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Top Line: Ahh, post-prostatectomy radiation is just full of fun debates: Adjuvant or salvage? With androgen therapy (ADT) and for how long? Nodal irradiation? Dose??
The Study: This last question has been less hotly debated, so let’s spice things up. A large multi-institutional analysis demonstrated in 2016 that doses <66 Gy conferred a 30% relative decrease in biochemical control when compared to doses >70 Gy. However, there was no difference for the 66-69 Gy dose range compared to >70Gy. Here we have an actual randomized trial, albeit small (n=144) and at a single center in Beijing, comparing disease outcomes after either 66 Gy in 33 fractions or 72 Gy in 36 fractions for men receiving salvage radiation for pT3/4 disease, positive surgical margins, or a rising PSA. IGRT/IMRT was used for all patients, and androgen deprivation was not allowed. Patients with with pT3/4 or Gleason 8+ disease or with a PSA >20 also received pelvic radiation (which ended up being nearly 90% of patients). Remembering the trial was small, there was no statistical difference in 4 year biochemical progression-free survival (bPFS) after 66 Gy (76%) versus 72 Gy (83%)—though one might wonder if a true difference would be detectable in a larger population. Among the small subset of patients with GS 8+ disease (n=55), that difference became pretty large (and statistically significant) with a 4-year bPFS of 56% versus 80%, respectively. There were no major differences in acute or late GI or GU toxicity between groups.
TBL: Though this trial is small, heterogeneous, and did not show an improvement in biochemical control with dose beyond 66 Gy, it leaves us with some open questions that may be answered by larger trials. | Qi, Int J Radiat Oncol Biol Phys 2019