Early and Multiple PSA Bounces Can Occur Following High Dose Prostate Stereotactic Body Radiation Therapy: Subset Analysis of a Phase I/II Trial

Publication date: Available online 24 June 2016
Source:Practical Radiation Oncology
Author(s): D. Nathan Kim, Christopher Straka, L. Chinsoo Cho, Yair Lotan, Jingsheng Yan, Brian Kavanagh, David Raben, Susan Cooley, Jeffrey Brindle, Xian Jin Xie, David Pistenmaa, Robert Timmerman
Purpose/ObjectivesWe hypothesized that high dose Stereotactic Body Radiation Therapy (SBRT) would lead to faster time to nadir and lower nadir values compared to conventional radiation therapy experiences. We now report PSA kinetics following high dose SBRT in patients treated with radiation alone.Materials/Methods91 patients were enrolled on the phase I/II dose escalation study of SBRT for localized prostate cancer (PCa). All patients with at least 36months (m) of follow up and without hormone therapy were included for this analysis (n=47). Treatment response parameters evaluated include time to nadir, nadir value, occurrence of PSA bounces (rise of ≥0.2ng/mL followed by a subsequent fall), magnitude of bounces, duration of bounces and correlation of bounces with clinical outcomes.ResultsMedian follow up was 42m (range 36–78m). Treatment dose levels were 45 Gray (Gy) (n=10), 47.5Gy (n=8) and 50Gy (n=29) in 5 fractions. Biochemical control rate was 98%. Median PSA at follow up was 0.10±0.20ng/mL. Median time to nadir was 36±11m. 24/47 (51.1%) patients had ≥1 PSA bounce. Median magnitude of PSA rise during bounce was 0.50±1.2ng/mL. Median time to first bounce was 9±7.0m. Median bounce duration was 3±2.3m for the first bounce and 6±5.2m for subsequent bounces. Prostate volumes <30cc were associated with a decreased likelihood of bounce (p=0.0202), and increasing prostate volume correlated with increasingly likelihood of having ≥2 bounces (p=0.027). Patients reaching PSA nadir of ≤0.1ng/mL were less likely to experience any bounce (p=0.0044).ConclusionsCompared to other SBRT experiences, our study demonstrated a higher PSA bounce rate, a similar or shorter median time to bounce and a very low nadir. Prostate volume appears correlated with bounce.



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