Using VirtualFields in variable cakephp

I created a virtual field , but I do not have much concept about it, until today I only used it to make pagination, how do I use the result of this virtual in a variable?

public $virtualFields = array(
    'js_dt_inicio' => '(CASE WHEN inicio_de IS NOT NULL AND inicio_de!=\'\' AND DATE_ADD(CURDATE(), INTERVAL 30 DAY)<=inicio_de THEN inicio_de ELSE DATE_ADD(CURDATE(), INTERVAL 30 DAY) END)',
);