.83, p < 0.001. This value matches the imaging findings better.

Conclusion

The ratio threshold value of SUVmax, LBR, has improved clinical and research applicability compared with the absolute value of SUVmax. A higher threshold value than the background’s uptake can dovetail the imaging findings on MRI better. It reduces the bias from using absolute background uptake value as the threshold value.

[68Ga]Ga-PSMA-11 in prostate cancer: a comprehensive review

Imaging of the prostate-specific membrane antigen (PSMA) has become an important tool for managing patients with recurrent prostate cancer, and one of the most frequently employed radiopharmaceuticals is [68Ga]Ga-PSMA-11. Herein, we summarize the preclinical development and the clinical applications of [68Ga]Ga-PSMA-11 and present side-by-side comparisons with other radiopharmaceuticals or imaging modalities, in order to assist imagers and clinicians in recommending, performing, and interpreting the results of [68Ga]Ga-PSMA-11 PET scans in patients with prostate cancer.

Comparison of Manual and Semi-Automatic [18F]PSMA-1007 PET Based Contouring Techniques for Intraprostatic Tumor Delineation in Patients With Primary Prostate Cancer and Validation With Histopathology as Standard of Reference

PURPOSE

Accurate contouring of intraprostatic gross tumor volume (GTV) is pivotal for successful delivery of focal therapies and for biopsy guidance in patients with primary prostate cancer (PCa). Contouring of GTVs, using 18-Fluor labeled tracer prostate specific membrane antigen positron emission tomography ([18F]PSMA-1007/PET) has not been examined yet.

PATIENTS AND METHODS

Ten Patients with primary PCa who underwent [18F]PSMA-1007 PET followed by radical prostatectomy were prospectively enrolled. Coregistered histopathological gross tumor volume (GTV-Histo) was used as standard of reference. PSMA-PET images were contoured on two ways: (1) manual contouring with PET scaling SUVmin-max: 0-10 was performed by three teams with different levels of experience. Team 1 repeated contouring at a different time point, resulting in n = 4 manual contours. (2) Semi-automatic contouring approaches using SUVmax thresholds of 20-50% were performed. Interobserver agreement was assessed for manual contouring by calculating the Dice Similarity Coefficient (DSC) and for all approaches sensitivity, specificity were calculated by dividing the prostate in each CT slice into four equal quadrants under consideration of histopathology as standard of reference.

RESULTS

Manual contouring yielded an excellent interobserver agreement with a median DSC of 0.90 (range 0.87-0.94). Volumes derived from scaling SUVmin-max 0-10 showed no statistically significant difference from GTV-Histo and high sensitivities (median 87%, range 84-90%) and specificities (median 96%, range 96-100%). GTVs using semi-automatic segmentation applying a threshold of 20-40% of SUVmax showed no significant difference in absolute volumes to GTV-Histo, GTV-SUV50% was significantly smaller. Best performing semi-automatic contour (GTV-SUV20%) achieved high sensitivity (median 93%) and specificity (median 96%). There was no statistically significant difference to SUVmin-max 0-10.

CONCLUSION

Manual contouring with PET scaling SUVmin-max 0-10 and semi-automatic contouring applying a threshold of 20% of SUVmax achieved high sensitivities and very high specificities and are recommended for [18F]PSMA-1007 PET based focal therapy approaches. Providing high specificities, semi-automatic approaches applying thresholds of 30-40% of SUVmax are recommend for biopsy guidance.

Correlation between Intraprostatic PSMA Uptake and MRI PI-RADS of [68Ga]Ga-PSMA-11 PET/MRI in Patients with Prostate Cancer: Comparison of PI-RADS Version 2.0 and PI-RADS Version 2.1

PURPOSE

We aimed to evaluate the correlation between PSMA uptake and magnetic resonance imaging (MRI) PI-RADS of simultaneous [68Ga]Ga-PSMA-11 PET/MRI regarding PI-RADS version 2.0 and 2.1 respectively and compared the difference between these two versions.

MATERIALS AND METHODS

We retrospectively analyzed a total of forty-six patients with biopsy-proven prostate cancer who underwent simultaneous [68Ga]Ga-PSMA-11 PET/MRI. We classified the lesions regarding PI-RADS version 2.0 and 2.1, peripheral zone (PZ), and transitional zone (TZ), respectively. Based on regions of interest (ROI), standardized uptake values maximum (SUVmax), and corresponding lesion-to-background ratios (LBR) of SUVmax of each category, PI-RADS score 1 to 5, were measured. A comparison between PI-RADS version 2.0 and PI-RADS version 2.1 was performed.

RESULTS

A total of 215 focal prostate lesions were analyzed, including two subgroups, 125 TZ and 90 PZ. Data are reported as median and interquartile range (IQR). Regarding PI-RADS version 2.1, TZ SUVmax of each category were 1.5 (0.5, 1.9), 1.9 (0.8, 2.3), 3.3 (2.1, 4.6), 4.2 (3.1, 5.7), 7.3 (5.2, 9.7). PZ SUVmax of each category were 1.0 (0.8, 1.6), 2.5 (1.5, 3.2), 3.3 (1.9, 4.5), 4.3 (3.0, 5.4), 7.4 (5.0, 9.3). Regarding the inter-reader agreement of the overall PI-RADS assessment category, the kappa value was 0.723 for version 2.0 and 0.853 for version 2.1.

CONCLUSION

Revisions of PI-RADS version 2.1 results in variations in lesions classification. Lesions with the PI-RADS category of 3, 4, and 5 present relatively higher intraprostatic PSMA uptake, while lesions with the PI-RADS category of 1 and 2 present relatively lower and similar uptake. Version 2.1 has higher inter-reader reproducibility than version 2.0.

Isotropic Expansion of the Intraprostatic Gross Tumor Volume of Primary Prostate Cancer Patients Defined in MRI-A Correlation Study With Whole Mount Histopathological Information as Reference

Introduction

An accurate delineation of the intraprostatic gross tumor volume (GTV) is of importance for focal treatment in patients with primary prostate cancer (PCa). Multiparametric MRI (mpMRI) is the standard of care for lesion detection but has been shown to underestimate GTV. This study investigated how far the GTV has to be expanded in MRI in order to reach concordance with the histopathological reference and whether this strategy is practicable in clinical routine.

Patients and Methods

Twenty-two patients with planned prostatectomy and preceded 3 Tesla mpMRI were prospectively examined. After surgery, PCa contours delineated on histopathological slides (GTV-Histo) were superimposed on MRI using ex-vivo imaging as support for co-registration. According to the PI-RADSv2 classification, GTV was manually delineated in MRI (GTV-MRI) by two experts in consensus. For volumetric analysis, we compared GTV-MRI and GTV-Histo. Subsequently, we isotropically enlarged GTV-MRI in 1 mm increments within the prostate and also compared those with GTV-Histo regarding the absolute volumes. For evaluating the spatial accuracy, we considered the coverage ratio of GTV-Histo, the Sørensen–Dice coefficient (DSC), as well as the contact with the urethra.

Results

In 19 of 22 patients MRI underestimated the intraprostatic tumor volume compared to histopathological reference: median GTV-Histo (4.7 cm³, IQR: 2.5–18.8) was significantly (p<0.001) lager than median GTV-MRI (2.6 cm³, IQR: 1.2–6.9). A median expansion of 1 mm (range: 0–4 mm) adjusted the initial GTV-MRI to at least the volume of GTV-Histo (GTV^exp-MRI). Original GTV-MRI and expansion with 1, 2, 3, and 4 mm covered in median 39% (IQR: 2%–78%), 62% (10%–91%), 70% (15%–95%), 80% (21–100), 87% (25%–100%) of GTV-Histo, respectively. Best DSC (median: 0.54) between GTV-Histo and GTV-MRI was achieved by median expansion of 2 mm. The urethra was covered by initial GTVs-MRI in eight patients (36%). After applying an expansion with 2 mm the urethra was covered in one more patient by GTV-MRI.

Conclusion

Using histopathology as reference, we demonstrated that MRI underestimates intraprostatic tumor volume. A 2 mm–expansion may improve accurate GTV-delineation while respecting the balance between histological tumor coverage and overtreatment.

Uncovering the invisible-prevalence, characteristics, and radiomics feature-based detection of visually undetectable intraprostatic tumor lesions in 68GaPSMA-11 PET images of patients with primary prostate cancer

Introduction

Primary prostate cancer (PCa) can be visualized on prostate-specific membrane antigen positron emission tomography (PSMA-PET) with high accuracy. However, intraprostatic lesions may be missed by visual PSMA-PET interpretation. In this work, we quantified and characterized the intraprostatic lesions which have been missed by visual PSMA-PET image interpretation. In addition, we investigated whether PSMA-PET-derived radiomics features (RFs) could detect these lesions.

