Complex interventional and diagnostic x-ray angiographic (XA) procedures may yield patient skin doses exceeding the
threshold for radiation induced skin injuries. Skin dose is conventionally determined by converting the incident air kerma
free-in-air into entrance surface air kerma, a process that requires the use of backscatter factors. Subsequently, the
entrance surface air kerma is converted into skin kerma using mass energy-absorption coefficient ratios tissue-to-air,
which for the photon energies used in XA is identical to the skin dose. The purpose of this work was to investigate how
the cranial bone affects backscatter factors for the dosimetry of interventional neuroradiology procedures.
The PENELOPE Monte Carlo system was used to calculate backscatter factors at the entrance surface of a spherical and
a cubic water phantom that includes a cranial bone layer. The simulations were performed for different clinical x-ray
spectra, field sizes, and thicknesses of the bone layer.
The results show a reduction of up to 15% when a cranial bone layer is included in the simulations, compared with
conventional backscatter factors calculated for a homogeneous water phantom. The reduction increases for thicker bone
layers, softer incident beam qualities, and larger field sizes, indicating that, due to the increased photoelectric crosssection
of cranial bone compared to water, the bone layer acts primarily as an absorber of low-energy photons.
For neurointerventional radiology procedures, backscatter factors calculated at the entrance surface of a water phantom
containing a cranial bone layer increase the accuracy of the skin dose determination.