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An In-Line Helical CT-Couch System for IGRT and Adaptive Radiation Therapy

J Wong*, N Chernavsky , J Siewerdsen , Johns Hopkins University, Baltimore, MD


(Sunday, 7/14/2019) 4:00 PM - 5:00 PM

Room: 221AB

Purpose: We propose a novel in-room, in-line “CT-Couch� solution based on a multi-detector CT (MDCT) scanner that does not interfere with the linac gantry. We aim to provide high quality CT images in support of efficient IGRT workflow and real-time Adaptive Radiation Therapy (ART).

Methods: We conceived and designed the concept of an in-line CT-Couch with the recently available slim-body (40 cm wide), big-bore (107 cm) MDCT system (TruCT, Mobius Imaging, MA). The current prototype incorporates a 32-row MDCT detector capable of scanning 20 cm length in 8 sec, producing image quality similar to a CT-simulator. Feasibility studies using static, free-of motion, phantoms were made by comparing the imaging performance of the TruCT with a linac-mounted flat panel (FP) CBCT. The potential for reducing uncertainty in soft tissue target localization using the TruCT was simulated by comparing the inter-user variability of 4 users delineating a low contrast, nodal volume (GTV) target on the initial planning CT and on-treatment CBCT images for 6 head and neck patients.

Results: Using comparable imaging dose and reconstruction voxel dimensions, TruCT provided quantitatively superior uniformity and contrast-to-noise performance, and qualitatively improved visualization of an anthropomorphic abdomen phantom. The inter-user variability in delineation of nodal volume, in terms of coefficient of variation, using planning CT was 3x less than using on-treatment CBCT.

Conclusion: The CT-Couch overcomes many shortfalls of FP-CBCT including detector performance, x-ray scatter, and motion artifacts due to long scan time. It replaces the conventional treatment couch and preserves much of the functionality of the linac, with minimal requirements for room and shielding modifications. The system avoids workflow bottleneck of CT-on-rails. The CT numbers from TruCT are directly amendable for real-time dose calculation for a new paradigm of dose-based setup adjustment. The CT-Couch holds potential to transform the broad practice of real-time ART.


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