Virtual unenhanced dual-energy computed tomography for photon radiotherapy: The effect on dose distribution and cone-beam computed tomography based position verification

Maryam Afifah; Marloes C Bulthuis; Karin N Goudschaal; Jolanda M Verbeek-Spijkerman; Tezontl S Rosario; Duncan den Boer; Karel A Hinnen; Arjan Bel; Zdenko van Kesteren

doi:10.1016/j.phro.2024.100545

Virtual unenhanced dual-energy computed tomography for photon radiotherapy: The effect on dose distribution and cone-beam computed tomography based position verification

Phys Imaging Radiat Oncol. 2024 Feb 2:29:100545. doi: 10.1016/j.phro.2024.100545. eCollection 2024 Jan.

Authors

Maryam Afifah¹, Marloes C Bulthuis², Karin N Goudschaal², Jolanda M Verbeek-Spijkerman², Tezontl S Rosario¹, Duncan den Boer¹, Karel A Hinnen², Arjan Bel², Zdenko van Kesteren²

Affiliations

¹ Amsterdam UMC, Location Vrije Universiteit, Department of Radiation Oncology, De Boelelaan 1118, Amsterdam, the Netherlands.
² Amsterdam UMC, Location University of Amsterdam, Department of Radiation Oncology, Meibergdreef 9, Amsterdam, the Netherlands.

Abstract

Background and purpose: Virtual Unenhanced images (VUE) from contrast-enhanced dual-energy computed tomography (DECT) eliminate manual suppression of contrast-enhanced structures (CES) or pre-contrast scans. CT intensity decreases in high-density structures outside the CES following VUE algorithm application. This study assesses VUE's impact on the radiotherapy workflow of gynecological tumors, comparing dose distribution and cone-beam CT-based (CBCT) position verification to contrast-enhanced CT (CECT) images.

Materials and methods: A total of 14 gynecological patients with contrast-enhanced CT simulation were included. Two CT images were reconstructed: CECT and VUE. Volumetric Modulated Arc Therapy (VMAT) plans generated on CECT were recalculated on VUE using both the CECT lookup table (LUT) and a dedicated VUE LUT. Gamma analysis assessed 3D dose distributions. CECT and VUE images were retrospectively registered to daily CBCT using Chamfer matching algorithm..

Results: Planning target volume (PTV) dose agreement with CECT was within 0.35% for D_2%, D_mean, and D_98%. Organs at risk (OARs) D_2% agreed within 0.36%. A dedicated VUE LUT lead to smaller dose differences, achieving a 100% gamma pass rate for all subjects. VUE imaging showed similar translations and rotations to CECT, with significant but minor translation differences (<0.02 cm). VUE-based registration outperformed CECT. In 24% of CBCT-CECT registrations, inadequate registration was observed due to contrast-related issues, while corresponding VUE images achieved clinically acceptable registrations.

Conclusions: VUE imaging in the radiotherapy workflow is feasible, showing comparable dose distributions and improved CBCT registration results compared to CECT. VUE enables automated bone registration, limiting inter-observer variation in the Image-Guided Radiation Therapy (IGRT) process.

Keywords: Contrast-enhanced CT; Dual-energy CT; Gynecological irradiation; Photon therapy; Virtual non-contrast; Virtual unenhanced.