C Sharp :: How To Bind WPF Datagrid Radio-button Column To Entities Class

In my WPF application I created a LINQ to SQL entities class. Then I created a partial class and there add code to my entity class. Below is the code of it:

namespace Mynamespace {
    partial class rts_index {
        #region Fields  
        /// <summary>
        /// Status:
        /// "Selected" - true, "Unselected" - false.
        /// </summary>
        private bool _is_selected;

[code]....

Then I executed LINQ to SQL. Works perfectly well. Then I bound WPF Datagrid radiobutton column to is_selected property of the partial class. Below is XAML code:

.
.
.
<Window.Resources>
<CollectionViewSource x:Key="rts_indexViewSource" d:DesignSource="{d:DesignInstance my:rts_index, CreateList=True}" />
</Window.Resources>

[code]....

And here I have the problem. When I'm changing the radiobutton status from Unchecked to Checked it doesn't change the value of is_selected property from false to true in the partial class. I don't know why.