Antigen Positron Emission Tomography Imaging Research Articles

Comparative Analysis of Recurrent Glioblastoma Target Contours via 11C-Methionine, 68Ga-Prostate-Specific Membrane Antigen Positron Emission Tomography Imaging, and Magnetic Resonance Imaging: Implications for Precision Radiotherapy Planning

PurposeGlioblastoma (GBM) recurrence poses challenges in radiotherapy treatment planning as reirradiation has limited leeway needing for precise target delineation. Though effective radiotracers are emerging for treatment planning, comparisons of 11C-methionine positron emission tomography (MET-PET), 68Ga-prostate-specific membrane antigen PET (PSMA-PET), and magnetic resonance imaging (MRI) for contouring recurrent GBMs are lacking in the literature. This case study aims to highlight the differences and similarities in target contours delineated from three examinations, aiming to raise doubts about the adequacy of current radiotherapy planning practices. Methods and MaterialsA 37-year-old female patient with recurrent IDH1/2 wild-type GBM underwent MRI, MET-PET, and PSMA-PET scans. Target delineations were performed, and volumes were compared using the Dice Similarity Coefficient (DSC), Conformity Index (CI), and Overlap Volume (OV), considering different planning target volume (PTV) margins. ResultsWe found that MET-PET and MRI volumes showed superior agreement compared to PSMA-PET across all similarity parameters, indicating a more marked discrepancy between PSMA-PET and other modalities. Increasing PTV margins demonstrated progressive convergence in inter-volume discrepancies. Notably, PSMA-PET delineated larger volumes extending beyond MRI-based volumes. ConclusionsThus, MRI alone may not suffice for target delineation in recurrent GBMs. PET imaging modalities offer complementary insights. Combined PET-MRI guidance could improve tumor boundary detection in target delineation for reirradiation. Prospective trials are necessary to ascertain its impact on patient outcomes.

Considerations on Integrating Prostate-Specific Membrane Antigen Positron Emission Tomography Imaging Into Clinical Prostate Cancer Trials by National Clinical Trials Network Cooperative Groups.

As prostate-specific membrane antigen (PSMA) positron emission tomography (PET) becomes increasingly available in the United States, the greater sensitivity of the technology in comparison to conventional imaging poses challenges for clinical trials. The NCI Clinical Imaging Steering Committee (CISC) PSMA PET Working Group was convened to coordinate the identification of these challenges in various clinical scenarios and to develop consensus recommendations on how best to integrate PSMA PET into ongoing and upcoming National Clinical Trials Network (NCTN) trials. NCI CISC and NCI Genitourinary Steering Committee members and leadership nominated clinicians, biostatisticians, patient advocates, and other imaging experts for inclusion in the PSMA PET Working Group. From April to July 2021, the working group met independently and in conjunction with the CISC to frame challenges, including stage migration, response assessment, trial logistics, and statistical challenges, and to discuss proposed solutions. An anonymous, open-ended survey was distributed to members to collect feedback on challenges faced. Representatives from each NCTN group were invited to present an overview of affected trials. From these discussions, the consensus document was developed and circulated for the inclusion of multiple rounds of feedback from both the Working Group and CISC. The current consensus document outlines the key challenges for clinical prostate cancer trials resulting from the increasing availability of PSMA PET. We discuss implications for patient selection and definition of end points and provide guidance and potential solutions for different clinical scenarios, particularly with regard to best practices in defining eligibility criteria and outcome measures. This article provides guidance regarding clinical trial design and conduct, and the interpretation of trial results.

Prostate specific membrane antigen positron emission tomography for lesion-directed high-dose-rate brachytherapy dose escalation

Prostate specific membrane antigen positron emission tomography imaging (PSMA-PET) has demonstrated potential for intra-prostatic lesion localization. We leveraged our existing database of co-registered PSMA-PET imaging with cross sectional digitized pathology to model dose coverage of histologically-defined prostate cancer when tailoring brachytherapy dose escalation based on PSMA-PET imaging. Using a previously-developed automated approach, we created segmentation volumes delineating underlying dominant intraprostatic lesions for ten men with co-registered pathology-imaging datasets. To simulate realistic high-dose-rate brachytherapy (HDR-BT) treatments, we registered the PSMA-PET-defined segmentation volumes and underlying cancer to 3D trans-rectal ultrasound images of HDR-BT cases where 15 Gray (Gy) was delivered. We applied dose/volume optimization to focally target the dominant intraprostatic lesion identified on PSMA-PET. We then compared histopathology dose for all high-grade cancer within whole-gland treatment plans versus PSMA-PET-targeted plans. Histopathology dose was analyzed for all clinically significant cancer with a Gleason score of 7or greater. The standard whole-gland plans achieved a median [interquartile range] D98 of 15.2 [13.8-16.4] Gy to the histologically-defined cancer, while the targeted plans achieved a significantly higher D98 of 16.5 [15.0-19.0] Gy (p=0.007). This study is the first to use digital histology to confirm the effectiveness of PSMA-PET HDR-BT dose escalation using automatically generated contours. Based on the findings of this study, PSMA-PET lesiondose escalation can lead to increased dose to the ground truth histologically defined cancer.

Can Local Ablative Radiotherapy Revert Castration-resistant Prostate Cancer to an Earlier Stage of Disease?

In prostate cancer, disease progression after primary treatment and subsequent androgen deprivation therapy is common. Intensification of systemic treatment is the standard of care. Recently, 68Ga prostate-specific membrane antigen positron emission tomography (PSMA-PET) imaging was introduced to identify oligometastatic prostate cancer patients. In this retrospective, exploratory study, we report on the efficacy of PSMA-PET-guided local ablative radiotherapy (aRT) in 15 oligometastatic castration-resistant prostate cancer (CRPC) patients, selected from our prospective institutional database and treated between 2013 and 2016. After multidisciplinary discussion, aRT was delivered with two different schedules. Androgen deprivation therapy remained unchanged. Prostate-specific antigen (PSA) response and time to PSA progression were analysed. For comparison, individual time to PSA progression without aRT was estimated by individual PSA doubling time (PSADT). PSA response was observed in 11 patients (73%). Mean time to PSA progression or last follow-up was 17.9mo, as opposed to 2.9mo estimated from the PSADT without aRT (p<0.001). A relevant subset of CRPC patients had a PSA response with aRT to PET-positive lead metastases. A prospective trial is in preparation. Patient summaryIn selected patients with prostate-specific antigen (PSA) increase during androgen deprivation, metastases were detected with prostate-specific membrane antigen positron emission tomography imaging. Fifteen patients with three or fewer metastases were treated with high-dose radiotherapy. Subsequently, PSA values dropped in 11 patients and in six patients no PSA progression was detected for >12mo.