Get querystring from URLReferrer
You could do
HttpUtility.ParseQueryString(Request.UrlReferrer.Query)["SYSTEM"]
That is c# in vb is is probably something like
HttpUtility.ParseQueryString(Request.UrlReferrer.Query())("SYSTEM")
In VB.NET, one way to get the value of "SYSTEM" from the UrlReferrer is:
HttpUtility.ParseQueryString(Request.UrlReferrer.Query).GetValues("SYSTEM")(0)