Fabrication and evaluation of 3D-printed customizable boluses for optimized radiotherapy applications

Background: Commercial radiotherapy boluses often fail to conform accurately to patient anatomy, resulting in air gaps and surface dose inaccuracy. Threedimensional (3D) printing using fused deposition modeling with polylactic acid (PLA) offers a customizable alternative, but clinical implementation requires a reproducible fabrication workflow that ensures both radiological consistency and geometric conformity. Objectives: To evaluate the effect of infill density on radiological properties and assess the feasibility of a consistent fabrication approach for both standard and patient-specific boluses. Materials and methods: Standard PLA boluses (10×10×1 cm) were fabricated at 75-95% infill density using a line infill pattern, while customized boluses were created from a head-and-neck phantom and printed at 90-95% infill density. All boluses underwent CT imaging and were analyzed in the Eclipse treatment planning system (TPS) to determine Hounsfield unit (HU), mass density, and relative electron density (RED). Air gap measurements and dose distributions were evaluated in the TPS with a 6 MV photon beam. Results: As infill density increased from 75%-95%, HU values rose from -184.6 to +48.5, with 90–94% infill yielding HU values within the acceptable ±50 HU range. Standard and customized boluses demonstrated comparable radiological behavior, with mass density and RED near unity. Customized boluses reduced air gaps (0.21±0.02 cm vs 0.54±0.16 cm) and improved surface-dose build-up and isodose coverage in complex regions. Conclusion: Optimized infill density settings support a reproducible 3D printing workflow. Both standard and customized PLA boluses can achieve radiological accuracy and surface conformity suitable for clinical implementation.