ESTRO 2020 Abstract book

S1066 ESTRO 2020

structure and both a pre-treatment (collected within one year of radiotherapy start) and an End-of-Radiotherapy (EoRT) peripheral blood count (collected within six months after radiotherapy ended). Kernel-weighted polynomial smoothing of all available blood counts within 12 months before and after radiotherapy start was used to illustrate kinetics. The association of the volume of the body irradiated with the degree of hematological toxicity was analyzed. For blood components markedly affected by irradiation, linear regression was used to evaluate the association of square root transformed EoRT counts with age, gender, Charlson comorbidity score, chemotherapy (prior, sequential and concomitant), fractionation schemes and volume of the body exposed to at least 2 (V2) and 40 (V40) Gy, adjusting for pre-treatment blood counts and cancer diagnoses. Results We included 4,314 patients with available pre-treatment and EoRT platelet and leukocyte counts, of whom 2,479 patients also had neutrophil and lymphocyte counts. All blood components declined after start of radiotherapy. Decline of platelet, leukocyte and neutrophil counts was modest and recovered rapidly after radiotherapy, whereas the lymphocyte count decline was clinically significant and remained low (Fig 1). The higher the volume of the body exposed to radiation (both low dose and high dose), the higher the percentage of patients who experienced hematological toxicity in the first 3 months after radiotherapy, but this association only persisted for longer periods for lymphocytes (Fig 2 for V2). Older age (≥70 vs. <50 years old [coef. -0.037, 95% CI: -0.072 to -0.001, p=0.046]), female gender (-0.076, -0.100 to -0.051, p<0.001), number of fractions (per 1 fraction increase: - 0.003, -0.006 to -0.001, p=0.004), dose-volume (V2 ≥11 vs. <3 L [-0.258, -0.311 to -0.204, p<0.001]) and concomitant use of chemotherapy, particularly the use of platinum compounds vs. none (-0.192, -0.233 to -0.150, p<0.001) were independently associated with a lower EoRT lymphocyte count. Estimates were similar for V40, though volumes were smaller (V40 ≥2.1 vs <0.4 L [-0.183, -0.228 to -0.139, p<0.001]). Comparable results may have been due to correlation between V2 and V40 (Spearman’s rho=0.73, p<0.001).

Conclusion Radiation has a selective, negatively persistent and clinically significant effect on the lymphocytes, whereas the decline of platelets and neutrophils after radiotherapy quickly recovers. The effect on lymphocytes is partly driven by the volume of the body exposed to a given dose of radiation. PO‐1818 Cytogenetic and immunological markers to predict side effects and tumour control in cancer patients Z. Juranyi 1 , Z. Kocsis S. 1 , K. Lumniczky 2 , K. Balázs 2 , P. Ágoston 3 , G. Farkas 1 , M. Kun-Gazda 1 , G. Székely 1 , T. Major 3 , C. Pesznyák 3 , G. Stelczer 3 , K. Jorgo 3 , L. Gesztesi 3 , C. Polgár 4 , G. Sáfrány 2 1 National Institute of Oncology, Centre of Radiotherapy- Department of Radiobiology and Diagnostic Onco- Cytogenetics, Budapest, Hungary ; 2 National Public Health Center, Department of Radiation Medicine- Division of Radiobiology and Radiohygiene, Budapest, Hungary ; 3 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary ; 4 National Institute of Oncology- Semmelweis University, NIO Centre of Radiotherapy- SE Department of Oncology, Budapest, Hungary Purpose or Objective Biomarkers would be beneficial for predicting individual radiosensitivity and to follow immunological responses due to radiotherapy. Analysis of chromosome aberrations is an established biomarker for absorbed dose and might offer predictive value for late side effects. Recent data provided evidences that radiotherapy might stimulate antitumor immune responses, which may also be important in future immunotherapeutic aspects. Material and Methods Blood samples from 113 prostate cancer patients were collected. According to the type of radiotherapy (RT) patients were divided in four arms: Cyberknife, LINAC, LDR and HDR brachytherapy. Changes in cytogenetic and immune parameters were investigated before, right after then 3, 6, 9, 12, 24, 36 months after therapy. Clinical data were recorded using RTOG/EORTC genitourinary (GU) and gastrointestinal (GI) grade, IPSS (International Prostate Symptom Score) and QoL (Quality of life) questionnaires. Results LINAC and Cyberknife therapy markedly increased the frequency of chromosome aberrations in peripheral blood lymphocytes (4.1 ± 0.4 to16.1 ± 1.8 and 4.1 ± 1.5 to 10.8 ± 4.4 total aberration/100 cells at three months), LDR and HDR therapy caused moderate increase (2.7 ± 0.4 to 6.4 ± 0.6 and 2.5 ± 0.3 to 4.2 ± 0.3), which decreased to baseline at 24 months after RT, except for LINAC. The fraction of CD4 + cells decreased after seed implantation. LDR brachytherapy led to a progressive elevation in the proportion of Treg cells. Proliferation of CD4 + cells was significantly higher before treatment, after brachytherapy the Ki67 expression decreased. CTLA-4