ESTRO 2020 Abstract book

S223 ESTRO 2020

5-7% of LABC patients, and these patients may be better treated with protons. Protons are characterized by virtually no entry and exit doses, thus sharp dose gradients can be achieved. A major challenge using proton RT is the need for robustness, thus minor anatomical differences happening to the patient during the RT course may seriously influence the delivery and safety of the proton therapy. There are only few published results from small underpowered and usually retrospective studies investigating protons in LABC patients. In LABC patients, proton therapy is currently being tested in randomized trials, since the therapy is still considered experimental. The primary endpoint in those trials is late effects, primarily major cardiac disease and risk of second cancer, but it is also expected that proton therapy has potential to improve breast cancer distant failures due to better target coverage especially of the internal mammary nodes. The integration of MRI with a linear accelerator (MR-linac) offers great potential for high-precision delivery of RT. High-precision RT is needed in LABC patients who e.g . are candidate for nodal boost. Nodal boost is often difficult to deliver because of the proximity to the brachial plexus, but with higher precision in daily RT delivery it may be possible to use narrower margins and potentially a higher dose. At present there is no data supporting use of MR- linacs for breast cancer RT, however, it is likely that studies will be initiated to demonstrate the potential of MR-linacs for nodal boost and perhaps also in patients treated with pre-operative RT. Indeed, further studies are highly needed for both proton RT and MR-linacs. SP-0384 Re-irradiation versus mastectomy for recurrent breast cancer D. Gabrys 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Department, Gliwice, Poland Abstract text Ipsilateral breast tumor recurrence (IBRT) represents a challenge for clinicians where the balance between quality of life and local control has to be weighed against the side effects of re-irradiation therapy. Moreover, the management is not standardized and require not only multidisciplinary tumour board decision with individualized oncologic treatment options but also the consideration of patients' needs, expectations and priorities. The final outcome of breast re-irradiation is difficult to assess because of the wide range of variable treatments that a patient may have undergone. Treatment options for breast tumor recurrence involve surgery, chemotherapy and irradiation with or without hyperthermia. Even though mastectomy is regarded as the standard of care for patients with IBTR, in a selected group of patients second breast conserving therapy is an attractive alternative to mastectomy. There are studies which challenged this approach, and strategies for a second BCT after IBTR are being investigated for selected patients. Re-irradiation for breast cancer is mostly applied as partial breast irradiation and can be delivered either as conformal external beam irradiation (with photons or electrons), interstitial brachytherapy or as intraoperative radiation therapy (IORT). This approach yields high breast preservation rates, does not seem to compromise oncologic safety and is associated with an acceptable incidence of side effects, such as fibrosis, pain, rib fracture, infection, lymphedema, but less acceptable results with regard to cosmesis. Heterogeneity of early and late toxicity reporting together with a variability of

applied schedules composed of variable radiotherapy total and fraction doses, hyperthermia schemas, surgical and systemic treatment does not allow to create a clear consensus on the optimal treatment schedule for recurrent breast cancer to achieve best long-term local control and survival with less toxicity. Nevertheless, available results present re-irradiation as an effective and safe modality for the management of recurrent breast cancer. Therefore, the aim of this talk is to present the mentioned points and review the current status of the treatment for recurrent breast cancer. SP-0385 Do we really know what is the best radiotherapy schedule for locally advanced breast cancer? I. Meattini 1 Abstract text Locally advanced breast cancer (LABC) patients are generally classified as stage III disease at presentation with large primary breast cancers and positive regional nodes; cases with skin and/or chest wall involvement, breast edema, or a combination, clinical inflammatory breast cancer (IBC), or advanced clinical regional nodal disease. Some guidelines have included also stage IIB. Optimal treatments for patients presenting with LABC have changed over time and now include multimodality therapy using systemic/target therapy, surgery, and radiation therapy. Sequence of treatments depends on multiple factors, including the extent of disease at diagnosis. Primary systemic therapy (PST) use is increasing, mostly in case of patients affected by triple-negative, HER2- positive, clinically node-positive disease, and in case of inoperable disease. The old-fashioned rationale for use of PST to allow unresectable disease operable has been overcame, integrating tumor biology. Surgical approaches for LABC is also fast evolving: in the majority of case modified mastectomy is used, although some selected cases if non-inflammatory breast cancer are nowadays considered for a breast conserving-surgery strategy. The role of axillary staging, mostly after PST, is also under investigation. Response to PST assessment might allow potential tailoring of therapies, and it has been integrated into current clinical trials design. Postmastectomy radiation therapy (PMRT) trials showed significantly improved locoregional and – in selected high- risk cases - overall survival rates. However, there is a lack of studies specifically evaluating LABC cases, including IBC. Locoregional radiation targets volumes (chest wall/breast and regional nodes) and fractionation (conventional/hypofractionation) is currently under investigation. A multidisciplinary management is crucial to warrant the optimal outcome for these patients. Future perspectives include a tailored approach based on patient-individual risk for disease control failure and tumor biology. Improved outcomes call for high-level multidisciplinary cooperation. 1 University of Florence - Azienda Ospedaliero Universitaria Careggi, Radiation Oncology Unit - Oncology Department, Florence, Italy