Patient dose survey and determination of diagnostic reference levels for routine computed tomography examinations in Uttarakhand, India.

The increasing application of computed tomography (CT) has raised concerns regarding patient radiation exposure. The aim of this study was to estimate patient doses associated with three routine CT examinations-head, thorax, and abdomen-conducted across CT centres in Uttarakhand state of India. A total of 49 CT scanners were surveyed, with dosimetric and patient-specific parameters recorded for 15 adult patients per examination type at each site. Dose metrics, including the volume CT dose index (CTDIvol) and dose-length product (DLP), were collected. The third quartile values of these metrics were established as local diagnostic reference levels (DRLs). CTDIvol values for head and body scans were also measured using a pencil-type ionization chamber within polymethylmethacrylate (PMMA) phantoms and showed strong correlation with the corresponding values recorded from the CT console (R = 0.98 for head; R = 0.97 for body). DLP values were used to derive effective doses (ED) using established conversion coefficients. The proposed DRLs (CTDIvol/DLP) were 42 mGy/532 mGy cm (head), 10 mGy/271 mGy cm (thorax), and 10 mGy/392 mGy cm (abdomen). Corresponding mean EDs were 0.82 mSv, 3.25 mSv, and 4.24 mSv, respectively. The majority of DRL and all ED values were consistent with published international data. Routine implementation of quality assurance (QA), optimization of scan parameters (e.g., scan length, mAs), and adherence to DRLs are recommended to minimize radiation exposure without compromising diagnostic quality.