Prostate-specific Membrane Antigen Positron Research Articles

The Quantitative Impact of Prostate Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (PSMA PET/CT) staging in Newly Diagnosed Metastatic Prostate Cancer and Treatment-Decision Implications

Abstract Objectives To quantify the stage-shift with PSMA PET/CT imaging in metastatic prostate cancer and explore treatment implications. Methods Single-centre, retrospective analysis of patients with newly diagnosed [18F]PSMA-1007 or [68Ga]Ga-PSMA-11 PET/CT-detected metastatic prostate cancer who had baseline bone scintigraphy between January 2015 and May 2021. Patients were subclassified into oligometastatic and polymetastatic disease utilising the STAMPEDE2 trial (ISRCTN66357938/NCT06320067) definition. Patient, tumour, and treatment characteristics were collected. PSMA PET/CT concordance with conventional imaging (bone scintigraphy and low-dose CT of PET) was identified by number and site of metastases, and subgroup assigned. Spearman’s rank correlation and linear regression modelling determined the association between the imaging modalities. Results We analysed 62 patients with a median age was 72 years (range 48-86). On PSMA PET/CT, 31/62 (50%) patients had oligometastatic disease, and 31/62 (50%) had polymetastatic disease. Prostate radiotherapy was delivered in 20/31 (65%) patients with oligometastatic disease and 17/31 (55%) with polymetastatic disease. 23/62 (37%) patients were reclassified as M0 on conventional imaging. PSMA PET/CT had a 2.9-fold increase in detecting bone metastases. Bone metastases concordance was found in 10/50 (20%) by number and 30/33 (91%) by site. PSMA PET/CT had a 2.2-fold increase in detecting nodal metastases. Nodal metastases concordance was found in 5/46 (11%) by number and 25/26 (96%) by site. There was significant positive correlation between PSMA PET/CT and conventional imaging for detecting bone (R2= 0.25 [p < 0.001]) and nodal metastases (R2= 0.19 [p < 0.001]). 16/31 (52%) had oligometastatic disease concordance. Conclusion The magnitude of PSMA PET/CT-driven stage-shift is highly variable and unpredictable with implications on treatment decisions, future trial design and potentially clinical outcomes.

Detection of Apical Cancer with Novel Imaging Modalities to Predict Apical Margin Positivity in Robotic Assisted Radical Prostatectomy

ObjectivesTo evaluate margin positivity at apex utilizing preoperative magnetic resonance imaging [MRI], micro-ultrasound [MUS], prostate specific membrane antigen positron emission tomography PSMA PET] scan, biopsy location and intraoperative timing of deep venous complex [DVC] ligation during robot assisted radical prostatectomy [RARP]. MethodsInstitution review board approved retrospective study underwent RARP between November 2022 to March 2024. All patients underwent preoperative MRI, MUS and PSMA PET scan. Patients underwent RARP using either standard DVC [done prior apical dissection] ligation or delayed DVC [after prostate removal] technique. All patients underwent intra operative frozen section analysis by an experienced genitourinary pathologist. Descriptive statistics were performed. Data analyzed using R software version 4.3.3. ResultsTotal 619 prostate cancer patients underwent RARP. Of these, 365 men underwent RARP using delayed DVC ligation technique and 254 men using standard DVC ligation technique. There was no statically significant difference in 2 groups on demographic parameters, MRI, MUS and PSMA-PET scan features. Sensitivity of MRI, MUS, PSMA-PET and prostate biopsy for detection of apical positive margin were 66%, 81%, 81% and 73% respectively. Specificity of MRI, MUS, PSMA-PET and prostate biopsy for detection of apical positive margin were 45%, 14%, 16% and 30% respectively. When all modalities are used accumulatively, apical cancer was missed only in 1% of cases. ConclusionsWith proper preoperative understanding of apical lesion location, timing of DVC ligation [standard vs delayed] doesn't impact apical positive surgical margins. Combination of MRI, MUS, PSMA-PET and prostate biopsy reduce apical positive surgical margin rates significantly.

Predictors of Metastasis in 68GA-Prostate Specific Membrane Antigen Pet-CT in the Primary Staging of Prostate Cancer.

Background: The objective of this study was to investigate factors influencing Gallium 68 Prostate Specific Membrane Antigen Positron Emission Tomography (Ga68 PSMA PET-CT) uptake for primary staging in prostate cancer. Methods: Retrospective analysis was conducted on 499 non-metastatic and 243 de novo metastatic prostate cancer cases undergoing Ga68 PSMA PET-CT. Demographic, clinical, and imaging data were collected and analyzed. Multivariate logistic regression determined independent risk factors for metastasis detection on Ga68 PSMA PET-CT. Results: Metastatic cases showed higher levels of total PSA, PSA density (dPSA) and biopsy ISUP grade group compared to non-metastatic cases. Multivariate analysis identified cT2 stage and dPSA as independent predictors of metastasis detection on Ga68 PSMA PET-CT. Conclusions: Ga68 PSMA PET-CT plays a crucial role in prostate cancer staging, with identified factors such as clinical T stage and dPSA significantly impacting its diagnostic accuracy. These findings underscore the importance of Ga68 PSMA PET-CT in refining clinical staging and guiding treatment decisions for prostate cancer patients.

