Nuclear Medicine · MU Sofia

14. Application of Gallium-68 PET-CT in the diagnosis of prostate cancer and neuroendocrine tumors, staging, monitoring the effect of treatment and prognosis.

Covers the use of gallium-68 PET/CT in prostate cancer, using PSMA-targeted tracers for initial staging, lymph-node and bone assessment, biochemical recurrence, restaging, and selection for radionuclide therapy. It then turns to somatostatin-receptor tracers in neuroendocrine tumours, covering detection, staging, PRRT selection, and prognosis. A table compares gallium-68 and FDG uptake across tumour differentiation grades, and the note lists normal distribution and false-positive and false-negative pitfalls for each tracer.

Inside: 17 sections · 1 table · 16 flashcards · 9 min

Topic 14 of 50 in the MU Sofia syllabus for Nuclear Medicine (Medicine, Year 4). The free AceMed note covers it in 17 sections, about 1,376 words (9 min of reading), with 16 flashcards.

In this note

  1. Topic 14: Application of Gallium-68 PET/CT in Prostate Cancer and Neuroendocrine Tumors
  2. PART I — GALLIUM-68 PSMA PET/CT IN PROSTATE CANCER
  3. PRIMARY TUMOR ASSESSMENT
  4. LYMPH-NODE STAGING
  5. BONE METASTASES
  6. VISCERAL METASTASES
  7. BIOCHEMICAL RECURRENCE
  8. RESTAGING OF KNOWN METASTATIC DISEASE
  9. SELECTION FOR PSMA-TARGETED RADIONUCLIDE THERAPY
  10. TREATMENT-RESPONSE ASSESSMENT
  11. ⁶⁸Ga-PSMA PET/CT PREPARATION AND PROCEDURE
  12. PART II — GALLIUM-68 SOMATOSTATIN-RECEPTOR PET/CT IN NEUROENDOCRINE TUMORS
  13. NEUROENDOCRINE TUMORS
  14. ASSESSMENT OF SOMATOSTATIN-RECEPTOR EXPRESSION
  15. SELECTION FOR PEPTIDE RECEPTOR RADIONUCLIDE THERAPY
  16. PROGNOSIS
  17. DUAL-TRACER IMAGING IN NEUROENDOCRINE TUMORS

Topic 14: Application of Gallium-68 PET/CT in Prostate Cancer and Neuroendocrine Tumors

What is Gallium-68?

Gallium-68 (⁶⁸Ga) is a positron-emitting radionuclide used for PET imaging.

Main physical characteristics:

  • Emits positrons.
  • Physical half-life: approximately 68 minutes.
  • Obtained mainly from a ⁶⁸Ge/⁶⁸Ga generator.
  • Does not necessarily require an on-site cyclotron.
  • After positron emission, annihilation produces two 511 keV photons, detected by PET.

Gallium-68 can be attached to different molecules that target specific receptors or antigens.

The main tracers in this topic are:

  • ⁶⁸Ga-PSMA for prostate cancer.
  • ⁶⁸Ga-DOTATOC, ⁶⁸Ga-DOTATATE, or ⁶⁸Ga-DOTANOC for neuroendocrine tumors.

PART I — GALLIUM-68 PSMA PET/CT IN PROSTATE CANCER

PSMA means: Prostate-Specific Membrane Antigen

It is a transmembrane glycoprotein expressed on prostate cells.

Its expression is usually markedly increased in prostate cancer, especially in:

  • High-grade tumors.
  • Metastatic disease.
  • Castration-resistant prostate cancer.
  • Recurrent prostate cancer.

Although called prostate-specific, PSMA is not completely exclusive to prostate tissue and may also be expressed in:

  • Salivary glands.
  • Kidneys.
  • Small intestine.
  • Lacrimal glands.

⁶⁸Ga-PSMA RADIOPHARMACEUTICAL

The radiopharmaceutical consists of:

  • Gallium-68 as the positron emitter.
  • A ligand that binds to PSMA.

After intravenous injection:

⁶⁸Ga-PSMA circulates in the blood.

↓

Binds to PSMA on prostate cancer cells.

↓

The ligand-receptor complex is internalized.

↓

Tracer accumulates within the tumor.

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PET detects the lesion as an area of increased uptake.

NORMAL PHYSIOLOGICAL DISTRIBUTION

Normal uptake may be seen in:

  • Lacrimal glands.
  • Salivary glands.
  • Liver.
  • Spleen.
  • Kidneys.
  • Small intestine.
  • Sympathetic ganglia.
  • Ureters.
  • Urinary bladder.

The urinary tract may be very bright because many PSMA tracers are excreted through the kidneys.

This can make lesions near the:

  • Prostate bed.
  • Ureters.
  • Bladder. more difficult to detect.

MAIN INDICATIONS OF ⁶⁸Ga-PSMA PET/CT

1. Initial Staging of Prostate Cancer

Used particularly in patients with:

  • High-risk prostate cancer.
  • Unfavorable intermediate-risk disease.
  • High PSA.
  • High Gleason score or ISUP grade group.
  • Suspicion of lymph-node or distant metastases.

PET/CT may evaluate:

  • Primary prostate lesion.
  • Pelvic lymph nodes.
  • Para-aortic lymph nodes.
  • Bone metastases.
  • Visceral metastases.

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