Technical Note: Using virtual noncontrast images from dual-energy CT to eliminate the need of precontrast CT for x-ray radiation treatment planning of abdominal tumors†.

Purpose Radiation therapy (RT) planning frequently utilizes contrast-enhanced CT. However, dose calculations should not be performed on a contrast-enhanced CT because the patient will not receive bolus during treatment. It is typical to acquire CT twice during RT simulation: once before injection of bolus and once after. The registration between these datasets introduces errors. In this work, we investigate the use of virtual non-contrast images (VNC) derived from dual-energy CT (DECT) to eliminate the pre-contrast CT and the registration error. Methods CT datasets, including conventional 120 kVp pre- and post-contrast CTs and post-contrast DECT, acquired for 10 pancreatic cancer patients were evaluated. The DECTs were acquired simultaneously using a dual source (DS) CT simulator. VNC and virtual mono-energetic images (VMI) were derived from DECTs. Gross tumor volumes (GTV), planning target volumes (PTV) and organs at risks (OAR) were delineated on the post-contrast CT and then populated to the pre-contrast CT and the VNC. An IMRT plan (50.4 Gy in 28 fractions) was then optimized on the pre-contrast CT. Dose distributions were recalculated on the VNC images. Contours from the pre- and post-contrast CTs and the dose distributions based on both were compared. Results On average, the distance of centroids of the populated duodenum contours on pre-contrast CT differed by 6.0±4.0 mm from those on post-contrast CTs. The dose distributions on the pre-contrast CT and VNC were almost identical. The PTV mean and maximum doses differed by 0.1% and 0.2% between the two plans, respectively. Conclusion The VNC derived from DECT can be used to replace the conventional pre-contrast CT scan for RT planning, eliminating the need for an additional pre-contrast CT scan and eliminating the registration errors. Thus, VNC can become an important asset to the future of RT.