Association of Pre-Treatment Serum Testosterone Levels with Prostate Cancer: A Prospective Study

Introduction: It has been widely accepted that prostate cancer (PCa) growth is related to serum testosterone (ST). A direct correlation between pre-treatment ST level and PCa growth and progression has been reported. However, recent studies have shown that pre-treatment ST levels have a negative correlation with PCa. Thus, the literature is, at best, conflicting. In this study, we examined the pre-treatment serum total testosterone (ST) levels in PCa. Methods: In this prospective observational study, suspected cases of PCa underwent digital rectal examination, routine blood investigation, Prostate-Specific Antigen (PSA) measurement, and prostate biopsy. Diagnosed cases of PCa without any risk factors affecting testosterone levels were included. Their pre-treatment total ST levels were measured. All patients underwent staging evaluation with either Magnetic Resonance Imaging (MRI) & Bone scan or Ga-68 Prostate Specific Membrane Antigen Positron Emission Tomography (PSMA PET). ST levels were also measured in patients with Benign Prostatic Hyperplasia (BPH) and compared with those in PCa patients. ST levels were also assessed according to Gleason Score (GS) and clinical stage in PCa. Results: 110 cases and 54 patients with BPH were included in the study. The median ST level in PCa patients was significantly lower as compared to BPH patients [352.28 ng/dL (Interquartile Range (IQR) 224.99-563.17) vs. 448.29 ng/dL (IQR 400.97-596.42) (p =0.004)]. The median ST level in metastatic PCa was significantly lower than the localized PCa group [298.20 ng/dL vs. 452.30 ng/dL (p=0.0001)]. Moreover, the median ST level was also significantly lower in patients with Gleason Score ≥ 8 than those with Gleason Score ≤ 7 [285.92 ng/dL (149.97-560.40) vs. 425.13 ng/dL (320.43-571.46) (p=0.002)]. Conclusion: This study shows lower ST levels in patients with PCa compared to patients with BPH, thus supporting a potential association as described in previous studies. ST levels may have prognostic value since a low pre-treatment ST level is associated with a higher clinical stage and aggressive PCa.

Neural blind deconvolution for deblurring and supersampling PSMA PET.

Objective. To simultaneously deblur and supersample prostate specific membrane antigen (PSMA) positron emission tomography (PET) images using neural blind deconvolution.Approach. Blind deconvolution is a method of estimating the hypothetical 'deblurred' image along with the blur kernel (related to the point spread function) simultaneously. Traditionalmaximum a posterioriblind deconvolution methods require stringent assumptions and suffer from convergence to a trivial solution. A method of modelling the deblurred image and kernel with independent neural networks, called 'neural blind deconvolution' had demonstrated success for deblurring 2D natural images in 2020. In this work, we adapt neural blind deconvolution to deblur PSMA PET images while simultaneous supersampling to double the original resolution. We compare this methodology with several interpolation methods in terms of resultant blind image quality metrics and test the model's ability to predict accurate kernels by re-running the model after applying artificial 'pseudokernels' to deblurred images. The methodology was tested on a retrospective set of 30 prostate patients as well as phantom images containing spherical lesions of various volumes.Main results. Neural blind deconvolution led to improvements in image quality over other interpolation methods in terms of blind image quality metrics, recovery coefficients, and visual assessment. Predicted kernels were similar between patients, and the model accurately predicted several artificially-applied pseudokernels. Localization of activity in phantom spheres was improved after deblurring, allowing small lesions to be more accurately defined.Significance. The intrinsically low spatial resolution of PSMA PET leads to partial volume effects (PVEs) which negatively impact uptake quantification in small regions. The proposed method can be used to mitigate this issue, and can be straightforwardly adapted for other imaging modalities.

Abstract 4150: Development of a three-dimensional spatialomics map of lethal prostate cancer driven by clinical imaging

