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In recent years, the benefits of dual-energy computed tomography (DECT) for radiotherapy treatment planning were intensively investigated. In short, DECT imaging comprises the acquisition of two image sets of the same volume within the patient, each acquired with a different CT spectrum. These two image sets can be decomposed to achieve estimations of different radiological quantities. Physical and mathematical models can be applied to the acquired images or sinograms, resulting in maps of estimated electron/mass density, effective atomic number, relative stopping power (RSP), or elemental compositions. These maps have found the largest application in treatment planning and dose calculation of photon and particle therapy.

Multiple research studies demonstrate that DECT-based estimates of electron/mass densities and RSP are superior to single-energy CT (SECT) estimates of the same quantity. For example, experimental studies investigating the accuracy of predicted RSP values for proton therapy in porcine and bovine tissues consistently report RSP predictions better than 1% accuracy using DECT as compared to over 2% using SECT. To take this a step further, it was demonstrated by multiple research groups independently that this improved RSP prediction leads to decreased beam range uncertainty.

The advantages of a better RSP prediction and therefore decreased proton range uncertainty have direct consequences to the patient. Comparisons of proton treatment plans calculated on SECT vs DECT show clinically relevant range and dose differences in head/neck and pelvic patients, adults as well as children. Consequently, the reduction of the treatment margins from the conventional 3.5% range uncertainty to 2% is considered by proton centres using DECT for treatment planning.

Despite the clinical availability of dual-energy CT and the vast literature showing the advantages of DECT over SECT in radiotherapy planning, the full clinical translation still faces its challenges. Those challenges include the technical implementation of DECT algorithms into the clinical workflow, the lack of recommendations concerning the safe application of DECT-derived quantities, and the standardisation of DECT calibration and validation across clinics.

In this short summary, we will explore the most recent clinical findings in DECT for radiotherapy, with a focus on applications to protons. We will discuss the challenges involved in clinical translation and future directions.