Treatment constraints for single dose external beam preoperative partial breast irradiation in early-stage breast cancer

Abstract Background Following breast-conserving surgery and post-operative 3D-conformal accelerated partial breast irradiation (APBI), suboptimal cosmetic results have been reported. Preoperative radiation delivery to the intact tumor enables better target visualization and treatment volume reduction. Single dose preoperative APBI has the potential to improve toxicity profiles, reduce treatment burden and enable in vivo exploration of breast cancer radiogenomics. Purpose Develop practical guidelines for single dose external beam preoperative APBI. Methods Recommended dose constraints were derived from pooled dosimetry estimates from 2 clinical trials. In an American dose escalation trial, a uniform 15, 18 or 21Gy dose has previously been evaluated for non-lobular cT1N0 or low/intermediate grade DCIS n =32). In the Netherlands, the feasibility of ablative APBI (20Gy to GTV, 15Gy to CTV) to non-lobular cT1N0 in supine position, is currently being explored ( n =15). The dosimetric adherence to the developed constraints was evaluated in new APBI plans with a 21Gy uniform dose but an extended CTV margin ( n =32). Results Dosimetric data pooling enabled the development of practical guidelines for single dose preoperative APBI. Conclusion The developed guidelines will allow further explorations in the promising field of single dose preoperative external beam APBI for breast cancer treatment.