What are your considerations in choosing partial breast irradiation versus external beam hypofractionated whole breast RT for early stage breast cancer?

Accelerated partial breast irradiation has become a standard of care option for appropriately selected patients. Currently, patients who can be offered APBI come from the ASTRO guidelines or the more recently updated ABS partial breast guidelines released.

In general, I will consider APBI for node negative patients 50 years or older with tumors 2 cm or less that are ER positive. I offer patients both hypofractionated whole breast +/- boost (depending on factors) and APBI in such cases. Following the publication of the University of Florence trial and more recently, IMPORT LOW, I am offering external beam APBI more frequently using IMRT rather than 3D-CRT.

Partial breast irradiation can be delivered via EBRT, IORT, HDR, and electronic brachytherapy.

As far as who would be a good candidate for PBI, ASTRO updated their consensus statement and made a few changes, but patients that they consider to be "cautionary" or "unsuitable" may be neither, based on institutional data of thousands of patients. There are many others reporting similar findings, so it's not clear whether the ASTRO statement is meaningful. It is similar to saying that younger women tend to have higher IBTR after BCS + whole breast RT, so they shouldn't get BCS. In any case ...

There has been a published trial of ~2000 patients randomized to whole breast to 40 Gy, partial breast to 40 Gy, and whole breast to 36 Gy with a 4 Gy boos...