Methodology

This study consists of two cohorts of primary PCa patients: a prospective training cohort (n = 20) and an external validation cohort (n = 52). All patients underwent ⁶⁸Ga-PSMA-11 PET/CT and histology sections were obtained after surgery. PCa lesions missed by visual PET image interpretation were counted and their International Society of Urological Pathology score (ISUP) was obtained. Finally, 154 RFs were derived from the PET images and the discriminative power to differentiate between prostates with or without visually undetectable lesions was assessed and areas under the receiver-operating curve (ROC-AUC) as well as sensitivities/specificities were calculated.

Results

In the training cohort, visual PET image interpretation missed 134 tumor lesions in 60% (12/20) of the patients, and of these patients, 75% had clinically significant (ISUP > 1) PCa. The median diameter of the missed lesions was 2.2 mm (range: 1–6). Standard clinical parameters like the NCCN risk group were equally distributed between patients with and without visually missed lesions (p < 0.05). Two RFs (local binary pattern (LBP) size-zone non-uniformality normalized and LBP small-area emphasis) were found to perform excellently in visually unknown PCa detection (Mann-Whitney U: p < 0.01, ROC-AUC: ≥ 0.93). In the validation cohort, PCa was missed in 50% (26/52) of the patients and 77% of these patients possessed clinically significant PCa. The sensitivities of both RFs in the validation cohort were ≥ 0.8.

Conclusion

Visual PSMA-PET image interpretation may miss small but clinically significant PCa in a relevant number of patients and RFs can be implemented to uncover them. This could be used for guiding personalized treatments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05111-3.

Stereotactic radiotherapy with focal boost for intermediate and high-risk prostate cancer: Initial results of the SPARC trial

INTRODUCTION

Dose escalation to dominant intraprostatic lesions (DILs) is a novel method to increase the therapeutic ratio in localised prostate cancer. The Stereotactic Prostate Augmented Radiotherapy with Cyberknife (SPARC) trial was designed to determine the feasibility of a focal boost defined with multiparametric magnetic resonance imaging (mpMRI) using stereotactic ablative body radiotherapy (SABR).

MATERIALS AND METHODS

Patients were included with newly diagnosed intermediate to high risk prostate cancer with at least one of: Gleason score 4 + 3, stage T3a, or PSA > 20 ng/ml. Visible disease on mpMRI was mandatory and up to 2 separate nodules were allowed. All patients received androgen deprivation. Patients received 36.25 Gy in 5 fractions using CyberKnife® and the DIL received a simultaneous boost to a maximum of 47.5 Gy, as allowed by OAR constraints. Genitourinary (GU) and gastrointestinal (GI) toxicity was reported using the RTOG scoring criteria. International Index of Erectile Function (IIEF) and EQ-5D global health scores were regularly captured.

RESULTS

An interim safety analysis was performed on the first 8 patients, recruited between July 2013 and December 2015. Median follow up was 56 months (range 50-74). Median D95 values for the prostate PTV and boost volume were 36.55 Gy (range 35.87-36.99) and 46.62 Gy (range 44.85-48.25) respectively. Of the dose constraints, 10/80 were not achieved but all were minor dose variations. Grade 2+ acute GU and GI toxicities were 37.5% respectively while grade 2+ late GU and GI toxicities were 12.5% and 0% respectively. IIEF and quality of life scores recovered over time and all patients remain in biochemical remission.

CONCLUSION

The first patients have been successfully treated with prostate SABR and focal boost on the SPARC trial, with excellent adherence to the planning protocol. Toxicity and efficacy results are promising and further recruitment is underway.

Intraprostatic Tumor Segmentation on PSMA PET Images in Patients with Primary Prostate Cancer with a Convolutional Neural Network

Accurate delineation of the intraprostatic gross tumor volume (GTV) is a prerequisite for treatment approaches in patients with primary prostate cancer (PCa). Prostate-specific membrane antigen PET (PSMA PET) may outperform MRI in GTV detection. However, visual GTV delineation underlies interobserver heterogeneity and is time consuming. The aim of this study was to develop a convolutional neural network (CNN) for automated segmentation of intraprostatic tumor (GTV-CNN) in PSMA PET. Methods: The CNN (3D U-Net) was trained on the ⁶⁸Ga-PSMA PET images of 152 patients from 2 different institutions, and the training labels were generated manually using a validated technique. The CNN was tested on 2 independent internal (cohort 1: ⁶⁸Ga-PSMA PET, n = 18 and cohort 2: ¹⁸F-PSMA PET, n = 19) and 1 external (cohort 3: ⁶⁸Ga-PSMA PET, n = 20) test datasets. Accordance between manual contours and GTV-CNN was assessed with the Dice-Sørensen coefficient (DSC). Sensitivity and specificity were calculated for the 2 internal test datasets (cohort 1: n = 18, cohort 2: n = 11) using whole-mount histology. Results: The median DSCs for cohorts 1-3 were 0.84 (range: 0.32-0.95), 0.81 (range: 0.28-0.93), and 0.83 (range: 0.32-0.93), respectively. Sensitivities and specificities for the GTV-CNN were comparable with manual expert contours: 0.98 and 0.76 (cohort 1) and 1 and 0.57 (cohort 2), respectively. Computation time was around 6 s for a standard dataset. Conclusion: The application of a CNN for automated contouring of intraprostatic GTV in ⁶⁸Ga-PSMA and ¹⁸F-PSMA PET images resulted in a high concordance with expert contours and in high sensitivities and specificities in comparison with histology as a reference. This robust, accurate and fast technique may be implemented for treatment concepts in primary prostate cancer. The trained model and the study's source code are available in an open source repository.

Histopathological features of prostate cancer conspicuity on multiparametric MRI: protocol for a systematic review and meta-analysis

INTRODUCTION

Multiparametric MRI (mpMRI) has improved risk stratification for men with suspected prostate cancer. Indeed, mpMRI-visible tumours tend to be larger and of higher pathological grade than mpMRI-invisible tumours; however, concern remains around significant cancer that is undetected by mpMRI. There has been considerable recent interest to investigate whether tumour conspicuity on mpMRI is associated with additional histopathological features (including cellular density, microvessel density and unusual prostate cancer subtypes), which may have important clinical implications in both diagnosis and prognosis. Furthermore, analysis of these features may help reveal the radiobiology that underpins the actual mechanisms of mpMRI visibility (and invisibility) of prostate tumours. Here, we describe a protocol for a systematic review of the histopathological basis of prostate cancer conspicuity on mpMRI.

METHODS AND ANALYSIS

A systematic search of the MEDLINE, PubMed, Embase and Cochrane databases will be conducted. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines will be used to guide screening, thematic reporting and conclusions drawn from all eligible studies. Included papers will be full-text, English-language articles, comparing the histopathological characteristics of mpMRI-visible lesions and mpMRI-invisible tumours. All studies published between January 1950 and January 2020 will be eligible for inclusion. Studies using confirmatory immunohistochemistry for the identification of immune subsets or structural components will be included. Study bias and quality will be assessed using a modified Newcastle-Ottawa scale. To ensure methodological rigour, this protocol is written in accordance with the PRISMA Protocol 2015 checklist. If appropriate, a meta-analysis will be conducted comparing histopathological feature frequency between mpMRI-visible and mpMRI-invisible disease.

ETHICS AND DISSEMINATION

No ethical approval will be required as this is an academic review of published literature. Findings will be disseminated through publications in peer-reviewed journals and presentations at national and international conferences.

PROSPERO REGISTRATION NUMBER

CRD42020176049.

Evaluating F-18-PSMA-1007-PET in primary prostate cancer and comparing it to multi-parametric MRI and histopathology

BACKGROUND

PSMA-PET is a novel imaging modality for the staging of prostate cancer (PCa). While there are several PSMA ligands available, F-18-PSMA-1007 is particularly of interest as it is not renally excreted and therefore does not impair the imaging of the pelvic area. Hence, this study aimed to investigate the F-18-PSMA-1007-PET for the primary staging of PCa and compared it to multi-parametric (mp) MRI and histopathology.

METHODS

A retrospective study was performed of men with intermediate and high-risk PCa patients that underwent a F-18-PSMA-1007-PET after mpMRI with subsequent MR-guided target biopsy (MRGB). Suspicious mpMRI lesions and F-18-PSMA-1007-PET were simultaneously reviewed on both a per patient and per-lesion basis. Results were subsequently evaluated with histopathological outcome of MRGB, and if performed, the radical prostatectomy specimen.

RESULTS

A total of 66 suspicious mpMRI lesions were identified in 53 patients and underwent MRGB. Two lesions had a maximum standardized uptake value (SUV_max) less than the mean SUV_max of healthy prostate tissue and were considered as non-PSMA-expressing. All PSMA avid tumors had higher SUV_max than the mean SUV_mean of the bladder/urine, therefore all lesions were clearly distinguishable in the pelvic area. Twenty-three patients received a radical prostatectomy of which the histopathology specimens were evaluated. F-18-PSMA-1007-PET/CT correctly staged seminal vesicle invasion (i.e. pT3b) more often than mpMRI (90 vs. 76%), whereas mpMRI more accurately detected extracapsular extension (i.e. pT3a) compared to F-18-PSMA-1007-PET (90% vs 57%).

