Impact of photon cross section systematic uncertainties on Monte Carlo-determined depth-dose distributions

TL;DR

This study quantifies how systematic uncertainties in photon interaction cross sections affect Monte Carlo-calculated depth-dose distributions, revealing depth-dependent sensitivity factors that can estimate dose uncertainty.

Contribution

It introduces a method to quantify photon cross section uncertainties' impact on depth-dose curves using sensitivity factors derived from Monte Carlo simulations.

Findings

Sensitivity factors depend on depth and change sign at equilibrium depth.

Equilibrium depths align with the mean free path of incident photons.

Photon cross section uncertainties significantly influence dose distribution accuracy.

Abstract

This work studies the impact of systematic uncertainties associated to interaction cross sections on depth dose curves determined by Monte Carlo simulations. The corresponding sensitivity factors are quantified by changing cross sections in a given amount and determining the variation in the dose. The influence of total cross sections for all particles, photons and only for Compton scattering is addressed. The PENELOPE code was used in all simulations. It was found that photon cross section sensitivity factors depend on depth. In addition, they are positive and negative for depths below and above an equilibrium depth, respectively. At this depth, sensitivity factors are null. The equilibrium depths found in this work agree very well with the mean free path of the corresponding incident photon energy. Using the sensitivity factors reported here, it is possible to estimate the impact of photon cross section uncertainties on the uncertainty of Monte Carlo-determined depth dose curves.