Abstract Prostate adenocarcinoma (PCa) is the most common malignancy and the second leading cause of cancer-related mortality in United States men. Following treatment for localized PCa, up to 50% of these men can experience disease recurrence, with subsequent metastasis and death. This indicates that there is suboptimal identification of lethal PCa at the time of diagnosis, despite advancements in imaging, genomics, and biomarkers. To improve the noninvasive diagnosis of lethal PCa at initial diagnosis, we have developed a novel magnetic resonance imaging (MRI) method, diffusion basis spectrum imaging (DBSI), that noninvasively measures cancer, stromal, and immune cell contributions to the prostate tumor microenvironment (TME). To validate DBSI for PCa, we have applied novel technologies to matched prostatectomy specimens that include (i) fully automated tissue section processing with serial 2-photon tomographic (STP) imaging of the sections to generate 3D volumetric structural maps of the tumor tissue and (ii) multiplex MALDI mass spectrometry imaging of untargeted glycans and extracellular matrix (ECM) peptides and of proteins targeted with novel photocleavable-mass-tagged antibodies (MALDI-IHC) to spatially resolve hundreds of biomolecules from the TME. To establish the feasibility of this approach, we recruited a patient with an unusually aggressive prostate cancer consisting of Gleason 5+4 acinar adenocarcinoma histology with intraductal growth that was locally invasive and lymph node positive at prostatectomy (stage T3bN1). This patient also had the unusual finding of low activity on prostate specific membrane antigen positron emission tomography (PSMA-PET). Following gross sectioning of the prostate with MRI-guided 3D printed molds to co-register clinical DBSI with histology, a 5-mm thick tissue cross-section containing tumor and normal prostate was imaged with high resolution ex vivo DBSI followed by 3D structural mapping with STP imaging. Selected slides in the 3D stack were subject to multiplexed MALDI imaging to identify relationships between cellular and molecular heterogeneity with tumor structure identified with DBSI and STP imaging. We discovered unique structural differences in the prostate tumor compared with the surrounding stroma based upon collagen and glycan modifications to the ECM that were recapitulated with second harmonic maps of collagen from STP imaging as well as stromal maps generated from DBSI imaging. Additional novel protein and glycan ECM components were expressed in this tumor known to be associated with poor patient outcomes. Together, these data represent the first evidence successfully linking noninvasive in vivo clinical imaging and de novo spatialomics technologies with potential to improve PCa diagnostics. This advanced imaging workflow can be applied to any tissue type, underscoring its relevance to translational cancer research. Citation Format: Joseph E. Ippolito, David H. Ballard, Karla Bergeron, Ritesh Chidambaram, Anusha Elumalai, Tyler J. Fraum, Huaping Jing, Peter Kamelin, Eric H. Kim, Catherine Kita, Aleksandra Klim, Anthony Knesis, Mark Lim, José Marcio Luna, Hani Nakhoul, Timothy Ragan, Kenneth J. Rothschild, Sheng-Kwei Song, Kainen Utt, Cody Weimholt, Gargey Yagnik, Elijah Yew, Peggi M. Angel, Richard R. Drake. Development of a three-dimensional spatialomics map of lethal prostate cancer driven by clinical imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4150.

PSMA PET/CT as a predictive tool for subregional importance estimates in the parotid gland

Objective. Xerostomia and radiation-induced salivary gland dysfunction remain a common side effect for head-and-neck radiotherapy patients, and attempts have been made to quantify the heterogeneity of the dose response within parotid glands. Prostate Specific Membrane Antigen (PSMA) ligands have demonstrated high uptake in salivary glands, which has been shown to correlate with gland functionality. Here we compare several models of parotid gland subregional relative importance with PSMA positron emission tomography (PET) uptake. We then develop a predictive model for Clark et al's relative importance estimates using PSMA PET and CT radiomic features, and demonstrate a methodology for predicting patient-specific importance deviations from the population. Approach. Intra-parotid gland uptake was compared with four regional importance models using 30 [18F]DCFPyL PSMA PET images. The correlation of uptake and importance was ascertained when numerous non-overlapping subregions were defined, while a paired t-test was used to compare binary region pairs. A radiomics-based predictive model of population importance was developed using a double cross-validation methodology. A model was then devised for supplementing population-level subregional importance estimates for each patient using patient-specific radiomic features. Main Results. Anticorrelative relationships were found to exist between PSMA PET uptake and four independent models of subregional parotid gland importance from the literature. Kernel Ridge Regression with principal component analysis feature selection performed best over test sets (Mean Absolute Error = 0.08), with gray level co-occurrence matrix (GLCM) features being particularly important. Deblurring PSMA PET images with neural blind deconvolution strengthened correlations and improved model performance. Significance. This study suggests that regions of relatively low PSMA PET uptake in parotid glands may exhibit relatively high dose-sensitivity. We’ve demonstrated the utility of PSMA PET radiomic features for predicting relative importance within subregions of parotid glands. PSMA PET appears to be a promising quantitative imaging modality for analyzing salivary gland functionality.

Temporal and regional patterns of prostate cancer positron emission tomography imaging among commercial insurance beneficiaries in the United States.

34 Background: Prostate specific membrane antigen positron emission tomography (PSMA-PET) imaging improves prostate cancer visualization and has been proposed as a tool to guide treatment decisions. As PSMA-PET imaging agents were not approved in the United States (US) until December 2020, little is known about national patterns of PET imaging utilization. Methods: We conducted a dynamic cohort study to evaluate use of PET imaging among insurance beneficiaries aged 40-89 years with a diagnosis of prostate cancer using deidentified administrative claims from Blue Cross Blue Shield Axis. We calculated the proportions of patients undergoing PET imaging in semiannual periods from January 1, 2016, through December 31, 2022, examining tracers specific to prostate cancer, including PSMA-targeted agents as well as fluciclovine, sodium fluoride, and choline tracers. Cochran-Armitage tests were used to evaluate trends in the proportion of individuals receiving PET imaging over time. We also assessed the association between regional [hospital referral region (HRR)] level contextual sociodemographic and healthcare characteristics and regional use of PSMA-PET imaging in 2022 using chi-square tests. Results: There were 410,505 beneficiaries with prostate cancer identified in the study period. The semiannual proportion of patients undergoing PET imaging increased from 4.5 [(95% confidence interval (CI) 4.1-5.0] per 1,000 in the first half of 2016 to 41.7 (95% CI 40.6-42.9) per 1,000 in the second half of 2022, p<0.001. Increases in PET imaging were driven by uptake of PSMA-PET imaging, which increased from 0.7 (95% CI 0.6-0.9) per 1000 in the second half of 2021 to 37.5 (95% CI 36.4-38.6) per 1,000 in the second half of 2022, p<0.001. Following approvals of PSMA-PET agents, other forms of PET imaging rapidly decreased – from 18.2 (95% CI 17.4-18.9) per 1000 in the second half of 2021 to 4.6 (95% CI 4.3-5.0) per 1,000 in the same period of 2022, p<0.001. Compared to HRRs in quartile 1 (Q1), HRRs in Q4 of PSMA-PET use in 2022 had higher levels of education (25.0% with college education or higher in Q1 versus 29.4% in Q4, p=0.005) and median household income ($50,200 in Q1 versus $60,900 in Q4, p<0.001). Conclusions: In this study from a large commercial US health insurer, PSMA-PET was rapidly incorporated into clinical practice and is now the dominant prostate cancer radiotracer. However, the initial uptake of PSMA-PET may be accompanied by disparity, as our data suggests less use in areas with lower income and education measures.

