They are entirely different. The confusion is their fault, not yours.
Stereotactic ABlative Radiation Therapy is usually abbreviated SABR is exactly the same thing as what is usually called Stereotactic Body Radiation Therapy (SBRT). The most popular brand is CyberKnife, although it is given on a variety of platforms these days. As far as I can tell, someone was trying to be cutesy with the acronyms, and wanted it to sound like the popular brands that had a "knife" or "saber" in the name, like CyberKnife or GammaKnife. I suppose the "knife" is supposed to connote how sharply the radiation falls off around the target and its sub-millimeter accuracy. Despite the name, it isn't really ablative at all because it doesn't destroy the cells of the prostate like laser, HIFU, cryo, and PDT do. To add to the confusion, there is a new ablative technique that uses Irreversible Electroporation (IRE) and the brand name is NanoKnife. They call it that because it destroys single cells and not any nearby cells as other kinds of thermal ablation (e.g., laser) do.
So whether you call it SBRT or SABR, I can recommend it highly (see my signature).
Allen - not an MD
•PSA=7.3, prostate volume=55cc, 8/17 cores G6 5-35% involvement
•SBRT 6 year results
treated 10/2010 at age 57 at UCLA
•PSA since treatment:
1/11:3.9 5/11:3.0 8/11:3.7 5/12:1.2 9/12:1.3 5/13:0.4
• SEs of treatment:
after 2 wks: mild urinary & rectal - last 1 wk
1 yr after: mild urinary - last 2 months