Nuclear imaging for prostate cancer: What’s new? Dr. Debra Freeman July 25, 2017

Disclosures Employed by CyberKnife Centers of Tampa Bay Active board member of the CyberKnife Coalition (CKC) Co-director of the Registry for Prostate Cancer Radiosurgery

The basics of nuclear imaging A radioisotope is attached to an inert molecule to create a radiotracer Step 1 Radiotracer is injected into the patient Gamma rays are emitted as the radiotracer decays Step 2 Emissions are measured using a gamma detector Measurements are summed and reformatted to create visible images Step 3

Hospitals generally use two types of gamma emission detectors: Single photon emission scanner (SPECT) Positron emission tomography scanner (PET/CT)

SPE(CT) scans

Standard whole body bone scan Technetium-99 (radioisotope) is attached to methylene disphosphonate (inert molecule) to create the radiotracer Radiotracer is injected and taken up at sites of bone rebuilding (osteoblastic) activity Images are acquired using 2-D gamma camera or 3-D SPECT scanner 78-80% sensitivity for detection of bone metastases from prostate cancer

Normal scan Bone metastases

ProstaScint scan Indium-11 (radioisotope) attached to prostate specific membrane antigen (PSMA)-a prostate cell surface protein Radiotracer is absorbed primarily in soft tissues Overall accuracy of approx. 68% for detection of recurrent disease Better if fused with CT or MRI scans

ProstaScint scan CT scan Fused study

PET/CT scans

F-18 FDG-PET Fluorine-18 (radioisotope) is attached to 2-deoxy-2-fluoro-D-glucose to create radiotracer Actively dividing cells, like cancer cells, take up more glucose than normal cells False positive results: inflammation infection False negative results: slow growing tumors* small lesions (<5mm) hyperglycemia

FDG-PET for prostate cancer Limited use for detection and initial staging of primary prostate cancer More useful for detection of aggressive disease, evaluation of metastatic disease and response to therapy

18-F NaF PET bone scan Fluorine-18 (radioisotope) attached to sodium fluoride to create the radiotracer 18-F NaF is a highly sensitive radiotracer for skeletal metastases Emission data acquired with positron emission tomography (same detector as FDG-PET) More sensitive than Tc-99 bone scan for early detection of bone metastases

18-F fluciclovine (Axumin) PET scan Fluorine-18 (radioisotope) attached to an amino acid analog of L-leucine, creating the radiotracer (Axumin) Levels of many amino acids are increased within prostate cancer cells, as compared to normal tissues Gamma emissions detected using positron emission tomography (again , same scanner as FDG-PET) Axumin may be superior other radiotracers for detection of recurrent disease in the setting of PSA failure

Other radiotracers being studied for prostate cancer imaging Carbon-11 (radioisotope) attached to choline Carbon-11 attached to acetate (metabolized into acetyl-CoA) F-18 attached to fluoro-dihydrotesterone (FDHT)

The future… PET/MRI fusion scans GE and Siemens already have scanners in production Functional MRI Androgen receptor PET scans