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

Both TPU-based boluses with 60% infill/10 mm thickness achieved surface doses of ≥95% for both FF and FFF beams, closely matching the surface dose achieved by the 10-mm-thick gel bolus. Radiological thickness showed a strong correlation with the surface dose (R2 = 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.