Is a Prostate Specific Antigen (PSA) test necessary after brachytherapy for prostate cancer?

PSA Monitoring After Brachytherapy for Prostate Cancer

Yes, PSA monitoring is necessary after brachytherapy for prostate cancer to detect recurrence and evaluate treatment success. Regular PSA testing is an essential component of post-brachytherapy follow-up care, though there is some variation in recommended testing schedules across guidelines.

PSA Response After Brachytherapy

• Unlike radical prostatectomy (where PSA should become undetectable), PSA after brachytherapy follows a different pattern:
  • PSA decreases gradually over time
  • May not reach nadir until 18-30 months after treatment 1
  • PSA values <0.2 ng/mL are uncommon after brachytherapy 1

Recommended PSA Monitoring Schedule

Based on guidelines, the following PSA monitoring schedule is recommended:

• First PSA test: 3-12 months after brachytherapy 1
• Year 1-2: Every 3 months 1
• Years 2-5: Every 6 months 1
• Beyond 5 years: Annual monitoring 1

The British Columbia Cancer Agency specifically recommends PSA testing every 3 months for 2 years, then every 6 months thereafter for brachytherapy patients 1.

PSA Bounce Phenomenon

A critical consideration in post-brachytherapy PSA monitoring is the "PSA bounce" phenomenon:

• Definition: Temporary PSA rise of ≥0.2 ng/mL above nadir followed by spontaneous decline without treatment 2, 3
• Incidence: Occurs in 24-46% of patients 2, 4
• Timing: Typically occurs around 12-15 months post-treatment 2, 4
• Magnitude: Median increase of 0.76-0.78 ng/mL, though can exceed 2 ng/mL in 15% of cases 2, 4
• Clinical significance: Associated with better biochemical control and lower risk of biochemical failure 2

Defining Biochemical Failure

The American Society for Therapeutic Radiology and Oncology (ASTRO) and Radiation Therapy Oncology Group define biochemical failure after brachytherapy as:

• A rise in PSA of ≥2 ng/mL above the nadir value (Phoenix definition) 1

Important Considerations

1. Distinguish bounce from recurrence: The timing of PSA rise helps differentiate bounce (median 15 months) from true biochemical failure (median 30 months) 3

2. Avoid premature intervention: Due to the bounce phenomenon, clinicians should monitor PSA for at least 3 years before concluding treatment failure 5

3. Age factor: Younger patients are more likely to experience PSA bounce 2, 3

4. Prognostic value: A PSA ≤0.2 ng/mL measured 6-12 months after brachytherapy appears to be a useful predictive marker for treatment success 6

Pitfalls to Avoid

• Misinterpreting a PSA bounce as biochemical failure, potentially leading to unnecessary interventions
• Relying on isolated PSA values rather than trends
• Evaluating response too early (before 3 years) may lead to incorrect conclusions about treatment efficacy 5
• Failing to consider that PSA kinetics after brachytherapy differ significantly from those after radical prostatectomy

In conclusion, while there is some variation in guidelines, PSA monitoring is clearly necessary after brachytherapy and should follow a structured schedule to properly evaluate treatment response and detect potential recurrence.