hey i just giving a initial idea, try it..
use following namespace for
using System.Web.Caching;
string[] sDependencies = new string[1];
sDependencies[0] = "key_original";
CacheDependency dependency = new CacheDependency(null, sDependencies);
Cache.Insert("key_dependent", "This item depends on OriginalItem", dependency);
or have one more..
Cache.Insert("Key", value, new CacheDependency (Server.MapPath("~/myConfig.xml")));