PSA Levels After Prostate Radiation
After prostate radiation therapy, PSA levels fall slowly over 6 months to several years, reaching a target nadir of less than 1.0 ng/mL, unlike the rapid drop to undetectable levels seen after surgery. 1
Expected PSA Trajectory
PSA decline after radiation is gradual and prolonged:
- PSA continues to decrease for up to 12 months or longer, with the nadir (lowest point) typically reached between 6 months to several years after treatment 1, 2
- The median PSA half-life during and after radiation is approximately 54-62 days, significantly longer than the rapid clearance seen post-prostatectomy 3
- PSA values below 0.2 ng/mL are uncommon after external beam radiotherapy because radiation does not ablate all prostate tissue 1
Target PSA Goals
The target PSA nadir after radiation therapy is less than 1.0 ng/mL:
- Achieving a nadir PSA below 1.0 ng/mL is associated with significantly better outcomes, with only a 17% 5-year relapse rate 1, 2
- For brachytherapy specifically, a PSA level below 0.7 ng/mL at 5 years is reasonable, with median levels around 0.1 ng/mL 1
- Patients who fail to achieve a nadir below 1.0 ng/mL have substantially higher failure rates, even if the PSA appears "low" 2
PSA Bounce Phenomenon
A temporary PSA rise called "PSA bounce" can occur and should not be mistaken for recurrence:
- PSA bounce typically occurs within the first 2 years after treatment and is self-limited 1, 4
- This phenomenon is characterized by PSA rising and then spontaneously declining without intervention 1
- PSA bounce is more common after brachytherapy, where intermittent rises are well-documented 1
- Confirmation with repeat PSA in 3 months and consultation with the radiation oncologist is recommended when PSA rises 1
Defining Biochemical Recurrence
Biochemical recurrence after radiation is defined by the Phoenix Consensus criteria:
- A PSA rise of 2.0 ng/mL or more above the nadir indicates treatment failure, regardless of whether androgen deprivation was used 1, 4
- Alternatively, three consecutive PSA rises also indicate recurrence 1
- The date of failure should not be backdated to the first PSA rise 1
Critical Monitoring Pitfalls
Several factors predict poor outcomes and require early recognition:
- PSA half-life exceeding 88 days during or immediately after radiation suggests residual disease and predicts higher relapse rates 3
- Persistent elevated PSA levels beyond 6 months post-treatment are associated with treatment failure 3
- Patients with pretreatment PSA exceeding 30 ng/mL have a 40% failure rate at 5 years even when achieving a nadir below 1.0 ng/mL 2
- Any rising PSA trend after reaching nadir warrants referral to the radiation oncologist, even when absolute values remain low 1
Surveillance Schedule
Ongoing PSA monitoring is essential for detecting recurrence:
- PSA should be measured every 6 months for the first 5 years, then annually thereafter 1, 4, 5
- Digital rectal examination should accompany PSA testing to monitor for local recurrence 1, 5
- Surveillance should remain under the care of the treating radiation oncologist until explicit transfer to primary care occurs 1