Radiation Attenuation Simulation of 3D-Printed Polymers Across Variable Infill Densities and Phase Angles Using EpiXS Program

1. Introduction

The use of ionizing radiation in medical treatments has been highly effective in treating various forms of cancer, but it also presents inherent risks, especially to healthcare practitioners. Professionals consistently exposed to radiation over extended periods are at increased risk of developing radiation-induced health issues, including both acute and chronic conditions. Studies have shown that radiation exposure can result in a spectrum of health effects, ranging from mild radiation sickness to severe illnesses such as cancer. Long-term exposure has even been linked to fatalities in some instances [1,2,3,4].

Global health reports indicate that over 1,000 healthcare professionals worldwide experience significant radiation exposure annually, underscoring the urgent need for more effective protective measures [3,5]. Despite the clear risks, the prohibitive cost of radiation shielding equipment remains a challenge. Modern radiation protective gear can cost from Php 2,500 (per piece) to Php 35,500 (per set), making accessibility difficult for many institutions [6]. As both healthcare workers and patients undergoing radiation therapy or diagnostic procedures face these risks, the scientific community has focused on developing lightweight, wearer-specific, and cost-effective radiation protection gear to mitigate exposure and improve safety [7,8,9,10,11].

Additive manufacturing, particularly 3D printing, has emerged as a promising solution for addressing these challenges in radiation protection[12,13]. Unlike traditional manufacturing methods, 3D printing allows for the creation of custom-fitted radiation treatment aid, such as boluses, which can be tailored to the patient’s anatomy[5,14,15]. This approach enhances treatment accuracy by ensuring that the radiation dose is delivered precisely to the targeted areas, minimizing unnecessary exposure to surrounding tissues. Furthermore, fitted designs are crucial not only for patient safety but also for the medical staff, whose protective gear must offer both comfort and adequate shielding. In contrast to commercially available radiation protection garments, which are often bulky and ill-fitting, 3D-printed, patient-specific designs offer significant advantages in both protection and comfort [5,14].

The integration of additive manufacturing into the production of radiation protection equipment offers significant potential to reduce costs, improve the effectiveness of radiotherapy treatments, and increase the safety of healthcare professionals. By utilizing advanced materials and innovative design techniques, 3D printing can overcome the limitations of traditional radiation shielding gear, paving the way for more efficient and accessible solutions in radiotherapy. This study seeks to design and develop radiation protective gear by employing 3D printing technology, specifically varying infill densities and phase angles, to optimize radiation attenuation.

2. Materials and Methods

The study implementation was subdivided into Computer-Aided Design (CAD) and density calculation, radiation attenuation simulation, and statistical analysis of attenuation effects.

2.1. Computer-Aided Design (CAD) and Theoretical Density Calculation

The design of the test specimens for the irradiation tests were generated using a CAD software, Dassault Solidworks version 2020. The sample is a cylinder-shape block with 50mm in diameter and 20mm in height, see Figure 1. The wall and infill thicknesses are both two (2) millimeters. The infill was modeled first using an extruded boss/base command, then extruded cut for the profile of the cylinder. Lastly, the shell of the specimen was created using extrude-thin command.

Based on the design of experiment presented in the previous subsection, distance between infills, see Figure 2. Computed distances are presented in Table 1. A configuration table was used to easily produce CAD models with varying properties in a single “.sldprt” file.

The densities of ABS, PLA, and TPU were obtained from the manufacturers’ datasheets. The relative densities of the materials were then calculated, accounting for the air gaps within the infill structure, which effectively reduced the overall mass of the samples. Using CAD software, the volume of the infill was determined, and from this, the relative mass of each sample was computed. Given that the sample was enclosed by a solid outer wall, the total volume was fixed at 39.25 cm³, corresponding to a cylindrical geometry.

2.2. Radiation Attenuation Simulation

The attenuation modulation of ABS, PLA, and TPU was investigated using EpiXS software (Figure 3) developed by the DOST - Philippine Nuclear Research Institution (PNRI) [16]. This free software requires Windows operating system and can be downloaded through their official website. This study utilized the EPICS2017 photolibrary. Linear attenuation coefficient was extracted from the software by inputting the calculated densities from CAD. Chemical formula of ABS, PLA, and TPU were also included in the simulation parameter as well as the colorant, which is the titanium dioxide. The concentration was based on the manufacturer’s datasheet. To have a uniform comparison, the color selection is limited to white.

2.3. Statistical Analysis of Linear Attenuation Coefficients

Varying the infill density and phase angles imposed varying linear attenuation coefficients. These differences were statistically analyzed using the non-parametric Kruskal-Wallis test and regression analysis through Python/Jupyter Notebook. The statistical analysis provided insights to the modulation effect of varying the infill densities and phase angles of different polymers for the X-ray radiation region.

3. Results and Discussion

The main advantage of 3D printing in designing radiation protective gears allows introduction of airgaps in a uniform pattern. From Table 2, the gray areas represent the 3D printed and the black ones represent the airgaps. Phase angle orientation is based on the +x-axis as zero angle and in counterclockwise direction. Based on the CAD models, with the increasing infill density, the airgaps were uniformly minimized.

The relative densities of each sample were determined by calculating the volumes using Computer-Aided Design (CAD) software. These calculations provided the total volume of the 3D-printed parts, including both the solid material and any air gaps present in the infill structure. The calculated volumes, detailed in Table 3, allowed for the computation of the relative densities by dividing the measured mass of each sample by its corresponding volume. This method provided a more accurate representation of the material’s density, accounting for variations in infill patterns and the introduction of air gaps, which can significantly impact the overall density of the printed parts.

