CT Scan Colon Cancer

My dad had a CT scan done on Sunday regarding the (suspected?) cancer that they found when doing a colonoscopy the previous Sunday.  They have said it takes 2-3 weeks for the results to come through.  Dad also had a biopsy done a fortnight ago.

Why does a CT scan take so long to get results from, as all that time cancer could be spreading to other areas of the body if it hasn't done so already?  Is it just that there are insufficient radiographers to decipher the images?