How do I access query string parameters in asp.net mvc?

so far the best way I figured out is to create a copy of ViewContext.RouteData.Values
and inject QueryString values into it.
and then modify it before every ActionLink usage.
still trying to figure out how to use .Union() instead of modifying a dictionary all the time.

<% RouteValueDictionary   tRVD = new RouteValueDictionary(ViewContext.RouteData.Values); %>

<% foreach (string key in Request.QueryString.Keys )
    {
         tRVD[key]=Request.QueryString[key].ToString();
    } %>

<%tRVD["SortBy"] = "Name"; %>
                <%= Html.ActionLink("Name", "Index", tRVD)%>