Attenuation properties of 3D-printed materials for an Ir-192 high dose rate source using Valencia skin applicators

Objective

To evaluate the physical properties of commonly used 3D-printed materials and the dose attenuation around a high-dose-rate ¹⁹²Ir source, in order to provide a reference for selecting appropriate 3D-printed materials for brachytherapy.

Methods

Fifteen 3D-printed materials (12 non-metallic material and 3 metallic material) were assessed. Each material was fabricated into a wafer with a diameter of 30 ​mm and thickness of 3 ​mm using 3D printing. The CT number of each material was measured, and attenuation measurements were conducted with a Valencia skin applicator and well-type ionization chamber. ¹⁹²Ir was used as the radioactive source, and the attenuated ionization charges were normalized against that obtained in the presence of a solid water phantom at the same depth.

Results

The CT number of nylon was (−7.78 ​± ​3.36) HU, closest to water among all materials. The CT numbers of the other 11 non-metallic materials were below 300 HU. Moreover, the CT number of the Al alloy was (1,350.89 ​± ​374.55) HU, while the CT numbers of the Ti alloy and stainless steel exceeded 2,976 HU, reaching the upper limit of the CT number range. The results of the attenuation measurements were normalized with the solid water phantom. The average attenuation coefficients of a polyamide, epoxy resin, photosensitive resin, carbon fiber, silica gel, Al alloy, Ti alloy, and stainless steel were 1.003, 0.994, 0.992, 0.995, 0.995, 0.967, 0.939, and 0.866, respectively.

Conclusions

Among the common 3D-printed materials with a density similar to that of water, nylon exhibited the best performance, while the metallic materials caused significant dose attenuation and exhibited CT number distortion. As a result, care should be taken when metallic materials are used as 3D-printed materials for brachytherapy.