Surrogate Modelling of Proton Dose with Monte Carlo Dropout Uncertainty Quantification
This work addresses a bottleneck in proton therapy workflows by enabling faster, uncertainty-aware dose predictions, though it is incremental as it builds on existing surrogate modeling and dropout techniques.
The paper tackles the computational demand of Monte Carlo proton dose calculations by developing a neural surrogate with Monte Carlo dropout, achieving significant speedups while providing voxelwise predictive uncertainty for applications like robust planning and adaptive workflows.
Accurate proton dose calculation using Monte Carlo (MC) is computationally demanding in workflows like robust optimisation, adaptive replanning, and probabilistic inference, which require repeated evaluations. To address this, we develop a neural surrogate that integrates Monte Carlo dropout to provide fast, differentiable dose predictions along with voxelwise predictive uncertainty. The method is validated through a series of experiments, starting with a one-dimensional analytic benchmark that establishes accuracy, convergence, and variance decomposition. Two-dimensional bone-water phantoms, generated using TOPAS Geant4, demonstrate the method's behavior under domain heterogeneity and beam uncertainty, while a three-dimensional water phantom confirms scalability for volumetric dose prediction. Across these settings, we separate epistemic (model) from parametric (input) contributions, showing that epistemic variance increases under distribution shift, while parametric variance dominates at material boundaries. The approach achieves significant speedups over MC while retaining uncertainty information, making it suitable for integration into robust planning, adaptive workflows, and uncertainty-aware optimisation in proton therapy.