ESTRO 2024 - Abstract Book

S5280

Radiobiology - Normal tissue radiobiology

ESTRO 2024

Purpose/Objective:

Radiation-Induced Lymphocyte Apoptosis (RILA) was proved to be a reliable clinical method for predicting intrinsic radiosensitivity in breast and prostate cancer patients. However, its clinical utility is still unknown for locally advanced cervical cancer treated with radiochemotherapy. Thresholds can vary between patient groups, so our aim was to establish a threshold for the method, improve the efficiency of the workflow and achieve a clinical validation in this target group.

Material/Methods:

Blood samples were collected from locally advanced cervical cancer patients treated with radiochemotherapy before radiotherapy, 3 months, 1 year, and 2 years after treatment completion. At these time points, side effects were assessed by the EMBRACE II, EORTC-QoL-C30, and EORTC-Cx24 questionnaires. Gastrointestinal side effects will also be quantified with citrulline measurements. We mix the blood with RPMI (20% FBS) medium and irradiate it with a total dose of 8 Gy (6MV photon, 100 MU/minute). Two days later, lymphocytes were labelled with CD8 FITC and CD4-eFluor506 antibodies. After erythrolysis, the samples were treated with propidium iodide and RNase, followed by a flow cytometry analysis. We investigated the impact of different incubation times on RILA values. The need for CO2 addition during the culture step was also investigated. The elimination of the pre irradiation time was also tested, reducing the total test time from 4 days to 3 days, with the aim of making the method more practical for clinical use. We also investigated whether irradiation could be replaced by bleomycin to avoid the need for an irradiation machine (in our case, the linear accelerator used in the clinic).

Results:

We measured radiation-induced apoptosis levels (8 Gy) in CD8+ and CD4+ lymphocytes in samples from 89 patients scheduled for definitive radiochemotherapy. Our current threshold values were -0.03% for CD8+ and 0.28% for CD4+ lymphocytes. Only in the case of CD4+ lymphocytes did the increase of the post-irradiation time affect the RILA values. However, this can be resolved if the samples are always irradiated and the processing is initiated at the same time. Thus, the method has been successfully established. We demonstrated that the use of CO2 during cultivation can be omitted. Our initial results show similar outcomes to historical controls (7.4% CD8+ RILA), but clinical validation is still needed. Adding 70 and 80 μg/ml bleomycin to samples 24 hours before flow cytometry measurements for 5 hours gave values most similar to irradiation.

Conclusion:

We have successfully established the threshold for the RILA method in cervical cancer patients at our center, but clinical validation against side effects is still in progress. Further fine-tuning of the method is ongoing to improve workflow efficiency and facilitate its introduction into the clinical practice.

Keywords: RILA, cervix, radiation sensitivity

2345

Proffered Paper

Modification of the adverse effects of radiotherapy on normal brain with the ATM inhibitor AZD1390