ESTRO 2020 Abstract book

S1065 ESTRO 2020

PO‐1816 Impact of radiotherapy in immunological parameters in brain metastases by SRS A. Gonzalez-Pose 1 , A. Garcia-Perez 1 , M. Gonzalez- Rodriguez 2 , A. Lopez Medina 1 , S. Mirete Bachiller 3 , V. Ochagavia 2 , I. Nieto 2 , F.J. Salvador 1 , V.M. Muñoz Garzón 2 1 Hospital do Meixoeiro, Medical Physics, Vigo Pontevedra, Spain ; 2 Hospital do Meixoeiro, Radiation Oncology, Vigo, Spain ; 3 Hospital do Meixoeiro, Inmulogía, Vigo, Spain Purpose or Objective The aim of this study was to observe how fractionation affects immunity system in patients with brain metastases. Ionizing radiation liberates antigens from within the tumor that can activate an antitumor immune response through attraction, invasion and priming of CD8 T cells in the tumor microenvironment. Higher doses induce more T-cell infiltration in the tumor, and also in its microenvironment, as well as, antigen-presenting cells in draining lymph nodes. Additionally, antitumor responses are reduced due to the presence of PD1 proteins. Material and Methods Eleven patients, recruited to HeNeBra Project, with brain metastases, treated with stereotactic radiosurgery (SRS) and different fractionation schedules (5 x 4 Gy (n = 1), 5 x 5 Gy (n = 2), 3 x 7 Gy (n = 2), 3 x 8 Gy (n = 2), 3 x 9 Gy (n = 1), 1 x 21 Gy (n = 2), 1 x 25 Gy (n = 1)) were choosen to analyze their immunological parameters. The variation of different types of lymphocytes and the PD1 protein in peripheral blood were measured before treatment and one month after completion. These lymphocytes were CD3 (encompassing all T lymphocytes with antitumor activity), CD4 (take part in cellular immunity), CD8 or cytotoxic T- cells; and Natural Killer cells (NK) (cytotoxic cells without T cell receptor). Patients were grouped into two samples depending on fractionation schedule: fractionated or single dose. Results Figure 1 shows the variation in lymphocytes population because radiotherapy treatment (before and one month after treatment). CD3, CD4 and NK cells levels in the peripheral blood of patients who received fractionated treatment were decreased while CD8 cell levels remain practically constant. However, variations of CD3, CD4, CD8 and NK in patients treated with a single dose show a substantial increase between pre-treatment and one month post-radiotherapy. Figure 2 displays the concentration of PD1 in peripheral blood before and after the treatment. The standard deviation of PD1 concentration of patients treated by single-dose scheme decreases from 17.9 pg/ml to 2.9 pg/ml, and the average value changes from 42.2 pg/ml to 17.1 pg/ml, while these values don't change significantly in fractionated schemes. These results (increase in CD8, in NK, and decrease in PD1 for single dose treatment) suggest immune response is enhanced by radiotherapy for one- session treatments.

Conclusion An increase of T-cells, specific cytotoxic cells, in surrounding non-irradiated environment when an higher dose per fraction was delivered to primary tumor, reveals that these fractionations are more effective in terms on antitumor immune response. Althought the small number of patients, our study seems to mean that a better immunologic antitumor response, in terms of cytotoxic lymphocytes, to patients treated with single fraction SRS versus fractionated schedules. Futures paths can be establish a more accurate threshold in fractionation dose, as well as, the durability and potency of that effect. Funded by ISCIII PI17/01735 grant (cofunded by FEDER). PO‐1817 Kinetics and dose‐volume effect of radiotherapy on leucocyte and platelet blood cell components C. Terrones Campos 1 , B. Ledergerber 1 , I. Vogelius 2 , M. Helleberg 1 , L. Specht 2 , J. Lundgren 1 1 Rigshospitalet, Centre of Excellence for Health- Immunity and Infections CHIP- Department of Infectious Diseases, Copenhagen, Denmark ; 2 Rigshospitalet, Department of Oncology, Copenhagen, Denmark Purpose or Objective We aimed to assess the kinetics and dose-volume association of external beam irradiation on platelets, leukocytes, neutrophils and lymphocytes in a large well- characterized cohort of patients with solid tumor diagnosis undergoing their first course of radiotherapy with curative intent. Material and Methods Patients were included from 2009 to 2016 at a single site, with available dosimetric data for the delineated body