PSMA-PET follow-up to assess response in patients not receiving PSMA therapy: Is there value beyond localization of disease?

Introduction: Prostate Specific Membrane Antigen Positron Emission Tomography (PSMA-PET) is routinely used for the staging of patients with prostate cancer, but data on response assessment are sparse and primarily stem from metastatic castration-resistant prostate cancer (mCRPC) patients treated with PSMA radioligand therapy. Still, follow-up PSMA-PET is employed in earlier disease stages in case of clinical suspicion of disease persistence, recurrence or progression to decide if localized or systemic treatment is indicated. Therefore, the prognostic value of PSMA-PET derived tumor volumes in earlier disease stages (i.e., hormone-sensitive prostate cancer (HSPC) and non-[177Lu]Lu-PSMA-617 (LuPSMA) therapy castration resistant prostate cancer (CRPC)) are evaluated in this manuscript. Methods: A total number of 73 patients (6 primary staging, 42 HSPC, 25 CRPC) underwent two (i.e., baseline and follow-up, median interval: 379 days) whole-body [68Ga]Ga-PSMA-11 PET/CT scans between Nov 2014 and Dec 2018. Analysis was restricted to non-LuPSMA therapy patients. PSMA-PETs were retrospectively analyzed and primary tumor, lymph node-, visceral-, and bone metastases were segmented. Body weight-adjusted organ-specific and total tumor volumes (PSMAvol: sum of PET volumes of all lesions) were measured for baseline and follow-up. PSMAvol response was calculated as the absolute difference of whole-body tumor volumes. High metastatic burden (>5 metastases), RECIP 1.0 and PSMA-PET Progression Criteria (PPP) were determined. Survival data were sourced from the cancer registry. Results: The average number of tumor lesions per patient on the initial PET examination was 10.3 (SD 28.4). At baseline, PSMAvol was strongly associated with OS (HR 3.92, p <0.001; n = 73). Likewise, response in PSMAvol was significantly associated with OS (HR 10.48, p < 0.005; n = 73). PPP achieved significance as well (HR 2.19, p <0.05, n = 73). Patients with hormone sensitive disease and poor PSMAvol response (upper quartile of PSMAvol change) in follow-up had shorter outcome (p < 0.05; n = 42). PSMAvol in bones was the most relevant parameter for OS prognostication at baseline and for response assessment (HR 31.11 p < 0.001; HR 32.27, p < 0.001; n = 73). Conclusion: PPP and response in PSMAvol were significantly associated with OS in the present heterogeneous cohort. Bone tumor volume was the relevant miTNM region for OS prognostication. Future prospective evaluation of the performance of organ specific PSMAvol in more homogeneous cohorts seems warranted.

Massive pre-prostatic nodal metastasis from localized aggressive prostate cancer removed during robotic-assisted radical prostatectomy with extended pelvic lymph node dissection: a case report with brief literature review

BackgroundDuring robotic-assisted radical prostatectomy (RARP) for prostate cancer (PCa), few attention is given to pre-prostatic fat tissue (PPT) even during pelvic lymph node dissection (PLND). However, the rare potential involvement of PPT lymph nodes (LN) by PCa metastasis has already been reported by several authors and may influence therapeutic strategy in intermediate and high-risk patients. We present the case of a 69-year-old man who underwent RARP with extended PLND (ePLND) for aggressive PCa with massive pre-prostatic nodal metastasis, sampled during prostate biopsies. We sought to report this case for the particular preoperative images and reinforce benefits of resecting PPT during PLND for PCa.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 1 Given name: [Moncef] Last name [Al Barajraji].OkCase presentationA 69-year-old man consulted our department for high serum prostate specific antigen level (57 ng/mL). He had familial history of PCa only at first degree. On digital rectal evaluation, induration of left prostatic lobe was felt. Transrectal ultrasonography showed hypoechogenic lesion in left prostatic lobe with supra-centimetric nodule in PPT. Pelvic magnetic resonance revealed two lesions in the peripheral zone with a 19-mm nodule on right paramedian side of PPT (see Fig. 1). Transrectal ultrasound-guided prostate biopsies were performed, including the nodule. On left side, 2 biopsies out 6 showed Gleason 10 prostate cancer. On right side, all biopsies showed Gleason 9 prostate cancer. The PPT nodule showed Gleason 9 prostate cancer. Prostate specific membrane antigen (PSMA) positron emission tomography computed tomography scan showed hypermetabolic expression from left prostate lesions and PPT nodule. Transperitoneal RARP with ePLND was performed including PPT. Histopathological study revealed advanced prostate cancer with lymphovascular invasion and ECE (see Fig. 2). Evaluation of ePLND material showed metastasis in on pelvic LN and 23 mm nodal metastasis in PPT (see Fig. 2). Therefore, adjuvant therapy was initiated.Please check the edit made in the article title.OPkConclusionsPPT resection is not part of routine RARP with ePLND for PCa. However, this tissue might contain LN harbouring metastasis independently from pelvic LN, indicating adjuvant therapy in case of upstaging. Considering the low morbidity of resecting PPT and its facility, it should always been resected and sent for analysis in intermediate and high-risk PCa.

