Dosimetric comparison of organs at risk in ultra-hypofractionated versus hypofractionated postoperative radiotherapy for early breast cancer: single center clinical study.

Abstract

Background: Growing evidence of safety and feasibility has prompted a shift toward ultra-hypofractionated (UHF) schedules in postoperative radiotherapy in early breast cancer.

Patients and methods: Eighty patients over 50 years of age with early breast cancer (T1-2 and N0-1) who underwent postoperative, 3D conformal, free-breathing whole breast radiotherapy were included. The prospective arm consisted of 40 patients treated with UHF (26 Gy/5 fractions/one week) from 2023-2024, whereas the control arm was retrospective and represented by data from 40 patients treated with hypofractionated radiotherapy (HF) (40.5-42.2Gy/15-16 fractions/3 weeks) between 2015 and 2020. Dosimetric parameters for organs at risk (OARs) (heart and ipsilateral lung) were derived from the dose-volume histograms. Statistical evaluation was done with paired sample t-test and Mann-Whitney U test.

Results: Dosimetric analysis revealed that patients treated with UHF schedule received significantly lower equivalent doses in 2 Gy fractions (EQD₂Gy) to OARs compared with those treated with the HF schedule. The mean ipsilateral lung EQD₂Gy dose was significantly lower in the UHF group (3.94 ± 2.1 Gy) than in the HF group (6.24 ± 2.4 Gy; p < 0.01). Among patients with left-sided breast cancer, the mean heart EQD₂Gy dose was also significantly reduced in the UHF group (1.34 ± 0.5 Gy) compared with the HF group (3.02 ± 1.4 Gy; p < 0.01).

Conclusions: These findings indicate a consistent dosimetric advantage of the UHF schedule, particularly in reducing radiation exposure to the heart and ipsilateral lung. These results support the dosimetric safety and feasibility of UHF schedules in early breast cancer treatment.