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PET/CT Imaging New Tracer Guide

Posted on: 03.30.18

The landscape of PET/CT imaging is rapidly changing. Traditionally, physicians have used a sugar based radiopharmaceutical, 18Fluorodeoxyglucose or 18FDG, to perform the majority of PET/CT imaging. Over the past 20 years, this imaging agent was the only option available to many facilities across the United States.

Recent breakthroughs in research, reimbursement, and radiopharmaceutical manufacturing have made it so that physicians and patients will begin to have access to medicine that is designed for their unique situations.

RECENTLY APPROVED TRACERS

Prostate Cancer

Indication

Axumin (18F-Fluciclovine) is indicated for PET imaging in men with suspected prostate cancer recurrence based on elevated blood prostate specific antigen (PSA) levels following prior treatment.

Mechanism of localization

It has been found that there is an over expression of amino acid transporters in certain cancer cells. This overabundance of amino acid transporters is typically easier to identify among normal, healthy tissue than traditional imaging methods. The body recognizes this drug as an amino acid and actively transports it to potential areas of concern.

Why look into this radiopharmaceutical?

  • Axumin allows healthcare providers to pinpoint the overexpression of amino acids associated with prostate cancer.
  • Increased visualization of the prostate bed— no bladder interference during imaging, as with traditional 18FDG.
  • PET imaging with Axumin can lead to quicker detectionof tumors. Other imaging methods rely on physical (structural) changes in the body for tumor detection, whereas Axumin detects changes on the physiological (cellular) level, which can occur weeks, even months quicker than physical changes.

Prescribing information and use

  • A standard 10 mCi dose of 18F-Fluciclovine is provided
  • Patient is injected and imaged immediately
  • Exam takes less than 30 minutes from start to finish

Axumin is a great tool for visualizing the prostate bed which can be challenging using traditional methods.

 

Neuroendocrine Tumors

Indication

NETSPOT (68Ga-Dotatate) is indicated for use withPET for localization of somatostatin neureceptor positive neuroendocrine tumors (NETs) in adult and pediatric patients.

Mechanism of localization

68Ga-Dotatate binds to somatostatin receptors, with highest affinity for subtype 2 receptors (sstr2). It binds to cells that express somatostatin receptors including malignant cells, which overexpress sstr2 receptors.

Why look into this radiopharmaceutical?

Improved image quality over the traditional Gold Standard

The Gold Standard method of imaging NETs has traditionally been an Octreotide scan

  • Often times leaves physicians without answers
  • Takes up to a week to acquire the entire exam
  • Results are only qualitative

NETSPOT imaging

  • Results are conclusive
  • Improved patient satisfaction: no bowel prep needed or dietary restrictions, 3 hours to complete examination
  • Results are quantitative and qualitative

The FDA has recently approved a therapy for NETs that uses the same Dotatate as the PET imaging agent and replaces the 68Ga with 177Lu. The theranostic (see it,  treat it) approach to treatment has finally become a reality!

Prescribing information and use

  • A patient specific, weight based dose of 68Ga- Dotatate is provided
  • Patient is injected and imaged at 40-90 minutes post administration
  • Must be off somatostatin receptor blocking agents

Same Patient— Different Outcome

A) Standard imaging using Octreotide

B) Improved tumor visualization and treatment planning using 68Ga-Dotatate

 

Alzheimer’s Disease

Indication

  • Adults with cognitive impairment who are being evaluated for Alzheimer’s disease and other possible causes of cognitive decline
  • Currently 3 approved PET/CT imaging agents areavailable: Neuraceq (18F-Florbetaben), Amyvid (18F-Florbetapir), Vizamyl (18F-Flutemetamol)

Mechanism of localization

  • There are many studies that demonstrate a relationship between increased β-amyloid plaque and Alzheimer’s disease.
  • The radiopharmaceuticals bind to this β-amyloid plaque.

Why look into this radiopharmaceutical?

  • Until recently, there was no way to image the presence of the physiological changes associated with Alzheimer’s disease:
  • A positive scan indicates an increase β-amyloid plaque which is consistent with AD and other cognitive disorders: To be used in conjunction with other neurological testing to establish a diagnosis
  • A negative scan indicates that there is a low amountof β- amyloid plaque which is inconsistent with a neuropathological diagnosis of AD
  • Helps to rule out the possibility of AD

Prescribing information and use

  • Each radiopharmaceutical has its own prescribing and dosing information
  • Patient is injected and imaged
  • Entire exam takes less than 90 minutes from start to finish

 

TRADITIONAL TRACERS

18FDG

Indications

  • Cancer—most common
  • Infection & inflammation
  • Viable myocardium (cardiac)
  • Brain – seizure, epilepsy, Alzheimer’s disease, dementia, tumors

Mechanism of localization

18Fluorodeoxyglucose (18FDG) is a sugar molecule that concentrates in areas of high glucose metabolism. Healthcare providers are seeking to determine whether there is an abnormal amount of uptake of this tracer in a particular area of the body which may be indicative of a particular health concern.

Why look into this radiopharmaceutical?

This is the most widely used imaging agent in the world of oncology. Many referring physicians are familiar with this drug and its applications for oncologic purposes. It is generally accepted as the drug to use for most cancers.

Many physicians and facilities are not familiar with the other indications and usages of this imaging agent. Examples include: Viable myocardium—this drug can be used to determine what sections of the heart are still viable and have living, functioning cells.

Brain – Many times, 18FDG can add valuable information that a neurosurgeon needs prior to surgery. Functional changes occur much earlier than physical changes—PET/CT images often compliment CT or MRI images.

 

NaF18

Indication

This radiopharmaceutical is most commonly used to identify cancers of the bone or cancers that have metastasized (spread) into the bone. The Sodium 18Fluoride (NaF18) ions are deposited directly into the bone matrix and bone surface. Common sites are newly mineralized bone, such as during growth, infection, malignancy (primary or secondary), after trauma, or during inflammation.

Why look into this radiopharmaceutical?

This drug is much better at targeting skeletal activity than FDG and provides a much clearer image than traditional nuclear medicine bone scans. These 3D images are also quantitative which allows physicians to precisely measure the activity within a lesion – allows for a more accurate interpretation of the response to treatment.

Prescribing information and use

  • The imaging agent is ordered and delivered for each specific patient
  • There is no patient prep
  • Patient is injected and imaged
  • Entire exam takes roughly 90-120 minutes


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