Dose perturbation by metallic biliary stent in external beam radiotherapy of pancreato-biliary cancers

This study aims to investigate dose perturbations caused by a metallic biliary stent (MBS) in patients undergoing external beam radiotherapy for cancers in the pancreato-biliary region. Four MBSs with nitinol mesh were examined in the EasyCube® phantom including a custom stent holder fabricated by a 3D printer. For experimental models, three-dimensional conformal radiotherapy plans using a single anterior –posterior (AP) and four-field box (4FB) as well as volumetric modulated arc therapy (VMAT) plan were prepared to deliver the photon beam of 8 Gy to the stent holder. EBT3 film was used to measure dose distributions at four sides surrounding MBS. All MBSs in the AP beam demonstrated mean dose enh ancements of 2.3–8.2% at the proximal, left, and right sides. Maximum dose enhancements of 12.3–19.5% appeared at regions surrounding the radiopaque markers. At the location distal to the source, there were mean dose reductions of − 3.6 to − 10.9% and minimum doses of − 11.1 to −  9.5%. The mean and maximum doses with the 4FB plan were in the ranges of − 0.1 to 3.6% and 6.7–14.9%, respectively. The VMAT produced mean doses of − 0.9 to 4.8% and maximum doses of 6.0–15.3%. Dose perturbations were observed with maximum and minimum spots near the stent surface. The use of multiple beams including parallel-opposed pairs reduced dose perturbations caused by the nitinol and radiopaque components within the stent. Special attention is required for p...
Source: Australasian Physical and Engineering Sciences in Medicine - Category: Biomedical Engineering Source Type: research