RESUMEN
This work reports an optimized method to experimentally quantify the Gd-nanoparticle dose enhancement generated by electronic brachytherapy. The dose enhancement was evaluated considering energy beams of 50 kVp and 70 kVp, determining the Gd-nanoparticle concentration ranges that would optimize the process for each energy. The evaluation was performed using delaminated radiochromic films and a Poly(methyl methacrylate) (PMMA) phantom covered on one side by a thin 2.5 µm Mylar filter acting as an interface between the region with Gd suspension and the radiosensitive film substrate. The results for the 70 kVp beam quality showed dose increments of 6±6%, 22±7%, and 9±7% at different concentrations of 10, 20, and 30 mg/mL, respectively, verifying the competitive mechanisms of enhancement and attenuation. For the 50 kVp beam quality, no increase in dose was recorded for the concentrations studied, indicating that the major contribution to enhancement is from the K-edge interaction. In order to separate the contributions of attenuation and enhancement to the total dose, measurements were replicated with a 12 µm Mylar filter, obtaining a dose enhancement attributable to the K-edge of 29±7% and 34±7% at 20 and 30 mg/mL, respectively, evidencing a significant additional dose proportional to the Gd concentration.
RESUMEN
This work evaluates the radiation shielding capabilities of the PLA-W composite for MV energy photons emitted by a linear accelerator and the feasibility of manufacturing a clinically-used collimator grid in spatially fractionated radiotherapy (SFRT) using the material extrusion (MEX) 3D printing technique. The PLA-W filament used has a W concentration of 93% w/w and a green density of 7.51 g/cm3, characteristics that make it suitable for this purpose. Relevant parameters such as the density and homogeneity distribution of W in the manufactured samples determine the mass attenuation coefficient, directly affecting the radiation shielding capacities, so different printing parameters were evaluated, such as layer height, deposition speed, nozzle temperature, and infill, to improve the protection performance of the samples. Additionally, physical and mechanical tests were conducted to ensure structural stability and spatial variability over time, which are critical to ensure precise spatial modulation of radiation. Finally, a complete collimator grid measuring 9.3 × 9.3 × 7.1 cm3 (consisting of 39 conical collimators with a diameter of 0.92 cm and center-to-center spacing of 1.42 cm) was manufactured and experimentally evaluated on a clinical linear accelerator to measure the radiation shielding and dosimetric parameters such as mass attenuation coefficient, half-value layer (HVL), dosimetric collimator field size, and inter-collimator transmission using radiochromic films and 2D diode array detectors, obtaining values of 0.04692 cm2/g, 2.138 cm, 1.40 cm, and 15.6%, respectively, for the parameters in the study. This shows the viability of constructing a clinically-used collimator grid through 3D printing.