Android Question How to hide RadioButton Circle?

Sub Activity_Create(FirstTime As Boolean)
    Activity.LoadLayout("main")

    AddStatelistRadioButton(rbtTest1, "Flag_GB_1.png", "Flag_GB_2.png", "Flag_GB_3.png", Gravity.CENTER)
    AddStatelistRadioButton(rbtTest2, "Flag_F_1.png", "Flag_F_2.png", "Flag_F_3.png", Gravity.CENTER)
 
End Sub

Sub AddStatelistRadioButton(rbt As RadioButton, ImageEnabled As String, ImageChecked As String, ImagePressed As String, mGravity As Int)
    Dim sdw As StateListDrawable
    sdw.Initialize
    Dim bdwEnabled, bdwChecked, bdwPressed As BitmapDrawable
    bdwEnabled.Initialize(LoadBitmap(File.DirAssets, ImageEnabled))
    bdwEnabled.Gravity = mGravity
    bdwChecked.Initialize(LoadBitmap(File.DirAssets, ImageChecked))
    bdwChecked.Gravity = mGravity
    bdwPressed.Initialize(LoadBitmap(File.DirAssets, ImagePressed))
    bdwPressed.Gravity = mGravity
    sdw.AddState(sdw.State_Checked, bdwChecked)
    sdw.AddState(sdw.State_Pressed, bdwPressed)
    sdw.AddCatchAllState(bdwEnabled)
    rbt.Background = sdw
End Sub