Parsing RSS feed using PHP to insert into my SQL - php

Question

I am able to get my script to parse the items and insert into mySQL OK when using the Channel->items. I now need to insert the url of the thumbnail which is located in items but in a sub-item "folder" for lack of knowing what to call it, but cannot get to it since its a in another level of the item "media:thumbnail" the rss feed is: http://feeds.bbci.co.uk/sport/0/audiovideo/rugby-league-av/rss.xml#
libxml_use_internal_errors(true);
$RSS_DOC = simpleXML_load_file($feed_url);
if (!$RSS_DOC) {
echo "Failed loading XML\n";
foreach(libxml_get_errors() as $error) {
echo "\t", $error->message;
}
}
/* Get title, link, managing editor, and copyright from the document */
$rss_title = $RSS_DOC->channel->title;
$rss_link = $RSS_DOC->channel->link;
$rss_description = $RSS_DOC->channel->description;
$rss_copyright = $RSS_DOC->channel->guid;
$rss_date = $RSS_DOC->channel->pubDate;
//Loop through each item in the RSS document
foreach($RSS_DOC->channel->item as $RSSitem)
{
$item_id = md5($RSSitem->title);
$fetch_date = date("Y-m-j G:i:s"); //NOTE: we don't use a DB SQL function so its database independent
$item_title = $RSSitem->title;
$item_description = $RSSitem->description;
$item_date = date("Y-m-j G:i:s", strtotime($RSSitem->pubDate));
$item_url = $RSSitem->link;
$image_url =($RSSitem->media:thumbnails)->url;
echo "Processing item '" , $item_id , "' on " , $fetch_date , "<br/>";
echo $item_title, " - ";
echo $item_date, "<br/>";
echo $item_description, "<br/>";
echo $item_url, "<br/>";
echo $image_url, "<br/>";
// Does record already exist? Only insert if new item...
$item_exists_sql = "SELECT item_id FROM $db_database.`rssingest` where item_id = '" . $item_id . "'";
$item_exists = mysqli_query($db,$item_exists_sql);
if(mysqli_num_rows($item_exists)<1)
{
echo "<font color=green>Inserting new item..</font><br/>";
$item_insert_sql = "INSERT INTO $db_database.`rssingest`(item_id, feed_url, item_title, item_date, item_url, fetch_date,image_url) VALUES ('" . $item_id . "', '" . $feed_url . "', '" . $item_title . "', '" . $item_date . "', '" . $item_url . "', '" . $fetch_date . "', '" . $image_url . "')";
$insert_item = mysqli_query($db,$item_insert_sql);
}
else
{
echo "<font color=blue>Not inserting existing item..</font><br/>";
}
echo "<br/>";
}