How bad would it be to have two ct scans of the chest in a month?

Not very dangerous: The info provided on the chart if you go to the link below should be very helpful. It will show you the radiation dose for many different radiology exams. http://www.radiologyinfo.org/en/safety/?pg=sfty_xray in general, the risk from the two exams you mention is very low.

If the CT scans: are medically necessary, then the benefit outweighs the small theoretical risk. For two standard chest CT scans, the theoretical additional lifetime cancer risk is 0.08% or about 1 in 1130. You can calculate the risks of various radiology studies with an interactive tool at xrayrisk.com