What fractionation regimen do you use for combination EBRT and HDR for high-risk prostate cancer?

There is a range of appropriate HDR boost fractionation options.

The 2018 NCCN Guidelines list the following options:

45-50.4 Gy + 10.75 Gy x 2

37.5 Gy (2.5 Gy fractions) + 12-15 Gy

RTOG 0815 (allows brachy boost as an option): 45 Gy +10.5 Gy x 2

RTOG 0924 (allows brachy boost as an option): 45Gy+ 15Gy x...

The best evidence for fractionation schedule in combination with 15 Gy HDR boost is the 37.5 Gy in 15 fraction schedule. In my practice at UVA, I start with the prostate HDR boost (15 Gy in 1 fraction), which allows me to place prostate-rectal spacer at time of brachytherapy. Then, I use 45 Gy in 1....