As Saratchand suggest, that's the only option you can use to clear Query String Parameters. See Below
// Get the NameValueCollection
PropertyInfo isreadonly = typeof(System.Collections.Specialized.NameValueCollection).GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic);
// make collection editable
isreadonly.SetValue(this.Request.QueryString, false, null);
Don't forget to add following Using Statement
I know you asked this question in December Last year and by now you may have solved the issue, but this will be helpful for other users.
RajPrabu_Spark, if this helps please login to Mark As Answer. | Alert Moderator