3012 - Development of a Novel Variable Density Range Modulator for Patient Specific FLASH Proton Therapy
Presenter(s)
W. Gu1, L. Yin1, A. Lin1, W. Zou1, J. Setianegara1, E. S. Diffenderfer1, M. M. Kim2, K. Mei3, P. Noël3, and K. K. Teo1; 1Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 2Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 3Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
Purpose/Objective(s): To enable ultrafast dose delivery in proton FLASH therapy using a single-energy beam, we introduce a novel class of 3D-printed variable-density range-modulating devices (VDRMDs) designed for patient-specific treatments.
Materials/Methods:
PixelPrint is a high-resolution 3D-printing method that controls the filament-to-air ratio at the voxel level to create spatially varying material density. Three retrospective head-and-neck IMPT cases were selected. One to two beams were chosen based on patient geometry to deliver 40 Gy to the clinical target volume (CTV). We developed a patient-specific density design and planning framework that (1) imports the patient CT, contours, and beam geometry, and computes target proximal and distal water-equivalent thickness (WET) in beam’s-eye view (BEV); (2) performs inverse optimization to generate a VDRMD density map that modulates range across the device plane to match the target proximal and distal WET in BEV; (3) optimizes spot intensities using robust optimization; and (4) density-map re-optimization to improve target conformity. Device density was constrained to 0.2–1.1 g/cm³. Plans used a 225 MeV spot-scanning proton beam with the beam path including the simulated VDRMD, an aluminum range shifter, and a brass aperture with a 5 mm margin to sharpen the lateral penumbra. Dose was calculated with MCsquare and plan was optimized using an in-house treatment planning platform. Plan quality metrics were used to assess the feasibility of patient-specific modulation with VDRMDs under realistic anatomical conditions and beam geometries.Results: Patient-specific conformal proton FLASH plans were generated using a single-energy layer with the VDRMD and proposed framework. The mean conformity index (V100%/VTV) was 1.38, and the heterogeneity index (D2%/D98%) was 1.08. Target coverage and sparing of critical structures were maintained under the evaluated patient-specific geometries.
Conclusion: VDRMDs can produce clinically relevant conformal proton dose distributions while maintaining the efficiency of single-energy delivery needed for FLASH. Compared with fixed-density 3D-printed modulators, voxel-level density control offers improved mechanical integrity and finer modulation control, supporting translation to both preclinical and clinical proton FLASH applications.