Time- and dose-dependent cytotoxicity of SBRT in HepG2 cells: insights into radiosensitivity and recovery

Purpose Hepatocellular carcinoma (HCC) often does not present for surgery and also demands local non-surgical therapies. Stereotactic body radiotherapy (SBRT) approach is becoming an effective tool and the temporal dynamics of cytotoxicity and recovery from SBRT in HepG2 hepatocellular carcinoma cells is poorly characterized. This work set out to investigate how HepG2 cells respond dose-time under clinically relevant SBRT fractionation, and the critical window of cytotoxicity.Materials and methods HepG2 cells were irradiated on a clinical LINAC with CT-based treatment planning containing three SBRT (12, 16, 20 Gy × 3) groups (total 36, 48, and 60 Gy). Viability was measured by MTT assay at 9 time points (6–336 h) with supporting morphological changes through phase-contrast microscopic data, morphological changes up to 120 h by phase-contrast microscopy. Logarithmic MTT-derived viability fraction (log10VF), time-to-50% viability (T½), and area under the viability–time curve (AUC) were determined to account for both kinetic and cumulative influences.Results Cell viability exhibited a dose–time dependence. All irradiated conditions achieved an early plateau followed by a viability minimum at ∼72 h, after which the residual was only partially recovered. Recovery was most evident at 36 and 48 Gy, whereas 60 Gy produced a pronounced early decline and limited late recovery; the shortest T½ occurred at 48 Gy (≈11.4 h). Morphological changes accompanied the time and dose dependent decline in viability and included features consistent with radiation-related cellular injury, such as cell shrinkage, membrane blebbing, apoptotic body like structures, and necrotic-like morphology.Conclusion In this HepG2 SBRT-mimetic in vitro model, MTT-based viability consistently reached a minimum at approximately 72 h across regimens, suggesting a practical window for kinetic sampling. Confirmation of long-term reproductive cell death would require additional assays, particularly clonogenic analyses.