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Top Line: The Phoenix Consensus has defined PSA kinetics after prostate radiation for over a decade, but that definition is based on conventional fractionation.
The Study: So are PSA kinetics different after SBRT? This large multi-institutional analysis pooled data from over 1K patients at 5 centers who were treated with SBRT. Unfortunately, we don’t have a city (yet) to name it after. Patients had either low- (52%) or intermediate-risk (28% favorable, 20% unfavorable) disease. The vast majority (88%) received either 36.25 Gy or 40 Gy in 5 fractions. Now, there are two important aspects to PSA kinetics: how low and how fast? Median nadir across risk-groups was ~0.2 ng/ml. Overall, nadir after SBRT was lower than we’re used to with >75% of patients—including close to 90% of low-risk—achieving a nadir ≤0.5 ng/ml. However, time to nadir was much longer for disease that was low-risk (49 months) compared to unfavorable intermediate-risk (31 months). PSA bounce occured in 25-30% of patients with a magnitude of ~0.5 ng/ml at 18-24 months after SBRT. Those who eventually had a biochemical failure typically nadired at a higher value (~1.0 ng/ml) and sooner (15 months) than those who didn’t. 
TBL: After prostate SBRT, expect a rapid PSA decline with a quarter of men experiencing a 0.5 ng/ml bounce at 18 months followed by a nadir < 0.5 ng/ml at 3-5 years. | Jiang, Int J Radiat Oncol Biol Phys 2019


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