Mycobacterial spindle cell pseudotumor of the spinal cord: Case report and literature review

We report the first description of spinal cord mycobacterial spindle cell pseudotumor. A patient with newly diagnosed advanced HIV presented with recent-onset bilateral leg weakness and was found to have a hypermetabolic spinal cord mass on structural and molecular imaging. Biopsy and cultures from blood and cerebrospinal fluid confirmed spindle cell pseudotumor due to Mycobacterium avium-intracellulare. Despite control of HIV and initial reduction in pseudotumor volume on antiretrovirals and antimycobacterials (azithromycin, ethambutol, rifampin/rifabutin), he ultimately experienced progressive leg weakness due to pseudotumor re-expansion. Here, we review literature and discuss multidisciplinary diagnosis, monitoring and management challenges, including immune reconstitution inflammatory syndrome.

68 Ga-DOTATATE PET to Characterize Lesions in the Neuroaxis

AIM

The differentiation of paragangliomas, schwannomas, meningiomas, and other neuroaxis tumors in the head and neck remains difficult when conventional MRI is inconclusive. This study assesses the utility of 68 Ga-DOTATATE PET/CT as an adjunct to hone the diagnosis.

PATIENTS AND METHODS

This retrospective study considered 70 neuroaxis lesions in 52 patients with 68 Ga-DOTATATE PET/CT examinations; 22 lesions (31%) had pathologic confirmation. Lesions were grouped based on pathological diagnosis and best radiologic diagnosis when pathology was not available. Wilcoxon rank sum tests were used to test for differences in SUV max among paragangliomas, schwannomas, and meningiomas. Receiver operator characteristic curves were constructed.

RESULTS

Paragangliomas had a significantly greater 68 Ga-DOTATATE uptake (median SUV max , 62; interquartile range [IQR], 89) than nonparagangliomas. Schwannomas had near-zero 68 Ga-DOTATATE uptake (median SUV max , 2; IQR, 1). Intermediate 68 Ga-DOTATATE uptake was seen for meningiomas (median SUV max , 19; IQR, 6) and other neuroaxis lesions (median SUV max , 7; IQR, 9). Receiver operator characteristic analysis demonstrated an area under the curve of 0.87 for paragangliomas versus all other lesions and 0.97 for schwannomas versus all other lesions.

CONCLUSIONS

Marked 68 Ga-DOTATATE uptake (>50 SUV max ) favors a diagnosis of paraganglioma, although paragangliomas exhibit a wide variability of uptake. Low to moderate level 68 Ga-DOTATATE uptake is nonspecific and may represent diverse pathophysiology including paraganglioma, meningioma, and other neuroaxis tumors but essentially excludes schwannomas, which exhibited virtually no uptake.

Fluorine-18-Labeled Fluoroestradiol PET/CT: Current Status, Gaps in Knowledge, and Controversies-AJR Expert Panel Narrative Review

PET/CT using 16α-[18F]-fluoro-17β-estradiol (FES) noninvasively images tissues expressing estrogen receptors (ERs). FES has undergone extensive clinicopathologic validation for ER+ breast cancer and received FDA approval in 2020 for clinical use as an adjunct to biopsy in patients with recurrent or metastatic ER+ breast cancer. Clinical use of FES PET/CT is increasing, but is not widespread in the United States. This AJR Expert Panel Narrative Review explores the present status and future directions of FES PET/CT, including image interpretation, existing and emerging uses, knowledge gaps, and current controversies. Specific controversies discussed include whether both FES PET/CT and FDG PET/CT are warranted in certain scenarios, whether further workup is required after negative FES PET/CT results, whether FES PET/CT findings should inform endocrine therapy selection, and whether immunohistochemistry should remain the standalone reference standard for determining ER status for all breast cancers. Consensus opinions from the panel include agreement with the appropriate clinical uses of FES PET/CT published by a multidisciplinary expert workgroup in 2023; anticipated expanded clinical use of FES PET/CT for staging ER-positive invasive lobular carcinomas and low-grade invasive ductal carcinomas pending ongoing clinical trial results; and the need for further research regarding use of FES PET/CT for ER-expressing nonbreast malignancies.

Other Novel PET Radiotracers for Breast Cancer

Many novel PET radiotracers have demonstrated potential use in breast cancer. Although not currently approved for clinical use in the breast cancer population, these innovative imaging agents may one day play a role in the diagnosis, staging, management, and even treatment of breast cancer.

PSMA Uptake in a Subdural Hematoma

ABSTRACT

An 81-year-old man with known metastatic prostate cancer with recent biochemical progression underwent a PSMA PET/CT (18F-piflufolastat) for restaging. Review of the images demonstrated an acute or chronic left cerebral convexity subdural hematoma on CT with corresponding radiotracer activity throughout the collection on PET. Analysis of the patient's prior imaging showed that this subdural hematoma had significantly increased in size when compared with a head CT obtained 2 months prior. The patient was referred to a nearby emergency department and underwent repeat imaging and subdural drain placement. Unfortunately, the patient died secondary to rapid reaccumulation of subdural blood products after intervention.

Abstract 5610: [18F]FluorThanatrace ([18F]FTT) PET Imaging of PARP-inhibitor drug-target engagement as a biomarker of response in ovarian cancer

Purpose: Poly(ADP-ribose) polymerase enzyme inhibitors (PARPi) have become the standard-of-care treatment for homologous recombination deficient (HRD) high-grade serous ovarian cancer (HGSOC). However, not all HRD tumors respond to PARPi and biomarkers to predict response are needed. [18F]FluorThanatrace (FTT) is a PARPi-analog PET radiotracer that non-invasively measures PARP-1 expression. Herein, we evaluate the ability of FTT uptake to serve as a biomarker to predict response to PARPi in patient-derived xenograft (PDX) models and patients with HGSOC.

Patients and Methods: In PDX models, FTT-PET was performed before and after PARPi (olaparib), ataxia-telangiectasia inhibitor (ATRi), or both. Changes in FTT were correlated with tumor size changes. Patients with HRD and HGSOC that were enrolled in CAPRI (PARPi+ATRi), LIGHT (PARPi only), or off-trial (PARPi only) were selected for this single-center, prospective, cohort, IRB-approved study. FTT-PET/CT imagining was obtained from the skull base to the proximal thighs on an Ingenuity TF scanner (Philips Healthcare) 60-90 minutes after intravenous infusion of 8-12 mCi FTT. Subjects were imaged with FTT-PET at baseline and after ~1 week of PARPi monotherapy treatment. Target lesions (primary tumor and/or metastases) were identified at the time of the baseline imaging on correlative anatomic imaging using RECIST 1.1 and maximum standardized uptake value (SUVmax) data, normalized by body weight, was collected. Changes in FTT-PET uptake were compared to changes in tumor size, CA-125, and progression free survival (PFS).

Results: A decrease in FTT tumor uptake after 1 week of PARPi treatment correlated with response to PARPi+ATRi treatment in PARPi-resistant PDX models (r=0.81-0.83, P=0.1-0.22). In HGSOC patients (n=13), percent differences in FTT-PET after ~7 days of PARPi compared to baseline correlated with the first RECIST response (r=0.60, P=0.034), best RECIST response (r=0.75, P=0.01), best CA-125 response (r=0.73, P=0.033), and PFS (r=0.67, P=0.027). All patients with >50% reduction in FTT uptake had >6-month PFS and >50% reduction in CA-125 (P=0.004 and P=0.016, respectively). Utilizing only baseline FTT uptake correlated to best RECIST response (r=-0.65, P=0.035) but did not predict response when corelated with other measures. Importantly, a decrease in FTT uptake does not appear to be associated with a reduction in tumor burden or apoptosis in response to drug cytotoxic activity at this early timepoint, indicating specificity for drug-target engagement.

Conclusions: The decline in FTT uptake shortly after PARPi initiation compared to baseline provides an in vivo measure of drug-target engagement and shows promise as an early biomarker to guide PARPi therapy. FTT-PET has both pre-clinical and clinical applications warranting further study, including guiding PARPi combination therapy.

