Physical and dosimetric characterization of 3D-printed bolus materials for radiotherapy: from rigid plastics to flexible TPU

PURPOSE: In this study, the dosimetric suitability of selected flexible 3D-printed materials was evaluated as alternatives to conventional tissue-equivalent gel boluses and rigid well-characterized PLA and ABS boluses. The physical, imaging, and dosimetric characteristics of the materials were analyzed. MATERIALS AND METHODS: Two flexible TPU(TPU 93A and TPU 40D) and two rigid (PLA and ABS) thermoplastics were used to fabricate 3D-printed boluses. Various infill densities and thicknesses were tested. Print accuracy, homogeneity of printed samples, HUvalues, printing time and costs were evaluated. PDD curves were measured for 6MV flattened (FF) and flattening-filter-free (FFF) photon beams and compared between materials and Eclipse treatment-planning-system calculations. All characteristics were also compared with the characteristics of gel boluses. Radiological thickness was correlated with the surface dose and depth of the maximum dose. RESULTS: = 0.860 for FF and 0.844 for FFF), independent of the material type. Differences between the calculated and measured depths of the maximum dose were less than 1 mm. Print repeatability was high, with >99.5% of dose points meeting the ≤1% difference criterion. CONCLUSIONS: Flexible 3D-printed boluses exhibit clinically acceptable dosimetric properties and may serve as alternatives to gel boluses. Radiological thickness is identified as a robust predictor of dose modification, offering a practical parameter for bolus design.