External-beam Radiation

Different physicians follow different guidelines for brachytherapy versus external beam radiation for breast cancer. We typically follow the American Brachytherapy Society guidelines for APBI:
Age ≥ 50-years-old; Histology (Infiltrating Ductal Carcinoma); Clinical stage (T1, and T2 ≤ 3.0 cm, N0, M0: no distant metastases.)
This is the website: http://www.americanbrachytherapy.org/guidelines/abs_breast_brachytherapy_taskgroup.pdf
It is also very important that your surgeon is on board as often times closure of the lumpectomy cavity will factor in.
As we are selective in which patients are good candidates, both types have been equally successful in my practice.