A 60-year-old with known prostate cancer and rising PSA post-prostatectomy undergoes Ga-68 PSMA PET-CT. The PSMA ligand targets prostate-specific membrane antigen. Compared to F-18 FDG PET-CT, what is the major advantage of Ga-68 PSMA PET-CT for prostate cancer?

• A No radiation exposure compared to FDG
• B Better assessment of primary tumour grade
• C Superior detection of visceral metastases over FDG
• D High sensitivity for biochemical recurrence even at very low PSA levels (> 0.2 ng/mL), detecting small nodal and bone metastases invisible to FDG and conventional imaging ✓

Explanation

Ga-68 PSMA PET-CT exploits overexpression of PSMA on prostate cancer cells (10–1000 fold higher than normal prostate tissue). Its major advantage over FDG is high sensitivity for detecting biochemical recurrence at PSA levels as low as 0.2–0.5 ng/mL, identifying small nodal (< 5 mm) and osseous metastases that are FDG-negative and occult on CT/bone scan. FDG has limited sensitivity in prostate cancer due to the cancer's low glycolytic rate. Both involve radiation. PSMA does not grade the primary tumour.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.