Photoman,
Welcome to HW.
As you will discover, the term "external beam radiation" is a catch all that includes IMRT and IGRT, and is not often used here, as it is very generic. Ten years ago, it was the proper term, but the ways of delivering it have been greatly refined.
I had adjuvant IGRT (image-guided radiation therapy using Calypso markers), which is a type of EBRT, but nowhere in any of my posts do I refer to having had EBRT (think in terms of saying you have a BMW or Jeep as opposed to a metal-framed motorized transportation device). I hope this will help you sort out that many of us have had RT, and many of those as a primary treatment.
IGRT is very appropriate for those patients who have extension beyond the prostate, or have medical issues that make surgery a difficult proposition.