CONCLUSIONS

The present study of a selected cohort suggest that dual imaging with mpMRI and F-18-PSMA-1007-PET may improve staging of primary PCa. F-18-PSMA-1007-PET/CT had low renal clearance, which could assist the evaluation of tumors in proximity of the bladder.

Diagnostic ability of Ga-68 PSMA PET to detect dominant and non-dominant tumors, upgrading and adverse pathology in patients with PIRADS 4-5 index lesions undergoing radical prostatectomy

BACKGROUND

To evaluate the additive role of Ga-68 PSMA PET as a primary staging tool in patients bearing prostate cancer in single PIRADS 4 or 5 index lesions.

METHODS

Eighty-one biopsy-naive patients with preoperative mpMRI and Ga-68 PSMA PET who underwent radical prostatectomy (RP) were evaluated retrospectively. Forty-nine patients had PIRADS 4 and 32 had PIRADS 5 index lesions. The localization, grade, and volumetric properties of dominant (DT) and non-dominant tumors (NDT) in RP were compared to the index lesions of mpMRI and Ga-68 PSMA PET.

RESULTS

The median age and PSA level were 62 (IQR; 59-69) years and 7 (IQR; 2-8) ng/ml, respectively. Ga-68 PSMA PET detected DTs in 100% of the patients including 13 patients in whom mpMR failed. In 45 patients an NDT was reported in RP. Ga-68 PSMA PET accurately detected NDT in 24 of 45 (53.3%) patients. Six patients (12.2%) in PIRADS 4 and 8 (25%) in PIRADS 5 group showed upgrading. In PIRADS 4, Ga-68 PSMA PET localized DT in all patients with upgraded tumors whereas mpMRI missed exact location in 2 of 6 (33.3%). In PIRADS 5 both mpMRI and Ga-68 PSMA PET accurately located all DTs. Overall detection rates of extracapsular extension (ECE) and seminal vesicle invasion (SVI) by mpMRI were 51.1% and 53.8%, respectively. Ga-68 PSMA PET detected ECE and SVI in 27.9% and 30.7%, respectively. When mpMRI and Ga-68 PSMA PET were used in combination detection rates of ECE and SVI increased to 65.1 and 61.5%. Ga-68 PSMA PET-detected six of ten patients with positive lymph nodes whereas mpMRI could not identify any.

CONCLUSIONS

Ga-68 PSMA PET has a better diagnostic accuracy in detecting DT, NDT, upgrading, adverse pathology in patients with PIRADS 4 index lesions. However, mpMRI better predicted ECE and SVI than Ga-68 PSMA PET.

An Intelligent Decision-Making Support System for the Detection and Staging of Prostate Cancer in Developing Countries

Most developing countries face huge challenges in the medical field; scarce medical resources and inadequate medical personnel will affect the development and stability of the society. Therefore, for most developing countries, the development of intelligent medical systems can greatly alleviate the social contradictions arising from this problem. In this study, a new data decision-making intelligent system for prostate cancer based on perceptron neural network is proposed, which mainly makes decisions by associating some relevant disease indicators and combining them with medical images. Through data collection, analysis and integration of medical data, as well as the disease detection and decision-making process, patients are given an auxiliary diagnosis and treatment, so as to solve the problems and social contradictions faced by most developing countries. Through the study of hospitalization information of more than 8,000 prostate patients in three hospitals, about 2,156,528 data items were collected and compiled for experiment purposes. Experimental data shows that when the patient base increases from 200 to 8,000, the accuracy of the machine-assisted diagnostic system will increase from 61% to 87%, and the doctor's diagnosis rate will be reduced to 81%. From the study, it is concluded that when the patient base reaches a certain number, the diagnostic accuracy of the machine-assisted diagnosis system will exceed the doctor's expertise. Therefore, intelligent systems can help doctors and medical experts treat patients more effectively.

Automatic Tumor Segmentation With a Convolutional Neural Network in Multiparametric MRI: Influence of Distortion Correction

Precise tumor segmentation is a crucial task in radiation therapy planning. Convolutional neural networks (CNNs) are among the highest scoring automatic approaches for tumor segmentation. We investigate the difference in segmentation performance of geometrically distorted and corrected diffusion-weighted data using data of patients with head and neck tumors; 18 patients with head and neck tumors underwent multiparametric magnetic resonance imaging, including T2w, T1w, T2*, perfusion (k_trans), and apparent diffusion coefficient (ADC) measurements. Owing to strong geometrical distortions in diffusion-weighted echo planar imaging in the head and neck region, ADC data were additionally distortion corrected. To investigate the influence of geometrical correction, first 14 CNNs were trained on data with geometrically corrected ADC and another 14 CNNs were trained using data without the correction on different samples of 13 patients for training and 4 patients for validation each. The different sets were each trained from scratch using randomly initialized weights, but the training data distributions were pairwise equal for corrected and uncorrected data. Segmentation performance was evaluated on the remaining 1 test-patient for each of the 14 sets. The CNN segmentation performance scored an average Dice coefficient of 0.40 ± 0.18 for data including distortion-corrected ADC and 0.37 ± 0.21 for uncorrected data. Paired t test revealed that the performance was not significantly different (P = .313). Thus, geometrical distortion on diffusion-weighted imaging data in patients with head and neck tumor does not significantly impair CNN segmentation performance in use.

Novel PET imaging methods for prostate cancer

INTRODUCTION

Prostate cancer is a common neoplasm but conventional imaging methods such as CT and bone scan are often insensitive. A new class of PET agents have emerged to diagnose and manage prostate cancer.

METHODS

The relevant literature on PET imaging agents for prostate cancer was reviewed.

RESULTS

This review shows a broad range of PET imaging agents, the most successful of which is prostate specific membrane antigen (PSMA) PET. Other agents either lack the sensitivity or specificity of PSMA PET.

CONCLUSION

Among the available PET agents for prostate cancer, PSMA PET has emerged as the leader. It is likely to have great impact on the diagnosis, staging and management of prostate cancer patients.

Interim Results of a Prospective Prostate-Specific Membrane Antigen-Directed Focal Stereotactic Reirradiation Trial for Locally Recurrent Prostate Cancer

PURPOSE

To report the feasibility, toxicity, and preliminary outcomes (metabolic and biochemical) of ⁶⁸Ga-prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT)-directed focal prostate reirradiation using linear accelerator (LINAC)-based stereotactic body radiation treatment (SBRT).

METHODS AND MATERIALS

From March 2016 to March 2019, 25 patients were enrolled in a prospective single institution trial (ACTRN12617000035325). Eligibility criteria included patients with biopsy proven isolated prostate recurrence after definitive irradiation, with concordant multiparametric MRI and ⁶⁸Ga-PSMA PET/CT findings, and a prostate-specific antigen of less than 15 ng/mL at the time of recurrence. The study included a sequential dose escalation component with the first 18 patients receiving 36 Gy in 6 fractions on alternate days with subsequent patients receiving 38 Gy in 6 fractions assuming acceptable toxicity.

RESULTS

Median age was 72 years (range, 62-83) with a median time between first radiation treatment and salvage SBRT of 8.3 years (range, 4.5- 13.6). Median prostate-specific antigen at reirradiation was 4.1 (range, 1.1-16.6). The median follow-up was 25 months (range, 13-46). Acute grade 1 and 2 genitourinary (GU) toxicity occurred in 6 (24%) and 1 (4%) men, respectively. Acute grade 1 gastrointestinal (GI) toxicity occurred in 8% with one acute grade 3 GI toxicity (4%) due to a rectal ulcer overlying the hydrogel. Late grade 1 and 2 GU toxicity occurred in 28% and 4%. Late grade 1 GI toxicity occurred in 8% with no grade 2 or greater toxicity. Twenty-four patients have undergone per-protocol 12-month ⁶⁸Ga-PSMA PET/CT, of which 23 (92%) demonstrated a complete metabolic response. Biochemical freedom from failure was 80% at 2 years with 3 out of 4 of the biochemical failures exhibiting recurrent local disease.

CONCLUSIONS

PSMA-directed salvage focal reirradiation to the prostate using linear accelerator-based SBRT is feasible and safe. Toxicity was low, with very favorable short term local and biochemical control in a carefully selected cohort of patients.

