167 - Impact of a Clinical Prototype Linac Dual-Layer Kv Detector on Contrast and Metal Artifact Reduction in Patient Conebeam CTs

05:05pm - 05:15pm PT

Room 155/157

Presenter(s)

Thomas Harris, PhD, DABR - Dana-Farber/Brigham and Women's Cancer Center, Boston, MA

T. C. Harris¹, M. Jacobson¹, R. Fueglistaller², R. Bruegger², D. Ferguson¹, Y. H. Hu¹, V. Birrer², M. Lehmann², P. Corral Arroyo², M. Myronakis¹, R. Etemadpour¹, F. De Kermenguy¹, and R. I. Berbeco¹; ¹Department of Radiation Oncology, Brigham and Women’s Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA, ²Varian Medical Systems, Baden-Dattwil, Switzerland

Purpose/Objective(s): Dual-energy imaging can enhance image quality with additional functionality, such as metal artifact reduction and improved soft tissue contrast, both of which are crucial for precise radiation treatment planning. While dual-energy imaging is commercially available in CT scanners, its integration with a clinical linac has not been extensively explored. This study investigates the use of a novel dual-layer kV detector installed directly on a clinical linac to capture patient data and assess its impact on cone-beam CT (CBCT) imaging.

Materials/Methods:

A prototype dual-layer kV detector was installed on a clinical linac, and patient data was collected under IRB supervision. The top layer was identical to the stock detector, allowing direct comparison with standard image quality. CBCT projections were obtained from 7 head and neck and 3 pelvic cancer patients, with energies ranging from 100 to 140 keV. The projections were decomposed into two primary materials—adipose and titanium—using an iterative least squares solution to the poly-energetic Beer’s Law equations, regularized by Huber roughness penalties. These decomposed projections were then reconstructed into virtual monoenergetic images (VMIs), with 120 keV reconstructions used to assess metal artifact reduction (MAR) and 40 keV reconstructions used to improve soft tissue contrast.

MAR was assessed by comparing uniformity in matched regions of interest (ROIs) in the 120 keV VMI and the standard CBCT. Clearly artifact-affected and clear regions were segmented. Soft tissue contrast was calculated comparing the 40 keV and standard CBCT. Matched muscle-adipose and prostate-adipose (for the pelvis patients) ROIs were contoured.

Results: In metal artifact regions, uniformity improved by an average of 48.7%, while clear regions saw a 13.3% increase in uniformity. For head and neck imaging, soft tissue contrast between adipose and muscle improved by an average of 1.7x, with a <10% significant reduction in contrast-to-noise ratio (CNR). In pelvic imaging, prostate-adipose contrast improved by 2.4x, although this came with a 36.3% reduction in CNR, indicating a trade-off between contrast enhancement and noise.

Conclusion: This study demonstrates the successful integration of dual-energy imaging with a clinical linac using a novel dual-layer kV detector, and for possibly the first time capturing real patient data. The results show substantial improvements in metal artifact reduction and soft tissue contrast. These enhancements could provide valuable improvements to radiation treatment adaptive planning by increasing accuracy of contouring and dose delivery. Future work will explore optimizing VMI energy for different anatomy and objectives, and minimizing noise at lower energy VMIs. Furthermore, additional dual-energy capabilities will be investigated to further refine onboard clinical imaging for oncology applications.