How to make ListBoxItem stretch to width of ListBox

<ListBox x:Name="lstArticles" ItemsSource="{Binding}" VerticalAlignment="Top"

BorderThickness="0" SizeChanged="lstArticles_SizeChanged"

ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto" >

<ListBox.ItemTemplate>

<DataTemplate>

<Grid Loaded="Grid_Loaded">

<myCustomControl:ArticleEntry />

</Grid>

</DataTemplate>

</ListBox.ItemTemplate>
</ListBox>

private void lstArticles_SizeChanged(object sender, SizeChangedEventArgs e)

{

lstArticles.ItemTemplate = null;

lstArticles.ItemTemplate = dataTemplate;

}

private void Grid_Loaded(object sender, System.Windows.RoutedEventArgs e)

{

Grid vGrid = (Grid)sender;

if((Visibility)lstArticles.GetValue(ScrollViewer.ComputedVerticalScrollBarVisibilityProperty) == Visibility.Visible)

vGrid.Width = lstArticles.ActualWidth - 18;

else vGrid.Width = lstArticles.ActualWidth - 10;

}