Dynamic control of carbon-ion radiation dose distribution amid respiratory motion challenges: A review of prediction research using geant4 and deep learning physics-constrained models.

BACKGROUND

Carbon ion radiotherapy (CIRT) offers superior dose conformity and biological effectiveness; however, its precision is highly sensitive to respiratory motion, leading to dose uncertainty and interplay effects that compromise treatment accuracy.

METHODS

A comprehensive literature synthesis was conducted on studies employing motion-resolved imaging techniques (e.g. SMEIR), dynamic dose prediction, 4D robust planning, and hybrid adaptive methods for CIRT. The study emphasised the use of Geant4 Monte Carlo simulations combined with deep learning models, including physics-informed neural networks, to simulate and predict dose perturbations caused by respiratory motion. This review also examined clinical treatment planning systems, radiobiological modelling, and adaptive strategies to mitigate the effects of motion.

RESULTS

The integration of Geant4 with deep learning enabled high-fidelity, computationally efficient dose prediction under respiratory motion, improving accuracy in dose localization and adaptation. Motion management techniques such as respiratory gating, rescanning, and 4D robust optimization demonstrated enhanced tumor control and normal tissue sparing. Hybrid models combining Monte Carlo data and AI inference show promise for near-real-time adaptive therapy. Despite these advances, challenges remain, including limited motion-rich datasets, computational demands for real-time recalculations, and the complexity of incorporating variable relative biological effectiveness (RBE) into adaptive planning.

CONCLUSIONS

Combining Geant4-based Monte Carlo simulations with deep learning frameworks shows emerging promise for controlling carbon ion dose distributions amid respiratory motion, though direct clinical validation for this combination remains limited. These hybrid models may enhance the precision and adaptability of CIRT, offering improved outcomes. Future efforts should focus on clinical validation, standardization, and overcoming computational and data limitations to facilitate clinical translation of motion-adaptive CIRT. These approaches remain at Technology Readiness Levels (TRL 3-5) and require prospective clinical validation before routine implementation.