ESTRO 2025 - Abstract Book

S435

Clinical - Breast

ESTRO 2025

Two to three weeks post-RT, the rates were 51.5%, 41.9%, and 6.6%, respectively. Late Grade 2 toxicities were observed in 5.3%, 2.3%, 1.8%, 1.1%, and 0% of patients at 6 months, 1 year, 2 years, 3 years, and 4 years, respectively. Grade 3 toxicities were observed in 1.5%, 2.0%, 0.9%, 0%, and 0% at the same time points. Patient reported cosmetic outcomes were rated as good or excellent in 97.4% of cases. After a mean follow-up of 18 months (median 14 months, range 0–48 months), 1 local recurrence, 2 nodal recurrences, and 9 distant relapses were observed. Three non-tumor-related deaths were recorded. Conclusion: Our early and intermediate findings indicate that ultra-hypofractionated schedules, including a moderately hypofractionated boost, are feasible and well-tolerated. The observed acute toxicity, short-term late outcomes, and PROMs are favorably comparable to those reported in the FAST-Forward trial.

Keywords: Ultra-Hypofractionation, Boost, Risk-Adapted

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Digital Poster Prospective Study Evaluating the Impact of Deep Inspiratory Breath Hold in the Treatment of Right Breast Cancer with Regional Lymph Node Irradiation Mohammed Qambar 1,2 , Ala Allouzi 1 , Marwa Kashouqa 1 , Abdulla Alzibdeh 1 , Fawzi Abuhijla 1 , Hanan Al-Masri 1 , Fadwa Abdulrahman 1 , Anoud Al-Nsour 1 , Sara Mheid 1 , Mohamed Berawi 1 , Hamza Al-Soud 1 , Fadi Abdah 1 , Mohamed Al Smairat 1 , Hikmat Abdel-Razeq 3 , Abdellatif Al-Mousa 1 , Wafa Asha 1 1 Department of Radiation Oncology, King Hussein Cancer Center, Amman, Jordan. 2 Department of Radiation Oncology, Bahrain Oncolgy Center, Muarraq, Bahrain. 3 Department of Medical Oncology, King Hussein Cancer Center, Amman, Jordan Purpose/Objective: Deep Inspiratory Breath Hold (DIBH) is a well-established technique for minimizing cardiac and pulmonary radiation exposure in left-sided breast cancer; however, its application and benefits in right-sided breast cancer have limited data. This study investigates the effects of DIBH versus free breathing (FB), focusing on its impact with regional nodal irradiation (RNI). Material/Methods: We conducted a prospective study from November 2023 to October 2024 on patients with right-sided breast cancer requiring irradiation to the breast or chest wall, including regional lymph nodes (supraclavicular lymph nodes, axilla, or internal mammary lymph nodes (IMNs)). For each patient, two treatment plans were generated: one using FB and the other using DIBH. Dose-volume histograms (DVHs) evaluated key dosimetric parameters: mean lung dose, ipsilateral lung V20, V16, and V5, liver V20 and V30, liver Dmax, mean heart dose, heart V25 and V5, and coverage of the IMNs clinical target volume (CTV) and planning target volume (PTV) at 95% and 90%. Wilcoxon signed-rank test assessed dosimetric differences between FB and DIBH, with mean differences analyzed for correlations with patient factors using multiple linear regression. Results: A comparison of 60 FB and DIBH plans on 30 patients revealed significant reductions in lung and liver dose parameters with DIBH. The mean lung dose decreased from 14 Gy to 10 Gy (P < .0001), V20 from 31% to 21% (P < .0001), V16 from 34% to 24% (P < .0001), and V5 from 55% to 43% (P < .0001). Liver Dmax was reduced from 40 Gy to 19 Gy (P < .0001), V20 from 1.9% to 0.00% (P < .0001), and V30 from 0.73% to 0.00% (P < .0001). For the heart, the mean dose decreased from 1 Gy to 0.85 Gy (P < .0001), and V5 decreased from 0.43% to 0.00% (P = .0001), while heart V25 remained unchanged (P > .5000). No significant improvements were observed in IMN CTV and PTV coverage with DIBH. The differences in the aftermentioned dosimetric parameters between FB and DIBH did not seem to correlate