get radio input value wordpress - php

Question

I'm using a plugin which retrieves the value of some radio buttons based on what values I type in the plugin dashboard.
I want to change that function with a function which retrieves the post meta of a post as the value.
This is the function for retrieving the post meta :
<?php echo get_post_meta($post->ID, 'key', true); ?>
and this is the actual code for retrieving the values:
<?php
/* Radio form */
class ECF_Radio extends ECF_Field_Type {
protected $name = 'radio';
public function form_field( $ref, $field ) {
global $ecfdb;
$name = $ecfdb->html_string( $field->name );
echo "<div class='ecf-form-field-title'>$name</div>\n";
$values = preg_split( '/, ?/', $field->values );
echo '<div class=\'ecf-form-field-input\'>';
foreach ( $values as $i => $value ) {
$checked = checked( $i, 1, false );
echo "<p><label><input type='radio' name='$ref' "
. "value='$value'$checked /> $value</p></label>\n";
}
echo '</div>';
}
public function get_description() {
return "Radio selection field";
}
}
new ECF_Radio();
?>
My question is how can I use the function for retrieving the post meta for values?
What exactly do I need to change inside the code to retrieve the post meta not the values written in a filed.
Thank you!