Set value to form Field from Html web resource

I have created one Html page in Crm and call that HTML webresource in ribbon button.In html I have the radio button.Inside the html page's javascript fuction i get the selected radio button value.

now i need to set the selected radio button value in Form?

I used the following code but its not working

 window.parent.Xrm.Page.data.entity.attributes.get("description").setValue(radioButtonValue);