Measured and Monte Carlo simulated surface dose reduction for superficial X‐rays incident on tissue with underlying air or bone

Abstract

This work demonstrates the feasibility of using an Advanced Markus chamber with entrance window facing downstream to investigate surface dose reduction with underlying air or bone in tissue. As the field size decreases and beam quality increases surface dose with underlying bone tends to full backscatter values even though tissue thicknesses are below those normally associated with full backscatter. Conversely with underlying bone close to the surface dose will increasingly fall below full backscatter values as the beam energy is reduced and field size is increased.

Clinical treatment planning for kilovoltage radiotherapy using EGSnrc and Python

“…It was previously shown that surface dose is reduced by up to 12.5% with the presence of underlying bone or 10.5% with shielding material such as lead. 2 , 3 , 4 , 5 , 6 , 7 , 8 There are also significant absorbed dose differences between different tissue types due to the differences in mass energy absorption coefficients. 9 , 10 , 11 Second, the use of an inverse square law correction, or similar, for an average source‐to‐surface distance in the treatment field is a crude mechanism in dealing with highly irregular surfaces present in the head and neck region.…”

“…First, it does not account for the presence of tissue inhomogeneity under skin surface in the region of clinical interest. It was previously shown that surface dose is reduced by up to 12.5% with the presence of underlying bone or 10.5% with shielding material such as lead 2–8 . There are also significant absorbed dose differences between different tissue types due to the differences in mass energy absorption coefficients 9–11 .…”