LET_d Optimization Verification With an SOI Microdosimeter

A first of its kind experimental verification of dose-averaged linear energy transfer (LET_d) optimized treatment plans for proton therapy has been carried out using a silicon-on-insulator microdosimeter at the Massachusetts General Hospital (MGH), Boston, USA.

Three clinical treatment plans of a typical ependymoma structure set were designed using the standard clinical approach, the proposed protocol approach, and a one-field approach. The plans were then reoptimized to reduce the LET_d-weighted dose in the brain stem. All six plans were delivered in a solid water phantom and the experimental y_D‾ measured.

After LET_d optimization, a reduction in y_D‾ was found within the brain stem by an average of 12%, 19%, and 4% for the clinical, protocol, and one-field plans, respectively, while maintaining adequate coverage of the tumor structure. The experimental LET_d-weighted doses were in agreement with the treatment planning system calculations and Monte Carlo simulations and reinforced the improvement of the optimization.

This work demonstrates the first experimental verification of the clinical implementation of LET_d optimization for patient treatment with proton therapy.