Comparison of 68Ga-PSMA-617 PET/CT with mpMRI for the detection of PCa in patients with a PSA level of 4-20 ng/ml before the initial biopsy

The study was aimed at assessing the diagnostic performance of ⁶⁸Ga-PSMA-617 PET/CT in the detection of prostate cancer (PCa) in patients with a prostate-specific antigen (PSA) level of 4–20 ng/ml and to compare its efficacy with that of multiparametric MRI (mpMRI). We analyzed the data of 67 consecutive patients with PSA levels of 4–20 ng/ml who almost simultaneously underwent ⁶⁸Ga-PSMA-617 PET/CT and mpMRI. ⁶⁸Ga-PSMA-617 PET/CT and mpMRI diagnostic performances were compared via receiver operating characteristic (ROC) curve analysis. Of the 67 suspected PCa cases, 33 had pathologically confirmed PCa. ⁶⁸Ga-PSMA-617 PET/CT showed a patient-based sensitivity, specificity, and positive and negative predictive values (PPVs and NPVs) of 87.88%, 88.24%, 87.88%, and 88.24%, respectively. The corresponding values for mpMRI were 84.85%, 52.94%, 63.64%, and 78.26%. The area under the curve values for ⁶⁸Ga-PSMA-617 PET/CT and mpMRI were 0.881 and 0.689, respectively. ⁶⁸Ga-PSMA-617 PET/CT showed a better diagnostic performance than mpMRI in the detection of PCa in patients with PSA levels of 4–20 ng/ml.

Analysis of PSMA expression and outcome in patients with advanced Prostate Cancer receiving 177Lu-PSMA-617 Radioligand Therapy

Rationale: PSMA-PET-CT enables measuring molecular expression of prostate-specific membrane antigen (PSMA) in vivo, which is the target molecule of ¹⁷⁷Lu-PSMA-617 (Lu-PSMA) therapy. However, the correlation of PSMA expression and overall survival (OS) in patients treated with Lu-PSMA therapy is currently unclear; especially with regard to coexistence of high and low PSMA expressing metastases. To this end, this retrospective single arm study elucidates the correlation of PSMA expression and overall survival in patients treated with Lu-PSMA therapy. Additionally, PET based criteria to define low PSMA expression were explored. Methods: Eighty-five patients referred to Lu-PSMA therapy were included in the analysis. Pretherapeutic ⁶⁸Ga-PSMA-PET-CT scans were available for all patients. SUV_max of the highest PSMA expressing metastasis (PSMA_max), SUV_max of the lowest PSMA expressing metastasis (PSMA_min), and average SUV_max of all metastases (PSMA_average) amongst other PET parameters were measured for each patient. A log-rank cutoff-finder was used to determine low (lowPSMA_average) and high (highPSMA_average) average PSMA expression as well as low (lowPSMA_min) and high (highPSMA_min) minimal PSMA expression. Results: PSMA_average was a significant prognosticator of overall survival in contrast to PSMA_max (HR: 0.959; p = 0.047 vs. HR: 0.992; p = 0.231). Optimal log rank cut-offs were: PSMA_average = 14.3; PSMA_min = 10.2. Patients with low average PSMA expression (lowPSMA_average) had significantly shorter survival compared to those with high average expression (highPSMA_average) (5.3 vs. 15.1 months; p < 0.001; HR: 3.738, 95%CI = 1.953-7.154; p < 0.001). Patients with low PSMA expressing metastases (lowPSMA_min) had shorter survival compared to those without a low PSMA expressing metastasis (highPSMA_min) (p = 0.003; 7.9 months vs. 21.3; HR: 4.303, 95%CI = 1.521-12.178; p = 0.006). Patients that were classified as highPSMA_average but with lowPSMA_min had an intermediate overall survival (11.4 months; longer compared to lowPSMA_average, 5.3 months, p = 0.002; but shorter compared to highPSMA_min, 21.3 months, p = 0.02). Conclusion: Low average PSMA expression is a negative prognosticator of overall survival. Absence of low PSMA expressing metastases is associated with best overall survival and the maximum PSMA expression seems not suited to prognosticate overall survival. Low PSMA expression might therefore be a negative prognosticator for the outcome of patients treated with Lu-PSMA therapy. Future studies are warranted to elucidate the degree of low PSMA expression tolerable for Lu-PSMA therapy.

Intraindividual comparison between 68Ga-PSMA-PET/CT and mpMRI for intraprostatic tumor delineation in patients with primary prostate cancer: a retrospective analysis in 101 patients

PURPOSE

Accurate delineation of intraprostatic gross tumor volume (GTV) is mandatory for successful fusion biopsy guidance and focal therapy planning of prostate cancer (PCa). Multiparametric magnetic resonance imaging (mpMRI) is the current gold standard for GTV delineation; however, prostate-specific membrane antigen positron emission tomography (PSMA-PET) is emerging as a promising alternative. This study compares GTV delineation between mpMRI and ⁶⁸Ga-PSMA-PET in a large number of patients using validated contouring approaches.

METHODS

One hundred one patients with biopsy-proven primary PCa who underwent mpMRI and ⁶⁸Ga-PSMA-PET within 3 months before primary treatment were retrospectively enrolled. Clinical parameters (age, PSA, Gleason score in biopsy) were documented. GTV based on MRI and PET images were delineated; volumes measured and laterality determined. Additionally, biopsy data from 77 patients was analyzed. Univariate and multivariate binary logistic regression analyses were performed using concordance in laterality as the endpoint.

RESULTS

In total mpMRI and ⁶⁸Ga-PSMA-PET detected 151 and 159 lesions, respectively. Median GTV-MRI (2.8 ml, 95% CI 2.31-3.38 ml) was significantly (p < 0.0001) smaller than median GTV-PET (4.9 ml, 95% CI 3.9-6.6 ml). ⁶⁸Ga-PSMA-PET detected significantly more bilateral lesions than mpMRI (71 vs 57, p = 0.03). Analysis of patients with bilateral lesions in biopsy showed a significant higher concordance of laterality in ⁶⁸Ga-PSMA-PET (p = 0.03). In univariate analysis, PSA level and volume of GTV-MRI had an impact on concordance in laterality (p = 0.02 and p = 0.01), whereas in multivariate analysis, only GTV-MRI volume remained significant (p = 0.04).

CONCLUSION

MpMRI and ⁶⁸Ga-PSMA-PET detect a similar amount of PCa lesions. However, GTV-PET had approximately twice the volume (median 4.9 ml vs 2.8 ml) and detected significantly more bilateral lesions than mpMRI. Thus, ⁶⁸Ga-PSMA-PET gives highly important complementary information. Since we could not find any strong evidence for parameters to guide when ⁶⁸Ga-PSMA-PET is dispensable, it should be performed additionally to MRI in patients with intermediate and high-risk PCa according to D'Amico classification to improve GTV delineation.

Recent advances of PET imaging in clinical radiation oncology

Radiotherapy and radiation oncology play a key role in the clinical management of patients suffering from oncological diseases. In clinical routine, anatomic imaging such as contrast-enhanced CT and MRI are widely available and are usually used to improve the target volume delineation for subsequent radiotherapy. Moreover, these modalities are also used for treatment monitoring after radiotherapy. However, some diagnostic questions cannot be sufficiently addressed by the mere use standard morphological imaging. Therefore, positron emission tomography (PET) imaging gains increasing clinical significance in the management of oncological patients undergoing radiotherapy, as PET allows the visualization and quantification of tumoral features on a molecular level beyond the mere morphological extent shown by conventional imaging, such as tumor metabolism or receptor expression. The tumor metabolism or receptor expression information derived from PET can be used as tool for visualization of tumor extent, for assessing response during and after therapy, for prediction of patterns of failure and for definition of the volume in need of dose-escalation. This review focuses on recent and current advances of PET imaging within the field of clinical radiotherapy / radiation oncology in several oncological entities (neuro-oncology, head & neck cancer, lung cancer, gastrointestinal tumors and prostate cancer) with particular emphasis on radiotherapy planning, response assessment after radiotherapy and prognostication.

Dosimetric Evaluation of PSMA PET-Delineated Dominant Intraprostatic Lesion Simultaneous Infield Boosts

PURPOSE

Prostate cancer is multifocal. However, there often exists a single dominant focus in the gland responsible for driving the biology of the disease. Dose escalation to the dominant lesion is a proposed strategy to increase tumor control. We applied radiobiological modeling to evaluate the dosimetric feasibility and benefit of dominant intraprostatic lesion simultaneous in-field boosts (DIL-SIB) to the gross tumor volume (GTV), defined using a novel molecular positron emission tomography (PET) probe (18F-DCFPyL) directed against prostate specific membrane antigen (PSMA).

