Dual-Energy X-ray imaging for TargEting in Radiotherapy – DEXTER

The DEXTER project aims at investigating the opportunities for image guided radiotherapy (IGRT) offered by a new scanner, a Patient Alignment system with an integrated x-ray Imaging Ring (PAIR), developed by a spin-off company of the Paracelsus Medical University (PMU) Salzburg, Austria. A new collaboration will emerge from this project between the CREATIS (Lyon, France) and the radART (Salzburg, Austria) laboratories in order to gather the expertise in medical physics and medical image processing which is required to take advantage of the new scanner possibilities. A PAIR unit will soon be available for research purposes in Salzburg (spring 2013). The project focuses on innovative software solutions that exploit the clinical use of future units installed at photon and hadron radiation therapy centers. Three axes have been identified as potential breakthrough for image guided radiotherapy brought by the new capabilities of the scanner.

First, the x-ray source and the flat panel detector can rotate independently around the PAIR which potentially enables a larger field of view (FOV) than current cone-beam computed tomography (CBCT) scanners used in IGRT. Depending on the CBCT acquisition protocol, the flat panel is tilted with respect to the central x-ray. This necessitates the development of a new reconstruction algorithm to obtain large FOV CBCT images from oblique projection images.

The second axis takes advantage of the potential of the x-ray tube to cover a large range of fastly switchable energies from 40 kV to 120 kV along with remotely exchangable filters which enables multi-energy radiographs. Dual-energy could be essential in hadron if multi-energy CBCT images improve the estimation of the proton and carbon ion range in patients. Today, about 3% margin of the proton range is required around the target which increases the irradiation of healthy tissues and lower the potential of proton therapy. The investigations will use hybrid Monte Carlo / deterministic simulations based on the experience of CREATIS in x-ray and hadron therapy simulations with potential validation in the new
Austrian hadron therapy center, MedAustron, where four PAIR units will be installed. The clinical end result will be the reduction of uncertainty in ion range and its associated treatment margin.

The third and last axis is the potential of the PAIR scanner in the context of 2D/3D image registration which is especially required in intrafractional position verification and online treatment guidance because 3D image acquisition is too slow and would deposit too much dose in the patient if continuously involved. One problem that is often encountered in 2D/3D registration is the presence of high-contrast structures such as bone in front of the target which degrade the accuracy of the spatial alignment. Similarly to the second axis, we aim at adequately using multi-energy radiographies to virtually remove these structures and, thereby, improve 2D/3D registration robustness. A further goal is the reduction of the imaging dose implied by single or continuous x-ray acquisition by taking advantage of the remotely controllable collimation jaws of the PAIR system.

These three research axes investigate challenging problems for image guidance in photon and hadron therapy rooms using a novel, innovative hardware solution. The end results of the collaboration between radART and CREATIS will be a set of open source algorithms, data and publications which are expected to contribute significantly to diffusion of the worked out concepts and findings in the radiotherapy community. The two teams involved in this project are internationally recognized in the field of IGRT and they have the means to translate the findings of this project rapidly into clinical solutions, radART being one of the few centers in the world capable of clinically translating their developments via the open-radART radiotherapy software system.