Using correlation and factor analysis to estimate the relationship between effective dose to a patient and specific CT settings

To optimize patient protection in computed tomography and to ensure that patient doses are as low as reasonably achievable for the specific CT examination the protocols tailored to patient age or size, anatomical area of imaging should be applied. Because dose estimates from different imaging modalities vary substantially, standardization of dose and reduction in variation in dose without affecting the clinical purpose, development of examination-specific CT protocols for different patient groups is required. The presented study is dictated by the need to develop national examination and patient specific diagnostic reference levels (DRL) for computed tomography (CT). The purpose of the study is to examine the feasibility of using correlation and factor analysis to estimate relationship between effective dose to a patient and CT settings. To solve the task 12 CT protocols in 199 single-phase scans included head, thoracic, abdominal and pelvic organs, as well as scans included several body parts were examined. The following was found: strong correlation (0.77-1.0) between effective radiation dose and absorbed radiation dose (Dose Length Product - DLP, and CT Dose Index - CTDI); moderate correlation (0.48-0.64) between effective dose and body mass, and CT characteristics (slice thickness and collimation); in case of simultaneous scanning of several body parts moderate correlation - 0.59 - was found between effective radiation dose and scanned areas (dose coefficient EDLP). Obtained results allow authors to conclude that for calculating diagnostic reference levels for specific healthcare facility development of a CT-specific and anatomical area-specific databases is required.