Design and Optimization of a Novel Translating Checkerboard Range Shifter to Enable Efficient Proton Arc Therapy
Abstract
Purpose
Clinical implementation of proton arc therapy is partly hindered by the low speed of beam energy switching upstream of the nozzle. To achieve fast and multiple post-nozzle energies, we propose a novel range shifter, termed the Checkerboard Range Shifter (CRS), which converts a single pre-nozzle proton energy into multiple discrete post-nozzle energies using a polycarbonate structure composed of multiple discrete thicknesses.
Methods
The CRS consists of a 48 × 48 cm² polycarbonate plate subdivided into a 3 × 3 array of unit cells each containing four squares (8 × 8 cm² per section) of distinct thicknesses. The CRS translates in two dimensions with 2-cm step increments to selectively intercept the beam and generate four post-nozzle energies from a single pre-nozzle energy. To determine optimal square thicknesses, 298 retrospectively treated in-house head and neck proton therapy plans—selected due to their strong potential benefit from proton arc therapy—were analyzed to identify the four most frequently delivered energies based on total monitor units.
Results
A total of 298 retrospectively treated head and neck proton therapy plans were analyzed. Based on cumulative monitor units delivered across all plans, the four most frequently used proton energies were identified as 93 MeV, 99 MeV, 102 MeV, and 104 MeV. Conversion of these energies to water-equivalent thicknesses and subsequently to physical polycarbonate thicknesses resulted in optimal CRS square thicknesses of 5.73 cm, 6.40 cm, 6.75 cm, and 6.99 cm, respectively.
Conclusion
A novel translating range shifter for proton arc therapy has been developed and optimized using large-scale retrospective clinical data. The proposed CRS enables multi-energy delivery from a single pre-nozzle beam and has the potential to reduce energy switching time by a factor of approximately 2–10.