Ultra-hypofractionation versus standard hypofractionation in post-mastectomy radiotherapy (PMRT): a prospective randomised dosimetric and clinical comparison study.

BACKGROUND: 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. METHODS: This prospective randomised study enrolled 50 women with stage II-IIIA invasive breast cancer treated with modified radical mastectomy. Patients were randomised 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 3D conformal radiotherapy or volumetric-modulated arc therapy 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 tumours (68% versus 40%) and fewer node-positive cases (44% versus 72%). Both regimens achieved excellent planning target volume coverage (>95%). Ultra-hypofractionation (26 Gy/5) yielded lower ipsilateral lung exposure (V30 = 17% versus Group A V20 = 27%), reduced contralateral lung (300 versus 384 cGy), contralateral breast (247 versus 320 cGy) and spinal cord dose (938 versus 2,206 cGy). Mean heart dose was slightly higher in Group B (275 versus 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. A longer follow-up is warranted to validate late toxicity and survival outcomes.