For the three stent models, the 3D dose rates along the axial axis as estimated by MCNPX simulations are shown in [Figure 3].
When using the TPS for calculation of dose, the stent and the medium around it are simulated as water, ignoring the structure inhomogeneities with only limited dose uncertainties.[sup] The TPS in this study calculated the dose using point source simulations, which in fact agreed to be within about 2% with the full geometric simulations at all distances between 1 cm and 10 cm;[sup] thus, within this practical range, TPS agrees very well with the TLD measurements and MCNPX. Therefore, the TPS utilized by us can be reliably used for clinical applications involving biliary stents.
To obtain the most accurate data, a full seed simulation was performed by MCNPX, though a point source simulation is a fast and efficient way to check a full seed simulation.[sup] In DE and DF input cards, we entered a point-wise response function (the American National Standards Institute standard flux-to-dose conversion factors) to modify the regular tally card.
 "The MCNPX Monte Carlo radiation transport code," ESS Technical Design Report ESS-doc-274, 2013.
Durkee et al., "The MCNPX Monte Carlo radiation transport code," in Proceedings of the Hadronic Shower Simulation Workshop, vol.
MCNPX's standard physics models were employed with their default settings and included photoelectric absorption, coherent and incoherent scattering, pair production, fluorescence, and bremsstrahlung generation (from electrons liberated by photon interactions).
MCNPX results are shown for two different decay data libraries from which the emission probabilities for all x-rays and gamma-rays with energies greater than 1 keV were extracted.
For comparison purposes these values are listed together with the corresponding calculated values using the point source approximation (with a cut-off energy of 40 keV) and MCNPX method (using the LNHB decay library).
Dose percentage calculation methodologies were carried out through multiple interpolations, first taking the absorbed dose percentage values in the voxels of PDD located over the beam axis and below the phantom surface; in addition, the profile percentage values were the maximum dose registered under the simulation with MCNPX, as indicated in
It was necessary to calculate the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] values from the lineal interpolation between pixels and the initial PDD voxel's values and the values [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] correspond to the pixels in the voxels of the absorbed dose profile, both previously obtained from the simulation with the MCNPX code shown in (2) and illustrated in Figure 4:
The labyrinth was modelled with the Monte Carlo code MCNPX v.
MCNPX was run in photon and electron mode (mode PE) to pick up bremsstrahlung photons.