Is a close (<1mm) posterior margin an indication for lumpectomy cavity boost in a patient with early stage breast cancer when dissection was carried down to the pectoral fascia?

In the setting of invasive breast cancer, a meta-analysis and guidelines have determined a negative margin is no tumor on ink. So as long as margin is > 0, I would not consider a close margin (often considered for 0-2 mm) to be a sole reason to boost.

In the setting of pure DCIS, current guidelines ...