Structural and physicochemical stability of 3D-printed bolus materials used in radiotherapy

In radiotherapy, boluses ensure dose buildup at the skin and adapt to complex anatomy, requiring stable, well-conforming materials. This study aimed to investigate the effect of ionising radiation (70 Gy, 6 MV) on changes in the physicochemical properties of two materials used for 3D printing bolus materials for radiotherapy: acrylonitrile butadiene styrene ABS and thermoplastic copolyester TPC. Surface roughness, tribological parameters, hardness, dimensional stability, Fourier transform infrared spectra FTIR, and differential scanning calorimetry DSC data were assessed. After irradiation, small statistically significant changes in roughness parameters were observed for both materials, with ABS exhibiting greater surface degradation. In tribological tests, ABS demonstrated a 70% reduction in coefficient of friction, while TPC remained stable. FTIR spectra revealed changes characteristic of ABS degradation and oxidation (decreases in the intensity of butadiene bands, CH₂ shifts, and increases in carbonyl bands). Subtle chemical stability and potential cross-linking were observed in TPC. DSC suggests no changes in TPC and a decrease in the glass transition temperature of ABS, suggesting slight structural degradation. A slight increase in hardness was observed in ABS and TPC after irradiation, with only minimal dimensional changes in ABS. Based on the data obtained, X-ray radiation affected the tested materials differently. Although both retain their function after exposure to therapeutic doses, TPC exhibits greater chemical and mechanical resistance. Combined with its greater flexibility, this may result in improved clinical adhesion and reproducibility during radiotherapy. Further studies will include analysis of adhesion and dose distribution (Part 2).