how to filter items from a selected dropdown list

Hi, am trying to filter items from a dropdownlist..i have written a select SQL statement in the xml table..below is the respective codes..the name of my filter is TreatmentGroup

the xml table with select statement code












SELECT
TreatmentItems.TreatmentGroup As TreatmentGroup,
MedicalSchemeDetail.*
FROM
MedicalSchemeDetail JOIN TreatmentItems ON
MedicalSchemeDetail.CompanyID = TreatmentItems.CompanyID AND
MedicalSchemeDetail.BranchID = TreatmentItems.BranchID AND
MedicalSchemeDetail.DepartmentID = TreatmentItems.DepartmentID AND
MedicalSchemeDetail.ItemID = TreatmentItems.TreatmentID
WHERE
TreatmentGroup=@TreatmentGroup
AND MedicalSchemeDetail.CompanyID = @CompanyID
AND MedicalSchemeDetail.BranchID = @BranchID
AND MedicalSchemeDetail.DepartmentID = @DepartmentID
AND MedicalSchemeDetail.MedicalSchemeID = @MedicalSchemeID
AND IsNull(MedicalSchemeDetail.Excluded,0) = 0


below here is the aspx code with the dropdown list




ALL
Lab Test
RADIOLOGY
NURSING
Prescription
VACCINES


this is the code behind with the filter

protected void ddlPeriodStamp_SelectedIndexChanged(object sender, System.EventArgs e)
{

DropDownList ddlItemGroup = (DropDownList)sender;

if (ddlItemGroup.SelectedValue != null)
ApplyGridFilter();

}

protected void ApplyGridFilter()
{

DBDataSource1.State.BusinessObject.DataPump.FormFilters.Clear();
DBDataSource1.State.BusinessObject.DataPump.FormFilters.Add("TreatmentGroup", TreatmentGroup);
DBDataSource1.State.BusinessObject.Fill(null);
MedicalSchemeDetailGrid.DataBind();
}

kindly help me