Favorable Rates of Excellent or Good Cosmetic Outcomes in Patients Treated With Carefully Planned Accelerated Partial Breast Irradiation Delivered Twice Daily or Once Every Other Day.

Purpose: Two randomized controlled trials of external beam accelerated partial breast irradiation (EB-APBI) using 38.5 Gy/10 fractions twice daily demonstrated excellent cancer control outcomes in appropriately selected patients, but with conflicting results regarding cosmesis. A recent randomized controlled trial reported high rates of acceptable cosmesis using 30 Gy/5 fractions every other day, calling into question the most appropriate schedule for EB-APBI. Our accelerated partial breast irradiation approach uses strict contouring, dosimetric, and planning guidelines. We report our experience with twice-daily and every-other-day EB-APBI, hypothesizing that our treatment planning approach would result in acceptable acute toxicity and cosmesis.

Methods and materials: We identified patients who received EB-APBI from April 2017 to December 2021. Clinical, pathologic, acute toxicity, cosmesis, and dosimetric data for the lumpectomy gross tumor volume, clinical target volume, and planning target volume were collected. Cosmesis was physician-reported using the 4-point Radiation Therapy Oncology Group (RTOG) global cosmetic score: excellent, good, fair (F), and poor (P). We report descriptive statistics to summarize our results.

Results: A total of 245 patients were included with a median follow-up of 19 months (IQR, 9-30 months); the median age was 66 years (IQR, 59-71 years), 82% had invasive breast cancer, 100% had invasive tumors that were hormone-receptor positive/human epidermal growth factor receptor 2 negative, and 96% had nodal surgery for invasive disease. Fractionation was twice daily in 55% of patients, and every other day in 45%. Three-dimensional conformal radiation was used in 88%, with a median of 6 fields, and 96% were treated prone. Most patients had no acute toxicity (55% grade 0 dermatitis; 57% grade 0 fatigue; 97% grade 0 pruritis). The rate of excellent/good cosmesis was 97.1% (n = 238), and F/P was 2.9% (n = 7). The ipsilateral breast V100 was marginally associated with increased odds of F/P cosmesis (odds ratio, 1.18; 95% CI, 0.99-1.42; P = .07).

Conclusions: With multiple-field 3-dimensional conformal radiation in the prone position, EB-APBI can be delivered with extremely low toxicity and great cosmetic results with twice-daily or every-other-day fractionation. Given the low rate of F/P cosmesis, longer follow-up is needed to confirm the stability of these results and to help identify optimal planning dose-volume parameters to help minimize the rate of F/P cosmesis.