E1495. It’s Fun to Read the P-S-M-A! A Review of PSMA-ligand PET Imaging
  1. James Loftus; University of Rochester Medical Center
  2. David Bass; University of Rochester Medical Center
  3. Andrew Clark; University of Rochester Medical Center
  4. Jeffery Kallas; University of Rochester Medical Center
  5. Stan Weiss; University of Rochester Medical Center
  6. Vikram Dogra; University of Rochester Medical Center
Prostate cancer is the most common malignancy amongst men in the United States and is the third leading cause of cancer deaths. Multiple modalities are available for the evaluation of prostate cancer, including transrectal ultrasound, multiparametric magnetic resonance imaging (MRI), and molecular imaging techniques including planar scintigraphy, single photon computed emission tomography (SPECT), and positron emission tomography (PET). Numerous radiotracers have been applied for the assessment of prostate cancer including those not specifically targeted to prostate tissue, such as F-18 fluciclovine and C-11 and F-18 choline and those targeted to prostate tissue such as In-111 capromab pendetide and Tc99m-HYNIC-Glu-Urea-A, used in planar or SPECT imaging, and recently developed PET agents including Ga68-Prostate-Specific Membrane Antigen (PSMA)-11 and F-18 DCFPyL. Of the molecular imaging techniques, the PSMA-ligand PET agents provide the greatest spatial resolution and best target-to-background ratio with growing evidence demonstrating superior performance for the assessment of prostate cancer.

Educational Goals / Teaching Points
After reviewing the exhibit, learners will understand the physiologic distribution of PMSA-ligand radiotracers on PET. Standardized interpretation of PMSA-ligand PET will be reviewed, including rating of relative radiotracer activity, proper local staging, and assessment of lymphatic and distant metastases. Learners will be competent in identifying pathologic findings related to prostate cancer as well as common pitfalls of normal variant uptake. Additionally, depictions of nonprostate-related disease demonstrating PSMA-ligand radiotracer activity will be reviewed.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
PSMA is a transmembrane protein expressed in normal prostate cells and upregulated prostate cancer cells. Unfortunately, PSMA is also expressed in other nonprostate epithelial cells, nonprostatic neoplasms, and the endothelial cells of tumor neo-vasculature. Normal biodistribution includes radiotracer activity in the salivary glands, liver, spleen, duodenum, kidneys, and bladder. Activity is scored based on uptake, i.e., less than blood pool is none; between blood pool and liver is low; between liver and parotid gland, intermediate; and greater than parotid gland is high. The molecular imaging T staging (miT) describes no local radiotracer activity after prostatectomy or radiation therapy as miT0, elevated activity confined to the gland as miT2, extraprostatic or seminal vesicle extension as miT3, and to adjacent structures as miT4. Common pitfalls include radiotracer activity within nerve ganglia, minor salivary gland activity, and activity within nonprostate-related disease.

We describe the normal biodistribution of PSMA-ligand PET with examples of pathology related to prostate cancer from activity scoring to local staging and the evaluation of metastatic disease. Common pitfalls of normal variant uptake and nonprostate PSMA-ligand avid diseases are also reviewed.