Use of photon scattering interactions in diagnosis and treatment of disease

Abstract

This chapter looks at photon scattering applications in medicine. In the energy range of interest there are two types of scattering events, incoherent (Compton) and coherent (Rayleigh) scattering, and this chapter looks at how these events can be usefully used in the diagnosis and treatment of disease. In the first part we present an overview of Compton cameras for gamma imaging in the context of proton beam therapy, where they can be used for proton range verification. Proton beam therapy is currently in need of range verification for quality assurance and to improve treatment efficacy and safety. We will first briefly introduce potential methods for in vivo proton range verification, of which prompt gamma imaging is a promising example. We describe the process of gamma emission during proton irradiation, as well as the challenges of its detection and interpretation. The use of Compton camera for prompt gamma imaging has advantages over other gamma detectors since it does not require mechanical collimators and has a typical field of view of 180. The Compton camera's principle of operation and design criteria for prompt gamma imaging are described, as well as image reconstruction techniques such as back-projection and stochastic origin ensemble. The second part of the chapter presents tissue diffraction, based upon coherent scattering as a diagnostic tool. X-ray diffraction (XRD) is a technique which can be used to calculate the atomic or molecular structure of a material by measuring X-ray scattering profiles. While XRD has been a longstanding tool in analytical and materials science, this section reviews the relatively new application of XRD to the differentiation of healthy and cancerous tissue and how the results compare to conventional histopathology. As well as outlining the typical signatures expected of different tissue types, the hardware and data processing requirements will be discussed, particularly in the context of the trade-offs that would need to be considered in the design and development of a clinically deployable system.