PSMA PET Scan

What It Shows

• Prostate cancer recurrence at PSA levels as low as 0.2 ng/mL
• Lymph node metastases missed by CT (detects nodes regardless of size — based on PSMA expression, not nodal enlargement)
• Bone metastases — earlier and more sensitive than bone scans
• Oligometastatic disease — identifying 1–3 metastatic sites eligible for SBRT or metastasis-directed therapy
• True extent of disease before salvage radiotherapy after prostatectomy
• PSMA expression level in metastases — predicts eligibility for PSMA-targeted radioligand therapy (177Lu-PSMA)

How It Works

The radiotracer (68Ga-PSMA-11 or 18F-PSMA) is injected intravenously. PSMA-targeting molecules bind specifically to PSMA protein on prostate cancer cells. PET imaging 1–2 hours post-injection detects the gamma rays emitted from the decaying radiotracer. CT images acquired simultaneously provide anatomical localisation. Because PSMA is a prostate cancer-specific target rather than generic glucose metabolism (FDG), the signal-to-background ratio is very high, enabling detection of very small lesions.

• Biochemical recurrence after prostatectomy (rising PSA ≥ 0.2 ng/mL)
• Biochemical recurrence after radiation therapy (PSA rise ≥ 2 ng/mL above nadir)
• Initial staging of high-risk or very high-risk prostate cancer (replacing CT + bone scan in many guidelines)
• Before salvage radiotherapy — to determine if recurrence is local or distant
• Identifying oligometastatic disease for metastasis-directed therapy
• Patient selection for 177Lu-PSMA-617 (Pluvicto) radioligand therapy — PSMA expression must be confirmed

PSMA PET has rapidly become the highest-level evidence imaging modality for prostate cancer. The proPSMA trial (Lancet 2020, N=302) showed PSMA PET superior to CT + bone scan for initial staging of high-risk prostate cancer (accuracy 92% vs 65%). The EMPIRE-1 trial demonstrated PSMA PET-guided radiation planning improved 4-year freedom from progression (46% vs 19%). FDA approved Gallium-68 PSMA-11 in 2020 and Piflufolastat F-18 in 2021. Multiple guidelines (EAU, NCCN, NICE) now recommend PSMA PET as preferred imaging for biochemical recurrence. The PSMA-VISION trial also established PSMA PET as the predictive biomarker for 177Lu-PSMA therapy eligibility.

Preparation & What to Expect

No fasting required (unlike FDG PET). No blood glucose restrictions. Avoid diuretics the day of scan. Arrive 30 minutes early. Injection followed by 1–2 hour wait. Total appointment 2.5–3 hours. Scan itself 25–35 minutes.

• PSMA-low prostate cancers (neuroendocrine differentiation, aggressive variants) may not be detected
• PSMA expression not 100% specific — bladder, kidneys, and some benign tissues express PSMA
• Limited to prostate cancer — not applicable to other cancer types
• Availability varies significantly by region — more centres in USA/Europe/Australia

• Low but non-zero radiation exposure — discuss with physician if repeated scans are planned
• Requires specialist nuclear medicine reporting — general radiologist may lack PSMA experience
• A positive PSMA PET for oligometastatic disease may lead to aggressive treatment of uncertain benefit — multidisciplinary team review essential