$builder
    ->add('myRadios', 'choice', array(
        'choices' => array(
            'one' => 'uno',
            'two' => 'due'),
        'multiple' => false,
        'attr' => array('class' => 'testClass'),
        'expanded' => true

<div class="control-group">
    <label class="control-label required">Myradios</label>
    <div class="controls">
        <label for="form_one_0" class="required radio">
            <input type="radio" id="form_one_0" name="form[one]" required="required" value="uno" />
            <span>Uno</span>
        </label>
        <label for="form_two_1" class="required radio">
            <input type="radio" id="form_two_1" name="form[two]" required="required" value="due" />
            <span>Due</span>
        </label>
    </div>
</div>