1787P Prostate specific membrane antigen positron emission tomography (PSMA PET)-directed clinical outcomes in metastatic hormone-sensitive prostate cancer (mHSPC): Implications for the STAMPEDE2 trial design

1787P Prostate specific membrane antigen positron emission tomography (PSMA PET)-directed clinical outcomes in metastatic hormone-sensitive prostate cancer (mHSPC): Implications for the STAMPEDE2 trial design

Towards simulation-free MR-linac treatment: utilizing male pelvis PSMA-PET/CT and population-based electron density assignments

Objective. This study aimed to investigate the dosimetric impact of using population-based relative electron density (RED) overrides in lieu of simulation computerized tomography (CT) in a magnetic resonance linear accelerator (MRL) workflow for male pelvis patients. Additionally, the feasibility of using prostate specific membrane antigen positron emission tomography/CT (PSMA-PET/CT) scans to assess patients’ eligibility for this proposed workflow was examined. Approach. In this study, 74 male pelvis patients treated on an Elekta Unity 1.5 T MRL were retrospectively selected. The patients’ individual RED values for 8 organs of interest were extracted from their simulation-CT images to establish population-based RED values. These values were used to generate individual (IndD) and population-based (PopD) RED dose plans, representing current and proposed MRL workflows, respectively. Lastly, this study compared RED values obtained from CT and PET-CT scanners in a phantom and a subset of patients. Results. Population-based RED values were mostly within two standard deviations of ICRU Report 46 values. PopD plans were comparable to IndD plans, with the average %difference magnitudes of 0.5%, 0.6%, and 0.6% for mean dose (all organs), D0.1cm 3 (non-target organs) and D95%/D98% (target organs), respectively. Both phantom and patient PET-CT derived RED values had high agreement with corresponding CT-derived values, with correlation coefficients ≥ 0.9. Significance. Population-based RED values were considered suitable in a simulation-free MRL treatment workflow. Utilizing these RED values resulted in similar dosimetric uncertainties as per the current workflow. Initial findings also suggested that PET-CT scans may be used to assess prospective patients’ eligibility for the proposed workflow. Future investigations will evaluate the clinical feasibility of implementing this workflow for prospective patients in the clinical setting. This is aimed to reduce patient burden during radiotherapy and increase department efficiencies.

Complex implementation factors demonstrated when evaluating cost-effectiveness and monitoring racial disparities associated with [18F]DCFPyL PET/CT in prostate cancer men

Prostate cancer (PC) staging with conventional imaging often includes multiparametric magnetic resonance (MR) of the prostate, computed tomography (CT) of the chest, abdomen, and pelvis, and whole-body bone scintigraphy. The recent development of highly sensitive and specific prostate specific membrane antigen (PSMA) positron emission tomography (PET) has suggested that prior imaging techniques may be insufficiently sensitive or specific, particularly when evaluating small pathologic lesions. As PSMA PET/CT is considered to be superior for multiple clinical indications, it is being deployed as the new multidisciplinary standard-of-care. Given this, we performed a cost-effectiveness analysis of [18F]DCFPyL PSMA PET/CT imaging in the evaluation of PC relative to conventional imaging and anti-3-[18F]FACBC (18F-Fluciclovine) PET/CT. We also conducted a single institution review of PSMA PET/CT scans performed primarily for research indications from January 2018 to October 2021. Our snapshot of this period of time in our catchment demonstrated that PSMA PET/CT imaging was disproportionately accessed by men of European ancestry (EA) and those residing in zip codes associated with a higher median household income. The cost-effectiveness analysis demonstrated that [18F]DCFPyL PET/CT should be considered as an alternative to anti-3-[18F]FACBC PET/CT and standard of care imaging for prostate cancer staging. [18F]DCFPyL PET/CT is a new imaging modality to evaluate PC patients with higher sensitivity and specificity in detecting disease than other prostate specific imaging studies. Despite this, access may be inequitable. This discrepancy will need to be addressed proactively as the distribution network of the radiotracer includes both academic and non-academic sites nationwide.

The use of Lutetium-177 PSMA radioligand therapy with high dose rate brachytherapy for locally recurrent prostate cancer after previous definitive radiation therapy: a randomized, single-institution, phase I/II study (ROADSTER).

