ESTRO 2025 - Abstract Book

S602

Clinical - Breast

ESTRO 2025

3874

Digital Poster adherence to different international guidelines for dose constraints in hypofractionated radiation therapy for breast cancer Heba Abdallah Gomaa 1 , Omar Kalantan 2 , Nisreen Shorbaji 2 , Elham Rashaidi 2 , Taghreed AL-alawi 2 , Baderaldeen Altazi 2 , Khalid Alsalman 1 , Maha Alidrisi 1 , Mohammed Al-Maghrabi 1 1 Radiation Oncology, King Abdullah Medical City, Makkah, Saudi Arabia. 2 Medical Physics, King Abdullah Medical City, Makkah, Saudi Arabia Purpose/Objective: Radiotherapy (RT) is vital for breast cancer treatment. Reviewing dose volume histogram (DVH) constraints for the heart and lungs is crucial as we shift toward hypofractionated regimens. The aim of our study is to assess the feasibility of implementing various international guidelines for dose constraints on the lung and heart during hypofractionated irradiation of the breast or chest wall +/- regional nodal irradiation (RNI). Material/Methods: This retrospective cohort study includes patients diagnosed with breast cancer referred to receive adjuvant RT of 40 Gy in 15 fractions either post conservative surgery or post mastectomy irradiation +/- RNI, from March 2023 to March 2024.

We analyzed DVH for each RT plan, focusing dosimetrically on: volume of the planning target volume receiving 90%, the mean dose to the heart, and the volume of the ipsilateral lung receiving ≤ 4, 8, 12, 16, and 17 Gy.

For left-sided breast cancer, we recorded the heart volume receiving ≤ 2, 8, 10, 16, and 35 Gy, while for right-sided breast cancer; we noted the heart volume receiving ≤ 2, 8, 10, and 16 Gy.

Results: 197 patients received 40 Gy in 15 fractions, all treated with 3D Conformal RT and 97% using the field-in-field technique. Of these, 50.2% were left-sided, and all treated with Deep Inspiration Breath Hold technique. Additionally, 7.6% were treated for breast only, while 92.3% received treatment for the chest wall or breast with RNI, including ipsilateral internal mammary nodes (IMNs) in 11.4% of cases.

Heart constraints are easily met for right-sided patients. Among them, 15% received a mean heart dose > 3 Gy (including 26.6% with ipsilateral IMNs), while 8% received a mean heart dose > 4 Gy.

For ipsilateral lung, a V17 Gy < 35% is easily achievable for all patients. A V12 Gy < 15% is achievable in 8.6% of patients. V4 Gy < 55% and V8 Gy < 40% are also easily achievable, while a V16 Gy < 20% achieved only in 31% of patients.

Conclusion: Achieving dose constraints in hypofractionated RT for breast cancer is challenging. RTOG constraints for heart dose are typically met, even in left-sided patients or those with involved IMNs. However, EORTC constraints for the ipsilateral lung are often not achievable, while DBCG guidelines are feasible for all patients. We should strive to meet the V16 Gy of the ipsilateral lung constraint to completely follow RTOG guidelines. Further studies are needed to correlate these findings with clinical outcomes.

Keywords: Hypofractionation, Breast cancer, Radiotherapy

References: 1. Darby, S et al. Effect of Radiotherapy after Breast-Conserving Surgery on 10-Year Recurrence and 15-Year Breast