Citation Format: Sarah B. Gitto, Austin R. Pantel, Mehran Makvandi, Hyoung Kim, Sergey Medvedev, Joanna K. Weeks, Drew A. Torigian, Chia-Ju Hsieh, Benjamin Ferman, Nawar A. Latif, Janos L. Tanyi, Lainie P. Martin, Shannon M. Lanzo, Fang Liu, Quy Cao, Gordon B. Mills, Robert K. Doot, David A. Mankoff, Robert H. Mach, Lilie L. Lin, Fiona Simpkins. [18F]FluorThanatrace ([18F]FTT) PET Imaging of PARP-inhibitor drug-target engagement as a biomarker of response in ovarian cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5610.

18F-Fluoroestradiol: Current Applications and Future Directions

In the United States, breast cancer is the second leading cause of cancer death in all women and the leading cause of cancer death in Black women. The breast cancer receptor profile, assessed with immunohistochemical staining of tissue samples, allows prediction of outcomes and direction of patient treatment. Approximately 80% of newly diagnosed breast cancers are hormone receptor (HR) positive, which is defined as estrogen receptor (ER) and/or progesterone receptor (PR) positive. Patients with ER-positive disease can be treated with therapies targeting the ER; however, the assessment of ER expression with immunohistochemical staining of biopsy specimens has several limitations including sampling error, false-negative results, challenging or inaccessible biopsy sites, and the inability to synchronously and serially assess all metastatic sites to identify spatial and/or temporal ER heterogeneity. In May 2020, after decades of research, the U.S. Food and Drug Administration approved the PET radiotracer fluorine 18 (¹⁸F) fluoroestradiol (FES) for clinical use in patients with ER-positive recurrent or metastatic breast cancer as an adjunct to biopsy. FES binds to the ER in the nucleus of ER-expressing cells, enabling whole-body in vivo assessment of ER expression. This article is focused on the approved uses of FES in the United States, including identification of a target lesion for confirmatory biopsy, in vivo assessment of biopsy-proven ER-positive disease, and evaluation of spatial and temporal ER heterogeneity. FES is an example of precision medicine that has been leveraged to optimize the care of patients with breast cancer. ^© RSNA, 2023 See the invited commentary by Fowler in this issue. Quiz questions for this article are available through the Online Learning Center.

PET/CT Imaging in Radiation Therapy Treatment Planning: A Review of PET Imaging Tracers and Methods to Incorporate PET/CT

Purpose

Positron emission tomography (PET)/computed tomography (CT) has become a critical tool in clinical oncology with an expanding role in guiding radiation treatment planning. As its application and availability grows, it is increasingly important for practicing radiation oncologists to have a comprehensive understanding of how molecular imaging can be incorporated into radiation planning and recognize its potential limitations and pitfalls. The purpose of this article is to review the major approved positron-emitting radiopharmaceuticals clinically being used today along with the methods used for their integration into radiation therapy including methods of image registration, target delineation, and emerging PET-guided protocols such as biologically-guided radiation therapy and PET-adaptive therapy.

Methods and Materials

A review approach was utilized using collective information from a broad review of the existing scientific literature sourced from PubMed search with relevant keywords and input from a multidisciplinary team of experts in medical physics, radiation treatment planning, nuclear medicine, and radiation therapy.

Results

A number of radiotracers imaging various targets and metabolic pathways of cancer are now commercially available. PET/CT data can be incorporated into radiation treatment planning through cognitive fusion, rigid registration, deformable registration, or PET/CT simulation techniques. PET imaging provides a number of benefits to radiation planning including improved identification and delineation of the radiation targets from normal tissue, potential automation of target delineation, reduction of intra- and inter-observer variability, and identification of tumor subvolumes at high risk for treatment failure which may benefit from dose intensification or adaptive protocols. However, PET/CT imaging has a number of technical and biologic limitations that must be understood when guiding radiation treatment.

Conclusion

For PET guided radiation planning to be successful, collaboration between radiation oncologists, nuclear medicine physicians, and medical physics is essential, as well as the development and adherence to strict PET-radiation planning protocols. When performed properly, PET-based radiation planning can reduce treatment volumes, reduce treatment variability, improve patient and target selection, and potentially enhance the therapeutic ratio accessing precision medicine in radiation therapy.

Distinguishing Progression from Pseudoprogression in Glioblastoma Using 18F-Fluciclovine PET

Rationale: Accurate differentiation between tumor progression (TP) and pseudoprogression remains a critical unmet need in neuro-oncology. ¹⁸F-fluciclovine is a widely available synthetic amino acid PET radiotracer. In this study, we aimed to assess the value of ¹⁸F-fluciclovine PET for differentiating pseudoprogression from TP in a prospective cohort of patients with suspected radiographic recurrence of glioblastoma. Methods: We enrolled 30 glioblastoma patients with radiographic progression after first-line chemoradiotherapy who were planned for surgical resection. Patients underwent pre-operative ¹⁸F-fluciclovine PET and MRI. Relative percentages of viable tumor and therapy-related changes observed in histopathology were quantified and categorized as TP (≥50% viable tumor), mixed TP (<50% and >10% viable tumor), or pseudoprogression (≤10% viable tumor). Results: Eighteen patients had TP, 4 mixed TP, and 8 pseudoprogression. Patients with TP/mixed TP had significantly higher 40-50 minutes SUV_max (6.64+ 1.88 vs 4.11± 1.52, P = 0.009) compared to patients with pseudoprogression. A 40-50 minutes SUV_max cut-off of 4.66 provided 90% sensitivity and 83% specificity for differentiation of TP/mixed TP from pseudoprogression (Area under the curve (AUC)=0.86). Relative cerebral blood volume (rCBVmax) cut-off 3.672 provided 90% sensitivity and 71% specificity for differentiation of TP/mixed TP from Pseudoprogression (AUC=0.779). Combining a 40-50 minutes SUV_max cut-off of 4.66 and a rCBVmax cut-off of 3.67 on MRI provided 100% sensitivity and 80% specificity for differentiating TP/mixed TP from Pseudoprogression (AUC=0.95). Conclusion: ¹⁸F-fluciclovine PET uptake can accurately differentiate pseudoprogression from TP in glioblastoma, with even greater accuracy when combined with multi-parametric MRI. Given the wide availability of ¹⁸F-fluciclovine, larger, multicenter studies are warranted to determine whether amino acid PET with ¹⁸F-fluciclovine should be used in the routine assessment of post-treatment glioblastoma.

Total-body PET: a new paradigm for molecular imaging

Total body (TB) positron emission tomography (PET) instruments have dramatically changed the paradigm of PET clinical and research studies due to their very high sensitivity and capability to image dynamic radiopharmaceutical distributions in the major organs of the body simultaneously. In this manuscript, we review the design of these systems and discuss general challenges and trade-offs to maximize the performance gains of current TB-PET systems. We then describe new concepts and technology that may impact future TB-PET systems. The manuscript summarizes what has been learned from the initial sites with TB-PET and explores potential research and clinical applications of TB-PET. The current generation of TB-PET systems range in axial field-of-view (AFOV) from 1 to 2 m and serve to illustrate the benefits and opportunities of a longer AFOV for various applications in PET. In only a few years of use these new TB-PET systems have shown that they will play an important role in expanding the field of molecular imaging and benefiting clinical practice.

[18F]FluorThanatrace ([18F]FTT) PET Imaging of PARP-inhibitor Drug-Target Engagement as a Biomarker of Response in Ovarian Cancer, a pilot study

Purpose: Poly(ADP-ribose) polymerase enzyme inhibitors (PARPi) have become the standard-of-care treatment for homologous recombination deficient (HRD) high-grade serous ovarian cancer (HGSOC). However, not all HRD tumors respond to PARPi. Biomarkers to predict response are needed. [18F]FluorThanatrace ([18F]FTT) is a PARPi-analog PET radiotracer that non-invasively measures PARP-1 expression. Herein, we evaluate [18F]FTT as a biomarker to predict response to PARPi in patient-derived xenograft (PDX) models and subjects with HRD HGSOC. Methods: In PDX models, [18F]FTT-PET was performed before and after PARPi (olaparib), ataxia-telangiectasia inhibitor (ATRi), or both (PARPi-ATRi). Changes in [18F]FTT were correlated with tumor volume changes. Subjects were imaged with [18F]FTT-PET at baseline and after ~1 week of PARPi. Changes in [18F]FTT-PET uptake were compared to changes in tumor size (RECIST1.1), CA-125, and progression-free survival (PFS). Results: A decrease in [18F]FTT tumor uptake after PARPi correlated with response to PARPi, or PARPi-ATRi treatment in PARPi-resistant PDX models (r=0.77-0.81). In subjects (n=11), percent difference in [18F]FTT-PET after ~7 days of PARPi compared to baseline correlated with best RECIST response (P=0.01), best CA-125 response (P=0.033), and PFS (P=0.027). All subjects with &gt;50% reduction in [18F]FTT uptake had &gt;6-month PFS and &gt;50% reduction in CA-125. Utilizing only baseline [18F]FTT uptake did not predict such responses. Conclusions: The decline in [18F]FTT uptake shortly after PARPi initiation provides a measure of drug-target engagement and shows promise as a biomarker to guide PARPi therapies in this pilot study. These results support additional pre-clinical mechanistic and clinical studies in subjects receiving PARPi +/- combination therapy.

