ESTRO 38 Abstract book

S111 ESTRO 38

Estro 38 Sunday 28 April

Teaching Lecture: Re-irradiation for breast cancer

SP-0212 Re-irradiation for breast cancer P. Poortmans 1 , O. Kaidar-Person 2 , S. Oldenborg 3 1 Institut Curie Ensemble Hospitalier, Department Of Radiation Oncology, Paris Cedex 05, France ; 2 Rambam Health Care Campus, Department Of Oncology- Radiation Oncology Unit, Haifa, Israel ; 3 Academic Medical Center, Departement of Radiation Oncology, Amsterdam, the Netherlands Abstract text Half of locoregional recurrences (LRR) after primary breast cancer treatment are isolated events. Re-staging should be done to rule out metastatic disease in order to select patients for potential curative salvage treatment. The treatment approach depends on the characteristics of the primary and recurrent cancer, previous locoregional and systemic treatments, site of recurrence, co- morbidities and the patient’s wishes. A multidisciplinary discussion should be associated to the shared decision- making process. As treatment has the potential to provide long-term disease-free survival, for radiation therapy (RT) meticulous target volume delineation and selection of the most appropriate techniques should be used to decrease the risk of toxicity, especially in patients who were previously treated with chemotherapy and/or RT.For patients who did not receive prior RT, resection followed by RT is the standard approach, including a boost to site of recurrent disease and with a higher radiation dose in case of residual macroscopic disease. Re-irradiation after previous RT should be considered also for all patients with isolated locoregional disease, preferably after surgical debulking. It can also be performed as primary treatment for gross disease, if surgery is not feasible or not accepted by the patient. The effective re-irradiation dose is generally limited to reduce adverse effects from the accumulated radiation dose. Combining lower re- irradiation doses combined with hyperthermia results in improved tumour control without additive toxicity. In selected patients, salvage breast-conserving surgery can be considered even in the case of earlier RT. Careful patient selection is needed and most experience is available with interstitial brachytherapy.Patients with LRR should also be considered for “adjuvant” systemic therapy as part of their treatment management, depending on the receptor status of the recurrent disease. Reference: Kaidar-Person O, Oldenborg S, Poortmans P. Re-irradiation and Hyperthermia in Breast Cancer. Clin Oncol (R Coll Radiol). 2018 Feb;30(2):73-84.

Teaching Lecture: Extracellular vesicles; are we there yet?

SP-0213 Extracellular vesicles and potential implications for radiation therapy A. Dal Pra 1,2

1 University of Miami, Department of Radiation Oncology, Miami, USA; 2 University of Bern, Radiation Oncology, Bern, Switzerland Abstract text Extracellular vesicles are a heterogeneous group of cell- derived membranous structures comprising exosomes and microvesicles that reflect the genetic and non-genetic materials of parent cancer cells. They are present in biological fluids and are involved in multiple physiological and pathological processes. Extracellular vesicles are