BackgroundIsolated local failure (ILF) can occur in patients who initially receive definitive radiation therapy for prostate cancer. Salvage therapy for ILF includes high dose rate (HDR) brachytherapy. Prostate Specific Membrane Antigen (PSMA) Positron Emission Tomography (PET) can accurately detect ILF and can exclude extraprostatic disease. Lutetium-177 PSMA Radioligand Therapy (RLT) is a novel treatment for prostate cancer that can target prostate cancer accurately, while sparing radiation dose to normal tissues.MethodsROADSTER is a phase I/II randomized, single-institution study. Patients with an ILF of prostate cancer after definitive initial radiation therapy are eligible. The ILF will be confirmed with biopsy, magnetic resonance imaging (MRI) and PSMA PET. Patients will be randomized between HDR brachytherapy in two fractions (a standard of care salvage treatment at our institution) (cohort 1) or one treatment of intravenous Lutetium-177 PSMA RLT, followed by one fraction of HDR brachytherapy (cohort 2). The primary endpoints for the phase I portion of the study (n = 12) will be feasibility, defined as 10 or more patients completing the study protocol within 24 months of study activation; and safety, defined as zero or one patients in cohort 2 experiencing grade 3 or higher toxicity in the first 6 months post-treatment. If feasibility and safety are achieved, the study will expand to a phase II study (n = 30 total) where preliminary efficacy data will be evaluated. Secondary endpoints include changes in prostate specific antigen levels, acute toxicity, changes in quality of life, and changes in translational biomarkers. Translational endpoints will include interrogation of blood, urine, and tissue for markers of DNA damage and immune activation with each treatment.DiscussionROADSTER explores a novel salvage therapy for ILF after primary radiotherapy with combined Lutetium-177 PSMA RLT and HDR brachytherapy. The randomized phase I/II design will provide a contemporaneous patient population treated with HDR alone to facilitate assessment of feasibility, tolerability, and biologic effects of this novel therapy.Trial registrationNCT05230251 (ClinicalTrials.gov).

PSMA-PET Guided Treatment in Prostate Cancer Patients with Oligorecurrent Progression after Previous Salvage Treatment

Prostate Specific Membrane Antigen-Positron Emission Tomography (PSMA-PET) is used to select recurrent prostate cancer (PCa) patients for metastases-directed therapy (MDT). We aimed to evaluate the oncologic outcomes of second-line PSMA-guided MDT in oligo-recurrent PCa patients. we performed a retrospective analysis of 113 recurrent PCa after previous radical prostatectomy and salvage therapies with oligorecurrent disease at PSMA-PET (≤3 lesions in N1/M1a-b) in three high-volume European centres. Patients underwent second-line salvage treatments: MDT targeted to PSMA (including surgery and/or radiotherapy), and the conventional approach (observation or Androgen Deprivation Therapy [ADT]). Patients were stratified according to treatments (MDT vs. conventional approach). Patients who underwent MDT were stratified according to stage in PSMA-PET (N1 vs. M1a-b). The primary outcome of the study was Progression-free survival (PFS). Secondary outcomes were Metastases-free survival (MFS) and Castration Resistant PCa free survival (CRPC-FS). Kaplan-Meier analyses assessed PFS, MFS and CRPC-FS. Multivariable Cox regression models identified predictors of progression and metastatic disease. Overall, 91 (80%) and 22 (20%) patients were treated with MDT and the conventional approach, respectively. The median follow-up after PSMA-PET was 31 months. Patients who underwent MDT had a similar PFS compared to the conventional approach (p = 0.3). Individuals referred to MDT had significantly higher MFS and CRPC-FS compared to those who were treated with the conventional approach (73.5% and 94.7% vs. 30.5% and 79.5%; all p ≤ 0.001). In patients undergoing MDT, no significant differences were found for PFS and MFS according to N1 vs. M1a-b disease, while CRPC-FS estimates were significantly higher in patients with N1 vs. M1a-b (100% vs. 86.1%; p = 0.02). At multivariable analyses, age (HR = 0.96) and ADT during second line salvage treatment (HR = 0.5) were independent predictors of PFS; MDT (HR 0.27) was the only independent predictor of MFS (all p ≤ 0.04) Conclusion: Patients who underwent second-line PSMA-guided MDT experienced higher MFS and CRPC-FS compared to men who received conventional management.

Patterns of Failure in Men With Radiorecurrent Prostate Cancer: A Post Hoc Analysis of 3 Prospective Gallium 68 Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography Imaging Trials

