How to get the collection of Items from DocumentGroup?

How to get the collection of Items from DocumentGroup?

I'm using MVVM in my project and I wonder if its possible to retreive the
collection Items from documentgroup in Shellview to my shellviewmodel.
This is the code I use in my Shellview:
<dxd:DockLayoutManager x:Name="dockLayoutManager" ActiveDockItem="{Binding
ActiveSelectedView, Mode=TwoWay}">
<dxd:LayoutGroup>
<dxd:LayoutGroup ItemWidth="3*" Orientation="Vertical">
<dxd:DocumentGroup Name="documentContainer"
ItemHeight="3*" Grid.Column="1"
prism:RegionManager.RegionName="{x:Static
res:Regions.MainRegion}"
ClosingBehavior="ImmediatelyRemove">
So I need the collection of Items from the documentgroup, binded to a
property or something..
Items="{Binding DockItemsSource, Mode=OneWayToSource"} is not possible
Any Ideas?
Greets