Printer Freindly php

[d239113g]

I've having a little trouble with parse XML onto my page. 

 

Most is working, but i just cannot get the $RSS_link to work.

The link in the RSS to the article is

http://www.medicalnewstoday.com/articles/133241.php

 

but what i want to show is

http://www.medicalnewstoday.com/printerfriendlynews.php?newsid=133241

 

which is the printer friendly version of the article. At the moment with my script, it is displaying

http://www.medicalnewstoday.com/printerfriendlynews.php?newsid=

 

but not the article id

 

$rss_document = simpleXML_load_file('http://www.medicalnewstoday.com/rss/allergy.xml');

$url = "http://www.medicalnewstoday.com/printerfriendlynews.php?newsid=" . substr("$RSS_item->link", 41, -4);   

foreach($RSS_doc->channel->item as $RSS_item) {
        //The variable $RSS_item will hold a different item for each loop
        //Write the current item's title to the screen in HTML tags
        echo "<h3>$RSS_item->title</h3>";
        echo "<a href='$url'>$url</a><br />";
        echo "<b>$RSS_item->pubDate</b><br />";
        echo "$RSS_item->description<br /><br />";
    }