NIMG-45. DISTINGUISHING PROGRESSION FROM PSEUDOPROGRESSION IN GLIOBLASTOMA: COMBINED USE OF 18F-FLUCICLOVINE PET AND MULTI-PARAMETRIC MRI

PURPOSE

Differentiation of tumor progression (TP) from pseudoprogression (PsP) is a major unmet need in post-treatment glioblastoma (GBM). 18F-Fluciclovine is a synthetic amino acid PET radiotracer with higher uptake in tumor tissue vs. areas of treatment-related change. We investigated the value of 18F-Fluciclovine PET for differentiating PsP from TP independent from and in combination with multi-parametric MRI.

METHODS

We prospectively enrolled 30 patients with GBM with a new or enlarging contrast-enhancing lesion on MRI after chemoradiotherapy who were planned for surgical resection of the lesion. Patients underwent pre-operative 18F-Fluciclovine PET and multi-parametric MRI. Following surgery, the relative percentages of viable tumor and therapy-related changes observed in histopathology were quantified. Patients were categorized as TP if viable tumor represented ≥ 50% of the specimen, mixed TP if &lt; 50% and &gt; 10%, and PsP if ≤ 10%.

RESULTS

18 patients had TP, 4 had mixed TP, and 8 PsP. Patients with TP/mixed TP had a significantly higher 40-50 minutes SUVmax (6.64 + 1.88 vs 4.11± 1.52, p=0.009) and an SUVmax cut-off of 4.66 provided 90% sensitivity and 83% specificity for differentiation of TP/mixed TP from PsP (AUC=0.856). A maximum cerebral blood volume (CBVmax) cut-off of 3.67 provided 90% sensitivity and 71% specificity for differentiation of TP/mixed TP from PsP (AUC=0.779). Combining a 40-50 minutes SUVmax cut-off of 4.662 and a relative CBVmax cut-off of 3.67 provided 100% sensitivity and 80% specificity for differentiating TP/mixed TP from PsP (AUC=0.95). The time activity curve patterns and time to peaks were not different between the groups. Normalization of PET parameters to normal brain parenchyma were not helpful to differentiate the groups due to variability in radiotracer uptake in normal brain between subjects.

CONCLUSION

18F-Fluciclovine PET uptake can accurately differentiate PsP from TP in GBM patients, with even more accurate differentiation achieved when combined with MRI.

Perfusion-only imaging in pregnant women: A comparative reader study with implications for practice patterns

This study seeks to understand the value of ventilation imaging in pregnant patients imaged for suspected pulmonary embolism (PE). Ventilation-perfusion (VQ) scans in this high-risk population were compared to ventilation-only scans. We hypothesize that in this relatively healthy population, the exclusion of ventilation scans will not impact the rate of scans interpreted as positive. This retrospective blinded comparative reader study on collated VQ scans performed on pregnant patients in the course of routine clinical care in a > 5 year period (03/2012 to 07/2017). Each set of VQ and perfusion only (Q) studies were reviewed by 8 readers (4 nuclear radiology fellows and 4 nuclear medicine faculty) in random order; the Q scans simply omitted the ventilation images. Readers recorded each study as PE, no PE, or non-diagnostic (prospective investigative study of acute PE diagnosis classifications). Logistic mixed effects models were used to test the association between scan type (VQ vs Q). 203 pairs of studies in 197 patients were included (6 patients had 2 scans). Subjects ranged from 14 to 45 years of age, with a median 28 years. A significant association between scan type and positive/negative classification. Q-scans received more positive classifications than VQ-scans (median of 7.6% vs 6.7%). No association was seen between scan type and positive/indeterminate classification, nor between scan type and negative/indeterminate classification. The exclusion of ventilation images in VQ-scans was associated with a higher rate of positive studies, but this difference was small (<1%). Given the overwhelmingly normal percentage of Q-exams (>90% in our study), and the benefits of omitting ventilation imaging, perfusion-only imaging should be considered a reasonable option for imaging the pregnant patient to exclude PE.

JNMT continuing education: 177Lu PSMA therapy

Radiopharmaceutical therapy utilizing ¹⁷⁷Lu-PSMA is an effective treatment for prostate cancer which has recently been approved by the United States Food and Drug Administration. This method leverages the success of PSMA targeted PET imaging, enabling the delivery of targeted radiopharmaceutical therapy, This agent has demonstrated a clear benefit in large prospective clinical trials, and promises to become part of the standard armamentarium of treatment for patients with prostate cancer. In this review, the evidence supporting the use of this agent is highlighted, along with important areas now under investigation. Practical information on technology aspects, dose administration, nursing, and the role of the treating physician is highlighted. Overall, ¹⁷⁷Lu-PSMA treatment requires close collaboration between referring physicians, nuclear medicine, technologists, radiopharmacy, and nursing, to enable streamlined patient care.

Abbreviated scan protocols to capture 18F-FDG kinetics for long axial FOV PET scanners

PURPOSE

Kinetic parameters from dynamic 18F-fluorodeoxyglucose (FDG) imaging offer complementary insights to the study of disease compared to static clinical imaging. However, dynamic imaging protocols are cumbersome due to the long acquisition time. Long axial field-of-view (LAFOV) PET scanners (> 70 cm) have two advantages for dynamic imaging over clinical PET scanners with a standard axial field-of-view (SAFOV; 16-30 cm). The large axial coverage enables multi-organ dynamic imaging in a single bed position, and the high sensitivity may enable clinically routine abbreviated dynamic imaging protocols.

METHODS

In this work, we studied two abbreviated protocols using data from a 65-min dynamic 18F-FDG scan: (A) dynamic imaging immediately post-injection (p.i.) for variable durations, and (B) dynamic imaging immediately p.i. for variable durations plus a 1-h p.i. (5-min-long) datapoint. Nine cancer patients were imaged on the Biograph Vision Quadra (Siemens Healthineers). Time-activity curves over the lesions (N = 39) were fitted using the Patlak graphical analysis and a 2-tissue-compartment (2C, k4 = 0) model for variable scan durations (5-60 min). Kinetic parameters from the complete dataset served as the reference. Lesions from all cancers were grouped into low, medium, and high flux groups, and bias and precision of Ki (Patlak) and Ki, K1, k2, and k3 (2C) were calculated for each group.

RESULTS

Using only early dynamic data with the 2C (or Patlak) model, accurate quantification of Ki required at least 50 (or 55) min of dynamic data for low flux lesions, at least 30 (or 40) min for medium flux lesions, and at least 15 (or 20) min for high flux lesions to achieve both 10% bias and precision. The addition of the final (5-min) datapoint allowed for accurate quantification of Ki with a bias and precision of 10% using only 10-15 min of early dynamic data for either model.

CONCLUSION

Dynamic imaging for 10-15 min immediately p.i. followed by a 5-min scan at 1-h p.i can accurately and precisely quantify 18F-FDG on a long axial FOV scanner, potentially allowing for more widespread use of dynamic 18F-FDG imaging.

