Room: Track 4
Purpose: Contrast-enhanced CT is frequently used in radiation therapy (RT) treatment planning; however, it it may not be used for dose calculation. Consequently, two CTs are acquired during RT simulation: before the injection of bolus and after. Registration between CTs is necessary but introduces error due to motion between acquisitions. We investigate the feasibility of using virtual non-contrast (VNC) images derived from dual-energy CT (DECT) to eliminate pre-contrast CTs.
Methods: Dual source DECT and conventional pre- and post-contrast CTs, acquired for 10 pancreatic cancer patients were analyzed. For each case, a VNC image was derived from the DECT and registered to the pre-contrast CT. The gross tumor volume (GTV) and organs at risk (OAR) were delineated on the contrast CT and then populated to the pre-contrast CT, which was used to generate an RT plan (50.4 Gy to the GTV in 28 fractions). The dose was reconstructed on the VNC image. Dose volume parameters of the original plan on the pre-contrast CT were compared to those from the reconstructed VNC plans.
Results: Differences in CT number between the pre-contrast CT and VNC image were observed: in the bone of the VNC, CT number dropped 65 HU on average. The dose distributions on the pre-contrast CT and VNC are almost identical. The average GTV mean and maximum dose differ by 0.1% and 0.2% respectively. For OAR, the maximum dose differences were 0.3% and 0.5% for the duodenum and cord; the liver mean dose differed by 0.1%; the kidney V15Gy differed by 1.0%.
Conclusion: VNC images derived from DECT can be used to replace conventional pre-contrast CT for RT planning, eliminating the need for pre-contrast CT scans in the current simulation process, improving clinical workflow and reducing imaging dose. The use of VNC also avoids registration errors between pre- and post-contrast CTs.
Funding Support, Disclosures, and Conflict of Interest: this work was supported by Siemens Healthineers