PSA bounces after brachytherapy HDR and external beam radiation therapy for prostate cancer

SummaryBackgroundThe serum prostate-specific antigen (PSA) test is the most commonly used method for confirming response of prostate cancer after definitive radiation therapy (RT). PSA levels are expected to decrease after radiotherapy but usually remain detectable. Three consecutive PSA rises above the post-treatment nadir have been defined as biochemical failure by the ASTRO consensus panel [1]. Rising serum PSA concentration after RT does not always indicate treatment failure. Some patients have a temporary PSA spike, usually within 12–30 months of radiation therapy [2–4]. Most PSA bounces have a magnitude of 1.0 ng/mL or less. This observation was first described by Wallner and colleagues in 1997 [5]. Although this phenomenon is a source of anxiety for both the patient and the physician, its relevance to biochemical failure is controversial.AimTo determine the clinical and dosimetric factors that predict prostate-specific antigen (PSA) bouncing following brachytherapy HDR and three-dimensional conformal radiation therapy (3D-CRT) for prostate cancer patients.Materials/MethodsThe evaluated population consisted of 71 hormone-naive patients with a minimum of 2 years of follow-up and at least 6 post-treatment PSA levels. All patients were treated using 3D-CRT combined with brachytherapy HDR. A bounce was defined as a PSA rise of ≥0.2 ng/mL above the nadir followed by a subsequent 120 decline of ≥0.2 ng/mL. Clinical factors evaluated included: patient age, Gleason score, maximum initial pretreatment PSA value (iPSAmax), clinical stage, prostate volume, median time to PSA nadir, median PSA nadir value and patient follow-up in months. Dosimetric factors evaluated included the percentage of the prostate volume receiving 100% (V100), 150% (V150) and 200% (V200) of the prescribed minimal peripheral dose.ResultsStatistically significant predictive factors for PSA bounce were age, V100, V150, V200, iPSAmax and median time to PSA nadir. Logistic regression model for multivariate analysis revealed that only age, iPSAmax and V200 were statistically significant predictors for PSA bounce. There were no statistical differences between median nadir among patients who exhibited a PSA bounce and those who did not, but non-bouncers reached PSA nadir earlier than bouncers; median time was 12.1 vs 17.2 months respectively.ConclusionPSA bouncing occurs in approximately one third (1/3) of patients treated with 3D-CRT and brachytherapy HDR. Bouncing is associated with age, higher pretreatment PSA level and increased V200 factor