You will need to either cast it or write a small conversion function which returns a true boolean value. The problem is that if you are not in control of the form, then you could be getting anything back from a check box.... red/blue, yes/no, up/down, 1/0, light/dark, whatever!
If you are specifically in control of the form, and your not going to mess up existing data, then I suggest that you always set your check boxes to use the values you prefer. Writing a conversion function could be useful because you can keep adding pairs to compare in there.