Evaluation of low-dose lung CT.

Abstract

Computed tomography (CT) is a radiographic examination used to assess different areas of the body, the chest being one of them. CT can be utilized as a screening tool for lung cancer by applying a low dose protocol. This screening program can include patients who are 40 years or older and with a long history of smoking. Several advantages are presented indicating the efficiency of low-dose CT (LDCT) such as - its high sensitivity and specificity, its reduction in patient dose as well as other factors such as decreased scanning time and the lack of necessity of contrast media, all of which increase patient acceptability. Such a screening examination is not available in Malta. This poses a problem since a national survey indicates that 54% of Maltese population smokes. To encourage its introduction the researcher's aims are to compare the image quality of the low-dose protocol and standard protocol and the patient dose of each to identify if LDCT is of a high enough standard to be used as a screening tool. There are a number of criteria which are required for a screening tool to be implemented. These include, amongst others, the importance of detecting lung lesions while they are still operable, that treatment is possible and that the test itself induces minimal morbidity. Images of high image quality are of vital importance to have proper evaluation. The three main factors contributing to this are spatial resolution, contrast resolution and noise. Specific methods exist as to objectively measure these parameters, using the appropriate test objects. Programs such as computed aided diagnosis and nodule enhanced viewing can be used to aid in the diagnosis of lung lesions. Excess exposure to radiation may have deterministic or stochastic effects, however, in the case of CT, it would be the latter. In this project, the method used to measure the radiation dose is the CT dose index a descriptor of which is CTDiw. In the methodology the research design is explained as being a quantitative, retrospective, non-experimental and comparative study. The target population for this project comprises radiologists working both privately and in the government hospital and patients who underwent a LDCT scan or standard CT of the thorax. To subjectively check the image quality 2 sets of images of a LDCT chest scan and another 2 sets of a standard chest CT scan were given to the participating radiologists, along with a check list of 12 anatomical structures. These radiologists were asked to grade the visibility of each structure in ascending order from 0 to 5. The validity and reliability tests and pilot study were done and any changes that resulted were reported. Other tests include the objective assessment of the parameters of the CT scanner and the reporting of the CTDIw. Ethical considerations and limitations were also listed as part of the methodology. The results, which were statistically reported in the form of tables, indicate that there is no significant difference between the protocols with regards to image quality however LDCT does indeed give a lower dose to the patient. In the final chapter, a list of recommendations of the area under study was given as well as the conclusion of the project as a whole.