Novel applications of molecular imaging to guide breast cancer therapy

The goals of precision oncology are to provide targeted drug therapy based on each individual’s specific tumor biology, and to enable the prediction and early assessment of treatment response to allow treatment modification when necessary. Thus, precision oncology aims to maximize treatment success while minimizing the side effects of inadequate or suboptimal therapies. Molecular imaging, through noninvasive assessment of clinically relevant tumor biomarkers across the entire disease burden, has the potential to revolutionize clinical oncology, including breast oncology. In this article, we review breast cancer positron emission tomography (PET) imaging biomarkers for providing early response assessment and predicting treatment outcomes. For 2-¹⁸fluoro-2-deoxy-D-glucose (FDG), a marker of cellular glucose metabolism that is well established for staging multiple types of malignancies including breast cancer, we highlight novel applications for early response assessment. We then review current and future applications of novel PET biomarkers for imaging the steroid receptors, including the estrogen and progesterone receptors, the HER2 receptor, cellular proliferation, and amino acid metabolism.

Principles of Tracer Kinetic Analysis in Oncology, Part II: Examples and Future Directions

Learning Objectives: On successful completion of this activity, participants should be able to (1) describe examples of the application of PET tracer kinetic analysis to oncology; (2) list applications research and possible clinical applications in oncology where kinetic analysis is helpful; and (3) discuss future applications of kinetic modeling to cancer research and possible clinical cancer imaging practice.Financial Disclosure: This work was supported by KL2 TR001879, R01 CA211337, R01 CA113941, R33 CA225310, Komen SAC130060, R50 CA211270, and K01 DA040023. Dr. Pantel is a consultant or advisor for Progenics and Blue Earth Diagnostics and is a meeting participant or lecturer for Blue Earth Diagnostics. Dr. Mankoff is on the scientific advisory boards of GE Healthcare, Philips Healthcare, Reflexion, and ImaginAb and is the owner of Trevarx; his wife is the chief executive officer of Trevarx. The authors of this article have indicated no other relevant relationships that could be perceived as a real or apparent conflict of interest.CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credits. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, SAM, and other credit types, participants can access this activity through the SNMMI website (http://www.snmmilearningcenter.org) through April 2025.Kinetic analysis of dynamic PET imaging enables the estimation of biologic processes relevant to disease. Through mathematic analysis of the interactions of a radiotracer with tissue, information can be gleaned from PET imaging beyond static uptake measures. Part I of this 2-part continuing education paper reviewed the underlying principles and methodology of kinetic modeling. In this second part, the benefits of kinetic modeling for oncologic imaging are illustrated through representative case examples that demonstrate the principles and benefits of kinetic analysis in oncology. Examples of the model types discussed in part I are reviewed here: a 1-tissue-compartment model (15O-water), an irreversible 2-tissue-compartment model (18F-FDG), and a reversible 2-tissue-compartment model (3'-deoxy-3'-18F-fluorothymidine). Kinetic approaches are contrasted with static uptake measures typically used in the clinic. Overall, this 2-part review provides the reader with background in kinetic analysis to understand related research and improve the interpretation of clinical nuclear medicine studies with a focus on oncologic imaging.

Principles of Tracer Kinetic Analysis in Oncology, Part I: Principles and Overview of Methodology

Learning Objectives: On successful completion of this activity, participants should be able to describe (1) describe principles of PET tracer kinetic analysis for oncologic applications; (2) list methods used for PET kinetic analysis for oncology; and (3) discuss application of kinetic modeling for cancer-specific diagnostic needs.Financial Disclosure: This work was supported by KL2 TR001879, R01 CA211337, R01 CA113941, R33 CA225310, Komen SAC130060, R50 CA211270, and K01 DA040023. Dr. Pantel is a consultant or advisor for Progenics and Blue Earth Diagnostics and is a meeting participant or lecturer for Blue Earth Diagnostics. Dr. Mankoff is on the scientific advisory boards of GE Healthcare, Philips Healthcare, Reflexion, and ImaginAb and is the owner of Trevarx; his wife is the chief executive officer of Trevarx. The authors of this article have indicated no other relevant relationships that could be perceived as a real or apparent conflict of interest.CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credits. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, SAM, and other credit types, participants can access this activity through the SNMMI website (http://www.snmmilearningcenter.org) through March 2025PET enables noninvasive imaging of regional in vivo cancer biology. By engineering a radiotracer to target specific biologic processes of relevance to cancer (e.g., cancer metabolism, blood flow, proliferation, and tumor receptor expression or ligand binding), PET can detect cancer spread, characterize the cancer phenotype, and assess its response to treatment. For example, imaging of glucose metabolism using the radiolabeled glucose analog ¹⁸F-FDG has widespread applications to all 3 of these tasks and plays an important role in cancer care. However, the current clinical practice of imaging at a single time point remote from tracer injection (i.e., static imaging) does not use all the information that PET cancer imaging can provide, especially to address questions beyond cancer detection. Reliance on tracer measures obtained only from static imaging may also lead to misleading results. In this 2-part continuing education paper, we describe the principles of tracer kinetic analysis for oncologic PET (part 1), followed by examples of specific implementations of kinetic analysis for cancer PET imaging that highlight the added benefits over static imaging (part 2). This review is designed to introduce nuclear medicine clinicians to basic concepts of kinetic analysis in oncologic imaging, with a goal of illustrating how kinetic analysis can augment our understanding of in vivo cancer biology, improve our approach to clinical decision making, and guide the interpretation of quantitative measures derived from static images.

Evolving Bilateral Hypermetabolic Axillary Lymphadenopathy on FDG PET/CT Following 2-Dose COVID-19 Vaccination

ABSTRACT

A 50-year-old woman with stage IV sigmoid adenocarcinoma presented for restaging FDG PET/CT status post neoadjuvant chemotherapy/immunotherapy and diverting sigmoid colostomy. FDG PET/CT demonstrated FDG uptake in the known sigmoid mass and in abdominopelvic lymph node metastases. Bilateral, asymmetric, hypermetabolic axillary lymphadenopathy was also observed, an atypical pattern of spread for colon cancer. Further investigation revealed the patient had received both doses of COVID-19 vaccine in the 2 months prior to presentation. The authors discuss immunogenic nodal hypermetabolism following vaccination against COVID-19 and incorporating vaccination history to aid in PET/CT interpretation, especially in malignancies involving the axillae.

18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Following Chimeric Antigen Receptor T-cell Therapy in Large B-cell Lymphoma

PURPOSE

18F-Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) is a well-established imaging modality to assess responses in patients with B-cell neoplasms. However, there is limited information about the utility of FDG PET/CT after chimeric antigen receptor T-cell (CART) therapies for large B-cell lymphomas. In this retrospective analysis, we aimed to evaluate how FDG PET/CT performs in patients receiving commercially available anti-CD19 CART therapies for relapsed/refractory (r/r) large B-cell lymphomas. In addition, we examined the time to repeat scan and the rate of pseudoprogression within this population. Lastly, the rates of radiographic response to CART therapy using FDG PET/CT are reported.

PROCEDURES

The pre-treatment and post-treatment scans were analyzed from a selected cohort of 43 patients from a single institution. Patients were stratified by diagnosis of either a first occurrence of diffuse large B-cell lymphoma: de novo diffuse large B-cell lymphoma (DLBCL); or a transformed diffuse large B-cell lymphoma arising from indolent non-Hodgkin lymphoma (t-iNHL).

RESULTS

More patients received CART therapy for DLBCL than t-iNHL (65 % vs 35 %). FDG PET/CT had a 99 % sensitivity and 100 % specificity for detecting recurrent disease in this group. The median time to initial response assessment was 86 days (IQR 79-91; full range 24-146) after infusion. There were no biopsy-proven cases of pseudoprogression identified. In this selected group of patients, the overall response rate by Lugano 2014 criteria was 56 %. All patients with a partial response (N = 6) eventually progressed despite additional therapy.

CONCLUSIONS

Due to its excellent test characteristics and ability to detect asymptomatic disease, routine surveillance with PET/CT at 3 months after CART infusion is supported by our data. Earlier PET/CT may be of value in select situations as we did not find any cases of pseudoprogression.

Combined Quantification of 18F-FDG and 68Ga-DOTATATE PET/CT for Prognosis in High-Grade Gastroenteropancreatic Neuroendocrine Neoplasms

RATIONALE AND OBJECTIVES

High-grade gastroenteropancreatic neuroendocrine neoplasms (G3 GEP-NENs) are pathologically classified into well differentiated neuroendocrine tumors (G3 NETs) and poorly differentiated neuroendocrine carcinomas (G3 NECs). Using a novel parameter, we examined the prognostic value of ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/CT quantification in comparison to pathologic assessment in G3 GEP-NENs.

