Implementation of quality concepts in radiotherapy: documentary basis and practical impacts on safety culture

Abstract

A new X-ray imaging technique, diffraction-enhanced imaging (DEI), has been developed at synchrotron radiation sources that can independently visualize the refraction and absorption of an object. The images are essentially scatter-free, allowing enhanced contrast of objects that develop small-angle scattering. The combination of these properties has resulted in images of mammography phantoms and human breast tissues that have dramatically improved contrast compared with standard imaging techniques. It is potentially applicable to mammography and other ®elds of medical X-ray imaging.X-ray diffraction from perfect crystals, with narrow re¯ection angular widths (a few microradians) and peak re¯ectivity of close to unity, provides the tools necessary to prepare and analyse X-ray beams traversing an object on the microradian scale. In DEI, an almost monochromatic imaging beam is produced by a crystal monochromator. This beam is then passed through the object being imaged as in conventional radiography. However, a matched crystal analyser is placed between the object and the detector. As the condition for diffraction from this crystal limits the X-rays which can be diffracted into the detector, it provides a high degree of scatter rejection and thus enhanced image contrast. The scatter rejected falls into the category of small-angle scattering which arises from diffraction of organized structures on the scale of microns. The scatter rejection contrast is called extinction contrast. The DEI image, which represents absorption of the object by X-rays, is referred to as the apparent absorption image as it has contrast derived both from absorption and extinction.The analyser rocking curve will introduce a sensitivity to refraction occurring within the object when the analyser crystal is de-tuned from the peak position. Density, thickness and/or material variations in the object will refract the X-rays. These small angular variations are generally in the sub-microradian range. The steep slopes of the re¯ectivity curve will convert the angle variations into intensity variations, giving rise to a refraction image. By acquiring images on each side of the rocking curve, DEI separates the refraction effects from the apparent absorption.The results of imaging of mammography phantoms and human breast tissue with tumour, as well as biological objects such as a mouse, will be presented for a range of X-ray beam energies. The images were obtained at Radiation and Nuclear Safety Authority (STUK), HelsinkiRadiation therapy is a multidisciplinary speciality involving complex equipment and procedures. This implies that both the parameters related to the patient and the procedures related to the technical aspects of therapy should be subjected to careful quality assurance (QA). Although it has long been recognized that QA is vital to ensure safe and effective treatment, it has increasingly been recognized that a more systematic approach to QA, in the form of quality systems, is needed.The vocabulary of quality terms and concepts is publish...