Comparison of h-BN material with metal implants in radiotherapy applications: Characterization and dose distribution measurements in LINAC

Patients with metal implants having high atomic numbers (Zeff) can be encountered in radiotherapy applications. These heterogeneous structures cause dose perturbations at the bone-tissue interface. These perturbations are undesired due to the lack of accurate dose calculation and contouring process through a higher image quality. In this study, the effect of 6–18 MV photon irradiation on hexagonal boron nitride (h-BN) in comparison with titanium and stainless-steel implants was proposed as an implant material due to its biocompatibility and low Zeff. First, h-BN material was characterized and its mass attenuation coefficient was determined. Then, the percent depth doses (PDD) were obtained for the implant materials. Next, the dose distributions were evaluated with both TPS using CT images and TLDs. A dose perturbation was not observed at the interface for h-BN material different from the metal implants as seen from the PDD distributions. The change in PDD varied between 1 and 3% for h-BN with respect to RW3 slab phantom, which was 4–7 times lower than that of metal implants, depending on the material thickness. No metal artifact was seen at h-BN implants compared to metal implants. Homogenous dose distribution was also seen from the isodose lines on the CT images, while dose perturbations were more pronounced in metal implants. In addition, a more severe dose reduction at the metal implant/bone tissue interface was observed at 6 MV photon beam energy compared to 18 MV. In contrast, no dose change was observed for the h-BN material at each photon beam energy. Hence, an accurate dose calculation can be done for h-BN as a result of these advantages. The results showed that, due to its biocompatible property, h-BN material can be evaluated as an implant material in radiotherapy applications if its mechanical properties were further improved.