How long does is take for platelets to come back to normal levels after chemo and radiaition?

It depends: Platelets often return quickly after treatment. You have a lot of reserve so that bleeding due to low platelets is less common. Some chemo drug do reduce the platelets for a longer time than others, so it depends on the drug and the amount of radiation.

Variable: Usually you see some recovery in a could of months but occasionally platelet levels will stay sub normal especially if your pelvis was radiated.