CheckComboBox Extended WPF

Hello,

Im using the CheckComboBox from WPF Extended Toolkit.

I managed to add items using the code below:

public class fillDoctorsCc { public int DocID { get; set; } public string fullName { get; set; } };
        private void fillDoctorsCC()
        {
            var refer = from b in conn.tblDoctors
                        orderby b.Surname
                        select new fillDoctorsCc { DocID = b.DocID, fullName = b.Initials + " " + b.Surname + " ["+ b.Address + "]" };

            cbRefCC.DisplayMemberPath = "fullName";
            cbRefCC.SelectedMemberPath = "DocID";
            cbRefCC.ItemsSource = refer;
        }

But I'm now trying to load and programmatically check specific items in the list that shows. Im a beginner and need help please

Thankyou in advance.