I just saw this thread. I think I said this in an email, but there are probably dozens of ROs in the US who can do a good job with SBRT. It doesn't have a steep learning curve like brachytherapy or surgery, but it does require care in working out an optimal plan. Of course, I think my (and Nomar's) RO, Chris King, who originated it in 2003 is the best, but I know I'm biased.
I chuckled over the discussion about
"scatter." Paxton is absolutely right that the dose scattered off of bones is minimal, probably less than 1-2 Gy and decreasing with the square of distance. But what you're talking about
isn't scatter, per se, it's the dose received by organs at risk (which is different).
I've heard this confusion about
internal radiation vs. external radiation before, and it seems to stem from a basic misunderstanding about
radiation. When we turn on a light bulb, the light, which is generated inside, doesn't stop at the bulb, of course. Similarly, the X-rays generated by brachytherapy seeds don't suddenly stop at the edge of the prostate capsule. There is always a dose received by nearby organs, and especially by the urethra. That dose is shown in a "dose volume histogram (DVH)." With seeds, they compute that post-operatively, I think, because with intra-operative planning they can't know in advance exactly where seeds will be placed.
With external beam radiation, the DVH (and the prostate dosimetry) is the heart of the plan. They minimize doses to organs at risk by delivering the beams from different places. Only the places where beams intersect within the prostate get a large enough dose to do anything. After the computer optimizes the plan, it is set to automatically run the linac to deliver the plan.
Complicating matters is that
how the radiation is delivered makes a big difference in the biologically effective doses (BED) received by the prostate. With seeds, the slow delivery of low dose radiation is close to the BED, while with SBRT or HDR brachy, the hypofractionation delivers a high BED to cancer tissue (due to a multiplier effect called the alpha/beta ratio) but a low BED to healthy tissue
Dosimetry is all very theoretical. What matters to the patient is not dosimetry but are his toxicity outcomes -- urinary, rectal and sexual. This is where SBRT (and HDR brachytherapy) excel. There's never been a randomized comparison, but the patient-reported outcomes have been compared using the same instrument. Note that the LDR brachy data comes, in part, from Cleveland Clinic:
/pcnrv.blogspot.com/2016/08/ldrbt-imrt-and-sbrt-quality-of-life.html