Volumetric Modulated Arc Therapy for 26 Gy in 5 Fractions Whole Breast Irradiation for Breast Cancer.

PURPOSE

To report the dosimetric and toxicity outcomes of patients treated with 26 Gy in 5 fractions ultrahypofractionated (uHF) whole breast irradiation (WBI) using volumetric arc therapy (VMAT).

METHODS AND MATERIALS

We identified 476 consecutive patients who underwent WBI using VMAT-uHF between 2020 and 2021. Study endpoints included acute toxicity and dosimetric parameters for target volume and organs at risk. The dosimetric results were compared with a historical cohort at the same institution who were treated with moderately hypofractionated WBI using 3-dimensional (3D)-conformal radiation therapy (3D-CRT, n = 392), with the total dose rescaled to 26 Gy.

RESULTS

VMAT-uHF achieved a mean D95% and Dmax of the planning target volume of 96.2% and 102.8% of the prescribed dose, respectively. The VMAT-uHF group demonstrated significantly superior planning target volume coverage and improved dose homogeneity, with a 30.6% higher D95 and a 0.7% lower Dmax compared with the 3D-CRT group (both < .05). Mean doses for the ipsilateral lung and heart were 3.12 ± 4.59 Gy and 0.92 ± 0.25 Gy, respectively, showing differences of < 0.3 Gy compared with the 3D-CRT group. The VMAT-uHF group exhibited a significantly lower left anterior descending artery Dmax (-3.73 Gy), while the contralateral breast showed a higher Dmean (+1.43 Gy), compared with the 3D-CRT group. Acute toxicity following VMAT-uHF was predominantly mild, with grade 1 toxicity observed in 114 out of 120 patients. No additional toxicities were reported after a median follow-up of 21.2 months.

CONCLUSIONS

The application of VMAT in ultrahypofractionation can enhance target coverage while maintaining radiation doses to organs at risk low, albeit with an increase in contralateral breast dose compared with 3D-CRT. Given the low toxicity profile observed in our cohort with VMAT-uHF, the clinical significance of these dosimetric differences requires further investigation.