Protected Sub Imgbtnesci_Click(sender As Object, e As System.Web.UI.ImageClickEventArgs) Handles Imgbtnesci.Click
        ClientScript.RegisterStartupScript(Me.GetType, "closeWindow", "<script type='text/javascript'>GetRadWindow().close('" & _image & "')</script>")
    End Sub

la variabile la dicharo così:

Public _image as string

e poi la vado a valorizzare quando eseguo questo comando in quest'altro button:

    Private Sub Imgbtnupload_Click(sender As Object, e As System.Web.UI.ImageClickEventArgs) Handles Imgbtnupload.Click
        If RadUpload1.UploadedFiles.Count > 0 Then
            _image = "/public/image_profile/" & RadUpload1.UploadedFiles.Item(0).FileName
        End If
    End Sub