Getting column index when clicking on editable GRID

I have an editable grid created in Ext. I added checkbox model on it.

I want column index, when I click on any cell in grid, and also by clicking on cell. The entire row should not be selected.

itemclick: function(data, record, item, index, e, eOpts){ 
        **var position = data.getPositionByEvent(e);**
        ColumnIndex = position.column;

by this, ColumnIndex of specific cell can be obtained.