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

## TL;DR

This study compares radiation doses to sensitive organs in two different radiotherapy schedules for early breast cancer, finding that the ultra-hypofractionated method reduces radiation exposure.

## Contribution

The study provides a dosimetric comparison of ultra-hypofractionated versus hypofractionated radiotherapy schedules in early breast cancer treatment.

## Key findings

- Patients treated with UHF received significantly lower equivalent doses to organs at risk compared to those treated with HF.
- The UHF group showed significantly lower mean ipsilateral lung and heart doses compared to the HF group.
- The results support the dosimetric safety and feasibility of UHF schedules in early breast cancer treatment.

## Abstract

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

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.

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).

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.