Ablative arbitration.

Top Line: ASCENDE-RT demonstrated that a brachytherapy boost following conventionally-fractionated radiation to the pelvis improves biochemical control of intermediate to high risk prostate cancer at the expense of more urinary toxicity.

The Study: So...which is more important? That answer ain’t easy. This French group thinks they have the solution wrapped in an ablative stereotactic external beam boost in lieu of brachy. The single-arm phase 2 CKNO-PRO trial treated 76 men with intermediate-risk prostate cancer with 2 Gy x 23 = 46 Gy to the prostate and proximal half of the seminal vesicles followed by a sequential stereotactic boost of 6 Gy x 3 = 18 Gy to the prostate alone. Assuming excellent biochemical control for this patient population, the primary endpoint (i.e., the true point to be made) here was toxicity. At a median follow-up of over 5 years, the cumulative rate of grade 2+ GI toxicity was 9% and of GU toxicity was only 1%. We emphasize cumulative because many take issue with this measure, which adds toxicities from all time points, most being transient. Compare this to ASCENDE-RT where the cumulative grade 3+ GI toxicity was 8% and the grade 3+ GU toxicity was an unsightly 18%. What’s more, there was no significant worsening of the IPSS quality of life score at 5 years from baseline. This all supports the safety of an ablative external beam boost to the prostate, though without treating the nodes, we’re not sure how to support incorporating conventional fractionation just to treat the proximal half of the seminal vesicles.

TBL: Though not directly addressed here, comparing an ablative external beam approach versus brachy as a prostate boost after conventional fractionation to the pelvis for high risk disease sounds like a good clinical trial, but only if 5 treatments to everything doesn’t pan out. | Pasquier, Int J of Radiat Oncol Biol Phys 2019