MATERIALS AND METHODS

A total of 31 patients with G3 GEP-NENs were reviewed. For each patient, the SUVmax on ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/CT were used to calculate the FDG-DOTATATE-Z (FDZ) score: a continuous parameter that increases with ⁶⁸Ga-DOTATATE uptake and decreases with ¹⁸F-FDG uptake. The variation in the FDZ score with respect to pathologic variables was examined. Kaplan-Meier and Cox regression analyses were performed to evaluate the effect of FDZ score on overall survival. An external cohort of 21 patients was used for validation.

RESULTS

The FDZ score was significantly higher in G3 NETs compared to G3 NECs (p<0.001), and was inversely correlated with Ki67 index (R²=0.33, p<0.001). Patients in the FDZ>0.05 group showed significantly longer survival compared to those in the FDZ≤0.05 group, with median of 34.9 vs. 12.0 months (p<0.001). On univariate regression, FDZ>0.05 (p=0.005), well differentiated disease (p=0.044), and lower Ki67 index (p=0.042) were predictors of survival. On multivariate regression, only FDZ>0.05 could independently predict longer survival with HR=0.16 (p=0.018), which was reproduced in the external validation cohort.

CONCLUSION

Combined quantification of ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/CT into a novel parameter, the FDZ score, reflects the pathologic characteristics of G3 GEP-NENs and is a prognostic indicator of overall survival independent of differentiation.

PSMA-targeted imaging with 18F-DCFPyL-PET/CT in patients (pts) withbiochemically recurrent prostate cancer (PCa): A phase 3 study (CONDOR)—A subanalysis of correct localization rate (CLR) and positive predictive value (PPV) by standard of truth

5023

Background: PSMA-targeted PET/CT is superior to conventional imaging modalities to localize biochemically recurrent (BCR) PCa after local therapy, particularly in pts with low PSA ( < 2 ng/mL). However, few studies have reported PSMA-targeted PET/CT accuracy compared to a pre-specified rigorous standard of truth (SOT) including histopathology, correlative imaging or treatment response in this population. Here, we report the CLR and PPV of PSMA-targeted 18F-DCFPyLPET/ CT, for each of the pre-defined SOT criteria for the CONDOR prospective phase 3 study. Methods: The study enrolled men with rising PSA after definitive therapy and negative or equivocal standard of care imaging (e.g., CT/MRI, bone scintigraphy, F-18 fluciclovine). A single 9 mCi (333 MBq) ± 20% dose of 18F-DCFPyL was injected, followed by PET/CT 1-2 hours later. Pts with positive 18F-DCFPyL-PET/CT scans based on local interpretation were scheduled for follow up within 60 days to verify suspected lesion(s) using a composite SOT. The primary endpoint was CLR defined as PPV with the requirement of anatomic lesion co-localization between 18F-DCFPyL-PET/CT and the SOT. The SOT consisted of, in descending priority: 1) histopathology, 2) subsequent correlative imaging findings determined by twocentral readers, or 3) post-radiation PSA response. The trial was successful if the lower bound of the 95% confidence interval for CLR exceeded 20% for at least two of three independent, blinded central 18F-DCFPyL-PET/CT reviewers. Results: 208 men (median PSA 0.8 ng/mL) underwent 18F-DCFPyL-PET/CT and the study achieved its primary endpoint: CLR was between 84.8% to 87.0% (lower bound of 95% CI: 77.8%-80.4%) among the three 18F-DCFPyL-PET/CT readers, against the composite SOT. The performance of 18F-DCFPyL-PET/CT by CLR (≥1 lesion co-localized) and PPV (≥1 lesion confirmed) was maintained through all 3 SOT categories. Histopathology (N = 31): 78.6-82.8% and 92.9-93.3% for CLR and PPV, respectively; correlative imaging (N = 100): 86.1-88.6% and 87.0-89.5% for CLR and PPV, respectively; and PSA response (N = 1): 100% for both CLR and PPV. Further analyses of the correlative imaging results showed CLR remained high across the different modalities used a) 18F-fluciclovine-PET/CT (N = 71): (86.8-90.9%); b) MRI (N = 23): (80.0-86.7%); and c) CT (n = 6): (80.0-100%). Conclusions: PSMA-targeted 18F-DCFPyL-PET/CT detected and localized metastatic lesions with high CLR and PPV regardless of which criterion defined CLR that was used, in men with BCR who had negative or equivocal baseline imaging. Clinicaltrials.gov: NCT03739684 Clinical trial information: NCT03739684.

In vivo visualization of PARP inhibitor pharmacodynamics

BACKGROUND

[¹⁸F]FluorThanatrace ([¹⁸F]FTT) is a radiolabeled poly (adenosine diphosphate-ribose) polymerase inhibitor (PARPi) that enables noninvasive quantification of PARP with potential to serve as a biomarker for patient selection for PARPi therapy. Here we report for the first time to our knowledge noninvasive in vivo visualization of drug-target engagement during PARPi treatment.

METHODS

Two single-arm, prospective, nonrandomized clinical trials were conducted at the University of Pennsylvania from May 2017 to March 2020. PARP expression in breast cancer was assessed in vivo via [¹⁸F]FTT PET before and after initiation of PARPi treatment and in vitro via [¹²⁵I]KX1 (an analog of [¹⁸F]FTT) binding to surgically removed breast cancer.

RESULTS

Thirteen patients had baseline [¹⁸F]FTT PET. Nine of these then had resection and in vitro evaluation of [¹⁸F]FTT uptake with an analog and uptake was blocked with PARPi. Of the other 4 patients, 3 had [¹⁸F]FTT PET uptake, and all had uptake blocked with treatment with a therapeutic PARPi. Initial in vivo [¹⁸F]FTT tumor uptake ranged from undetectable to robust. Following initiation of PARPi therapy, [¹⁸F]FTT uptake was not detectable above background in all cases. In vitro tumor treatment with a PARPi resulted in 82% reduction in [¹²⁵I]KX1 binding.

CONCLUSION

[¹⁸F]FTT noninvasively quantifies PARP-1 expression. Early results indicate ability to visualize PARPi drug-target engagement in vivo and suggest the utility of further study to test [¹⁸F]FTT PET as a predictive and pharmacodynamic biomarker.

TRIAL REGISTRATION

ClinicalTrials.gov identifiers NCT03083288 and NCT03846167.

FUNDING

Metavivor Translational Research Award, Susan G. Komen for the Cure (CCR 16376362), Department of Defense BC190315, and Abramson Cancer Center Breakthrough Bike Challenge.

Human PARP inhibitor drug-target engagement can be visualized, with future possibilities including a precision diagnostic and drug discovery tool.

Kinetic and Static Analysis of Poly-(Adenosine Diphosphate-Ribose) Polymerase-1-Targeted 18F-Fluorthanatrace PET Images of Ovarian Cancer

The poly-(adenosine diphosphate-ribose) polymerase (PARP) family of proteins participates in numerous functions, most notably the DNA damage response. Cancer vulnerability to DNA damage has led to development of several PARP inhibitors (PARPi). This class of drugs has demonstrated therapeutic efficacy in ovarian, breast, and prostate cancers, but with variable response. Consequently, clinics need to select patients likely to benefit from these targeted therapies. In vivo imaging of ¹⁸F-fluorthanatrace uptake has been shown to correspond to PARP-1 expression in tissue. This study characterized the pharmacokinetics of ¹⁸F-fluorthanatrace and tested kinetic and static models to guide metric selection in future studies assessing ¹⁸F-fluorthanatrace as a biomarker of response to PARPi therapy. Methods: Fourteen prospectively enrolled ovarian cancer patients were injected with ¹⁸F-fluorthanatrace and imaged dynamically for 60 min after injection followed by up to 2 whole-body scans, with venous blood activity and metabolite measurements. SUV_max and SUV_peak were extracted from dynamic images and whole-body scans. Kinetic parameter estimates and SUVs were assessed for correlations with tissue PARP-1 immunofluorescence (n = 7). Simulations of population kinetic parameters enabled estimation of measurement bias and precision in parameter estimates. Results: ¹⁸F-fluorthanatrace blood clearance was variable, but labeled metabolite profiles were similar across patients, supporting use of a population parent fraction curve. The total distribution volume from a reversible 2-tissue-compartment model and Logan reference tissue distribution volume ratio (DVR) from the first hour of PET acquisition correlated with tumor PARP-1 expression by immunofluorescence (r = 0.76 and 0.83, respectively; P < 0.05). DVR bias and precision estimates were 6.4% and 29.1%, respectively. SUV_max and SUV_peak acquired from images with midpoints of 57.5, 110 ± 3, and 199 ± 4 min highly correlated with PARP-1 expression (mean ± SD, r ≥ 0.79; P < 0.05). Conclusion: Tumor SUV_max and SUV_peak at 55-60 min after injection and later and DVR from at least 60 min appear to be robust noninvasive measures of PARP-1 binding. ¹⁸F-fluorthanatrace uptake in ovarian cancer was best described by models of reversible binding. However, pharmacokinetic patterns of tracer uptake were somewhat variable, especially at later time points.

