Periodic Reporting for period 1 - protonCBCT (Proton CT reconstruction with a Cone Beam CT prior)
Reporting period: 2017-06-01 to 2019-05-31
This project addressed a novel imaging modality called proton radiography and computed tomography (CT). It is supposed to complement X-ray CT imaging in the context of proton therapy. The challenge is to provide accurate volumetric images of a patient which can be used to plan the treatment, i.e. to decide how program the proton accelerator to best achieved the prescribed dose. While proton CT is more adapted to this task than X-ray based imaging, proton CT images have a lower resolution, i.e. they are blurrier than X-ray CT images. The overall objectives of this project were to develop the mathematical and algorithmic methods to combine both modalities while emphasizing the respective advantages. Such improved volumetric imaging could lead to more accurate patient specific proton therapy treatment planning in the future.
In a first step, a statistical framework was developed to be able to describe and compare the performance of different types of proton imaging systems which exist as prototypes or which are currently being developed world-wide. The results lead to a better understanding of how a system should be designed depended on clinical constraints. Furthermore, a method was developed and implemented as computer program which combines conventional X-ray CT images with proton radiographic images which can be acquired with relatively simple systems. The program produces an optimized, patient-specific 3D map of so-called relative stopping power of the patient – a physical property needed be the treatment planning system as input. The algorithm was tested on simulated data. In an experimental campaign, proton radiographic images were acquired in a proton therapy center with detector hardware which would potentially be available to medical physicists in clinical practice. Additional theoretical studies include a work on the impact of tissue heterogeneities on the estimation of proton trajectories in a patient as well as newly developed method to efficiently model and generate proton trajectories under the impact of multiple Coulomb scattering. The results were disseminated in four peer-reviewed articles in scientific journals and presented at ten international conferences and workshops.
Progress beyond state of the art include a comprehensive comparison based on a new statistical framework of different proton imaging systems which was previously lacking from the literature. Furthermore, important progress was made in the field by developing new algorithms to combine X-ray and proton images as well as to accurate process and construct proton radiographic images acquired with readily available detector hardware. These results combined provide the necessary tools to integrate proton imaging in a clinical treatment workflow. It could potentially be exploited either by manufacturers of detector systems and/or treatment planning software. To better coordinate research on proton and ion imaging, especially in Europe, two international workshops were organized: the first one in 2018 in Lyon, France, and the second one in 2019 in Manchester, UK. It is planned to have this evolve into a regular event. Such efforts are coordinated through the website ionimaging.org which has been created as part of this research project.