Cumulative Risk of Cosmetic Worsening Following Ultrahypofractionated Whole Breast Radiation Therapy With Simultaneous Integrated Boost: The Largest Real-World Data.

Abstract

Randomized trials have shown that ultrahypofractionated radiation therapy (uHFRT) is a safe alternative to moderately hypofractionated or conventional breast radiation therapy. However, its safety in patients requiring a tumor bed boost cannot be firmly established, as none of the patients in the FAST trial and only a quarter of the patients in the FAST-FORWARD trial were offered a tumor bed boost. We aimed to report the real-world experience of cosmetic outcomes after whole breast irradiation with uHFRT and a simultaneous integrated boost (SIB). The study population consisted of 354 breast cancer patients treated with uHFRT from 2020 to 2022. All patients received SIB either with electrons (n = 207) or photons (n = 147). The SIB dose was 33 Gy and 32 Gy for the FAST (n = 74) and FAST-FORWARD (n = 280) protocols, respectively. Cosmesis was assessed subjectively by the physicians and the patients and objectively by the BCCT.core software. The worsening of breast cosmesis was defined as a shift in the score from any lower to a higher category on a 4-point scale, ie, excellent (0), good (1), fair (3), and poor (4). The median follow-up time of the cohort was 31.31 months. As per the physicians' ratings, cosmetic deterioration at 1 year was 17% (13%, 21%), which doubled to 34% (29%, 39%) at 2 years. Patient-rated worsening was 9% (6.3%, 12%) at 1 year and 15% (12%, 19%) at 2 years. Similarly, the BCCT.core rating also showed temporal worsening: 17% (13%, 22%) at 1 year and 33% (28%, 38%) at 2 years. Multivariate analysis showed that higher body mass index, postmenopausal status, women with larger breast volumes, oncoplastic surgery, regional nodal irradiation, and the FAST-FORWARD protocol were factors associated with a higher risk of cosmetic worsening. We observed that uHFRT with SIB was associated with an early cosmetic deterioration that progressively worsened over time. These real-world findings offer valuable insights to support informed clinical decision-making.