1155 - Patient 2D Imaging and Enhancement with a Novel Dual-Layer Kv Imager

Purpose/Objective(s):

The on-board kV imager of therapeutic linear accelerators is essential in modern radiotherapy, which requires highly precise patient positioning before and during treatment. Planar imaging is often used for initial alignment and during treatment to monitor the patient’s position. however, these images can often be challenging to interpret correctly due to overlapping anatomy, increasing the uncertainty on target alignment requiring larger margins. We have developed a novel dual-layer kV imager, which inherently provides spectral imaging, allowing for image enhancement techniques to be used. Here we evaluate the improvements in visualization of key anatomy on planar imaging for setup verification, using patient images collected with the DLI installed on one of our clinically operational LINACs.

Materials/

Methods:

The DLI is constructed using with two detector layers, the top layer is equivalent to the current commercial imager and the bottom is a slightly modified version of the top. The data from each layer is read out simultaneously and saved for post-imaging analysis. The top layer image alone is used for clinical imaging, leaving the original patient workflow unchanged. Patient images were collected from a variety of treatment sites, including prostate, lung and head and neck. Combining the layers of the planar images collected using a weighted-log subtraction technique for material decomposition, we evaluate the reduction in bone visibility for the lung patients and improvement in fiducial visibility for the prostate patients.

Results:

Visually comparing the single layer image and bone subtracted image (using weighted-log subtraction) acquired of a lung patient, the appearance of the ribs is greatly reduced, with the structures of the lung becoming more defined without obstruction of the bone. Quantifying this by comparing the contrast of the bone against surrounding tissue, the appearance of rib was reduced by 20%. Comparing the appearance of fiducials on the images acquired for the prostate patient, particularly for lateral projections, their visibility was also improved on the weighed-log subtraction images, where we note an increased visibility of 19%.

Conclusion:

This preliminary evaluation of the first clinically operational dual-layer kV imager demonstrates the feasibility of using spectral imaging to improve the visibility of anatomy of interest. The opportunity to use image enhancement techniques could pave the way for reliable, accurate setup using planar imaging, reducing the reliance on CBCT and minimising patient imaging dose.