Comparison of experimental and radiobiological model-predicted survival of human laryngeal squamous cell carcinoma cells in a helium spread-out Bragg peak

Background and Purpose: Helium ion therapy offers favorable dose distributions and potential biological advantages over photon and proton therapies, yet data on cellular response in clinically relevant Spread-Out Bragg Peak (SOBP) configurations remain limited. This study measured the surviving fraction of radioresistant human laryngeal squamous cell carcinoma (SQ20B) cells irradiated in a helium SOBP and compared experimental results with predictions from NanOx, a nanodosimetry and oxidative stress model implemented in Monte Carlo simulations. Materials and Methods: SQ20B cells were irradiated at three positions along a helium SOBP using a passive beamline. Survival fractions were measured for doses between 1 and 4 Gy. The setup was simulated in GATE, and survival was predicted using the NanOx model via the Biodose Actor. Relative biological effectiveness (RBE) was derived from linear quadratic fits using photon reference parameters. Results: NanOx predicted decreasing survival towards the distal edge, with surviving fractions at 4 Gy of 11%, 7%, and 4% at the proximal edge, plateau, and distal edge, respectively. Experimentally, fitted surviving fractions at 4 Gy were 10%, 12%, and 8%, showing no spatial trend. Deviations between model predictions and experimental averages ranged from 20 to 37%. Experimental RBE values ranged from 2.1 to 2.4, in reasonable agreement with NanOx predictions (2.1-2.9). Conclusions: In this SQ20B cell model under the present experimental conditions, NanOx predictions differed from experimental data by 20-37% depending on position. These results support further validation of the model in a broader range of cell lines and helium ion irradiation configurations.