Breast cancer radiotherapy
IORT with electrons as boost strategy during breast conserving therapy in limited stage breast cancer: Long term results of an ISIORT pooled analysis

https://doi.org/10.1016/j.radonc.2013.05.031Get rights and content

Abstract

Purpose

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.

Material and methods

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 radiotherapy. A median IOERT dose of 10 Gy was applied (90% reference isodose), preceding WBI with 50–54 Gy (single doses 1.7–2 Gy).

Results

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 ⩾60 years, respectively.

Conclusion

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.

Section snippets

Patients and methods

A pooled analysis has been performed among 7 member institutions of the ISIORT-Europe (Table 1). Each institution conducted its own prospective program on breast boost IOERT preceding WBI in agreement with the requirements of their local ethic’s committees’ or internal review boards. All patients gave informed consent.

Data of 1235 consecutive patients were collected, with the vast majority treated between 10/98 and 10/05, and a smaller cohort of 50 patients from Montpellier dating back to the

Statistics

Univariate and multivariate Cox proportional hazards regression models were used to estimate the influence of patients’ or tumor characteristics on the risk of local recurrence for a 95% confidence level. SPSS (IBM PSWA Statistics 18, version 18.0.3) was used to perform the analyses [12].

Results

As of March 2009, a median follow up period of 72.4 months (range 0.8–239) was reached. The quality of follow-up was high, with lacking information for more than one year of only 107 patients (9.6%), the latter group still providing a median FU-time of 67.5 months (3.8–208.6). At the time of analysis, 951 patients were alive without evidence of breast disease.

110 patients had developed metastases, 106 patients have died, thereof 47 from breast cancer and 13 from other malignancies. The actuarial

Discussion

Frozen section histology as first estimation of resection margins [16] shows a specificity of 84% [17] and was in our study available in 79% of all cases. Final histopathological assessment might reveal discrepancies toward frozen section especially for in-situ tumor, leading to re-excisions in a second operation as necessary. In our series, this caused the vast majority of the 10% second resection rate. As to invasive components, frozen sections gave precise intraoperative informations on

Conclusion

IOERT during BCS as preceding boost strategy has possible advantages in terms of precision, patient comfort and in theory, also a potential beneficial influence on late cosmesis. Long term results provide outstanding in-breast tumor control rates in every risk group.

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    On behalf of the ISIORT Europe.

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