File Download end event hook

I am doing this on a click event:

Response.Clear()
Response.AddHeader("Content-Disposition", "attachment; filename=" & file.Name)
Response.AddHeader("Content-Length", file.Length.ToString())
Response.ContentType = "application/octet-stream"
Dim s As New System.IO.FileStream(file.FullName, IO.FileMode.Open)
Response.WriteFile(s.Handle, 0, file.Length)
Response.End()

Everything works ok, the file gets downloaded. But my problem is: I want to know if the user selected "Save" or "Cancel" in the download window. In other words I want to know if the download was succesful... Is there a way for that?

Thank you!!!