Speaker
Description
Objectives:
Beam delivery time (BDT) is an important consideration in particle arc therapy, particularly for carbon-ion arcs delivered using synchrotrons. Energy layer filtration can reduce BDT, but the current MU-based filtration may not optimally balance delivery efficiency and treatment quality. This study investigates alternative energy layer filtration strategies for upright static carbon arcs and evaluates their impact on the trade-off between treatment quality and BDT.
Methods:
Treatment plans were initialized using multiple beam directions and energy layers according to treatment site and case complexity. Three patients (two H&N and one intracranial) were robustly optimized using all investigated filtration approaches. During optimization, energy layers were filtered to a predefined number, with the required layers removed in a single filtration step. In addition to the MU-based filtration implemented in RayStation, three alternative strategies were investigated. First, a saliency-based approach inspired by Optimal Brain Damage published by LeCun et al. (OBD) was used to rank energy layers according to their contribution to the optimization objective and remove the least salient layers. Second, Group Lasso regularization was used to promote layer-wise sparsity, with groups defined according to either layer MU or cumulative saliency. Third, a delivery-time-aware strategy was developed by combining a traveling salesman problem (TSP) optimization of the delivery path with iterative removal of contiguous groups of layers having a low MU- or saliency-to-delivery-time ratio. The delivery path was recomputed after each filtration step.
Results:
OBD-based filtration reduced the objective value by more than 10% compared with MU-based filtration, while increasing BDT by approximately 5%. Group Lasso in conjunction with OBD provided an additional 2–3% improvement in objective value with little additional BDT (both relative to OBD). TSP-based filtration showed potential to further reduce BDT compared to MU-based filtering, with reductions of close to 10% and a deterioration of similar magnitude in objective value.
Outlook & Discussion:
Alternative energy layer filtration strategies show potential to improve the balance between treatment quality and delivery efficiency in upright static carbon arc therapy. Saliency-based filtration improved the optimization objective relative to MU-based filtration, while delivery-time-aware filtration demonstrated the potential for substantial BDT reduction albeit with a reduction in plan quality. Future work will evaluate the clinical relevance and robustness of these approaches and investigate more computationally efficient implementations of delivery-time-aware filtration.
Funded by EU GA No. 101168955