Room: Exhibit Hall
Purpose: To investigate the beam characteristics of the Hyperscan nozzle for spot scanning treatment, the nozzle components have been modeled in a Monte Carlo (MC) platform to perform the end-to-end simulation.
Methods: Nozzle components, including scanning magnets, strip ion chambers 1 and 2&3, energy selector(ES), adaptive aperture (AA) and exit window have been modeled in TOPAS MC software. The ES is composed of 18 Lexan plates with various thicknesses from 0.2 to 6.6cm WET to create a combination of 156 energies with range increment of 2mm WET. The AA is a mini-MLC consisting of 7 pairs of leaves made of nickel. The inner 5 and the outer 2 pairs have width of 0.5 and 2cm with a thickness 10cm. The beams are further trimmed by the AA before entering a patient. A single Gaussian source model has been used , and the initial spot sigmas, energies and energy spread have been optimized to match the measured spot size and pristine Bragg peak for the highest energy of 227MeV. A constant scanning magnets gradient was used to scan the beam. Five lower energy beams, 203, 176, 146, 110 and 64MeV, have been benchmarked against with measurements. Single spot, single-layer uniform spot maps, and single-field plans of cubic volumes were simulated with and without AA to investigate the penumbra sharpening effects.
Results: The simulation can faithfully reproduce the measured pristine Bragg peak with accuracy of 0.5mm range and spot sigma of 0.7mm. The simulation penumbra reduction by AA is 2 to 12mm from highest energy 227MeV to 64MeV for air gap between 5 and 15cm.
Conclusion: The Hyperscan nozzle has been successfully implemented in MC simulation platform and the MC simulation provides a benchmark tool to validate commercial TPS beam modeling and dose calculation accuracy.