The patient should be able to wait until their next scheduled dialysis session. In fact, the 2012 American College of Radiology's Manual on Contrast Media states, "Unless an unusually large volume of contrast medium is administered or there is substantial underlying cardiac dysfunction, there is no need for urgent dialysis after intravascular iodinated contrast medium administration."
As an FYI, the average amount of contrast volume infused for a typical CT scan is around 100 mL.
There you have it, although I'm sure you already knew (or at least suspected).
For a nephrologist's perspective, the Renal Fellow Network blog has a great post on this topic as well: http://renalfellow.blogspot.com/2009/08/prophylactic-hemodialysis-for-iv.html