Ultrahypofractionated Whole Breast Radiation Following Chemotherapy

Standard treatment approaches for patients with localized BC includes BCS followed WBI \[1\], which has demonstrated equivalent local control and survival when compared to mastectomy \[2,3\]. Although conventionally fractionated radiotherapy (RT) (50 Gy 2 Gy per fraction) administered in 25 fractions in 5 weeks was historically used, moderate hypofractionation RT trials utilizing shorter treatment times and higher doses per session have resulted in favorable outcomes \[4,5,6\]. In addition, increased local control and reduced toxicity rates observed in moderate hypofractionation RT trials \[5,6\] have resulted in studies evaluating the use of ultrahypofractionated breast RT which further shorten the treatment time. The results of the FAST-Forward RT trial have shown that adjuvant RT using 26 Gy/5.2 Gy per fraction, over 5 fractions administered in 1 week, was not inferior to the standard 40.05 Gy/15 fx/3 weeks for local tumor control and is equally safe in terms of effects on normal tissue \[7\]. Side effects associated with RT can be more pronounced in patients when RT is combined with surgery and/or chemotherapy \[9\]. There are abundant data describing the safety of combining conventionally fractionated RT following chemotherapy. Similarly, there are several trials which have reported outcomes of patients who have received hypofractionated RT, including subsets of patients who also received chemotherapy demonstrating similar acute and late toxicity profiles compared to standard fractionation regimens \[10, 11, 12, 13\]. Although the FAST-Forward trial included patients who received neoadjuvant and adjuvant chemotherapy and estimates of 5-year cumulative incidence of any moderate or marked clinician-assessed normal tissue effects in the breast or chest wall were reported to be similar for 40 Gy 15 fraction hypofractionated vs the 26 Gy 5 fraction ultrahypofractionated RT regimen (26·8% v 28·5%, respectively), the study was not designed to detect differences for those who had received prior chemotherapy compared to those who did not \[7\]. Retrospective subgroup analysis did not identify differences in adverse effects related to prior chemotherapy, however confidence intervals overlapped, and the power for these retrospective subgroup analyses was low \[19\]. Hence, there is limited data evaluating the toxicity of ultrahypofractionated adjuvant breast RT in patients who have received prior chemotherapy. This study is designed to evaluate the acute and late effects on the breast of ultrahypofractionated WBI using the FAST-forward regimen (26 Gy, 5.2 Gy per fraction delivered in 1 week) in patients \> 60 years of age with pathologically or clinically node-negative early-stage BC who undergo BCS and chemotherapy.