Set columns in DataTable when certain Roles are DownLoading data

Hi
Have  DownLoad , Print buttons on the form. Using below code successfully downloading data to CSV file. I am aware that using
if(User.IsInRole("userRole")) { //then do not get the columns specified //Not sure of the right place/do it }


Question

Now i like to set few columns to NULL when the users in certain roles trying to download the data
protected void btnDownLoad_Click(object sender, EventArgs e) { Response.ContentType = "text/csv"; Response.AddHeader("Content-Disposition", "Attachment;filename=EndUserRecord.csv"); //Get user record DataTable DataTable dt = GetUserRecord(); //Print column names foreach (DataColumn column in dt.Columns) { Response.Write(column.ToString().ToUpper() + ",") ...