ESTRO 2025 - Abstract Book

S522

Clinical - Breast

ESTRO 2025

DIBH appears more effective and safer than free breathing. A significant reduction was observed in both mean and maximum radiation doses to the heart; mean cardiac dose decreased by up to 44.75% in DIBH arm. The mean dose to the left lung was reduced by 6.32% when using DIBH. The time until treatment initiation was shorter with DIBH (35d vs 70d) suggesting more efficient implementation. Although DIBH improves quality of life by minimizing radiation exposure to healthy organs, patient feedback indicated high levels of stress related to their perceived responsibility for treatment efficacy; this raises an important question about whether such responsibility should be transferred from healthcare providers to patients themselves.

Keywords: DIBH, FAST FORWARD, Cost-Effectiveness

2352

Digital Poster Incidental dose to internal mammary nodes in breast cancer patients treated with hypofractionated radiotherapy: A single-institute dosimetric study Zilan Başkan 1 , Süleyman Burak Kılıçer 1 , Turgut Taşçi 2 , Tarık Ziyad Sütcü 2 , Özgür Boran 2 , Zerrin Özgen 1 , Mehmet Fuat Eren 3 1 Department of Radiation Oncology, Marmara University School of Medicine, Istanbul, Turkey. 2 Department of Physics, Marmara University Pendik Education and Research Hospital, Istanbul, Turkey. 3 Radiation Oncology Clinic, Marmara University Pendik Education and Research Hospital, Istanbul, Turkey Purpose/Objective: With the development of new techniques in radiotherapy, such as intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), we can now achieve better dose distribution than previous methods. We use VMAT technology for the irradiation of postoperative breast cancer patients. It is important to note that while VMAT technology provides an excellent dose distribution, surrounding tissues can still receive low doses of radiation. This study aims to measure the incidental doses of internal mammary nodes (IMN) not included in the clinical target volume (CTV) in patients treated with VMAT technology. Material/Methods: We included postoperatively irradiated breast cancer patients. All patients received 40.05 gray (Gy) radiotherapy in 15 fractions. Patients who required a boost received 48 Gy of radiotherapy to the tumor bed using the simultaneous integrated boost (SIB) method in 15 fractions. The internal mammary nodes (IMN), including intercostal spaces 1 to 3, were contoured but not irradiated in patients. Results: Ninety-four patients were included in the study with a median age of 57 (30-85) years. The mean CTV volume was 916 (198-2774) cc. The mean boost volume in patients who received a boost dose was 33 (6.5-99) cc. The mean of the minimal dose covering 95% of the CTV (CTV D95) was 39.1 (39.38-40.99) Gy. The mean average dose (Dmean) for incidental IMN was 25.57 (2.82-37.98) Gy. While the mean dose for the ipsilateral lung was 9.8 (3.2-15.6) Gy, the mean percentage of lung volume receiving ≥20 Gy (V20) was 14.24 (0-20.4). For the contralateral lung, the mean dose was 3.07 (0.6-17.6) Gy, while the mean percentage of lung volume receiving ≥5 Gy (V5) was 8.1 (0-77.4). The mean contralateral breast dose was 2.69 (0.9-16.84) Gy. In 47 out of 94 patients, the tumor was located in the right breast, while in the remaining patients; it was located in the left breast. The mean IMN dose for the right breast was 26.8 (7.4-37.98) Gy, while for the left breast, it was 24.35 (2.82-34.08) Gy. During a median follow-up period of 25 months, no patients experienced local or regional recurrence.