METHODS AND MATERIALS

Patients with clinically localized, biopsy-proven prostate cancer underwent preoperative [18F]-DCFPyL PET/computed tomography (CT). DIL-SIB plans were generated by importing the PET/CT into the RayStation treatment planning system. GTV-PET for the DIL-SIB was defined by the highest %SUVmax (percentage of maximum standardized uptake value) that generated a biologically plausible volume. Volumetric arc-based plans incorporating prostate plus DIL-SIB treatment were generated. Tumor control probability (TCP) and normal tissue complication probability (NTCP) with fractionation schemes and boost doses specified in the FLAME (Investigate the Benefit of a Focal Lesion Ablative Microboost in Prostate Cancer; NCT01168479), PROFIT (Prostate Fractionated Irradiation Trial; NCT00304759), PACE (Prostate Advances in Comparative Evidence; NCT01584258), and hypoFLAME (Hypofractionated Focal Lesion Ablative Microboost in prostatE Cancer 2.0; NCT02853110) protocols were compared.

RESULTS

Comparative DIL-SIB plans for 6 men were generated from preoperative [18F]-DCFPyL PET/CT. Median boost GTV volume was 1.015 cm3 (0.42-1.83 cm3). Median minimum (D99%) DIL-SIB dose for F35BS, F20BS, F5BS, and F5BSH were 97.3 Gy, 80.8 Gy, 46.5 Gy, and 51.5Gy. TCP within the GTV ranged from 84% to 88% for the standard plan and 95% to 96% for the DIL-SIB plans. Within the rest of the prostate, TCP ranged from 89% to 91% for the standard plans and 90% to 92% for the DIL-SIB plans. NTCP for the rectum NTCP was similar for the DIL-SIB plans (0.3%-2.7%) compared with standard plans (0.7%-2.6%). Overall, DIL-SIB plans yielded higher uncomplicated TCP (NTCP, 90%-94%) versus standard plans (NTCP, 83%-85%).

CONCLUSIONS

PSMA PET provides a novel approach to define GTV for SIB-DIL dose escalation. Work is ongoing to validate PSMA PET-delineated GTV through correlation to coregistered postprostatectomy digitized histopathology.

68Ga-PSMA PET/CT Combined with PET/Ultrasound-Guided Prostate Biopsy Can Diagnose Clinically Significant Prostate Cancer in Men with Previous Negative Biopsy Results

The purpose of this study was to investigate the feasibility and diagnostic efficacy of ⁶⁸Ga-prostate-specific membrane antigen (PSMA) PET/CT combined with PET/ultrasound-guided biopsy in the diagnosis of prostate cancer (PCa). Methods: In total, 31 patients with a previously negative prostate biopsy but persistent elevated serum prostate-specific antigen (PSA) were imaged with a ⁶⁸Ga-PSMA PET/CT ligand before undergoing repeat prostate biopsy. On the basis of the proposed Prostate Cancer Molecular Imaging Standardized Evaluation criteria, ⁶⁸Ga-PSMA PET/CT results were interpreted as negative (molecular-imaging-for-PSMA expression score [miPSMA-ES] of 0-1) or positive (miPSMA-ES of 2-3). All patients underwent standard template systematic biopsy with up to 4 additional PET/ultrasound-guided biopsy cores. The sensitivity, specificity, positive and negative predictive values, and accuracy of ⁶⁸Ga-PSMA PET/CT were determined. In addition, the correlation between the miPSMA-ES and the detection rate of PCa was also analyzed. Univariate logistic regression models were established using ⁶⁸Ga-PSMA PET/CT semiquantitative analysis parameters to predict the outcome of repeat prostate biopsy. Results: The median age of patients was 65 y (range, 53-81 y), and the median PSA level was 18.0 ng/mL (range, 5.48-49.77 ng/mL). PCa was detected in 15 of 31 patients (48.4%), and 12 of 31 patients (38.7%) had clinically significant PCa (csPCa). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ⁶⁸Ga-PSMA PET/CT in the diagnosis of csPCa were 100.0%, 68.4%, 66.7%, 100.0%, and 80.6%, respectively. The detection rate of PCa increased with the increase in miPSMA-ES. The detection rates of csPCa in the miPSMA-ES 0-1, 2, and 3 groups were 0%, 54.5%, and 85.7%, respectively. Semiquantitative analysis of ⁶⁸Ga-PSMA PET/CT images showed that predictive models based on the SUV_max of prostate lesion, tumor-to-normal-prostate background SUV_max, and tumor-to-normal-liver background SUV_max could effectively predict csPCa; area under the curves were 0.930, 0.877, and 0.956, respectively. Conclusion: This study preliminarily confirmed that ⁶⁸Ga-PSMA PET/CT imaging, combined with PET/ultrasound-guided prostate biopsy, can effectively detect csPCa. Prebiopsy ⁶⁸Ga-PSMA PET/CT had predictive value for csPCa in the studied patient population.

CEST MRI detectable liposomal hydrogels for multiparametric monitoring in the brain at 3T

Adjuvant treatment using local drug delivery is applied in treating glioblastoma multiforme (GBM) after tumor resection. However, there are no non-invasive imaging techniques available for tracking the compositional changes of hydrogel-based drug treatment.

Methods: We developed Chemical Exchange Saturation Transfer Magnetic Resonance Imaging (CEST MRI) detectable and injectable liposomal hydrogel to monitor these events in vivo at 3T clinical field. Mechanical attributes of these hydrogels and their in vitro and in vivo CEST imaging properties were systematically studied.

Results: The MRI detectable hydrogels were capable of generating multiparametric readouts for monitoring specific components of the hydrogel matrix simultaneously and independently. Herein, we report, for the first time, CEST contrast at -3.4 ppm provides an estimated number of liposomes and CEST contrast at 5 ppm provides an estimated amount of encapsulated drug. CEST contrast decreased by 1.57% at 5 ppm, while the contrast at -3.4 ppm remained constant over 3 d in vivo, demonstrating different release kinetics of these components from the hydrogel matrix. Furthermore, histology analysis confirmed that the CEST contrast at -3.4 ppm was associated with liposome concentrations.

Conclusion: This multiparametric CEST imaging of individual compositional changes in liposomal hydrogels, formulated with clinical-grade materials at 3T and described in this study, has the potential to facilitate the refinement of adjuvant treatment for GBM.

Simultaneous whole-body PET/MRI with integrated multiparametric MRI for primary staging of high-risk prostate cancer

PURPOSE

Whole-body positron emission tomography/magnetic resonance imaging (wbPET/MRI) is a promising diagnostic tool of recurrent prostate cancer (PC), but its role in primary staging of high-risk PC (hrPC) is not well defined. Thus, the aim was to compare the diagnostic accuracy for T-staging of PET-blinded reading (PBR) and PET/MRI.

METHODS

In this prospective study, hrPC patients scheduled to radical prostatectomy (RPx) with extended lymphadenectomy (eLND) were staged with wbPET/MRI and either ⁶⁸Ga-PSMA-11 or ¹¹C-choline including simultaneous multiparametric MRI (mpMRI). Images were assessed in two sessions, first as PBR (mpMRI and wbMRI) and second as wbPET/MRI. Prostate Imaging Reporting and Data System criteria (PIRADS v2) were used for T-staging. Results were correlated with the exact anatomical localization and extension as defined by histopathology. Diagnostic accuracy of cTNM stage according to PBR was compared to pathological pTNM stage as reference standard.

RESULTS

Thirty-four patients underwent wbPET/MRI of ⁶⁸Ga-PSMA-11 (n = 17) or ¹¹C-choline (n = 17). Twenty-four patients meeting the inclusion criteria of localized disease ± nodal disease based on imaging results underwent RPx and eLND, whereas ten patients were excluded from analysis due to metastatic disease. T-stage was best defined by mpMRI with underestimation of tumor lesion size by PET for both tracers. N-stage yielded a per patient sensitivity/specificity comparable to PBR.

CONCLUSION

MpMRI is the primary modality for T-staging in hrPC as PET underestimated T-stage in direct comparison to final pathology. In this selected study, cohort MRI shows no inferiority compared to wbPET/MRI considering N-staging.

Molecular Imaging in Photon Radiotherapy

Nowadays, more than ever before, the treatment of cancer patients requires an interdisciplinary approach more than ever. Radiation therapy (RT) has become an indispensable pillar of cancer treatment early on, offering a local, curative treatment option and symptom control in palliative cases.

Stereotactic body radiation therapy with optional focal lesion ablative microboost in prostate cancer: Topical review and multicenter consensus

Stereotactic body radiotherapy (SBRT) for prostate cancer (PCa) is gaining interest by the recent publication of the first phase III trials on prostate SBRT and the promising results of many other phase II trials. Before long term results became available, the major concern for implementing SBRT in PCa in daily clinical practice was the potential risk of late genitourinary (GU) and gastrointestinal (GI) toxicity. A number of recently published trials, including late outcome and toxicity data, contributed to the growing evidence for implementation of SBRT for PCa in daily clinical practice. However, there exists substantial variability in delivering SBRT for PCa. The aim of this topical review is to present a number of prospective trials and retrospective analyses of SBRT in the treatment of PCa. We focus on the treatment strategies and techniques used in these trials. In addition, recent literature on a simultaneous integrated boost to the tumor lesion, which could create an additional value in the SBRT treatment of PCa, was described. Furthermore, we discuss the multicenter consensus of the FLAME consortium on SBRT for PCa with a focal boost to the macroscopic intraprostatic tumor nodule(s).

Gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography compared with diagnostic computed tomography in relapsed prostate cancer

The aim of this study was to evaluate if prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has a higher detection rate compared to standard contrast CT imaging for patients with a rising prostate-specific antigen (PSA) following definitive treatment (i.e., curative radical prostatectomy, radiotherapy, and brachytherapy) for prostate cancer in a private hospital setting. A retrospective single-site clinical audit was conducted on 150 PSMA PET/CT scans done for patients with a rising PSA after definitive treatment for prostate cancer. All studies were performed using I and T Ga-68 PSMA produced on a Scintomics radiopharmaceutical unit (Munich). All scans were performed on a GE 710 PET/CT scanner. All studies were compared to standard CT and other imaging. Of the 150 patients who had a ⁶⁸Gallium (Ga)-PSMA PET/CT for a rise in their PSA levels, 102/150 (68%) of patients had PSMA-avid scans compared to the conventional imaging group which had an overall detection rate of 42% (63/150). The rates of detection were 100%, 90%, 92%, 67%, and 25% at PSA levels of >10 μg/L, 5–10 μg/L, >1.5 μg/L, 0.5–1.5 μg/L, and <0.5 μg/L, respectively. PSMA PET/CT also solely picked up 39/102 (38%) of prostate cancer relapses compared to the conventional imaging group. In our study of 150 patients with biochemical recurrence of prostate cancer, ⁶⁸Ga-PSMA PET/CT demonstrated a superior detection rate (P < 0.05) compared to conventional imaging, including patients with low PSA levels (<0.5 μg/L).

[68Ga-]PSMA-11 PET/CT and multiparametric MRI for gross tumor volume delineation in a slice by slice analysis with whole mount histopathology as a reference standard - Implications for focal radiotherapy planning in primary prostate cancer

BACKGROUND AND PURPOSE

Focal therapies are a promising approach to treat prostate cancer (PCa) more precisely instead of conventional whole gland treatment. Nowadays, multiparametric MRI (mpMRI) is routinely used for gross tumor volume (GTV) delineation. The aim of our study was to compare PSMA-PET/CT and mpMRI for the delineation of intraprostatic tumor burden by using whole mount histopathology as a reference standard.

MATERIAL AND METHODS

17 prospectively enrolled patients with primary PCa underwent [⁶⁸Ga-]PSMA-11 PET/CT and mpMRI before radical prostatectomy. PSMA-PET/CT, mpMRI and histopathology of the resected specimens were co-registered. Two teams of experts generated GTV contours for mpMRI and PET, respectively. The imaging was validated on a lesion level and slice by slice in quadrants based on the distribution of PCa in histopathology. Overall, 772 quadrants were analyzed with 414 being true positive for tumor (53.6%).

RESULTS

Median tumor volumes were 10.4 ml for GTV-histo, 10.8 ml for PSMA-PET and 4.5 ml for mpMRI. Median tumor volume in mpMRI was significant (p < 0.05) smaller than GTV-PET and GTV-histo, respectively. The sensitivity and specificity were 86% and 87% for PSMA-PET, 58% and 94% for mpMRI and 91% and 84% for their GTV-union. In 133 quadrants PSMA-PET/CT correctly identified tumor where mpMRI found none. MpMRI identified 19 true positive quadrants exclusively.

CONCLUSION

Our investigation demonstrates an increased consensus of PSMA-PET with histopathology compared to mpMRI for intraprostatic GTV delineation, especially with a higher sensitivity. Additionally mpMRI contours underestimate tumor volume significantly. Thus PSMA-PET may be a complementary augmentation for GTV delineation in focal therapies.

Validation of different PSMA-PET/CT-based contouring techniques for intraprostatic tumor definition using histopathology as standard of reference

PURPOSE

Accurate definition of the intraprostatic gross tumor volume (GTV) is crucial for diagnostic and therapeutic approaches in patients with primary prostate cancer (PCa). The optimal methodology for contouring of GTV using Prostate specific membrane antigen positron emission tomography (PSMA-PET) information has not yet been defined.

METHODS AND MATERIALS

PCa patients who underwent a [68Ga]PSMA-11-PET/CT followed by radical prostatectomy were prospectively enrolled (n = 20). Six observer teams with different levels of experience and using different PET image scaling techniques performed manual contouring of GTV. Additionally, semi-automatic segmentation of GTVs was performed using SUVmax thresholds of 20-50%. Coregistered histopathological gross tumor volume (GTV-Histo) served as reference. Inter-observer agreement was assessed by calculating the Dice similarity coefficient (DSC).

RESULTS

Most contouring methods provided high sensitivity and specificity. For manual delineation, scaling the PET images from SUVmin-max: 0-5 resulted in high sensitivity (>86%). The highest specificity (100%) was obtained by scaling the PET images from SUVmin-max: 0-SUVmax. High interobserver agreement (median DSC 0.8) was observed when using the same PET image scaling technique (PET images SUVmin-max: 0-5). For semi-automatic segmentation, a low SUVmax threshold of 20% optimized sensitivity (SUVmax threshold 20%, 100% sensitivity, 32% of prostatic volume), whereas a higher threshold optimized specificity (SUVmax threshold 40%-50%, 100% specificity).

CONCLUSIONS

Contouring of regions with high tracer-uptake resulted in very high specificities and should be used for biopsy guidance. Both manual and semi-automatic approaches using validated SUV scaling (SUVmin-max: 0-5) or thresholding (20%) may provide high sensitivity, and should be considered for PSMA-PET-based focal therapy approaches.

Comparison of preoperative locoregional Ga-68 PSMA-11 PET-CT and mp-MRI results with postoperative histopathology of prostate cancer

BACKGROUND

Conventional imaging modalities are inadequate to evaluate locoregional extension of prostate cancer (PCa). The aim of the current retrospective study was to investigate the diagnostic efficacy of Gallium-68 prostate-specific membrane antigen-11 (Ga-68 PSMA-11) positron emission tomography/computed tomography (PET/CT) and multiparametric magnetic resonance imaging (mp-MRI) for staging preoperative PCa patients with correlating histopathology.

MATERIALS AND METHODS

Twenty-four patients with histologically proven PCa underwent both Ga-68 PSMA-11 PET/CT and mp-MRI before robot-assisted laparoscopic radical prostatectomy. For each tumor area, correlations with histopathological results were defined for tumor localization, extraprostatic extension (EPE) of the tumor, invasion of seminal vesicle (SVI) and bladder neck invasion (BNI). In patients with regional lymph node (LN) dissection, histopathological results were also correlated with imaging modalities.

RESULTS

Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for detection of EPE and SVI were higher for mp-MRI than Ga-68 PSMA-11 PET/CT. On the other hand Ga-68 PSMA-11 PET/CT had significant successful results for detection of LN metastases when compared with mp-MRI. But for BNI detection both modalities had same insufficient results. Ga-68 PSMA-11 PET/CT had strong results for appropriate tumor localization in the gland.

CONCLUSION

Ga-68 PSMA PET/CT has superior results for assessing local LN metastases and for intraprostatic tumor localization. Whereas, mp-MRI must be the preferred modality for determining SVI and EPE. But both imaging modalities failed for determining BNI accurately. Both modalities should be used in conjunction with each other for better treatment planning.

Advances in prostate-specific membrane antigen PET of prostate cancer

PURPOSE OF REVIEW

In recent years, a large number of reports have been published on prostate-specific membrane antigen (PSMA)/PET in prostate cancer (PCa). This review highlights advances in PSMA PET in PCa during the past year.

RECENT FINDINGS

PSMA PET/computed tomography (CT) is useful in detection of biochemical recurrence, especially at low prostate-specific antigen (PSA) values. The detection rate of PSMA PET is influenced by PSA level. For primary PCa, PSMA PET/CT shows promise for tumour localization in the prostate, especially in combination with multiparametric MRI (mpMRI). For primary staging, PSMA PET/CT can be used in intermediate and high-risk PCa. Intraoperative PSMA radioligand guidance seems promising for detection of malignant lymph nodes. While the use of PSMA PET/MRI in primary localized disease is limited to high and intermediate-risk patients and localized staging, in the recurrence setting, PET/MRI can be particularly helpful when the lesions are subtle. PSMA PET/CT is superior to choline PET/CT and other conventional imaging modalities.

SUMMARY

Molecular imaging with PSMA PET continues to pave the way for personalized medicine in PCa.However, large prospective clinical studies are still needed to fully evaluate the role of PSMA PET/CT and PET/MRI in the clinical workflow of PCa.

