C# datagridview two checkboxes columns act like two radio buttons

i'm developing an application using c# i've add two checkboxes in the datagridview. i want them to act like two radio buttons. if first checkbox is checked the other one is unchecked automatically i tried some code but did't work for me.

private void datagridSB_CellContentClick(object sender, DataGridViewCellEventArgs e)
    {
        if (e.ColumnIndex == 15)
        {

            if (Convert.ToBoolean(datagridSB.CurrentRow.Cells[15].Value = true))
            {
                datagridSB.CurrentRow.Cells[17].Value = false;
                //uncheck the second checkbox
            }
            else if (Convert.ToBoolean(datagridSB.CurrentRow.Cells[15].Value = false))
            {
                datagridSB.CurrentRow.Cells[17].Value = true;
                //check the second checkbox
            }
        }
        if (e.ColumnIndex == 17)
        {
            if (Convert.ToBoolean(datagridSB.CurrentRow.Cells[17].Value = true))
            {
                datagridSB.CurrentRow.Cells[15].Value = false;
                //uncheck the first checkbox
            }
            else if (Convert.ToBoolean(datagridSB.CurrentRow.Cells[17].Value = false))
            {
                datagridSB.CurrentRow.Cells[15].Value = true;
                //check the first checkbox 
            }
        }   
    }

it's not working any help please