Quantum high energy density physics

Abstract:

The advent of x-ray free-electron lasers has enabled a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interactions. The femtosecond timescales of these interactions lead to the creation of transient high-energy-density plasmas, where both the electrons and the ions may be far from local thermodynamic equilibrium. Predictive modelling of such systems remains challenging because of the different timescales at which electrons and ions thermalize, and because of the vast number of atomic configurations required to describe highly-ionized plasmas. Here we present CCFLY, a code designed to model the time-dependent evolution of both electron distributions and ion states interacting with intense x-ray fields on ultra-short timescales, far from local thermodynamic equilibrium. We explore how the plasma relaxes to local thermodynamic equilibrium on femtosecond timescales in terms of the charge state distribution, electron density, and temperature.

Abstract:

Data generated for the figures in 'Development of a new quantum trajectory molecular dynamics framework' at https://dx.doi.org/10.1098/rsta.2022.0325 (and at https://doi.org/10.48550/arXiv.2211.08560) and statically compiled version of the code.

Abstract:

Background and purpose

The lack of equitable access to radiotherapy (RA) linear accelerators (LINACs) is a substantial barrier to cancer care in low- and middle-income countries (LMICs). These nations are expected to bear up to 75% of cancer-related deaths globally by 2030. State-of-the-art LINACs in LMICs experience major issues in terms of robustness, with mechanical and electrical breakdowns resulting in downtimes ranging from days to months. While existing research has identified the higher failure frequency and downtimes between LMICs (Nigeria, Botswana) compared to high-income countries (HICs, the UK), there has been a need for additional data and study particularly relating to multileaf collimators (MLCs).

Materials and methods

This study presents for the first time the analysis of data gathered through a dedicated survey and workshop including participants from 14 Indonesian hospitals, representing a total of 19 LINACs. We show the pathways to failure of radiotherapy LINACs and frequency of breakdowns with a focus on the MLC subsystem.

Results

This dataset shows that LINACs throughout Indonesia are out of operation for seven times longer than HICs, and the mean time between failures of a LINAC in Indonesia is 341.58 h or about 14 days. Furthermore, of the LINACs with an MLC fitted, 59 . 02 - 1.61 + 1.98 $59.02_{ - 1.61}^{ + 1.98}$ % of all mechanical faults are due to the MLC, and 57 . 14 - 1.27 + 0.78 $57.14_{ - 1.27}^{ + 0.78}$ % of cases requiring a replacement component are related to the MLC.

Conclusion

These results highlight the pressing need to improve robustness of RT technology for use in LMICs, highlighting the MLC as a particularly problematic component. This work motivates a reassessment of the current generation of RT LINACs and demonstrates the need for dedicated efforts toward a future where cancer treatment technology is robust for use in all environments where it is needed.