S281
Clinical - Breast
ESTRO 2026
Digital Poster Highlight 2596 Ultra-Hypofractionation vs Hypofractionation in Post-Mastectomy Radiotherapy (PMRT): A Prospective Randomized Dosimetric and Clinical Comparison Study Meghal Prajapati 1 , Anil Kumar Goel 2 , Yamini Patel 1 , Divyeshkumar Rana 1 , Lokesh S 1 , Pooja Panchal 1 , Dhruv Rathod 1 , Chandramouli Ramalingam 3 , Ajay Kumar Kondeti 4 1 Radiation Oncology, Medical College Baroda, and S.S.G. Hospital, Vadodara, India. 2 Radiation Oncology, AIIMS, Bathinda, Bathinda, India. 3 Radiation Oncology, AIIMS, Bibinagar, hyderabad, India. 4 Radiation Oncology, AIIMS, Bibinagar, Hyderabad, India Purpose/Objective: Post-mastectomy radiotherapy (PMRT) significantly reduces loco-regional recurrence and improves survival in breast cancer patients with node-positive or high-risk disease. The UK START trials established 40 Gy in 15 fractions as a safe and effective alternative to 50 Gy/25. The FAST-Forward trial later demonstrated non-inferiority of 26 Gy in 5 fractions, but only a minority of participants had undergone mastectomy. Limited prospective data exist for ultra- hypofractionated PMRT, particularly in the Indian setting, where shorter regimens could reduce patient and system burden. Material/Methods: This prospective randomized study enrolled 50 women with stage II–IIIA invasive breast cancer treated with modified radical mastectomy. Patients were randomized equally to receive PMRT as either 40 Gy in 15 fractions (Group A) or 26 Gy in 5 fractions (Group B). CT-based planning was performed using 3DCRT or VMAT techniques, with the Deep Inspiration Breath Hold (DIBH) technique implemented for left-sided cases to minimise cardiac dose. Results:
Baseline demographics were balanced, though Group B had more left-sided tumors (68% vs 40%) and fewer node-positive cases (44% vs 72%). Both regimens achieved excellent PTV coverage (>95%). Ultra- hypofractionation (26 Gy/5) yielded lower ipsilateral lung exposure (V30 = 17% vs Group A V20 = 27%), reduced contralateral lung (300 vs 384 cGy), contralateral breast (247 vs 320 cGy), and spinal cord dose (938 vs 2206 cGy). Mean heart dose was slightly higher in Group B (275 vs 181 cGy), but no patient exceeded a mean heart dose of 6 Gy, and all had V 25% <5%, consistent with international tolerance thresholds. Acute toxicity was minimal in both arms, limited to Grade 1 dermatitis; no Grade ≥ 2 toxicity was observed. At 6 months, all patients were alive and disease-free. Conclusion: Ultra-hypofractionated PMRT (26 Gy/5) is feasible, well- tolerated, and dosimetrically advantageous for lungs, contralateral breast, and spinal cord. Incorporating DIBH ensures safe heart sparing in left-sided disease. Longer follow-up is warranted to validate late toxicity and survival outcomes. References: 1. Brunt AM, Haviland JS, Wheatley DA, Sydenham MA, Alhasso A, Bloomfield DJ et al. Hypofractionated breast radiotherapy for 1 week versus 3 weeks (FAST-Forward): 5-year efficacy and late normal tissue effects results from a multicentre, non-inferiority, randomised, phase 3 trial. Lancet. 2020 May 23;395(10237):1613-16262. Brunt AM, Haviland JS. Hypofractionation: The standard for external beam breast irradiation. 20233. Brunt AM, Cafferty FH, Wheatley D, Sydenham MA, Kirby AM, Coles CE et al. Patient- and clinician-assessed five-year normal tissue effects following one-week versus three-week axillary radiotherapy for breast cancer: Results from the phase III FAST-Forward trial randomised nodal sub- study. Radiother Oncol. 2025 Keywords: PMRT, Hypofractionation, Ultra- Hypofractionation
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