KEY POINTS
- This prospective, nonrandomized multicenter study included 242 patients with early breast cancer treated after breast-conserving surgery between April and December 2020. All received 26 Gy in five consecutive daily fractions, with 157 patients receiving a simultaneous integrated boost (SIB) and 85 receiving whole-breast irradiation alone. Median follow-up was 64.7 months, and 221/242 patients (91.3%) completed their scheduled five-year assessment.
- Whole-breast RT delivered 26 Gy in five fractions (5.2 Gy/fraction), with an integrated tumor-bed boost to 29 Gy in five fractions (5.8 Gy/fraction) using conformal treatment planning, predominantly VMAT or IMRT. The median boost PTV was 47.2 cm³ (IQR 29.2–72.0), representing a median 6.3% of the whole-breast PTV, allowing completion of both whole-breast treatment and boost within one week.
- Among the 157 patients receiving SIB, cumulative five-year any-grade fibrosis was 8.9% and any-grade breast pain was 14.6%, predominantly low grade. Other late effects were uncommon: breast edema 5.1%, arm edema 0.6%, atrophy 1.9%, and telangiectasia 0.6%. No breast ulceration was reported, and two patients experienced grade 3 breast pain during follow-up.
- In the exploratory comparison, five-year breast pain was more frequent with SIB than without boost (14.6% vs 4.7%; p=0.019), an absolute difference of 9.9 percentage points. No significant differences were identified for fibrosis (8.9% vs 9.4%), breast edema (5.1% vs 3.5%), atrophy, telangiectasia, or ulceration. These comparisons were unadjusted, and boost allocation was determined by clinical indication rather than randomization.
- Chemotherapy was associated with a higher prevalence of persistent breast pain across the full 242-patient cohort. At annual assessments, pain occurred in approximately 22–23% of chemotherapy-treated patients versus 6–7% of those without chemotherapy, with odds ratios ranging from 3.6 to 5.0 (all p≤0.004). This association persisted after excluding patients undergoing axillary lymphadenectomy, but chemotherapy, boost use, age, and tumor characteristics were correlated, preventing causal attribution.
- Boost volume was not significantly associated with late toxicity severity, with Spearman correlation coefficients ranging from −0.13 to 0.02 across assessed endpoints (all p≥0.09). An initially significant association with one-month erythema (rho 0.16; p=0.038) did not survive multiplicity correction, suggesting that absolute boost volume alone did not explain the observed late pain signal.
- Oncological outcomes were favorable but descriptive. Among SIB-treated patients, two recurrences (1.3%) occurred during follow-up, neither within the original tumor quadrant, and six deaths (3.8%) were recorded. Median disease-free and overall survival were not reached. However, the low event numbers, lack of baseline breast pain assessment, and absence of systematic patient-reported cosmetic or quality-of-life outcomes prevent conclusions about oncological equivalence or definitive comparative toxicity.
CLINICAL TAKEAWAY
Delivering 26 Gy whole-breast irradiation with a simultaneous 29 Gy tumor-bed boost in five fractions was associated with low rates of objective late toxicity after more than five years, supporting its feasibility as a one-week treatment option. However, persistent breast pain was more frequent among boosted patients, and nonrandomized treatment selection and chemotherapy exposure prevent attribution of this difference to the boost itself; randomized comparisons with established boost schedules remain important.
SOURCE
International Journal of Radiation Oncology, Biology, Physics