An “eco-friendly” Approach for Proton Therapy Patient- and Experiment-Specific Devices

Purpose/Objective: The increasing interest in pFLASH radiotherapy has recently sparked a renewed focus on patient-specific devices and passive scattering technique (PS), which is currently used for treating ocular tumours in PT. The drawback of this technique is the use of (expensive) custom devices, like collimators and compensators, designed for single-use. Our project seeks to improve the existing approach by developing a flexible setup for PS that can be adapted to different needs. In this study, we investigate the reproducibility of this new approach and its feasibility in the complex case of small target structures. Materials: Each collimating or compensating element consists of 3D-(filament)printed containers of PLA filled with reusable copper or polypropylene spheres, respectively. Collimator functionality can be improved using Copper-filled Metal Composite HTPLA filament for the cylinder surface of the bore. We performed simulations in TOPAS-MC[1,2] and designed the elements using the modified Python package Porespy[3]. We evaluated the collimator's performance by comparing a solid collimator with the new proposed approach. As a feasibility study, we designed a PS setup of an eco-friendly compensator and collimator. Results: We validated the computational model for reproducing the new elements via depth dose curve and beam size measurement (Fig.1). The observed discrepancy between TOPAS and measurement falls within the detector’s inherent uncertainty. Simulations of collimating and compensating elements and experiments agree with a mean square error below 2%. We did not observe a difference in the dose profile between the solid and eco-friendly collimators for low energy. For higher energies (Fig.2A), the PLA in the inner cylinder affects the dose distribution, generating a dose halo around the aperture. The usage of more dense filaments (Copper-filled HTPLA) improves the results. To demonstrate the feasibility of this new PS approach, we designed and validated an “eco-friendly” setup for simple geometrical phantoms and more complex and challenging small structures like murine brain tumours (Fig.2B). 3D-printing allows the design of complex elements with low costs and within a short time (the total time required was <20min, and the filament costs <1$). Conclusion: We have proposed and validated an innovative, eco-friendly experimental setup that leverages the capabilities of 3D-printing. This method enables the creation of patient-specific shapes that can be produced quickly, owing to their hollow design. Additionally, by utilising reusable materials such as plastic or copper spheres, our approach reduces unnecessary waste. This development lowers costs, enhances conformity, and increases PS treatments and experiments' efficiency and environmental impact.