So I'm going to weigh in here even though I have not yet gone through my choice of treatment for my PCa - LDR Brachytherapy Monotherapy, so I don't know where I'll be when I come out on the other side - but I am completely confident in the research I have done that has lead me to my choice - and at the same time respectfully acknowledging that each of us needs to do this and my comments are not meant to challenge anyone's individual choice of treatment!
Where to start - Phenom your point is well taken, "But then where's the information coming from that would discourage these treatments and create such a precipitous decline in their usage over the last several years" - well first of all if we look at the most current data Brachy results are more favorable than other treatment approaches, given of course the right PCa stats where seeds make sense - see the "Grimm et all" and other current studies and stay away from the old stuff. I don't recall what the most recent data shows with respect to %'s of the various treatment choices is - but of course we do need to keep in mind that certain PCa conditions may suggest one treatment approach over others. I would also add that the recent trend of "Robotic RRP" has created a buzz that has lured many to use this as their choice of treatment - to your point about a decline in BT - although again I'm not sure if that is truly the case.
Additionally the old/dated data would show BT SE's such as rectal and continency issues, however the most current data absolutely refutes that. (Some forms of external beam however can result in SE issues, again ANY PCa treatment can) Performed by a successful/experienced RO the SE's for LDR BT are less than other treatment choices. (And again I do acknowledge the same goes for whatever choice of treatment we decide on, more important the Indian than the Arrow.)
In my own personal situation I did much research into bowel/rectal related SE's because I also deal with IBS - currently well under control by use of probiotics, but since I know what bowel/rectal issues can be like, I paid attention and did not find data to concern me regarding going the BT route.
In addition to the Grimm study, I also found additional current study results specifically regarding the topic of rectal issues from BT; for example in May 2011:
The American Cancer Society reports that bowel or rectal problems develop in less than 5 percent of brachytherapy patients.
Read more: http://www.livestrong.com/article/33264-radiation-seeds-side-effects/#ixzz26Dc9LlHG
And more from this year (September 2012) as well:
'Patient-reported long-term rectal function after permanent interstitial brachytherapy for clinically localized prostate cancer.'
"Long-term rectal function after prostate brachytherapy is favorable with a small number of patients reporting deterioration in bowel function. The judicious use of supplemental external beam radiation with particular attention to rectal doses may further improve long-term function."
So then again I would simply say study the statistics, and understand that statistics are simply that - bias always exists in statistics so again I would encourage all to not only study the stats, but more importantly INSIST on the absolute statistics of the pracitioner that will be performing YOUR treatment, no matter what your choice of treatment may be. . . . .