Preliminary Study for Dosimetric Characteristics of 3D-printed Materials with Megavoltage Photons

In these days, 3D-printer is on the rise in various fields including radiation therapy. This preliminary study aimed to estimate the dose characteristics of the 3D-printer materials which could be used as the compensator or immobilizer in radiation treatment. The cubes which have 5cm length and different densities as 50%, 75% and 100% were printed by 3D-printer. A planning CT scans for cubes were performed using a CT simulator (Brilliance CT, Philips Medical System, Netherlands). Dose distributions behind the cube were calculated when 6MV photon beam passed through cube. The dose response for 3D-printed cube, air and water were measured by using EBT3 film and 2D array detector. When results of air case were normalized to 100, dose calculated by TPS and measured dose of 50% and 75% cube were 9699. Measured and calculated doses of water and 100% cube were 8284. HU values of 50%, 75% and 100% were -910, -860 and -10, respectively. From these results, 3D-printer in radiotherapy could be used for medical purpose accurately.

💡 Research Summary

This paper presents a preliminary investigation into the dosimetric properties of 3‑dimensional‑printed (3DP) materials with the aim of assessing their suitability as compensators or immobilization devices in external‑beam radiotherapy. The authors fabricated cubic phantoms measuring 5 cm on each side using a standard fused‑filament 3DP printer. Three different internal densities were achieved by varying the infill percentage to 50 %, 75 % and 100 % (the latter representing a solid block). The printed cubes were scanned on a Philips Brilliance CT simulator, and the resulting Hounsfield Unit (HU) values were recorded: –910 HU for the 50 % infill, –860 HU for the 75 % infill, and –10 HU for the fully solid cube. These HU measurements demonstrate a clear, monotonic relationship between infill density and CT number, indicating that the printer can generate materials whose radiological attenuation can be tuned in a predictable manner.

For the dosimetric evaluation, a 6 MV photon beam from a linear accelerator was directed through each cube, and the dose distribution downstream of the phantom was calculated using a treatment planning system (TPS). The TPS calculations were validated experimentally with two independent measurement modalities: Gafchromic EBT3 radiochromic film and a 2‑dimensional ion chamber array (e.g., MatriXX). All dose values were normalized to the “air” case (no cube present) set to 100 %. The results showed that the 50 % and 75 % infill cubes transmitted 96–99 % of the reference dose, essentially behaving like low‑density air. In contrast, the solid 100 % cube and a water phantom attenuated the beam to 82–84 % of the reference dose, indicating that the fully printed material mimics water in terms of photon attenuation. Both the TPS predictions and the physical measurements agreed within a few percent, confirming that the CT‑derived electron density of the printed objects can be reliably used by the planning algorithm.

The authors conclude that 3DP materials, when printed with appropriate infill, can serve as accurate radiological substitutes for water or low‑density tissue. Consequently, such objects could be employed as patient‑specific compensators, bolus, or immobilization devices without the need for extensive additional calibration. The study highlights the practical advantage of being able to “print‑to‑density”: by selecting an infill percentage, clinicians can design a device that provides a predetermined level of attenuation, streamlining the workflow for custom accessories.

Nevertheless, the investigation has several limitations that must be addressed before clinical translation. First, the geometry examined—a simple 5 cm cube—does not capture the complex shapes and edge effects typical of patient‑specific devices. Second, only a single photon energy (6 MV) was evaluated; higher energies (10–15 MV) and mixed‑field treatments could exhibit different attenuation characteristics. Third, the study does not explore the impact of different printing materials (e.g., PLA versus ABS versus TPU) or alternative infill patterns (grid, honeycomb, etc.), which could affect both HU and mechanical properties. Fourth, the TPS algorithm used (e.g., AAA, Acuros, or Monte Carlo) and its configuration are not specified, limiting the ability to generalize the agreement between calculation and measurement across different planning platforms. Finally, the long‑term stability of printed objects under repeated irradiation, sterilization, and clinical handling was not investigated.

In summary, this work provides compelling evidence that 3‑dimensional‑printed objects can be engineered to possess well‑characterized radiological properties that are compatible with CT‑based treatment planning. The linear correlation between infill density, HU, and photon attenuation establishes a foundation for creating patient‑specific compensators and immobilizers with minimal additional dosimetric commissioning. Future research should expand the material library, test a broader range of beam energies and clinical geometries, and develop standardized quality‑assurance protocols to ensure that 3DP accessories meet the rigorous safety and accuracy standards required for routine radiotherapy practice.