In your PHP you could check $_GET['radio_option'] and based on the value redirect to other pages using header function, something like this:
switch($_GET['radio_option']) {
case 'val1':
header('location: page1.php');
exit;
case 'val2':
header('location: page2.php');
exit;
case 'val3':
header('location: page3.php');
exit;
}
//here handle everything else - although normally you shouldn't get here
The other alternative would be to use javascript to set the action attribute of the form before it is submitted. For example:
$(document).ready(function() {
$("input:radio[name=your_radio_naem]").click(function() {
var value = $(this).val();
var target = "main.php";
if(value == 'val1')
target = "page1.php";
else if(value == 'val2')
target = "page2.php";
else if(value == 'val3')
target = "page3.php";
$('#myform').attr('action', target);
});
});