In my form I have some checkboxes, but by default, I have :
You can overide the form_row function like that (modified to fit the temple label / checkbox of twitter bootstrap ) : (in that exemple it's "checkbox" but i think with "radio" it works the same)
{% extends 'form_div_layout.html.twig' %}
{% block field_row %}
{% spaceless %}
{% if 'checkbox' in types %}
{% if not compound %}
{% set label_attr = label_attr|merge({'for': id}) %}
{% endif %}
{% if required %}
{% set label_attr = label_attr|merge({'class': (label_attr.class|default('') ~ ' required')|trim}) %}
{% endif %}
{% if label is empty %}
{% set label = name|humanize %}
{% endif %}
{% else %}
{{ parent() }}
{% endif %}
{% endspaceless %}
{% endblock field_row %}