Field effects.

Top Line: Is local control with intraoperative radiation therapy (IORT) similar to accelerated partial breast irradiation (APBI)?

The Study: Single fraction IORT has typically been compared to whole breast radiation. Long-term results of the ELIOT trial recently reported a 10% (absolute) higher risk of ipsilateral breast tumor recurrence (IBTR) 15 years after electron-based IORT. But how does IORT compare to accelerated partial breast irradiation (APBI)? In this prospective multi-center cohort study, nearly 500 patients at one Dutch center were treated with electron IORT while patients at two other centers were treated with APBI. IORT consisted of 23.3Gy in 1 fraction using the Mobetron system while APBI was LINAC-based and consisted of 38.5Gy in 10 daily fractions. Despite a significantly higher rate of positive invasive margins (8.1% v 1.5%) and in situ margins (16.2% v 7.7%) with APBI, the rate of IBTR at 5 years was significantly lower than with IORT (3.7% v 10.6%). In the IORT cohort, 40% of IBTR events were considered in-field while 27% were along the biopsy/localization tract and 33% were new primaries. In the APBI arm, almost all IBTRs were new primaries.

TBL: IORT is associated with a higher risk of breast tumor recurrence compared to whole breast radiation and even external beam APBI. | Jacobs, Int J Radiat Oncol Biol Phys 2022