The Study: It goes by a lot of names including ultra-hypofractionation, extreme hypofractionation, SABR, and SBRT. We’re gonna ride with just “ultra” today. In the HYPO-RT-PC trial, over 1200 men with intermediate- and high-risk prostate cancer were randomized to receive either standard fractionation (2 Gy x 39 = 78 Gy) or ultra (6.1 Gy x 7 = 42.7 Gy)—this latter dose was chosen to be equi-effective for late normal tissue complications. While you may raise your eyebrows at the high-risk inclusion, barely 10% of enrollees ultimately fit this description. And while cT3a disease was also allowed, only 5% had it. So what we end up with is a largely intermediate-risk population, though nobody received androgen deprivation. The trial was initially designed to prove superior failure-free survival (FFS) at 5 years with ultra. However, an interim analysis demonstrated much better FFS (87%) than anticipated (70-80%) across the board, so the trial was switched to a non-inferiority design with a 4% absolute non-inferiority margin. At 5 years, the rate of FFS was 84% in both arms, which was deemed non-inferior. Convenient. Ultra resulted in slightly worse acute grade 2+ GU toxicity (28% versus 23%) but similar grade 2+ GI and GU toxicity at 5 years (<5%). Finally, rates of erectile function dropped from 70% at enrollment to 35% at 5 years with either treatment. Without a no-treatment arm, the role of Father Time remains unclear.
TBL: Ultra-hypofractionated prostate radiation (6.1 Gy x 7 = 42.7 Gy) appears to have non-inferior efficacy and safety compared to standard fractionation. | Widmark, Lancet 2019