Recommendations for simulating and measuring with biofabricated lung equivalent materials based on atomic composition analysis.

Monte Carlo simulations of lung equivalent materials often involve the density being artificially lowered rather than a true lung tissue (or equivalent plastic) and air composition being simulated. This study used atomic composition analysis to test the suitability of this method. Atomic composition analysis was also used to test the suitability of 3D printing PLA or ABS with air to simulate lung tissue. It was found that there was minimal atomic composition difference when using an artificially lowered density, with a 0.8 % difference in Nitrogen the largest observed. Therefore, excluding infill pattern effects, lowering the density of the lung tissue (or plastic) in simulations should be sufficiently accurate to simulate an inhaled lung, without the need to explicitly include the air component. The average electron density of 3D printed PLA and air, and ABS and air were just 0.3 % and 1.3 % different to inhaled lung, confirming their adequacy for MV photon dosimetry. However large average atomic number differences (5.6 % and 20.4 % respectively) mean that they are unlikely to be suitable for kV photon dosimetry.