Sort by Caption rather than by Title – Mod Assistance if possible

Hello.

This wonderful slice of code numerically sorts Masonry Gallery images by ‘Title’ :

function avia_change_posts_query($query, $params){
if(!empty($query[‘orderby’]) && $query[‘orderby’] == ‘post__in’){
$query[‘order’] = ‘ASC’;
$query[‘orderby’] = ‘title’;
}
return $query;
}
add_filter(‘avia_masonry_entries_query’, ‘avia_change_posts_query’, 10, 2);

Is it possible that code can sort by Caption rather that Title – I have, predictably, tried to exchange title for excerpt / caption and so forth with no joy so far …