This document provides guidance on the use of accelerated partial breast irradiation (APBI) based on published evidence and expert consensus. It proposes three patient groups: 1) "suitable" patients for whom APBI outside of trials is acceptable, 2) "cautionary" patients for whom APBI should only be considered in trials, and 3) "unsuitable" patients for whom APBI is not recommended. While APBI may be an option for select patients, whole breast irradiation remains the established standard treatment with longer-term data demonstrating effectiveness and safety. Patients choosing APBI should understand it is not as established as whole breast irradiation.