What is needed to demonstrate the benefit of dual-energy CT for particle treatment planning?


What is needed to demonstrate the benefit of dual-energy CT for particle treatment planning?

Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.

Purpose/Objective:

To thoroughly understand and quantify the benefit of dual-energy CT (DECT) for the reduction of range uncertainty in particle treatment planning.

Material/methods:

In a multi-step procedure, DECT-based direct prediction of stopping-power ratios (SPRs) was improved in accuracy, robustness and clinical applicability by optimizing CT scan protocols, as well as post-reconstruction voxelwise SPR calculation algorithms. Subsequently, it was verified by three independent, yet complementary, studies in comparison to the current clinical standard (single-energy CT, SECT): (A) a relative comparison in patient cases; two absolute comparisons in (B) a controlled experimental setting measuring photon and ion absorption in animal tissues and tissue base components; and in (C) an inhomogeneous head phantom providing a well-established ground truth (Figure 1).

Results:

For a large collective of proton therapy patients (A), substantial intra- and inter-patient variability in CT-number-to-SPR-conversion as well as relative range differences of about 1.5-2.5% between SECT- and DECT-based treatment plans were observed. Both reveal the relevance of accurate CT-based SPR prediction and the potential for improvement. While naturally missing in patient studies, a reliable ground truth was provided in (B) and (C) to allow for absolute evaluations of SPR accuracy. The DECT method hereby proved capable to correctly predict SPR of homogenized animal tissues, tissue base components and the tissue substitutes in the anthropomorphic head phantom within measurement uncertainty.

Conclusion:

Only with the all-encompassing combination of theoretical considerations, lab experiments and the analysis of patient data, we are able to demonstrate clinically relevant reduction of range uncertainty with DECT-based treatment planning.

All authors contributed equally.

Keywords: dual-energy CT; proton therapy; particle therapy; range uncertainty

  • Lecture (Conference)
    56th Annual Conference of the Particle Therapy Co-operative Group (PTCOG), 08.-13.05.2017, Kanagawa, Japan

Permalink: https://www.hzdr.de/publications/Publ-24659
Publ.-Id: 24659