You shoul use sendTransactional method. Like:
$mail = Mage::getModel('core/email_template');
$mail->setDesignConfig(array('area' => 'frontend', 'store' => Mage::app()->getStore()->getId()))
->sendTransactional(
Mage::getStoreConfig('customer/lowerprice_mail/toshop_template'),
$sender,
$email,
null,
array(
//params array
));