The total linear attenuation coefficient, calculated using the EpiXS program, was set within the 1-100 keV energy range, corresponding to the X-ray region of the radiation spectrum. This energy range is particularly relevant to medical imaging and radiation therapy, where precise control over attenuation is critical for optimizing treatment efficacy and minimizing exposure to surrounding tissues. The results revealed a decreasing trend in attenuation across all the material plots (see Figure 4). This behavior is consistent with the known phenomenon in radiation physics where higher energy photons interact less frequently with matter, leading to reduced photon-material interactions.

At lower photon energies, the probability of interactions, such as the photoelectric effect or Compton scattering, is higher, resulting in greater attenuation. However, as photon energy increases, these interaction probabilities decrease, which is reflected in the observed reduction in attenuation coefficients. This trend is typical for materials used in radiation shielding and imaging, as higher energy photons have enough energy to pass through the material with fewer interactions. Understanding this behavior is essential for designing materials and structures that can effectively modulate radiation exposure in medical and industrial applications.

Across all materials tested, consistent patterns were observed, see Figure 5. The median values and the interquartile range (IQR) remained stable, even with variations in infill densities. As expected, the materials showed the highest median values at 100% infill density. While there were some outliers and variations (represented by the whiskers), most data points clustered around consistent values, reflecting reliable trends.

Interestingly, there was a slight increase in the median as infill density increased, particularly at 100%. This suggests that infill density has a noticeable, though moderate, effect on the attenuation coefficient. However, the phase angle didn’t appear to cause significant changes in the distribution of values. This may be due to the fact that the software calculations were primarily based on material densities and atomic concentrations, leaving other variables, like phase angles, with limited impact.

To rigorously assess the data, a Kruskal-Wallis Test was applied to determine the statistical significance of the differences in attenuation across the materials, given the set parameters. The results of the test supported the initial observations from Figure 5, where an increase in infill density was associated with enhanced attenuation. This was confirmed by a p-value of less than 0.05, indicating a statistically significant effect of infill density on attenuation (Table 4).

Conversely, variations in phase angle did not yield statistically significant differences, as the p-value exceeded the 0.05 threshold. This finding aligns with the earlier discussion in Figure 5, reinforcing the conclusion that phase angle has a negligible effect on attenuation under the conditions examined in this study, which was summarized in Figure 6.

Among the three materials, TPU consistently exhibited higher linear attenuation coefficient values across both varying infill densities and phase angles. This can be attributed to its higher intrinsic density and greater atomic concentration compared to the other materials. These material properties contribute to TPU’s superior attenuation capabilities, allowing it to block more radiation than the other tested polymers.

The three materials demonstrated a linear relationship between infill densities and linear attenuation coefficients, as illustrated in Figure 7. Among the polymers, TPU exhibited the greatest sensitivity to changes in infill densities, with a slope of 1.1194, while ABS displayed the least sensitivity, with a slope of 0.7257. This suggests that TPU is the most compatible material for radiation shielding applications, particularly in contexts requiring a flexible interface, given its higher flexibility compared to the other two polymers. Furthermore, the data for all materials showed an excellent linear fit, indicating that interpolation for material design and modulation of attenuation is highly reliable.

When extrapolating to lower infill densities, TPU exhibited the highest baseline attenuation coefficient at 20.199 cm⁻¹, followed by PLA at 18.835 cm⁻¹, and ABS at 13.073 cm⁻¹. These results indicate that even at lower infill densities, such as 30%, TPU maintains effective radiation attenuation properties. PLA, with a relatively small difference from TPU, presents a viable alternative, particularly in situations where a stiffer and more cost-effective material is needed compared to TPU or ABS.

4. Conclusions

This study successfully demonstrated the potential of varying infill densities and phase angles in 3D-printed ABS, PLA, and TPU materials for radiation attenuation applications in the X-ray region. TPU exhibited the highest responsiveness to changes in infill density, with a slope of 1.1194, significantly outperforming ABS (slope of 0.7257) and PLA (slope of 0.9251). The baseline attenuation coefficient for TPU at 30% infill density was the highest at 20.199 cm⁻¹, compared to 18.835 cm⁻¹ for PLA and 13.073 cm⁻¹ for ABS. This indicates that TPU is particularly suited for radiation shielding, especially in applications requiring flexible materials.

The statistical analysis, using the Kruskal-Wallis test, confirmed the significant impact of infill density on attenuation, with p-values less than 0.05 across all materials. In contrast, phase angle did not significantly affect attenuation, with p-values exceeding 0.05, suggesting that phase angle is a parameter that cannot be directly simulated using the EpiXS program. These results highlight the importance of infill density as a key parameter in designing radiation protection materials.

Additionally, TPU’s superior attenuation properties even at lower infill densities, along with PLA’s comparable performance at a slightly lower attenuation (18.835 cm⁻¹ at 30% infill), makes them excellent candidates for radiation-shielding applications. PLA, being a stiffer yet cost-effective alternative to TPU, can also be used in cases where higher rigidity is required without compromising too much on radiation protection.

The integration of additive manufacturing in producing custom-designed radiation protection gear offers significant improvements in the accessibility, performance, and comfort of protective equipment in both medical and industrial contexts. These findings lay a strong foundation for future work, which can explore more complex infill geometries and phase angle combinations, as well as testing under different radiation spectra, to further optimize material design for radiation shielding.