Dual-energy CT for particle therapy – benefits and limitations

Due to the physical advantages of particles in energy deposition compared to photons, a high-conformal tumor coverage can be reached while sparing healthy tissue more effectively. However, particle treatment planning is currently associated with large uncertainties related to a CT-based stopping-power and eventually particle range prediction. To fully exploit the physical benefit of particles, this substantial part of the overall range uncertainty of approximately 3.5% of total range should be reduced.
Dual-energy CT (DECT) imaging is a promising technique to increase the accuracy of CT-based range predictions as already shown by many research groups. The effective benefit of DECT for particle treatment planning of cancer patients is currently proven using a comprehensive validation scheme to quantify the potential reduction of range uncertainties in daily clinical practise. In the framework of a joint project between DKFZ and OncoRay, extensive investigations on different levels (inhomogenous phantoms, biological tissue, clinical patient scans) have been performed. Here, a considerably improved accuracy of DECT compared to the current state-of-the-art, single-energy CT (SECT), could be shown in an anthropomorphic ground-truth phantom and biological tissues. Moreover, relative comparisons of predicted particle ranges in more than 100 proton treatment fields of patients reveal median range deviations of 1.5 – 2.0 % of total range between DECT and SECT. Based on these results, the clinical use of DECT-based range prediction would clearly improve the accuracy and robustness of particle treatment planning and is thus highly recommended to be the new standard imaging modality for treatment planning in particle therapy.