What are the preparation requirements for a Fluorodeoxyglucose (FDG) scan for metastatic prostate cancer?

FDG PET/CT Preparation Requirements for Metastatic Prostate Cancer

Patients must fast for at least 4 hours before an FDG PET/CT scan, avoid all beverages except plain water, maintain adequate hydration, and have blood glucose levels below 11 mmol/L (200 mg/dL) to ensure optimal image quality and diagnostic accuracy. 1

Pre-Scan Dietary Restrictions

• Fast from all food for at least 4 hours prior to FDG injection
• Avoid all beverages except plain, unflavored water
• For morning appointments: no food after midnight, only a light meal (low carbohydrate) the evening before
• For afternoon appointments: light breakfast allowed at least 4 hours before the scan
• Avoid coffee and caffeinated beverages, even if labeled "sugar-free" or "sugarless" 1, 2
• Medications can be taken as prescribed unless they contain glucose

Hydration Requirements

• Drink approximately 1 liter of plain water during the 2 hours before FDG injection 1, 2
• Adequate hydration ensures lower FDG concentration in urine (reducing artifacts) and enhances radiation safety 1
• Void immediately before entering the scanner to reduce bladder activity 1

Blood Glucose Management

• Blood glucose will be measured prior to FDG administration
• For clinical studies: glucose level must be below 11 mmol/L (200 mg/dL) 1
• For research studies: stricter thresholds apply (7-8.3 mmol/L or 126-150 mg/dL) 1
• Diabetic patients should have glucose checked upon arrival to allow time for correction if needed 1
• Parenteral nutrition and IV fluids containing glucose must be discontinued at least 4 hours before FDG injection 1

Physical Activity and Positioning

• Avoid strenuous exercise for at least 6 hours before the scan, preferably 24 hours 1
• During FDG uptake phase, remain seated or recumbent and quiet to minimize muscle uptake 1
• Keep warm starting 30-60 minutes before injection and throughout the procedure to minimize brown fat activation 1
• Be prepared to lie still for 20-45 minutes during the examination 1
• Position arms alongside the body or above the head as instructed by technologists 1

Special Considerations for Prostate Cancer Imaging

While FDG PET/CT is not the first-line imaging modality for prostate cancer, it may be useful in specific scenarios, particularly for aggressive tumors (Gleason score >7) and for treatment response assessment in metastatic castrate-resistant disease 3, 4. The standard preparation guidelines remain essential for optimal image quality.

Common Pitfalls to Avoid

1. Hyperglycemia: High blood glucose levels significantly reduce tumor FDG uptake and impair image quality 5
2. Muscle activation: Talking or moving during the uptake phase increases muscle uptake, potentially obscuring pathological findings 1
3. Cold-induced brown fat activation: This can be minimized by keeping the patient warm before and during the procedure 1
4. Inadequate hydration: Insufficient water intake leads to concentrated FDG in the urinary tract, causing artifacts 1
5. Recent exercise: Physical activity within 24 hours before the scan can alter FDG distribution 1

By following these preparation guidelines, patients with metastatic prostate cancer can ensure optimal FDG PET/CT image quality, enhancing the diagnostic value of the examination and improving clinical decision-making.