EP09.04 RADIATION ASSOCIATED LYMPHOPENIA IN GLIOBLASTOMA: PILOT RETROSPECTIVE EVALUATION OF BRAIN VESSELS DOSE-VOLUME CONSTRAINTS

Abstract BACKGROUND This study investigates the relationship between RT dose to brain vessels and the severity of lymphopenia in glioblastoma patients. Lymphocytes are highly sensitive to low doses of radiation, and severe lymphopenia negatively impacts prognosis and subsequent immunotherapy effectiveness. This highlights the role of circulating blood and blood vessels as critical factors in optimizing radiotherapy. Lymphopenia caused by radiotherapy is gaining attention due to its impact on cancer immunotherapy and the systemic effects of localized radiation. Radiation can remodel the tumor immune microenvironment, altering tumor immunogenicity by increasing specific tumor antigen expression. Although lymphopenia has traditionally been linked to red bone marrow irradiation, it also occurs in radiotherapy for tumors distant to axial skeleton. MATERIAL AND METHODS This retrospective study examined patients with newly diagnosed glioblastoma who were treated at a tertiary cancer center in 2021. Brain vessels were manually outlined using MRI, and a dose-volume analysis was carried out The dose-volume histograms (DVHs) were used to extract dosimetric parameters. Lymphopenia was graded according to CTCAE version 5.0. Statistical analyses were performed to assess potential correlations between irradiation of brain vessels and the severity of lymphopenia. RESULTS A total number of 28 patients were included, 16 (57%) irradiated to total dose of 60Gy, 21 (75%) with concurrent chemotherapy. Among these patients, 32% developed grade 1-3 lymphopenia. Among the group of patients treated with RT alone, 1 (14%) developed lymphopenia. In the group of 21 patients receiving CRT (75%), lymphopenia occurred in 8 (38%). The median PTV in patients without lymphopenia was 267 cm³ compared to 211 cm³ in patients who developed lymphopenia (p = 0.076). There was no statistically significant correlation between brain vessel irradiation doses and the severity of lymphopenia. Median volumes of irradiated vessels at specific doses (V30, V25, V20, V16, V10, V7,5, V6,5 and V5) were similar between groups with and without lymphopenia. CONCLUSION Although no significant association was found between brain vessel dose and the severity of lymphopenia, preserving lymphocyte counts remains essential for optimizing glioblastoma treatment. This study underscores the multifactorial nature of radiation-induced lymphopenia, which may be influenced not only by radiation dose but also by concurrent therapies such as chemotherapy and corticosteroids. Approaches like lymphocyte-sparing radiotherapy hold promise for reducing treatment-related lymphopenia. Prospective studies are warranted to further elucidate the underlying mechanisms and assess the impact of lymphopenia on clinical outcomes. Supported by NU23-03-00100 and NU22-03-00290.