Validation of 3D printing materials for high dose-rate brachytherapy using ionisation chamber and custom phantom

Abstract

Methods. Measurements were taken with the Exradin A20 (Standard Imaging) ionisation chamber, and the ‘homemade’ MARM phantom was made with the 3D Ultimaker 2+ printer using PLA material. The material used for validation was ABS Medical from Smart Materials 3D. The irradiation was undertaken with a 192Ir source by means of Varian’s GammaMed Plus iX HDR equipment. EBT3 films were used to run additional tests. We compared different measurements for PLA, ABS Medical, and water. Additional validation methods, described in the bibliography, were also compared. Results. The measurements with the ionisation chamber that we obtained using the MARM phantom with PLA and ABS within the clinically relevant range (0.5–1.5 cm) differ with respect to the measures in the water reference, by 2.3% and 0.94%, respectively. Discussion. The literature describes highly heterogeneous validation methods, complicating the performance of systematic reviews and comparisons between materials. Thus, creating a phantom represents a single effort that will quickly pay off. This system enables comparisons, ensuring that geometric conditions remain stable—something that is not always possible with radiochromic films. The use of a calibrated ionisation chamber in the corresponding energy range, combined with the ‘homemade’ MARM phantom applied according to the proposed methodology, allows a differentiation between the attenuation of the material itself and the drop in the dose due to distance. Conclusion. The validation method for 3D printing materials, using an ionisation chamber and the MARM PLA phantom, represents an accessible, standardisable solution for manufacturing brachytherapy applicators.