Depth and Fluence Scaling Factors for PLA, ABS and PETG

Three-dimensional (3D) printing has revolutionized the fabrication of customized phantoms and devices in radiotherapy, with thermoplastics such as PLA, ABS, and PETG widely used due to their mechanical properties and accessibility. However, their radiological equivalence to water—critical for accurate dosimetry—remains incompletely characterized, particularly for ABS and PETG. This study experimentally determined the depth scaling factor (c_{pl}) and fluence scaling factor (h_{pl}) for these materials using 3D-printed slab phantoms (20 × 20 cm²) adhering strictly to IAEA TRS-398 protocol recommendations for lateral scatter equilibrium. Ionization measurements were performed with electron beams of 6, 9, 12, and 16 MeV energies, and results were validated via Monte Carlo (MC) simulations using the Varian Eclipse eMC v18.0 algorithm. Densities measured for printed slabs were consistently lower than nominal filament values, reflecting inherent imperfection printing gaps from fused deposition modeling. PLA and PETG, denser than water, exhibited c_{pl}\ values greater than unity, while ABS showed c_{pl}\ below unity, consistent with density-dependent electron range behavior. No significant energy dependence was found for either scaling factor. MC simulations underestimated c_{pl}\ by up to 8.4%, whereas h_{pl}\ values showed closer agreement (within 3.3%), suggesting fluence scaling is less sensitive to material heterogeneity. The low cost and reproducibility of 3D-printed phantoms highlight their potential for personalized quality assurance in radiotherapy. Future work should explore scaling factor variability across printing parameters and assess long-term stability to optimize clinical integration. This study provides a robust, protocol-compliant dataset essential for the safe use of 3D-printed materials in electron beam relative dosimetry and clinical potential applications.