I would do it dynamically.
$xml = @simplexml_load_string($path) // loads your valid xml data
foreach($xml->channel->item as $entry) {
$namespaces = $entry->getNameSpaces(true);
foreach($namespaces as $ns=>$value)
{
$job = $entry->children($namespaces[$ns]);
$author = (string)$job->creator;
if ($author != "")
{
$someVariable = (string) $dc->creator;
}
}