Ultrahypofractionation and Simultaneous Integrated Boost in Breast Cancer: Early Side Effects Analysis

The FAST-Forward study paved the way for ultrahypofractionation (UHF) in breast cancer. We prospectively registered and analyzed our case series receiving UHF + simultaneous integrated boost (SIB) to further reduce the treatment to a total of 5 days. The study aimed to present the 6-month early side effects results of the first patients treated with this scheme in 16 radiation oncology centers in Spain.

A total of 242 breast cancer patients received adjuvant radiation therapy between April and December 2020. The median age was 61 years (interquartile range, 53-70). All patients underwent breast-conserving surgery. Chemotherapy (QT) was administered to 27.7%, and endocrine therapy to 85.1%. A SIB of 29 Gy was applied to 60.7% of the patients, while 39.3% did not have a boost indication. Breast radiation therapy (RT) with SIB to the tumor bed and regional node irradiation was done in 5.4 % of patients.

Most patients were treated with Volumetric modulated arc therapy (66.1%) and intensity modulated RT (30.6%). One patient received treatment by 3-dimensional techniques (0.4%) and 7 patients (2.9%) a combined intensity modulated RT-3-dimensional technique. Deep inspiration breath-hold was used in 16.9% of cases. At the end of treatment, erythema grade (G) 0 was presented in 56.1%, G1 in 43.1%, and G2 in 0.8%. G1 edema was observed in 14.6% and less than 1% had G2. After 6 months, 97% had G0 erythema, 3% G1, and 0% G2, while G1 edema was observed in 11.4% and G2 in 2.5%. No statistically significant impact on side effects was found for planning target volume breast and planning target volume boost volumes.

UHF with SIB of 29 Gy to the tumor bed in patients with early-stage breast cancer is clinically feasible, safe, and free of an excess of early side effects. Further analysis of late toxicity is needed.