Clinical application of dual-energy CT for improved proton stopping-power prediction


Clinical application of dual-energy CT for improved proton stopping-power prediction

Peters, N.; Wohlfahrt, P.; Möhler, C.; Enghardt, W.; Krause, M.; Troost, E.; Greilich, S.; Richter, C.

Purpose/Objective
The sub-percentage accuracy in proton stopping-power prediction of patient-individualized range prediction (PIRP) using dual-energy CT (DECT) was demonstrated in recent studies. Although DECT-derived pseudo-monoenergetic CT scans have been introduced into clinical routine, a heuristic conversion (HLUT) from CT number to stopping power ratio (SPR) is still necessary, Fig.1(1). We propose a method to refine the clinical HLUT by applying PIRP on a broad patient cohort as a step towards its clinical implementation.

Materials/Methods
Voxelwise correlations of CT number and SPR were obtained using DECT scans of 102 brain-tumor and 25 prostate-cancer patients treated with protons. The clinical HLUT was then refined by performing a step-wise weighted linear fit of the SPR distribution in different tissue regions, Fig.1(2). Furthermore, the intra- and inter-patient variability was quantified. To assess dose differences and range shifts, proton treatment plans were recalculated using the clinical and refined HLUT as well as PIRP.

Results
Between clinical HLUT and PIRP, mean range differences (±1SD) of (1.2±0.7)% for brain-cancer and (1.7±0.5)% for prostate-tumor patients were determined. On average, the clinical HLUT predicted larger SPR for brain, muscle and trabecular bone, leading to the systematic range deviations. They were significantly reduced (p≪0.001, two-sample t-test) below 0.3% by using the refined HLUT. However, an observed intra-patient soft-tissue diversity of 6% as well as an inter-patient bone diversity of 5% cannot be considered by any generic HLUT-based range prediction.

Conclusion
Retrospective application of PIRP allows for a reduction of systematic deviations found in clinical HLUT. In principal, this can also be transferred to particle-therapy centers not using DECT routinely. The refined HLUT was implemented at our institution as a step towards the currently ongoing full integration of PIRP. This includes the calibration, an end-to-end test as well as the quantification of prospects in safety margin reduction.

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27303
Publ.-Id: 27303