KEY POINTS
- Investigators at PSI developed target-specific passive-scattering devices using hollow PLA 3D-printed shells rather than conventional solid custom hardware. Collimators were filled with reusable 1-mm-radius copper spheres, while compensators used 1.191-mm-radius polypropylene spheres.
- All measurements were performed on PSI Gantry 2, with TOPAS Monte Carlo simulations used to model both the printed shells and the packed spheres. Measurements across proton energies of 100–220 MeV were used to validate depth-dose and lateral-profile behavior.
- For copper-filled devices, measured and simulated proton range differed by approximately 0.5%, while lateral beam size differed by about 3%. With polypropylene, range agreement remained within approximately 5%, although lateral-profile differences reached about 10%.
- A direct comparison of the printed copper-sphere collimator against a conventional solid copper collimator showed measured-versus-simulated beam-width differences of only 1–3% for a 90 MeV scattered beam. The experimental collimator itself required <20 minutes of printing and only 4 g of PLA.
- The principal technical weakness appeared at higher energies: protons traversed the PLA-defined bore, creating a measurable dose halo outside the intended aperture. Increasing the collimator length reduced but did not eliminate the problem, whereas replacing the bore with higher-density copper or copper-filled HTPLA was substantially more effective.
- For a 2-cm spherical target irradiated with a 120 MeV beam, the combined collimator and compensator used less than 10 g of filament, printed in 30 minutes, and achieved a mean squared error of <1% between simulated and measured dose profiles. A second setup demonstrated feasibility for a complex murine brain-like target.
- Across the complete experimental setups, printing required <45 minutes and less than $1 of filament. However, the authors explicitly limit the current application to preclinical experimentation: clinical translation would require validation of reproducibility, stopping power across clinical energies, neutron and leakage dose, residual activation and a formal QA workflow.
CLINICAL TAKEAWAY
For preclinical proton and FLASH research, the approach turns custom field-shaping hardware into something that can potentially be fabricated in under an hour while reusing the expensive high-density material. The concept is elegant and practical, but the high-energy halo and unresolved QA and radiation-protection questions mean this remains an experimental platform rather than a clinical device.