Linac-based intraoperative radiotherapy with electrons (IOERT) was implemented to prevent local recurrences after breast conserving therapy (BCT) and was delivered as an intraoperative boost to the tumor bed prior to whole breast radiotherapy (WBI). A collaborative analysis has been performed by European ISIORT member institutions for long term evaluation of this strategy.
METHODS AND MATERIALS
Until 10/2005, 1109 unselected patients of any risk group have been identiﬁed among seven centers using identical methods, sequencing and dosage for intra- and postoperative radio-therapy. A median IOERT dose of 10 Gy was applied (90% reference isodose), preceding WBI with 50–54 Gy (single doses 1.7–2 Gy).
At a median follow up of 72.4 months (0.8–239), only 16 in-breast recurrences were observed, yielding a local tumor control rate of 99.2%. Relapses occurred 12.5–151 months after primary treatment. In multivariate analysis only grade 3 reached signiﬁcance (p = 0.031) to be predictive for local recurrence development. Taking into account patient age, annual in-breast recurrence rates amounted 0.64%, 0.34%, 0.21% and 0.16% in patients <40 years; 40–49 years; 50–59 years and P60 years, respectively.
In all risk subgroups, a 10 Gy IOERT boost prior to WBI provided outstanding local control rates, comparing favourably to all trials with similar length of follow up.