How to get paper-radio-button, paper-checkbox or core-dropdown-menu values with PHP $_GET after submitting a form

I am using PHP as a programmation language adapting the MVC architecture. and the Polymer library as a view.

I found some problems particularly when I used some polymer elements in a form.

If I use the paper-radio-button, paper-checkbox or core-dropdown-menu, for example,

I can not recuperate them with $ _GET or $ _POST

.