Bridging the translational gap in radiotherapy: a human three-dimensional cell culture for evaluating neutron...

In radiation therapy, accurately estimating the relative biological effectiveness (RBE) is essential for the safe and effective clinical application of neutron radiation therapy. Current RBE evaluations primarily rely on two-dimensional (2D) colony formation assays. However, these models cannot fully capture tissue-level complexity and are not applicable to normal cells lacking colony-forming ability. This limits their clinical applicability. This study demonstrated that the dimensionality of the culture is a critical determinant of radiation sensitivity. While the biological effectiveness of neutron irradiation is systematically overestimated in conventional 2D monolayer systems, three-dimensional (3D) tissue-mimicking models more accurately reproduce the resistance of normal tissues observed in clinical settings. Specifically, we identified a dose-dependent thinning of the extracellular matrix at doses of 25 Gy or higher, suggesting that neutron-induced damage extends beyond cell death to include structural and microenvironmental damage. These findings offer direct insights into the estimation of clinical doses and the protection of normal tissues. While further refinement of model parameters, including cell density and microenvironmental composition, is necessary, the proposed 3D platform provides a clinically meaningful framework for evaluating radiation-induced toxicity in non-colony-forming normal tissues. By facilitating a more precise evaluation of radiation-induced tissue effects, this methodology has the potential to enhance the estimation of RBE and risk stratification, thus contributing to the development of more secure treatment protocols and the broader implementation of neutron therapy.