Intrinsically Zirconium-89-Labeled Manganese Oxide Nanoparticles for In Vivo Dual-Modality Positron Emission Tomography and Magnetic Resonance Imaging

Manganese-based nanoparticles (NPs) have recently attracted much attention in the field of biomedical imaging due to their impressive enhanced T1 contrast ability. Although the reported manganese-based NPs have exhibited good imaging capabilities as contrast agents, it is still urgent to develop novel multifunctional manganese-based imaging probes for future biomedical imaging, especially PET/MRI probes. Herein, we present chelator-free zirconium-89 (89Zr, t1/2: 78.4 h) labeling of manganese oxide NPs (Mn3O4@PEG) with ∼78% labeling yield and good stability. Serial positron emission tomography (PET) and magnetic resonance imaging (MRI) studies non-invasively assessed the biodistribution patterns of the NPs and the feasibility of in vivo dual-modality imaging and lymph-node mapping. Since Mn3O4 NPs exhibited desirable properties for enhanced T1 imaging and the simplicity of chelator-free radiolabeling, [89Zr]Mn3O4@PEG NPs offer a novel, simple, safe and accurate nanoplatforms for future precise cancer imaging and diagnosis.

Radiomic features from PSMA PET for non-invasive intraprostatic tumor discrimination and characterization in patients with intermediate- and high-risk prostate cancer - a comparison study with histology reference

Purpose: To evaluate the performance of radiomic features (RF) derived from PSMA PET for intraprostatic tumor discrimination and non-invasive characterization of Gleason score (GS) and pelvic lymph node status. Patients and methods: Patients with prostate cancer (PCa) who underwent [⁶⁸Ga]-PSMA-11 PET/CT followed by radical prostatectomy and pelvic lymph node dissection were prospectively enrolled (n=20). Coregistered histopathological gross tumor volume (GTV-Histo) in the prostate served as reference. 133 RF were derived from GTV-Histo and from manually created segmentations of the intraprostatic tumor volume (GTV-Exp). Spearman´s correlation coefficients (ρ) were assessed between RF derived from the different GTVs. We additionally analyzed the differences in RF values for PCa and non-PCa tissues. Furthermore, areas under receiver-operating characteristics curves (AUC) were calculated and uni- and multivariate analyses were performed to evaluate the RF based discrimination of GS 7 and ≥8 disease and of patients with nodal spread (pN1) and non-nodal spread (pN0) in surgical specimen. The results found in the latter analyses were validated by a retrospective cohort of 40 patients. Results: Most RF from GTV-Exp showed strong correlations with RF from GTV-Histo (86% with ρ>0.7). 81% and 76% of RF from GTV-Exp and GTV-Histo significantly discriminated between PCa and non-PCa tissue. The texture feature QSZHGE discriminated between GS 7 and ≥8 considering GTV-Histo (AUC=0.93) and GTV-Exp (prospective cohort: AUC=0.91 / validation cohort: AUC=0.84). QSZHGE also discriminated between pN1 and pN0 disease considering GTV-Histo (AUC=0.85) and GTV-Exp (prospective cohort: AUC=0.87 / validation cohort: AUC=0.85). In uni- and multivariate analyses including patients of both cohorts QSZHGE was a statistically significant (p<0.01) predictor for PCa patients with GS ≥8 tumors and pN1 status. Conclusion: RF derived from PSMA PET discriminated between PCa and non-PCa tissue within the prostate. Additionally, the texture feature QSZHGE discriminated between GS 7 and GS ≥8 tumors and between patients with pN1 and pN0 disease. Our results support the role of RF in PSMA PET as a new tool for non-invasive PCa discrimination and characterization of its biological properties.

Comparison of PET/MRI with multiparametric MRI in diagnosis of primary prostate cancer: A meta-analysis

OBJECTIVE

This meta-analysis aimed to compare the diagnostic performance of positron emission tomography (PET)/MRI using various radiotracers with multiparametric (mp) MRI for detection of primary prostate cancer (PCa).

METHODS

A systematic literature search up to January 2019 was performed to identify studies that evaluated the diagnostic value of PET/MRI and mpMRI for detection of PCa in the same patient cohorts and had sufficient data to construct 2 × 2 contingency tables for true-positive (TP), false-positive (FP), false-negative (FN), and true-negative (TN) results. The quality of each study was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool, and pooled sensitivity (SEN) and specificity (SPE) were calculated. Summary receiver operating characteristic (ROC) curves and area under the curves (AUCs) were used to compare the performances of PET/MRI and mpMRI.

RESULTS

We identified 9 eligible studies that included a total of 353 patients. PET/MRI had a SEN of 0.783 (95% CI, 0.758-0.807) and a SPE of 0.899 (95% CI, 0.879-0.917), and mpMRI had a SEN of 0.603 (95% CI, 0.574-0.631) and a SPE of 0.887 (95% CI, 0.866-0.906). PET/MRI had a higher AUC than mpMRI (0.9311, 95% CI, 0.8990-0.9632 vs. 0.8403, 95% CI, 0.7864-0.8942; P =  0.0036). There was no notable publication bias, but there was medium heterogeneity in outcomes. The meta-regression analysis showed the major potential cause of heterogeneity was the use of region-based rather than lesion-based analysis.

CONCLUSION

PET/MRI has very good diagnostic performance and outperforms mpMRI for the diagnosis of primary PCa.

New Targets for PET Molecular Imaging of Prostate Cancer

Prostate cancer (PCa) is the most common cancer in men worldwide, but it exhibits a highly variable biological behavior ranging from indolent to highly aggressive disease. The standard conventional imaging for staging PCa consists of CT, MRI, and bone scans, but this imaging has suboptimal accuracy for extraprostatic tumor detection, particularly in the scenario of early biochemical relapse when the prostate-specific antigen levels are still low indicating a low volume of recurrent disease. This gap between known disease (as indicated by a rising prostate-specific antigen) and the failure to detect it on conventional imaging, has led to the development of novel imaging probes most of which have positron emitting radioactive tags. In the last decade, multiple PET probes have demonstrated promising performance in detecting sites of recurrence and extent of disease in patients with PCa. The landscape of available PET radiotracers is changing rapidly and includes radiolabeled choline, anti1-amino-3-¹⁸F-fluorocyclobutane-1-carboxylic acid (¹⁸F-fluciclovine), bombesin, dihydrotestosterone, and prostate-specific membrane antigen (PSMA) ligands, among others. Of these, radiolabeled PSMA-PET agents have shown the most encouraging results in terms of sensitivity and are likely to become universally available for imaging PCa within a few years Other PET radiotracers such as bombesin-based radiotracers and antagonist of gastrin releasing-peptide receptor (RM2) are emerging as possible alternatives for PCa imaging. This review article discusses the current and near-future of PET molecular imaging probes.

Comparison of 68 Ga-PSMA ligand PET/CT versus conventional cross-sectional imaging for target volume delineation for metastasis-directed radiotherapy for metachronous lymph node metastases from prostate cancer

PURPOSE

To assess the differences in the target volume (TV) delineation of metachronous lymph node metastases between ⁶⁸ Ga-PSMA ligand PET/CT and conventional imaging in a comparative retrospective contouring study.

PATIENTS AND METHODS

Twenty-five patients with biochemical prostate cancer recurrence after primary prostatectomy underwent ⁶⁸ Ga-PSMA ligand PET/CT in addition to conventional imaging techniques such as CT and/or MR imaging for restaging. All patients were diagnosed with at least one lymph node metastasis. TVs were manually delineated in two different ways: (a) based on conventional imaging (CT/MRI) and (b) based on conventional imaging (CT/MRI) plus ⁶⁸ Ga-PSMA ligand PET/CT. The size of TVs, overlap rates, and subjective assessment of the difficulty of TV delineation reported by the radiation oncologist (easy/moderate/difficult) were compared.

RESULTS

With the additional information from PSMA ligand PET, 47 lymph node metastases were identified and included in the gross tumor volume (GTV). The median clinical target volume (CTV) of non-PET-based TV delineation was statistically larger than the CTV based on PET imaging (134.8 ml [range 6.9-565.2] versus 44.9 ml [range 4.9-481.3; p = 0.001]). The CTV based on CT/MRI enclosed only 81.3% (39/48) of PET-positive lymph nodes. The CT/MRI-based CTV did not enclose all PET-positive lymph nodes in 24% (6/25) of patients. In 12% (3/25) of patients, all PET-positive lymph nodes were outside of the CT/MRI-based CTV. The median overlap rates (TV_PET/TV_CT/MRI × 100) were 45.7% (range 0-96.9) for the GTV and 71.7% (range 9.8-98.2) for the CTV. The assessment of difficulty of contouring revealed that contouring with the additional imaging information of the PET was categorized as easy/moderate in 92% (23/25) and as difficult in 8% (2/25) of the cases, whereas contouring based on CT/MRI without PET was categorized as difficult in 56% (14/25) and as easy/moderate in 44% of the cases (11/25; p = 0.003).