Functional 4-D clustering for characterizing intratumor heterogeneity in dynamic imaging: evaluation in FDG PET as a prognostic biomarker for breast cancer

Purpose

Probe-based dynamic (4-D) imaging modalities capture breast intratumor heterogeneity both spatially and kinetically. Characterizing heterogeneity through tumor sub-populations with distinct functional behavior may elucidate tumor biology to improve targeted therapy specificity and enable precision clinical decision making.

Methods

We propose an unsupervised clustering algorithm for 4-D imaging that integrates Markov-Random Field (MRF) image segmentation with time-series analysis to characterize kinetic intratumor heterogeneity. We applied this to dynamic FDG PET scans by identifying distinct time-activity curve (TAC) profiles with spatial proximity constraints. We first evaluated algorithm performance using simulated dynamic data. We then applied our algorithm to a dataset of 50 women with locally advanced breast cancer imaged by dynamic FDG PET prior to treatment and followed to monitor for disease recurrence. A functional tumor heterogeneity (FTH) signature was then extracted from functionally distinct sub-regions within each tumor. Cross-validated time-to-event analysis was performed to assess the prognostic value of FTH signatures compared to established histopathological and kinetic prognostic markers.

Results

Adding FTH signatures to a baseline model of known predictors of disease recurrence and established FDG PET uptake and kinetic markers improved the concordance statistic (C-statistic) from 0.59 to 0.74 (p = 0.005). Unsupervised hierarchical clustering of the FTH signatures identified two significant (p < 0.001) phenotypes of tumor heterogeneity corresponding to high and low FTH. Distributions of FDG flux, or Ki, were significantly different (p = 0.04) across the two phenotypes.

Conclusions

Our findings suggest that imaging markers of FTH add independent value beyond standard PET imaging metrics in predicting recurrence-free survival in breast cancer and thus merit further study.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05265-8.

18F-Fluciclovine PET/CT in Therapeutic Decision Making for Prostate Cancer: A Large Single-Center Practice-Based Analysis

METHODS

We carried out a retrospective cohort study of patients with BR after primary treatment of PC who received imaging with 18F-fluciclovine PET/CT at our institution between January 2010 and January 2019. PET/CT results were compared with biopsy, conventional imaging results, and/or response to PC therapy. 18F-Fluciclovine PET/CT performance statistics and effects on treatment planning were calculated.

RESULTS

A total of 328 patients with a median age of 71 years (range, 47-90 years) and median serum prostate-specific antigen level of 1.6 ng/mL (0.02-186.7 ng/mL) were included. Three hundred thirty-six 18F-fluciclovine PET/CT scans were analyzed and classified as positive (65%), negative (25%), or equivocal (10%) based on radiology reports. Sensitivity was 93% (95% confidence interval, 86%-96%) and specificity was 63% (95% confidence interval, 45%-77%). Of patients with known management recommendations post-PET/CT, scan results changed or influenced pre-PET/CT management plans in 73%, and 58% of recommendations involved treatment modality decisions. Overall, 82% of patients' actual management was concordant with post-PET/CT recommendations. Of evaluable patients, 116 (35%) had some form of post-PET radiotherapy included in their care plans, with 95% receiving radiotherapy at a PET-avid target.

CONCLUSIONS

In the largest single-institutional cohort to date, 18F-fluciclovine PET/CT showed value in the workup of PC in the setting of BR, with noteworthy influence over clinical management decisions. Further studies are needed to evaluate whether PET/CT-based changes in management are associated with improved outcomes.

Diagnostic Performance of 18F-DCFPyL-PET/CT in Men with Biochemically Recurrent Prostate Cancer: Results from the CONDOR Phase III, Multicenter Study

PURPOSE

Current FDA-approved imaging modalities are inadequate for localizing prostate cancer biochemical recurrence (BCR). ¹⁸F-DCFPyL is a highly selective, small-molecule prostate-specific membrane antigen-targeted PET radiotracer. CONDOR was a prospective study designed to determine the performance of ¹⁸F-DCFPyL-PET/CT in patients with BCR and uninformative standard imaging.

EXPERIMENTAL DESIGN

Men with rising PSA ≥0.2 ng/mL after prostatectomy or ≥2 ng/mL above nadir after radiotherapy were eligible. The primary endpoint was correct localization rate (CLR), defined as positive predictive value with an additional requirement of anatomic lesion colocalization between ¹⁸F-DCFPyL-PET/CT and a composite standard of truth (SOT). The SOT consisted of, in descending priority (i) histopathology, (ii) subsequent correlative imaging findings, or (iii) post-radiation PSA response. The trial was considered a success if the lower bound of the 95% confidence interval (CI) for CLR exceeded 20% for two of three ¹⁸F-DCFPyL-PET/CT readers. Secondary endpoints included change in intended management and safety.

RESULTS

A total of 208 men with a median baseline PSA of 0.8 ng/mL (range: 0.2-98.4 ng/mL) underwent ¹⁸F-DCFPyL-PET/CT. The CLR was 84.8%-87.0% (lower bound of 95% CI: 77.8-80.4). A total of 63.9% of evaluable patients had a change in intended management after ¹⁸F-DCFPyL-PET/CT. The disease detection rate was 59% to 66% (at least one lesion detected per patient by ¹⁸F-DCFPyL-PET/CT by central readers).

CONCLUSIONS

Performance of ¹⁸F-DCFPyL-PET/CT achieved the study's primary endpoint, demonstrating disease localization in the setting of negative standard imaging and providing clinically meaningful and actionable information. These data further support the utility of ¹⁸F-DCFPyL-PET/CT to localize disease in men with recurrent prostate cancer.See related commentary by True and Chen, p. 3512.

PSMA-targeted imaging with 18F-DCFPyL-PET/CT in patients (pts) with biochemically recurrent prostate cancer (PCa): A phase III study (CONDOR)—A subanalysis of correct localization rate (CLR) and positive predictive value (PPV) by standard of truth

33

Background: PSMA-targeted PET/CT is superior to conventional imaging modalities to localize biochemically recurrent (BCR) PCa after local therapy, particularly in pts with low PSA (<2 ng/mL). However, few studies have reported PSMA-targeted PET/CT accuracy compared to a pre-specified rigorous standard of truth (SOT) including histopathology, correlative imaging or treatment response in this population. Here, we report the CLR and PPV of PSMA-targeted 18F-DCFPyL-PET/CT, for each of the pre-defined SOT criteria for the CONDOR prospective phase 3 study. Methods: The study enrolled men with rising PSA after definitive therapy and negative or equivocal standard of care imaging (e.g., CT/MRI, bone scintigraphy, F-18 fluciclovine). A single 9 mCi (333 MBq) ± 20% dose of 18F-DCFPyL was injected, followed by PET/CT 1-2 hours later. Pts with positive 18F-DCFPyL-PET/CT scans based on local interpretation were scheduled for follow up within 60 days to verify suspected lesion(s) using a composite SOT. The primary endpoint was CLR defined as PPV with the requirement of anatomic lesion co-localization between 18F-DCFPyL-PET/CT and the SOT. The SOT consisted of, in descending priority: 1) histopathology, 2) subsequent correlative imaging findings determined by two central readers, or 3) post-radiation PSA response. The trial was successful if the lower bound of the 95% confidence interval for CLR exceeded 20% for at least two of three independent, blinded central 18F-DCFPyL-PET/CT reviewers. Results: 208 men (median PSA 0.8 ng/mL) underwent 18F-DCFPyL-PET/CT and the study achieved its primary endpoint: CLR was between 84.8% to 87.0% (lower bound of 95% CI: 77.8%-80.4%) among the three 18F-DCFPyL-PET/CT readers, against the composite SOT. The performance of 18F-DCFPyL-PET/CT by CLR (≥1 lesion co-localized) and PPV (≥1 lesion confirmed) was maintained through all 3 SOT categories. Histopathology (N=31): 78.6-82.8% and 92.9-93.3% for CLR and PPV, respectively; correlative imaging (N=100): 86.1-88.6% and 87.0-89.5% for CLR and PPV, respectively; and PSA response (N=1): 100% for both CLR and PPV. Further analyses of the correlative imaging results showed CLR remained high across the different modalities used a) 18F-fluciclovine-PET/CT (N=71): (86.8-90.9%); b) MRI (N=23): (80.0-86.7%); and c) CT (n=6): (80.0-100%). Conclusions: PSMA-targeted 18F-DCFPyL-PET/CT detected and localized metastatic lesions with high CLR and PPV regardless of which criterion defined CLR that was used, in men with BCR who had negative or equivocal baseline imaging. Clinical trial information: NCT03739684.

