Intraoperative radiotherapy (IORT) as boost in breast cancer

Abstract

The term IORT (intraoperative radiotherapy) is currently used for various techniques that show huge differences in dose delivery and coverage of the tissue at risk. The largest evidence for boost IORT preceding whole breast irradiation (WBI) originates from intraoperative electron treatments (IOERT) with single doses around 10 Gy. At median follow-up periods at 6 years, outstandingly low local recurrence rates of less than 1% are observed. Higher local relapse rates were described for G3 tumors and triple negative breast cancers as well as for IORT following primary systemic treatment for locally advanced tumors. Even there, long term (>5y) local tumor control rates mostly beyond 95% were maintained. Compared to other boost methods, an intraoperative treatment has evident advantages in terms of precision (by avoiding a “spatial and/or temporal miss”), cosmetic outcome and patient comfort. Direct visualisation of a tumor bed during surgery guarantees for an accurate dose delivery, which has additionally gained importance in times of primary reconstruction techniques after lumpectomy, since IORT is performed before breast tissue including parts of the tumor bed is mobilized for plastic purposes. As a consequence of direct tissue exposure without distension by hematoma/seroma, IORT allows for small treatment volumes and complete skin sparing, both having a positive effect on late tissue tolerance and, hence, cosmetic appearance. Boost IORT marginally prolongs the surgical procedure, while significantly shortening postoperative radiotherapy. Its combination with external beam radiotherapy to the whole breast (WBI) is currently tested in two multicentric prospective trials: as kV-IORT in the multicentric TARGIT-B (oost) study, and as IOERT in the HIOB trial (3 weeks hypofractionated WBI preceded by IORT electron boost).

Intraoperative Electron Radiotherapy (IOERT) in the Treatment of Primary Breast Cancer

“…Four reports including about 500 patients have analyzed the cosmetic outcome after boost IORT [15]. In 2 smaller trials, no difference was noted for boost IORT patients compared to conventional radiotherapy: 86/91% good or excellent ratings for the IORT group and 81/96% for the control group [27,30].…”

“…A further aspect is the prevention of possible residual tumor cell repopulation between surgery and adjuvant radiotherapy (‘temporal miss'). Finally, a good oxygenation status of the tumor bed during surgery could also be a factor for enhanced biological effectiveness, which has not yet been investigated [15]. All these cellular and transcellular reactions of irradiated tissues and their particular impact on clonogenic cell inactivation are the subject of ongoing research [16].…”

The Role of Brachytherapy in the Treatment of Breast Cancer

“…Further research is required firstly to determine the optimal technique with regard to long-term local control and side effects, and secondly to define the best approach for individual patients. Patients with small breasts and planned eventual oncoplastic surgery might be the best candidates for external or intraoperative electron radiotherapy [52] as a boost or partial breast irradiation, while women with larger breasts might benefit more from different invasive techniques like MIB or balloon-based BT. Long-term follow-up data of BT, especially periods exceeding 10 years, are not currently available but are needed to support the efficacy of breast BT given the high survival rate of these patients.…”

Recent Developments in Radiation Oncology: An Overview of Individualised Treatment Strategies in Breast Cancer

“…Two known disadvantages are that an intraoperative boost prolongs the surgical procedure and that conventional fractionated WBI is usually still delivered after surgical wound healing. The combination with hypofractionated EBRT is currently under evaluation in 2 multicentric prospective trials: as kV-IORT in the TARGIT-B(oost) study and as IOERT in the HIOB trial (3 weeks hypofractionated WBI preceded by IORT electron boost) [19]. …”