Purpose: To measure and evaluate the dosimetric properties of a three-dimensional (3D) printing material, polylactic acid (PLA), for use in radiation therapy. This study evaluates the effect of several different infill percentages as well as the effect of infill pattern on the dose delivered to a phantom to establish reasonable guidelines for 3D printed bolus usage.
Methods: Six slabs of PLA, each with dimensions 5x5x1 cm³, were designed and printed. The cubic infill pattern was used for five slabs with infill percentages of 25%, 50%, 67%, 75%, and 100%. One slab with 50% infill and the tri-hexagonal pattern was printed. Preliminary dose calculations were made in RayStation, using two dose specification points, one at the surface between the slab and the backscatter material, and one at a depth of 1.5 cm into the backscatter material. The dose at each point was recorded from delivering 100 monitor units (MUs) to each slab material and density, with each photon energy, and for both 5x5 cm² and 10x10 cm² field sizes.
Results: The results present the ratios of calculated dose under the PLA bolus material to the dose with either no bolus (for data at 1.5 cm depth) or a water bolus (for data at the surface). The results show that the dose was consistent at 1.5 cm depth for multiple slabs with 10 MV energy, while 100% and 75% infill slabs were consistently similar to the water bolus.
Conclusion: PLA is an adequate replacement for traditional bolus material, and 3D printed, patient specific bolus materials could significantly improve patient outcomes. Additional studying of how the measured dose and the spatial dose distribution are affected by the choice of infill, as well as the effect on electron dose distribution, are ongoing.