Abstract
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 P < .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.