how many chemo cycles for xelox

my dad's aproching his 5th XELOX cycle and i wanted to find out how many cycles if typical for this treatment?

 I have read some articles about folfox mentioning that benifit of 8 vs 12 cycles has not been established. found no such studies for XELOX 

His PET CT a few weeks back did not show any disease and CEA was down to 4.2