Dynamic γ-H2AX response in blood lymphocytes for prediction of radiotherapy induced bladder toxicity in cervical cancer patients.

Background and objectives Radiotherapy for advanced cervical cancer (CaCx) often results in unintended genitourinary toxicities, notably bladder damage. Predicting such radiation-induced toxicity remains challenging. γ-H2AX, a marker of DNA double-strand breaks (DSBs), offers promise as a predictive biomarker for radiosensitivity. This study aimed to evaluate γ-H2AX foci kinetics in peripheral blood lymphocytes (PBLs) as a surrogate for DNA damage response and a predictor of bladder toxicity in CaCx patients undergoing pelvic radiotherapy. Methods In this prospective study, 43 FIGO stage IIIB CaCx patients were enrolled. Stage I (n=31) assessed γ-H2AX induction post-CT simulation (2-6 mGy); Stage II (n=34) evaluated γ-H2AX kinetics across three radiotherapy fractions (FR1, FR13, FR25) during external beam radiotherapy (50 Gy in 25 fractions ± cisplatin). Blood samples were collected at baseline, 1-, 4-, and 24-h post-irradiation. γ-H2AX foci were quantified via flow cytometry. Bladder toxicity was graded usingRadiation Therapy Oncology Group (RTOG) criteria. Results CT and radiotherapy both induced significant γ-H2AX foci, peaking at 1 h. Patients without bladder toxicity showed higher foci induction and faster decay (1→4h: 48.9% vs. 39.4%; 1→24h: 43.6% vs. 12.8%) across all fractions. Persistent foci at 24 h correlated with increased toxicity risk, indicating deficient DNA repair capacity. Interpretation and conclusions γ-H2AX foci kinetics effectively reflect in vivo DNA repair efficiency and predict radiation-induced bladder toxicity. This minimally invasive biomarker may guide personalized radiotherapy, enabling early identification of high-risk patients and potential use of radioprotectors or treatment modifications.