CONCLUSION

⁶⁸ Ga-PSMA ligand PET/CT is superior to conventional cross-sectional imaging for the delineation of lymph node metastases from prostate cancer. PET-based TV delineation allows for smaller target volumes and should be considered the standard for irradiation of metachronous lymph node metastases in recurrent prostate cancer. Conventional imaging is not sufficiently sensitive for radio-oncological treatment concepts in oligometastatic prostate cancer.

Combination of 68Ga-PSMA PET/CT and Multiparametric MRI Improves the Detection of Clinically Significant Prostate Cancer: A Lesion-by-Lesion Analysis

Our purpose was to explore whether ⁶⁸Ga-PSMA PET/CT alone (PET/CT) or in combination with multiparametric MRI (PET/MRI) can improve the detection of clinically significant prostate cancer (PCa). Methods: We retrospectively enrolled 54 patients who underwent both MRI and PET/CT before radical prostatectomy. Regions of interest on MR images, PET/CT images, and pathologic images were marked. A lesion was defined as a region of interest marked on images obtained with any of the 3 modalities. All lesions were characterized using the prostate imaging reporting and data system (PI-RADS), the molecular imaging PSMA expression score, and the pathologic results and analyzed. Diagnostic performance was analyzed by receiver-operating-characteristic analysis. Specific improvement for lesions with different PI-RADS scores was analyzed using the net reclassification index (NRI). Results: In total, 90 lesions from 54 patients were analyzed, among which 66 lesions represented clinically significant PCa. Receiver-operating-characteristic analysis showed PET/MRI to perform better than MRI in detecting clinically significant PCa (change in area under the curve, 0.06; 95% confidence interval, 0.01-0.12; P < 0.05). With the calculated cutoff, PET/MRI performed significantly better than MRI (NRI, 21.9%; P < 0.01), with an improvement in sensitivity (89% vs. 76%, P < 0.01) at no sacrifice of specificity (96% vs. 88%, P > 0.05). Improvement in diagnosing clinically significant PCa occurred for lesions classified as PI-RADS 3 (NRI, 66.7%; P < 0.01). Conclusion: PET/MRI improves the detection of clinically significant PCa for PI-RADS 3 lesions.

Imaging as a Personalized Biomarker for Prostate Cancer Risk Stratification

Biomarkers provide objective data to guide clinicians in disease management. Prostate-specific antigen serves as a biomarker for screening of prostate cancer but has come under scrutiny for detection of clinically indolent disease. Multiple imaging techniques demonstrate promising results for diagnosing, staging, and determining definitive management of prostate cancer. One such modality, multiparametric magnetic resonance imaging (mpMRI), detects more clinically significant disease while missing lower volume and clinically insignificant disease. It also provides valuable information regarding tumor characteristics such as location and extraprostatic extension to guide surgical planning. Information from mpMRI may also help patients avoid unnecessary biopsies in the future. It can also be incorporated into targeted biopsies as well as following patients on active surveillance. Other novel techniques have also been developed to detect metastatic disease with advantages over traditional computer tomography and magnetic resonance imaging, which primarily rely on defined size criteria. These new techniques take advantage of underlying biological changes in prostate cancer tissue to identify metastatic disease. The purpose of this review is to present literature on imaging as a personalized biomarker for prostate cancer risk stratification.

Multimodal imaging for radiation therapy planning in patients with primary prostate cancer

Implementation of advanced imaging techniques like multiparametric magnetic resonance imaging (mpMRI) or Positron Emission Tomography (PET) in radiation therapy (RT) planning of patients with primary prostate cancer demands several preconditions: accurate staging of the extraprostatic and intraprostatic tumor mass, robust delineation of the intraprostatic gross tumor volume (GTV) and a reproducible characterization of the prostate cancer's biological properties. In the current review we searched for the currently available imaging techniques and we discussed their ability to fulfill these preconditions. We found that current pretreatment imaging was mainly performed with mpMRI and/or Prostate-specific membrane antigen PET imaging. Both techniques offered an accurate detection of the extraprostatic and intraprostatic tumor burden and had a major impact on RT concepts. However, some studies postulated that mpMRI and PSMA PET had complementary information for intraprostatic GTV detection. Moreover, interobserver differences for intraprostatic tumor delineation based on mpMRI were observed. It is currently unclear whether PET based GTV delineation underlies also interobserver heterogeneity. Further research is warranted to answer whether multimodal imaging is able to visualize biological processes related to prostate cancer pathophysiology and radiation resistance.

Diagnostic Accuracy of 68Ga-PSMA-11 PET/MRI Compared with Multiparametric MRI in the Detection of Prostate Cancer

Purpose To compare the diagnostic accuracy of gallium 68 (⁶⁸Ga)-labeled prostate-specific membrane antigen (PSMA)-11 PET/MRI with that of multiparametric MRI in the detection of prostate cancer. Materials and Methods The authors performed a retrospective study of men with biopsy-proven prostate cancer who underwent simultaneous ⁶⁸Ga-PSMA-11 PET/MRI before radical prostatectomy between December 2015 and June 2017. The reference standard was whole-mount pathologic examination. Readers were blinded to radiologic and pathologic findings. Tumor localization was based on 30 anatomic regions. Region-specific sensitivity and specificity were calculated for PET/MRI and multiparametric MRI by using raw stringent and alternative neighboring approaches. Maximum standardized uptake value (SUV_max) in the tumor and Prostate Imaging Reporting and Data System (PI-RADS) version 2 grade were compared with tumor Gleason score. Generalized estimating equations were used to estimate population-averaged sensitivity and specificity and to determine the association between tumor characteristics and SUV_max or PI-RADS score. Results Thirty-two men (median age, 68 years; interquartile range: 62-71 years) were imaged. The region-specific sensitivities of PET/MRI and multiparametric MRI were 74% (95% confidence interval [CI]: 70%, 77%) and 50% (95% CI: 45%, 0.54%), respectively, with the alternative neighboring approach (P < .001 for both) and 73% (95% CI: 68%, 79%) and 69% (95% CI: 62%, 75%), respectively, with the population-averaged generalized estimating equation (P = .04). Region-specific specificity of PET/MRI was similar to that of multiparametric MRI with the alternative neighboring approach (88% [95% CI: 85%, 91%] vs 90% [95% CI: 87%, 92%], P = .99) and in population-averaged estimates (70% [95% CI: 64%, 76%] vs 70% [95% CI: 64%, 75%], P = .99). SUV_max was associated with a Gleason score of 7 and higher (odds ratio: 1.71 [95% CI: 1.27, 2.31], P < .001). Conclusion The sensitivity of gallium 68-labeled prostate-specific membrane antigen-11 PET/MRI in the detection of prostate cancer is better than that of multiparametric MRI. © RSNA, 2018 See also the editorial by Civelek in this issue.

68Ga-PSMA-PET: added value and future applications in comparison to the current use of choline-PET and mpMRI in the workup of prostate cancer

Positron emission tomography (PET) has been commonly and successfully used, in combination with computed tomography (CT) and more recently magnetic resonance (MRI), in the workup of intermediate or high-risk prostate cancer (PCa). Nowadays, new specific receptor targeted PET tracers in prostate cancer imaging have been introduced; one of the most used is ⁶⁸Ga-PSMA, that evaluates the expression of prostate-specific membrane antigen (PSMA). This tracer has been rapidly taken into account for its better sensitivity and specificity compared to lipid metabolism tracers, such as ¹¹C/¹⁸F labelled fluorocholine. Besides, in the era of theranostics, this tracer is having a useful application not only for imaging but also for therapeutic purposes. The aim of this review article is, in the first part, to give an overview of the main indications and future development of ⁶⁸Ga-PSMA imaging, using PET/CT or PET/MRI, according to the clinical course of the disease and in view of the current use of multiparametric MRI (mpMRI) and choline PET in the management of PCa. In the second part, a brief overview of the promising ¹⁸F-labelled PSMA tracers and the current use of PSMA radionuclide therapy will be provided.

Nuclear Medicine Imaging of Prostate Cancer in the Elderly

Due to the increasing life expectancy, the diagnosis of malignancy and treatment of elderly patients is becoming more common. Prostate cancer is particularly frequent in this setting. Many different approaches are now available, but some of them imply significant risks or collateral effects. In those patients an accurate evaluation of risk-to-benefit ratio is needed, and functional imaging such as PET/CT is important for the clinician to make the appropriate choice. PET/CT in prostate cancer is a well-tolerated procedure that can be used to accurately assess the tumor extent during the entire clinical history of the disease. Nowadays there are several available radiopharmaceuticals for prostate cancer PET/CT imaging, each one with specific advantages and disadvantages. The two most promising and more widely employed in the clinical setting are 18F-Flucyclovine and 68Ga-PSMA. This paper will provide an overview of these two tracers for imaging prostate cancer in elderly patients.