Experimental and numerical studies on kV scattered x-ray imaging for real-time image guidance in radiation therapy

Abstract

Motion management is a critical component of image guided radiotherapy for lung cancer. We previously proposed a scheme using kV scattered x-ray photons for marker-less real-time image guidance in lung cancer radiotherapy. This study reports our recent progress using the photon counting detection technique to demonstrate potential feasibility of this method and using Monte Carlo (MC) simulations and ray-tracing calculations to characterize the performance. In our scheme, a thin slice of x-ray beam was directed to the target and we measured the outgoing scattered photons using a photon counting detector with a parallel-hole collimator to establish the correspondence between detector pixels and scatter positions. Image corrections of geometry, beam attenuation and scattering angle were performed to convert the raw image to the actual image of Compton attenuation coefficient. We set up a MC simulation system using an in-house developed GPU-based MC package modeling the image formation process. We also performed ray-tracing calculations to investigate the impacts of imaging system geometry on resulting image resolution. The experiment demonstrated feasibility of using a photon counting detector to measure scattered x-ray photons and generate the proposed scattered x-ray image. After correction, x-ray scattering image intensity and Compton scattering attenuation coefficient were linearly related, with R 2 greater than 0.9. Contrast to noise ratios of different objects were improved and the values in experimental results and MC simulation results agreed with each other. Ray-tracing calculations revealed the dependence of image resolution on imaging geometry. The image resolution increases with reduced source to object distance and increased collimator height. The study demonstrated potential feasibility of using scattered x-ray imaging as a real-time image guidance method in radiation therapy.

Feasibility assessment of real-time surface-guided intrafraction radiotherapy for prostate cancer without immobilization

“…Real-time image-guided technology can be roughly categorized into radiation-based and non-radiation-based approaches. Radiation-based technology, mainly X-ray imaging, enables direct collection of image data and accurate target area localization during radiotherapy [8,9]. In particular, real-time monitoring of prostate cancer images based on X-ray gold ducials tracking provides guidance for target delineation and position movement during treatment [10][11][12].However, this approach often consumes time and subjects patients to additional radiation, so it is primarily used for set-up position veri cation before radiotherapy.…”

Feasibility assessment of real-time surface-guided intrafraction radiotherapy for prostate cancer without body immobilization

“…KV-CBCT is mainly used to collect real-time motion image data of prostate cancer targets based on bone-marker or gold ducials implant tracking. These data are collected during radiotherapy to guide positional movement during treatment [Huang et al, 2021;Knybel et al, 2021]. However, the procedure of gold ducial implantation is often invasive and time-consuming, and real-time CBCT will result in additional radiation exposure to the patient Hence, they are primarily used for setup veri cation before radiotherapy.…”