Introduction

The emerging interest in preclinical proton irradiation, particularly for small, target-specific (TS) experiments, including but not limited to FLASH radiotherapy,1, 2 has increased the need for flexible and efficient TS devices utilized in passive scattering (PS), including compensators, collimators, and energy modulators. Furthermore, radiobiological advancements in the field necessitate extensive preclinical experiments, typically targeting small regions and implanted tumors in murine models. Producing TS-PS devices is resource-intensive, and they often become non-reusable after initial use. Researchers often repurpose older devices to reduce costs and preparation time, which can lead to suboptimal solutions.

In recent years, 3D printing has become an important tool in medical physics, offering innovative solutions for quality assurance phantoms, bolus, immobilizers, and field-shaping and patient-specific devices.3, 4, 5 3D printing offers advantages such as customization, reduced costs, and the ability to be manufactured in-house when an institute has access to a 3D printer. One downside is that printing materials are usually based on plastic because metal can be costly and requires specialized equipment, so it is seldom used to replace metal components like collimators. Additionally, current designs are limited to patient-specific, single-use applications. To address this challenge, a solution proposed for electron radiotherapy6 involves 3D-printed cutouts made of plastic shells filled with 2 mm tungsten ball bearings. A similar idea using alloy granules to fill up a compensator hollow was proposed for intensity-modulated radiotherapy.7 These solutions enable the creation of fast, reusable, TS devices with the only disposable component being the 3D-printed container, making them therefore low‑waste and reusable in an “eco‑friendly” sense.

Our study investigates, for the first time, the feasibility of “eco‑friendly” hollow 3D-printed compensators and collimators filled with plastic or copper spheres for PS proton therapy irradiation of small targets. Understanding the impact of such porous-like devices on dose distribution and developing a Monte Carlo simulation to accurately predict outcomes is crucial for optimizing the experimental setup. This innovative solution has the potential to reduce waste, lower costs, improve dose conformity, enhance the efficiency of PS experiments, and reduce their environmental impact.