2698 - Real-World Feasibility and Dosimetric Bottlenecks of the FAST-FORWARD Protocol in Right-Sided Whole Breast Radiotherapy
Presenter(s)
D. K. Bhatia1, A. Gupta1, I. Ahmad1, D. P. Umesh1, K. S. Chufal1, A. Miller2, R. Bajpai3, S. Singh4, M. Bhushan4, and M. Gairola1; 1Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India, 2Department of Radiation Oncology, Illawarra Cancer Care Centre, Wollongong, Australia, 3School of Medicine, Keele University, Staffordshire, United Kingdom, 4Department of Radiation Oncology, Division of Medical Physics, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India
Purpose/Objective(s): No published data exist on how often FAST-FORWARD (26Gy/5) dosimetric constraints can be met outside a trial setting. We quantified real-world feasibility of ultra-hypofractionated whole-breast irradiation (WBI) for right-sided breast cancer using two metrics (clinician plan acceptance and strict protocol compliance), identified which constraint limits eligibility most, and assessed the role of planning technique.
Materials/Methods: Between 2020 and 2026, 599 consecutive right-sided breast cancer patients received adjuvant RT at our institution; 115 (19.2%) received WBI alone and constituted the FAST-FORWARD eligible cohort. All were planned at 26Gy/5 on Eclipse v15.3 (FiF, IMRT, or VMAT), and evaluated against protocol constraints: PTV V95% =90%, V105% =7%, V107% =2%, Dmax =110%, ipsilateral lung V8Gy <15%, heart V1.5Gy <30%, heart V7Gy <5%. Two feasibility metrics were computed: clinical acceptance (patients treated with 26Gy/5) and strict dosimetric compliance (every constraint met per protocol operators). Between-group comparisons used Mann-Whitney U with BH-FDR correction and rank-biserial r as effect size. Threshold sensitivity relaxed each constraint individually while holding others at protocol values.
Results:
Clinical acceptance was 38/115 (33%, 95% CI 24.6–42.4) and strict compliance 30/115 (26%, 95% CI 18.3–35.1); population-level utilization was 38/599 (6.3%). Thirteen patients were treated despite borderline violations (10 involving lung V8Gy, median overshoot 0.80%); 5 compliant patients were not treated (all FiF). Feasibility depended on planning technique: FiF 8.1% (6/74), IMRT 53.8% (7/13), VMAT 89.3% (25/28); Fisher's exact p <0.001. Among accepted plans, 18/38 (47.4%) met all ideal objectives. Among rejected plans, lung V8Gy was the most frequently failed constraint (88.3%, 68/77), followed by PTV V95% (41.6%, 32/77). Of 39 single-constraint failures, 35 (89.7%) failed lung V8Gy alone. Between-group comparisons are presented in the table. Relaxing lung V8Gy from <15% to <17% improved strict compliance from 26% to 33%. No other constraint relaxation added more than 2 patients.Conclusion: The population-level utilization of 6.3% in our high-volume institution is attributable to RNI exclusion and highlights a ceiling on adoption. Our report also suggests that centres should consider VMAT planning to achieve FAST-FORWARD protocol constraints.
| Metric | Accepted Plans - Median (IQR) | Rejected Plans - Median (IQR) | p (BH) | Effect Size (r) | Effect Magnitude |
| PTV V95% | 95.0 (92.8–96.0) | 92.1 (84.0–94.2) | <0.001 | 0.494 | Medium |
| PTV V105% | 1.7 (0.4–3.6) | 1.4 (0.0–3.3) | 0.378 | 0.102 | Small |
| PTV V107% | 0.0 (0.0–0.1) | 0.0 (0.0–0.0) | 0.267 | 0.117 | Small |
| PTV Dmax | 108.2 (106.5–109.0) | 106.1 (105.4–107.1) | <0.001 | 0.492 | Medium |
| Lung V8Gy | 13.7 (12.3–15.1) | 23.5 (19.0–26.9) | <0.001 | -0.821 | Large |