The "out of the box" SSRS parameter interface won't let you conditionally hide parameters. You can either build your own interface to collect parameters or use cascading parameters, with a drop down, indicating that the parameter isn't needed.
To use cascading parameters, make your radio box parameter comes later in the parameter list than the dropdown on which it is dependent. Change from a radio box (boolean) to a drop down list. Have it select it's values from a dataset. This dataset can use the first parameter, and if the first parameter doesn't require the radio box, then it should only return "Not Applicable" or a similar value.