Narek

$allKeys = array(
            'Page' => array('page1', 'page2', ...),
);
function getKey($searchKey){
    foreach($allKeys as $mainKey => $keys){
        if (array_key_exists($searchKey, $keys[$mainKey])){
            return $keys[$maintKey][$searchKey];
        }
        return null;
    }
}
$key = getKey('page1');// or getKey('page2') // return Page
$cache->getItem($key);