Men with radiorecurrent prostate cancer (PCa) are often not offered curative treatment due to concerns regarding occult extraprostatic disease. Prostate specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) has significantly improved sensitivity for detecting extraprostatic disease compared with conventional imaging. We evaluated the patterns of PSMA-positivity in a cohort of men presenting for PSMA PET/CT to evaluate radiorecurrence. This was a post-hoc analysis of men from 3 prospective studies of PSMA PET/CT for radiorecurrent prostate cancer who had detailed clinicopathologic and treatment characteristics available and at least one positive PSMA PET/CT finding. Patterns of failure were defined as intraprostatic (including seminal vesicles) or extraprostatic (regional lymph node or distant metastatic disease with or without intraprostatic disease). Multivariable analyses (MVAs) were performed to evaluate for predictors of extraprostatic vs intraprostatic recurrence. Of the 128 patients included in this study, 17 (13%) were initially diagnosed with low-risk, 69 (54%) with intermediate-risk, and 42 (33%) with high-risk PCa. Median time since radiotherapy (RT) was 4.3 years (interquartile range [IQR], 2.7 - 7.2 years), and median PSA at time of PSMA PET/CT was 4.8 ng/mL (IQR, 2.8-10). Intraprostatic only failures were seen in 46 patients (36%), while extraprostatic failures were seen in 82 patients (64%). On MVA, greater years since RT was associated with decreased likelihood of extraprostatic recurrence (OR 0.89 [0.8 - 1.0], p=0.04) p=0.04) while increased PSA at PSMA PET/CT (OR 1.17 [1.05 - 1.29], p=0.003) and ADT use during initial treatment (OR 3.44 [1.0 - 11.85], p=0.05) were associated with extraprostatic recurrence. Nearly 1/3rd of patients with radiorecurrent disease who have identifiable disease on a PSMA PET/CT scan have intraprostatic recurrences only. Prospective studies evaluating salvage treatment approaches that integrate PSMA PET/CT imaging data are warranted.

Impact of 68Ga-PSMA PET/CT in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with enzalutamide.

48 Background: 68Ga prostate specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) is a highly sensitive diagnostic tool to detect prostate metastatic sites even at low levels of Prostate Specific Antigen (PSA). We evaluated the impact of 68Ga-PSMA PET/CT in patients treated with enzalutamide as first-line therapy for mCRPC. Methods: In an observational prospective study, 67 consecutive mCRPC patients were treated with enzalutamide 160 mg once daily in first-line for mCRPC. 68Ga-PSMA PET/CT was performed at baseline, after 3 months, during follow-up and at PSA/clinical progression. Patients were evaluated on a monthly basis for serological PSA response and safety. We measured at baseline the sum of metabolic total volume (SMTV), mean standardized uptake volume (SSUVmean), maximum standardized uptake volume (SSUVmax) and total lesion activity (STLA), which is the product of SMTV and SSUVmean, for a maximum of 20 lesions. These parameters together with baseline PSA level, Eastern Cooperative Oncology Group performance status (ECOG PS), Gleason Score (GS) and age were analyzed by univariate and multivariate Cox regression models as potential predictors of progression-free survival (PFS) and overall survival (OS). Results: At the moment of the present analysis, 58 mCRPC patients were considered fully evaluable. The median age was 75 years (range, 47-91), ECOG PS was 0 in 47 cases (81%), 1-2 in 11 (19%), GS was &lt;8 in 22 (38%), 8-10 in 36 (62%), the median baseline PSA was 2.66 µg/L (range 0.09-197). We observed a median SMTV of 5.73 cm3, median SSUVmax of 44.85, median SSUVmean of 25.80 and median STLA of 59.66. At the median follow-up of 52 months, median PFS was 28.9 months (95% CI 16.3-43.6), median OS was not reached (95% CI 36.8-not reached). In univariate analysis, SSUVmax and STLA were significant for PFS (p=0.015 and p=0.001, respectively) and OS (p=0.026 and p=0.019, respectively), while SSUVmean was significant only for OS (p=0.028). On multivariate analysis, STLA only remained significant for PFS (p&lt;0.001) and OS (p=0.026). Conclusions: The assessment of mCRPC by 68Ga-PSMA PET/CT before starting enzalutamide was associated with longer median PFS and OS compared to prior studies using standard imaging only. STLA, expression of both volume and intensity of 68Ga-PSMA uptake, appeared the strongest parameter able to predict PFS and OS.

The Impact of PSMA-PET on Oncologic Control in Prostate Cancer Patients Who Experienced PSA Persistence or Recurrence.

Background: Prostate Specific Membrane Antigen-Positron Emission Tomography (PSMA-PET) is currently recommended to restage prostate cancer (PCa) and to guide the delivery of salvage treatments. We aim to evaluate the oncologic outcomes of patients with recurrent PCa who received PSMA-PET. Methods: 324 hormone-sensitive PCa with PSA relapse after radical prostatectomy who underwent PSMA-PET in three high-volume European Centres. Patients have been stratified as pre-salvage who never received salvage treatments (n = 134), and post-salvage, including patients who received previous salvage therapies (n = 190). Patients with oligorecurrent (≤3 lesions), PSMA-positive disease underwent PSMA-directed treatments: salvage radiotherapy (sRT) or Metastases-directed therapy (MDT). Patients with polirecurrent (>3 lesions) PSMA-positive disease were treated with systemic therapy. Patients with negative PSMA-PET were treated with sRT or systemic therapies or observation. The primary outcome of the study was Progression-free survival (PFS). Secondary outcomes were: Metastases-free survival (MFS) and Castration Resistant Pca free survival (CRPC-FS). Results: median follow up was 23 months. In the pre-salvage setting, the PFS, MFS and CRPC-FS estimates at 3 years were 66.2% vs. 38.9%, 95.2% vs. 73.7% and 94.9% vs. 93.1% in patients with negative vs. positive PSMA-PET, respectively (all p ≥ 0.2). In the post-salvage setting, the PFS, MFS and CRPC-FS estimates at 3 years were 59.5% vs. 29.1%, 92.7% vs. 65.1% and 98.8% vs. 88.8% in patients with negative vs. positive PSMA-PET, respectively (all p ≤ 0.01). At multivariable analyses, a positive PSMA-PET was an independent predictor of progression (HR = 2.15) and metastatic disease (HR 2.37; all p ≤ 0.03). Conclusion: PSMA-PET in recurrent PCa detects the site of recurrence guiding salvage treatments and has a prognostic role in patients who received previous salvage treatments.

