Sherry,
It is a matter of cost for one thing. The machines are VERY expensive. If other machines are available to to focused rads, it can be a hard sell to purchase the CK.
Secondly, treatments to different areas must be taught. A CK Center needs to have people in place with experience in each types of treatment. It is usual that the brain tx is the first to be utilized. Then, hopefully, other body areas as personnel become knowledgable.
hope that helps,
pattyz
p.s. Here is the CK center home page:
http://www.accuray.com/