99mTc-Mebrofenin SPECT/CT in Hepatic Infarction

A 68-year-old man with hereditary hypercoagulability was referred to nuclear medicine for elevated aminotransferases after a recent living-donor liver transplant. A hepatic infarction was suspected. A Tc-mebrofenin SPECT/CT was performed and showed decreased radiotracer uptake in a wedge-shaped distribution in the anterior liver suggestive of a hepatic infarction. Subsequently, an enhanced MRI corroborated the diagnosis. Oral anticoagulation therapy was then initiated, and aminotransferases soon normalized.

Update on the PennPET Explorer: A Whole-body Imager with Scalable Axial Field-of-View

Following successful performance testing and human imaging of a prototype PennPET Explorer, the scanner has been expanded to a current axial field of view of 1.12 m. Initial studies on this instrument have demonstrated encouraging results for total-body positron emission tomography imaging. Planned studies will test the capabilities of the PennPET Explorer further and inform the design of further human imaging protocols.

Analysis of Four-Dimensional Data for Total Body PET Imaging

The high sensitivity and total-body coverage of total-body PET scanners will be valuable for a number of clinical and research applications outlined in this article.

Oncologic Applications of Long Axial Field-of-View PET/Computed Tomography

New protocols for imaging cancer have been developed to take advantage of the improved imaging capabilities of long axial field-of-view PET scanners. Both research and clinical applications have been pursued with encouraging early results. Clinical studies have demonstrated improved image quality and the ability to image with less injected activity or for shorter duration. With the increased sensitivity inherent in total-body PET scanners and new imaging paradigms, new challenges in image interpretation have emerged. New research applications have also emerged, including dosimetry, cell tracking, and dual-tracer applications.

Kinetic Modeling of 18F-(2S,4R)4-Fluoroglutamine in Mouse Models of Breast Cancer to Estimate Glutamine Pool Size as an Indicator of Tumor Glutamine Metabolism

The PET radiotracer ¹⁸F-(2S,4R)4-fluoroglutamine (¹⁸F-Gln) reflects glutamine transport and can be used to infer glutamine metabolism. Mouse xenograft studies have demonstrated that ¹⁸F-Gln uptake correlates directly with glutamine pool size and is inversely related to glutamine metabolism through the glutaminase enzyme. To provide a framework for the analysis of ¹⁸F-Gln-PET, we have examined ¹⁸F-Gln uptake kinetics in mouse models of breast cancer at baseline and after inhibition of glutaminase. We describe results of the preclinical analysis and computer simulations with the goal of model validation and performance assessment in anticipation of human breast cancer patient studies. Methods: Triple-negative breast cancer and receptor-positive xenografts were implanted in athymic mice. PET mouse imaging was performed at baseline and after treatment with a glutaminase inhibitor or a vehicle solution for 4 mouse groups. Dynamic PET images were obtained for 1 h beginning at the time of intravenous injection of ¹⁸F-Gln. Kinetic analysis and computer simulations were performed on representative time-activity curves, testing 1- and 2-compartment models to describe kinetics. Results: Dynamic imaging for 1 h captured blood and tumor time-activity curves indicative of largely reversible uptake of ¹⁸F-Gln in tumors. Consistent with this observation, a 2-compartment model indicated a relatively low estimate of the rate constant of tracer trapping, suggesting that the 1-compartment model is preferable. Logan plot graphical analysis demonstrated late linearity, supporting reversible kinetics and modeling with a single compartment. Analysis of the mouse data and simulations suggests that estimates of glutamine pool size, specifically the distribution volume (V_D) for ¹⁸F-Gln, were more reliable using the 1-compartment reversible model than the 2-compartment irreversible model. Tumor-to-blood ratios, a more practical potential proxy of V_D, correlated well with volume of distribution from single-compartment models and Logan analyses. Conclusion: Kinetic analysis of dynamic ¹⁸F-Gln-PET images demonstrated the ability to measure V_D to estimate glutamine pool size, a key indicator of cellular glutamine metabolism, by both a 1-compartment model and Logan analysis. Changes in V_D with glutaminase inhibition support the ability to assess response to glutamine metabolism-targeted therapy. Concordance of kinetic measures with tumor-to-blood ratios provides a clinically feasible approach to human imaging.

Prospective Study of Systemic Yttrium-90 Elution during Radioembolization of Hepatic Metastases

PURPOSE

To evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (⁹⁰Y) radioembolization and differences in BR based on delivery method.

MATERIALS AND METHODS

Twenty participants with hepatic metastases undergoing first radioembolization were prospectively enrolled from December 2017 to June 2018. Blood samples were drawn at baseline and 0, 10, 20, 60, and 120 minutes after ⁹⁰Y administration. BR was measured with a γ-counter and scaled by estimated blood volume. Percentage of instilled radioactivity in the bloodstream was calculated as area under the fitted curve, and differences between delivery methods were examined with nonparametric statistical tests.

RESULTS

In 10 participants, resin microspheres were instilled with 50% Isovue 300 diluted in saline solution in the D line, and 10 others were treated with dextrose 5% in water (D5W) in the D line. Median administered activities were 944 MBq (range, 746-1,993 MBq) and 1,213 MBq (range, 519-2,066 MBq), respectively. Fraction of ⁹⁰Y in blood was significantly higher with dilute contrast agent than with D5W (median, 0.5% of injected activity vs 0.2%; P = .001). Among all participants, the maximum activity delivered was 2,066 MBq, and a maximum of 1% of administered radioactivity was measured as free ⁹⁰Y in blood. Assuming these highest-case values and complete decay of all free ⁹⁰Y in bone, a dose to red marrow of 132.3 mGy was calculated by Organ Level INternal Dose Assessment/EXponential Modeling.

CONCLUSIONS

Blood sampling after radioembolization allowed for estimation of the time-activity curve and BR. Delivery with 50% contrast agent in saline solution resulted in a significant increase in BR vs D5W, even though the total BR for both groups was nominal.

Update on Quantitative Imaging for Predicting and Assessing Response in Oncology

Molecular imaging has revolutionized clinical oncology by imaging-specific facets of cancer biology. Through noninvasive measurements of tumor physiology, targeted radiotracers can serve as biomarkers for disease characterization, prognosis, response assessment, and predicting long-term response/survival. In turn, these imaging biomarkers can be utilized to tailor therapeutic regimens to tumor biology. In this article, we review biomarker applications for response assessment and predicting long-term outcomes. ¹⁸F-fluorodeoxyglucose (FDG), a measure of cellular glucose metabolism, is discussed in the context of lymphoma and breast and lung cancer. FDG has gained widespread clinical acceptance and has been integrated into the routine clinical care of several malignancies, most notably lymphoma. The novel radiotracers 16α-¹⁸F-fluoro-17β-estradiol and ¹⁸F-fluorothymidine are reviewed in application to the early prediction of response assessment of breast cancer. Through illustrative examples, we explore current and future applications of molecular imaging biomarkers in the advancement of precision medicine.

