Adjoint transport for dose in treatment trajectory optimization for external beam radiation therapy

The patent applies adjoint transport theory to invert the traditional dose calculation approach. Instead of forward transporting photons from each beamlet to calculate dose (forward transport), the method adjoint-transportes from ROI to source, evaluating dose response by tracing adjoint photons backward from the region of interest to the beam source. This inversion fundamentally reduces computational complexity while maintaining dose calculation accuracy, as the adjoint solution field can be reused across multiple beamlet evaluations.

The patent performs preliminary adjoint transport calculations to pre-compute the adjoint solution field from each ROI before evaluating candidate vertices and beamlets. This preliminary action creates a reusable adjoint fluence map that accelerates subsequent dose evaluations across multiple treatment geometry candidates. By preparing this foundational data structure in advance, the system efficiently explores multiple trajectories and field geometries without repeating expensive transport calculations, thus managing optimization complexity while maintaining high treatment plan quality.