The easiest way to do this is not to close the RadWindow from within the content page, but to directly navigate the parent page to the new one. Since RadWindow exists only in the context of the page it is created in, it will be automatically closed.
I assume that in your code, you are calling GetRadWindow().close()
to close the RadWindow. Try using
top.location.href = "http://newUrl/newpage.aspx"
the Telerik team