Practical applications of photon-counting CT in oncology: an organ-based pictorial review.

Spectral computed tomography (CT) has become an important extension of contrast-enhanced CT (CECT) in oncologic imaging by providing material-specific information beyond conventional morphologic assessment. Dual-energy CT (DECT), implemented on energy-integrating detector CT (EID-CT) platforms, has demonstrated the value of low-keV virtual monoenergetic imaging (VMI), iodine mapping, and material decomposition for improving tumor conspicuity, delineating local extent, and supporting tissue characterization. However, broader clinical adoption of EID-CT-based DECT has been limited by increased low-keV image noise and workflow complexity. Photon-counting detector CT (PCD-CT) addresses these limitations by offering improved energy resolution, reduced electronic noise, and routine acquisition of multi-energy data without dedicated dual-energy protocols. In particular, low-keV VMI around 40 keV can be generated with clinically acceptable noise, enabling consistent enhancement-based assessment in daily practice. Iodine-based reconstructions further complement morphologic evaluation by visualizing viable tumor enhancement and enabling quantitative analysis. This organ-based pictorial review summarizes practical applications of PCD-CT-based spectral imaging in oncology. Across organ systems, spectral CT may provide complementary problem-solving information by improving lesion detection, tumor extent delineation, and diagnostic confidence, particularly when conventional CT findings are equivocal, or MRI is unavailable, contraindicated, or limited. Emerging quantitative parameters, including electron density, effective atomic number, and advanced material decomposition, may further expand oncologic CT applications, although outcome-driven validation remains limited. Together, these features position PCD-CT as a practical spectral imaging platform for routine oncologic CT. KEY POINTS: Question How can PCD-CT address low-keV image noise and workflow barriers that have limited routine DECT-based spectral imaging in oncologic CT practice? Findings PCD-CT enables low-keV VMI and iodine-based reconstructions that may improve lesion conspicuity, tumor-extent assessment, and problem-solving across organ-specific oncologic workflows. Critical relevance statement This review clarifies practical, evidence-aware uses of PCD-CT spectral reconstructions in oncology, highlighting low-keV VMI as an adjunct, selective iodine-map problem-solving, and investigational quantitative parameters.