Using the magnitude of PSA bounce after MRI-guided prostate brachytherapy to distinguish recurrence, benign precipitating factors, and idiopathic bounce

Purpose: To identify events that precipitated a prostate-specific antigen (PSA) bounce and characterize the magnitude, duration, and time to PSA bounce after MRI-guided prostate brachytherapy. Methods and Materials: Between 1997 and 2001, 186 patients with low-risk prostate cancer underwent MRI-guided permanent ¹²⁵I source implantation, with or without external beam radiotherapy. A PSA bounce was defined as a ≥15% elevation in PSA compared with the most recent value, followed by a decline to a level at or less than the prebounce value. At the time of PSA measurement, data were prospectively collected on whether the patient had recent ejaculation, ongoing radiation proctitis, or recent instrumentation. Results: A total of 115 patients (61.8%) had a total of 156 PSA bounces. Of these, 36 patients had PSA bounces associated with ejaculation, proctitis, or instrumentation, and 79 experienced idiopathic PSA bounces (not associated with a precipitating event). The magnitude of the PSA bounce was significantly lower for the idiopathic PSA bounce (0.6 ng/mL) compared with that associated with ejaculation (p = 0.003), proctitis (p <0.0001), or instrumentation (p = 0.007). Patients with biopsy-proven local recurrence had a median PSA elevation of 1.2 ng/mL, significantly higher (p = 0.006) than the magnitude of the idiopathic PSA bounce, but not significantly different from the magnitude of the PSA bounce due to ejaculation, proctitis, or instrumentation. Conclusion: In patients treated with MRI-guided prostate brachytherapy, recent ejaculation, instrumentation, or ongoing radiation proctitis can cause a transient increase in PSA, the magnitude of which is significantly higher than that for idiopathic PSA bounce, but is similar to that in patients with recurrent disease.