Radiation-induced physicochemical changes in 3D-printed bolus materials for radiotherapy: Part 1 – surface degradation and structural stability

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 decrease in the coefficient of friction by up to 70%, while TPC remained stable. FTIR spectra revealed changes characteristic of ABS degradation and oxidation processes (reduction in the intensity of butadiene bands, CH₂ shifts, and an increase in carbonyl bands). Subtle chemical stability and potential signs of cross-linking were observed for TPC. DSC confirmed no changes in TPC and a decrease in the glass transition temperature of ABS, which may suggest slight structural degradation. A slight increase in hardness was observed for ABS and TPC after irradiation, and minimal dimensional changes were observed only for 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).