Remove nodes with date value older than today

In a C# application, if I have the following XML:

<SyncTable>
  <SyncEntry>
    <Cal_ID>1234</Cal_ID>
    <Cal_LastUpdated>2015-01-20T14:25:34.828-05:00</Cal_LastUpdated>
    <Cal_StartDateTime>2015-01-22T20:05:00-05:00</Cal_StartDateTime>
  </SyncEntry>
  <SyncEntry>
    <Cal_ID>4567</Cal_ID>
    <Cal_LastUpdated>2015-01-20T11:00:24.988-05:00</Cal_LastUpdated>
    <Cal_StartDateTime>2015-02-10T18:30:00-05:00</Cal_StartDateTime>
  </SyncEntry>
</SyncTable>

How can I search and delete the entries <SyncTable> where the <Cal_StartDateTime> entry is older than today?