Multi-institutional Analysis of Prostate-Specific Antigen Kinetics Following Stereotactic Body Radiotherapy (SBRT). International journal of radiation oncology, biology, physics Jiang, N. Y., Dang, A. T., Yuan, Y., Chu, F., Shabsovich, D., King, C. R., Collins, S. P., Aghdam, N., Suy, S., Mantz, C. A., Miszczyk, L., Napieralska, A., Namysl-Kaletka, A., Bagshaw, H., Prionas, N., Buyyounouski, M. K., Jackson, W. C., Spratt, D. E., Nickols, N. G., Steinberg, M. L., Kupelian, P. A., Kishan, A. U. 2019

Abstract

PURPOSE: Understanding prostate-specific antigen (PSA) kinetics after radiotherapy plays a large role in the management of prostate cancer (PCa) patients. This is particularly true regarding establishing expectations regarding PSA nadir (nPSA) and PSA bounces, which can be disconcerting. As increasingly more patients are being treated with stereotactic body radiotherapy (SBRT) for low- and intermediate-risk PCa, it is imperative to understand the PSA response to SBRT.METHODS&MATERIALS: PSA data from five institutions were retrospectively analyzed for localized PCa patients treated definitively with SBRT alone from 2004 to 2016. Patients received 35-40 Gy in five fractions per institutional standards. Patients who had less than 12 months of PSA data or received androgen deprivation therapy were excluded from this study. Linear and logistic multivariable analysis were performed to identify predictors of nPSA, bounce, and biochemical recurrence, and joint latent class models (JLCM) were developed to identify significant predictors of time to biochemical failure.RESULTS: 1062 patients were included in this study. Median follow-up was 66 months (interquartile range (IQR) 36.4 - 89.9 months). Biochemical failure per the Phoenix criteria occurred in 4% of patients. Median nPSA was 0.2 ng/ml, median time to nPSA was 40 months, 84% of patients had a nPSA <0.5 ng/ml, and 54% of patients had a nPSA <0.2 ng/ml. On multivariable analysis, nPSA was a significant predictor of biochemical failure. Benign PSA bounce was noted in 26% of patients. The median magnitude of PSA bounce was 0.52 ng/ml (IQR 0.3 - 1.0 ng/ml). Median time to PSA bounce was 18.1 months (IQR 12.0 - 31.1 months). On multivariable analysis, age and radiation dose were significantly associated with a lower incidence of bounce. JLCM modeling found that nPSA and radiation dose were significantly associated with longer time to biochemical failure.CONCLUSIONS: In this multi-institutional cohort of patients with long-term follow-up, we found that SBRT led to low nPSAs. In turn, lower nPSAs are associated with reduced incidence of, and longer time to, biochemical failure. Benign PSA bounces occurred in a quarter of patients, as late as several years after treatment. Further studies are needed to directly compare the PSA response of patients who receive SBRT versus other treatment modalities.

View details for DOI 10.1016/j.ijrobp.2019.06.2539

View details for PubMedID 31276777