  In the context of critical applications, such as shielding and radiation
protection, ensuring the quality of simulation software they depend on is of
utmost importance. The assessment of simulation software quality is important
not only to determine its adoption in experimental applications, but also to
guarantee reproducibility of outcome over time.
  In this study, we present initial results from an ongoing analysis of Geant4
code based on established software metrics. The analysis evaluates the current
status of the code to quantify its characteristics with respect to documented
quality standards; further assessments concern evolutions over a series of
release distributions. We describe the selected metrics that quantify software
attributes ranging from code complexity to maintainability, and highlight what
metrics are most effective at evaluating radiation transport software quality.
The quantitative assessment of the software is initially focused on a set of
Geant4 packages, which play a key role in a wide range of experimental
applications and are representative of different software development
processes. We provide an interpretation of the data resulting from measurements
on the selected Geant4 packages, and discuss methods to improve them.
  This work can be used as a baseline for evaluating correlations between
software quality embedded in the Geant4 development process and simulation
observables produced by Geant4-based applications. The result provide
constructive guidance both to improve key software tools, such as Geant4, and
to estimate their contribution in risk analyses concerning sensitive
applications.