Abbreviated Breast Magnetic Resonance Imaging for Supplemental Screening of Women With Dense Breasts and Average Risk

PURPOSE

Although mammography is the standard of care for breast cancer screening, dense breast tissue decreases mammographic sensitivity. We report the prevalent cancer detection rate (CDR) from the first clinical implementation of abbreviated breast magnetic resonance imaging (AB-MR) as a supplemental screening test in women with dense breasts.

METHODS

The study was approved by the institutional review board and is Health Insurance Portability and Accountability Act complaint. This retrospective review includes women who were imaged between January 1, 2016 and February 28, 2019. On a 1.5 Tesla magnet, the imaging protocol consisted of three sequences: Short-TI Inversion Recovery (STIR), precontrast, and postcontrast. A subtraction sequence and a maximum intensity projection were generated. We report the patient-level CDR and the positive predictive value of AB-MR examinations after negative/benign digital breast tomosynthesis (DBT).

RESULTS

Out of 511 prevalent rounds of AB-MR examinations, 36 women were excluded. The remaining 475 asymptomatic women with dense breasts had negative/benign DBT examinations before the AB-MR. There were 420 of 475 (88.4%) benign/negative examinations, 13 of 475 (2.7%) follow-up recommendations, and 42 biopsy recommendations. Thirty-nine biopsies were completed, resulting in 12/39 (30.8%) malignancies in 12 women: seven invasive carcinomas and five ductal carcinoma in situ. One additional patient was diagnosed with invasive ductal carcinoma at the time of 6-month follow-up. The CDR was 27.4 per 1,000 (13 of 475; 95% CI, 16.1 to 46.3). The size of invasive carcinomas ranged from 0.6-1.0 cm (mean, 0.5 cm). Of the seven women who underwent surgical evaluation of the axilla, zero of seven patients had positive nodes. There were no interval cancers at 1-year follow-up.

CONCLUSION

Preliminary results from clinical implementation of screening AB-MR resulted in a CDR of 27.4/1,000 at the patient level after DBT in women with dense breasts. Additional evaluation is warranted.

Quantifying bias and precision of kinetic parameter estimation on the PennPET Explorer, a long axial field-of-view scanner

Long axial field-of-view (AFOV) PET scanners allow for full-body dynamic imaging in a single bed-position at very high sensitivity. However, the benefits for kinetic parameter estimation have yet to be studied. This work uses (1) a dynamic GATE simulation of [¹⁸F]-fluorothymidine (FLT) in a modified NEMA IQ phantom and (2) a lesion embedding study of spheres in a dynamic [¹⁸F]-fluorodeoxyglucose (FDG) human subject imaged on the PennPET Explorer. Both studies were designed using published kinetic data of lung and liver cancers and modeled using two tissue compartments. Data were reconstructed at various emulated doses. Sphere time-activity curves (TACs) were measured on resulting dynamic images, and TACs were fit using a two-tissue-compartment model (k₄ ≠ 0) for the FLT study and both a two-tissue-compartment model (k₄ = 0) and Patlak graphical analysis for the FDG study to estimate flux (K_i) and delivery (K₁) parameters. Quantification of flux and K1 shows lower bias and better precision for both radiotracers on the long AFOV scanner, especially at low doses. Dynamic imaging on a long AFOV system can be achieved for a greater range of injected doses, as low as 0.5-2 mCi depending on the sphere size and flux, compared to a standard AFOV scanner, while maintaining good kinetic parameter estimation.

4D radiomic biomarker of functional tumor heterogeneity to predict breast cancer recurrence in pretreatment dynamic FDG-PET

e12573

Background: Breast cancer heterogeneity is thought to be associated with adverse outcomes. Dynamic molecular imaging modalities, including PET, permit 4-D sampling of tumor biologic properties and can therefore capture functional heterogeneity revealed by the temporal dimension of the dynamic tracer uptake. With the goal of improved non-invasive characterization of in vivo tumor biology, we have developed and tested a novel radiomic biomarker that characterizes 4-D functional tumor heterogeneity (FTH). We hypothesize subclonal populations are spatially contiguous regions of shared physiologic behavior that drive breast cancer heterogeneity and can be quantified. We describe an initial application of this approach to FDG PET imaging of breast cancer. Methods: We retrospectively analyzed data from a study of 50 patients with locally advanced breast cancer. Patients underwent 60-minute dynamic FDG PET over the chest prior to neoadjuvant chemotherapy and breast surgery and were followed for disease recurrence (DFS). A 3-D region bounding each tumor was identified by a radiologist and a novel Markov Random Field based 4-D segmentation paradigm segmented each tumor into three spatially constrained sub-regions with distinct time activity curve dynamics. From each tumor, an FTH imaging signature was extracted characterizing cluster compactness and separation. FTH imaging signatures were z-score normalized across all patients. Time-to-event analysis was used to assess the prognostic value of the FTH imaging signatures in predicting DFS. Discriminatory capacity compared to a baseline model of established prognostic factors (age, hormone receptor status, baseline tumor size) and standard PET uptake and kinetics markers (SUV, K1, and Ki) shown to be predictive of DFS (Dunnwald, J Clin Oncol 26:4449, 2008) was evaluated using the c-statistic and the log-likelihood statistical test. Results: 17 of 50 women (34%) had recurrence events. Adding FTH imaging signatures to the baseline model of age, baseline tumor size, and hormone receptor status improved a cross validated c-statistic from 0.51 to 0.74 (p < 0.05), and demonstrated higher discriminatory capacity over a model of age, tumor size, hormone receptor status, and standard PET measures (c-statistic = 0.59). Conclusions: Imaging biomarkers of 4-D metabolic tumor heterogeneity may add prognostic value in predicting recurrence-free survival in breast cancer and merit further study.

Impact of PSMA-targeted imaging with 18F-DCFPyL-PET/CT on clinical management of patients (pts) with biochemically recurrent (BCR) prostate cancer (PCa): Results from a phase III, prospective, multicenter study (CONDOR)

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Background: Current imaging modalities are inadequate for localizing and characterizing occult disease in men with BCR PCa, particularly in pts with low PSAs (<2 ng/mL). There is a need for improved diagnostic imaging to better inform treatment planning. 18F-DCFPyL (PyL) is a novel PET imaging agent that binds selectively with high affinity to PSMA, which is overexpressed in PCa cells. Methods: Men ≥18 years- with rising PSA after definitive therapy and negative or equivocal standard of care imaging (e.g., CT/MRI, bone scintigraphy) were enrolled. A single 9 mCi (333 MBq) ± 20% dose of PyL was injected, followed by PET/CT 1-2 hours later. Primary endpoint was correct localization rate (CLR), defined as percentage of pts with a 1:1 correspondence between at least one lesion identified by PyL-PET/CT and the composite standard of truth: pathology, correlative imaging, or PSA response. The trial was successful if the lower bound of the 95% confidence interval (LLCI) for CLR exceeded 20% for two of three independent, blinded central PyL-PET/CT reviewers. The secondary endpoint, impact of PyL-PET/CT on clinical management of pts was based on the treating physician’s documented clinical plans before and after PyL-PET/CT. Results: 208 men (median PSA 0.8 [0.2 - 98.4] ng/mL) underwent PyL PET/CT. The study achieved its primary endpoint: CLR of 84.8% to 87.0% among the three PyL-PET/CT readers; the LLCI for CLR by all three reviewers was >77%. Here we report the clinical impact. Based on local radiology assessment, PSMA-avid lesion(s) were identified in 69.3% (142/208) of pts. 63.9% (131/205) had a change in intended management after PyL-PET/CT, of which 78.6% (103/131) were attributable to positive PyL finding(s) and 21.4% (28/131) to negative PyL scans. Changes included: salvage local therapy to systemic therapy (n=58); observation before initiating therapy (n=49); noncurative systemic therapy to salvage local therapy (n=43); and planned treatment to observation (n=9). PyL was well tolerated with one drug-related SAE (hypersensitivity) and the most common AE being headache (n=4; 1.9%). Conclusions: PSMA-targeted PyL-PET/CT detected and localized occult disease in most men with BCR presenting with negative or equivocal conventional imaging. PyL-PET/CT led to changed management plans in the majority of pts, thus providing evidence that clinicians find PSMA PET imaging useful in men with recurrent or suspected metastatic PCa. Clinical trial information: NCT03739684 .