PP49 Financing The Line Of Care In The First Biochemical Relapse Of Prostate Cancer After [68Ga] PSMA PET- CT

IntroductionIt is estimated that prostate cancer will reach 66 thousand by the triennium 2020-2022 according to the National Cancer Institute (INCA). After initial diagnosis and staging the patient may undergo radical prostatectomy and/or curative radiotherapy. In patients with biochemical relapse (PSA &gt;0.2 ng/ml) initially treated with radical prostatectomy, salvage external radiotherapy is indicated. The [68Ga] Prostate Specific Membrane Antigen Positron Emission Tomography-Computed Tomography (PSMA PET-CT) scan is mainly used for localization of prostate cancer in the setting of first biochemical recurrence and can significantly influence the clinical management of the patient.MethodsThe overall objective of this work is to perform a treatment cost analysis for patients in first biochemical recurrence of prostate cancer after curative radical prostatectomy and after performing [68Ga] PSMA PET-CT from the perspective of the Brazilian Health System (SUS). A decision tree was constructed through consultation with experts to outline the patient’s entire treatment. Values per modelled therapeutic procedure were surveyed in two different scenarios, with and without [68Ga] PSMA PET-CT. The average treatment in scenario 1 was stereotaxic radiation therapy (SBRT), and rescue radiotherapy and androgen deprivation therapy (ADT). In scenario 2, it was salvage radiotherapy and ADT. The reimbursement table was prepared from data collected by SUS system. Variations were analyzed using a sensitivity study. Total average values included: individual procedure, according to medical management (up to 3 years) and population percentage with and without [68Ga] PSMA PET-CT.ResultsValues were calculated in Brazilian currency (BRL) for each procedure. The total amount calculated for scenario 1 was BRL 264,965,465.00 (USD 55,642,747.65) and for scenario 2 was BRL 123,585,612.72 (USD 26,162,978.67).ConclusionsThe reimbursement of line of care adopted after [68Ga] PSMA PET-CT is an important information to expand access to the Brazilian population. It shows an increased cost with [68Ga] PSMA PET-CT adoption. A prospective study should be considered with high follow up.

Can Perirectal Spacing Help Reduce GI Toxicity in Patients Undergoing Post-Prostatectomy Radiotherapy?

<h3>Purpose/Objective(s)</h3> To report single institutional feasibility of recto-vesical hyaluronic acid or hydrogel spacer insertion for patients undergoing post prostatectomy radiotherapy (PPRT). <h3>Materials/Methods</h3> Spacer insertion was considered in patients referred for PPRT following an intra or interfascial radical prostatectomy who had no radiological evidence of local recurrence (based on prostate specific membrane antigen positron emission tomography). The spacer was inserted into the perirectal fat between the bladder and anterior rectal wall using a transperineal approach under transrectal ultrasound guidance. Two gold seed fiducial markers were also inserted at the level of the vesico-urethral anastomosis for image guided radiation therapy as per institutional practice. Pre and post spacer computerized tomography planning scans, together with post spacer magnetic resonance imaging scans, were acquired for dosimetric comparison. The prostate bed clinical target volume (CTV) was delineated according to Australian guidelines and the CTV was uniformly expanded by 7mm to create the planning target volume (PTV). The prescribed dose to the prostate bed was 70.2Gy in 1.8 Gy fractions using volumetric arc radiation therapy. The PTV and rectal dosimetry for the two sets of planning scans (PTV 7mm/pre spacer and PTV 7mm/post spacer) were compared. <h3>Results</h3> Sixty-one patients were recruited between 9/18 to 10/21. Fifty-eight patients successfully underwent rectal spacer insertion without postoperative complications. We did not attempt spacer insertion in 3 patients as we were unable to hydrodissect the perirectal fat plane. Only 33 patients had pre spacer planning scans available for dosimetric comparison. The distance between the bladder and rectal wall was increased from ≤1mm to a median of 11mm (9-13) at its greatest extent. The rectal volume for all patients (N=61) receiving 42.2Gy (rV60%), 49.1Gy (rV70%), 56.2 Gy (rV80%), 63.2Gy (rV90%) and 70.2Gy (rV100%)] were 28.1%, 23%, 17.9%, 12.5% and 3.8% respectively. With spacing, a statistically significant reduction was seen on all rectal volume end points from rV60% to rV100% in the 33 patients with both pre and post planning scans (see Table 1). The median follow up was 10.5 months (3-31). The risk of any grade acute GI toxicity was 28% (grade 1 26% and grade 2 2%). The risk of late GI toxicity was 7% (all grade 1 proctitis). <h3>Conclusion</h3> More than 90% of our selected PPRT patients were able to achieve recto-vesical separation, with no surgical complications, resulting in a 43.7% reduction in rV90%. The reduction in acute and late grade 2 GI toxicity is of notable significance, albeit with short follow up. Table 1 Pre and Post Spacer Rectal Dosimetry