ABSTRACT
While the broad accessibility to computed tomography (CT) systems (see Section III, Chapter 32) and high-quality imaging technologies helped physicians in making better diagnoses, it also raised the question about the amount of radiation dose (see Section III, Chapter 38) received by patients (Lee et al. 2004; Brenner and Hall 2007; Hall and Brenner 2008). Over the last few decades, we have witnessed an increase in the number of CT scans of 10% per year in the USA, leading to up to 62 million CT examinations in 2006 (Dawson et al. 2006). Although other medical examinations using X-rays contribute to the total dose received by the general public (see Section III, Chapter 66), relatively high effective doses involved during CT examinations account for half of all medical exposures (NCRP 2009). This figure calls for closer radiation dose monitoring during CT examinations. Nonetheless, the delivered dose to patients is not measured during examinations, but estimated by an industry standard established quantity called the computed tomography dose index volume (CTDIvol), embedded in commercially available CT scanners. This quantity is calculated using measurements performed with a 10 cm long ionization chamber (CT ion chamber) inserted into one of the two different sized cylindrical polymethyl methacrylate (PMMA) phantoms representing head and body. The product of the CTDIvol value and its scan length, known as the dose length product (DLP), is another dose parameter commonly considered (Huda and Mettler 2011), but neither CTDIvol nor DLP is based on direct dose measurements on patients.
