ESTRO 2025 - Abstract Book

S2941

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

[2] Wickers, S, et al (2021). Identifying Surrogates for Heart and Ipsilateral Lung Dose to Guide Field Placement and Treatment Modality Selection during Virtual Simulation of Breast Radiotherapy. Clin Oncol (R Coll Radiol), 33(4), 224 229. https://doi.org/10.1016/j.clon.2020.12.005 [3] Taylor, C.W, et al (2009). Estimating Cardiac Exposure from Breast Cancer Radiotherapy in Clinical Practice. Int J Radiat Biol Phys, 15;73(4), 1061-8. https://doi.org/10.1016/j.ijrobp.2008.05.066

4561

Digital Poster Dosimetric comparison between IMRT and VMAT plans in breast cancer patients with silicone implants using Halcyon™ Hela Ayouni 1,2 , Bilel Daoud 3 , Amirreza Heshmat 3 , Balkiss Ben Ali 2 , Lotfi Ben Salem 4 , Semia Zarraa 2 , Chiraz Nasr 2 1 Medical physics, Higher Institute of Medical Technology of Tunis, Tunis, Tunisia. 2 Radiotherapy oncology, Institute Salah Azaiez, Tunis, Tunisia. 3 Imaging physics research, MD anderson cancer center, Texas, USA. 4 Medical physics, Institute Salah Azaiez, Tunis, Tunisia Purpose/Objective: Women who have undergone a mastectomy for breast cancer may elect to pursue implant-based reconstruction. However, postmastectomy radiation therapy (PMRT) can present challenges in terms of silicone implant sparing. In this context, there is a paucity of clear data on the optimal irradiation technique to protect silicone implants when FFF beams. This study aimed to compare the dosimetric performance between IMRT and VMAT in sparing these implants, while ensuring an optimal balance between target coverage and organ at risk (OARs) preservation using Halcyon™. Material/Methods: A total of 10 patients who had undergone a mastectomy were included in the study. A simulation of the creation of pre-pectoral silicone implants was conducted using Python scripts. The position of the wires marking the anatomical limits on the left and right sides was monitored. The final verification of the position of the implant in the craniocaudal and lateromedial directions was conducted by an experienced radiation oncologist, who also performed delineation in accordance with the new ESTRO-ACROP contouring guidelines. For each patient, 10 VMAT plans were initially created and subsequently replanned as IMRT plans (40.05 Gy in 15 fractions). The coverage of PTVs, the doses delivered to silicone implant and the doses delivered to organs at risk (OARs) were then compared. Results: The target coverage was comparable between IMRT and VMAT in terms of both the V93% of the PTV and the V95% of the PTVs (supra/infraclavicular and internal mammary nodes). The two techniques demonstrated comparable efficacy in sparing the heart, as evidenced by similar mean doses and V5 Gy values. The mean dose of the left lung was significantly reduced with VMAT, resulting in the lowest recorded value of 7.29 Gy. The degree of compliance with the V5 Gy and V20 Gy values for the left lung remained consistent across all irradiation techniques. For the right lung, the Dmean was respected in all cases treated with IMRT, in contrast to 50% of those treated with VMAT. Furthermore, IMRT demonstrated superior outcomes in preserving the right breast (Dmean). The dosimetric performance for the silicone implant exhibited equivalence between the two techniques, with a Dmean <30 Gy in 60% of patients.