Discussion

This study demonstrated the feasibility of hollow 3D-printed compensators and collimators filled with plastic or copper spheres as “eco-friendly” TS devices of small dimensions for small fields PS proton therapy. In addition, a workflow was designed to accurately reproduce them in TOPAS MC, utilizing the modified function available in Porespy16 and experimentally validated, which is a necessary step for experiment design. Although the use of 3D-printed cutouts made of plastic shells filled with small balls or pellets is not new in electron beam or conventional radiation therapy,6, 7, 18, 19 it has never been tested in proton therapy.

The proposed solution offers a sustainable and cost-effective approach, as the spheres, being the only component requiring an initial 1-time purchase, can be repeatedly used. Containers can be fabricated on demand through 3D printing, utilizing minimal filament due to their hollow structure. This design leads to further savings in both materials and production time, making the approach “eco-friendly.” Additionally, this method enables the fabrication of custom-designed collimator components tailored to each experimental setup, offering greater flexibility compared to reusing legacy hardware that may not be well-suited to current study requirements. The ability to quickly produce customized components improves efficiency and adaptability, especially in the context of small animal irradiations, where precision is crucial. Overall, this strategy not only facilitates more efficient production of PS devices but also helps reduce environmental impact.

Our project aims to conduct a feasibility study to demonstrate the viability of this idea. For clinical applications, it is crucial to ensure quality assurance and reproducibility. Concerns exist regarding the uniformity of sphere distribution, especially since the process of filling the 3D-printed container is performed manually. There may be a need to develop an automated machine for regular use to address this issue.7 Before clinical adoption, future work should also include stopping‑power validation across the full clinical energy range, neutron and leakage‑dose characterization, and residual‑activity measurements to ensure radiation‑protection requirements and disposal protocols remain unchanged. Nevertheless, this technique can be investigated for preclinical studies, as highlighted in this study. We found that special attention should be given to the design of the collimator, as the inner cylindrical 3D-printed bore may influence the dose distribution. However, this issue is not a concern when used for low-energy applications such as PS irradiation of mice. One challenge with constructing TS devices is their size. Larger devices require more small spheres, which can lead to increased weight. This issue could be addressed by using a simple box made of copper or plastic that features a predefined square or rectangular opening. We could place the TS device with the 3D-printed shape of our target inside this opening. While each specific target requires a uniquely 3D printed cover for the TS device, the larger copper or plastic holder and the spheres can be reused. Finally, the murine brain-like tumor case was included as a proof-of-concept to show that the proposed approach can be extended to more complex geometries. Within the scope of this technical note, the goal was to demonstrate feasibility rather than provide an exhaustive quantitative analysis. A more detailed anatomical and dosimetric evaluation would be valuable in future work.

In conclusion, our study has demonstrated the effectiveness of an innovative and “eco-friendly” method utilizing 3D-printed cutouts shaped to meet specific target requirements, filled with reusable plastic or copper spheres to create TS shapes. This technique enables rapid production due to its hollow design and the use of reusable materials, such as plastic and copper spheres. By adopting this approach, we reduce waste, lower costs, enhance conformity, and improve the efficiency of TS treatments and experiments.

Funding

This work was funded by the Swiss National Science Foundation (Grant No. 200882).