LOCAL STUDY OF DIAGNOSTIC REFERENCE LEVELS FOR COMPUTED TOMOGRAPHY EXAMINATIONS OF ADULT PATIENTS IN IZMIR, TURKEY.

PURPOSE: This study aims to develop local diagnostic reference levels (DRLs) for the most common computed tomography (CT) examinations carried out around Izmir, Turkey. METHODS: Five common CT examinations (head, neck, chest, abdomen-pelvis (AP), chest-abdomen-pelvis (CAP)) from four different radiology centres have been included in the study. CT dose index-volume (CTDIvol) and dose length product (DLP) values were recorded for 50 patients per exam in each centre. Third quartiles of CTDIvol and DLP values were determined as DRLs and compared with international findings. RESULTS: 51.3% of the patients were male and 48.7% were female, with a mean age of 57 (between 18 and 93). DRLs for CTDIvol were recorded as 70, 16, 15, 23 and 16 for head, neck, chest, AP and CAP examinations, respectively, while the corresponding DLPs were 1385, 604, 567, 998 and 1180 mGy.cm. CONCLUSION: Results are mostly comparable to the latest international data, except for the head examinations, which were observed to slightly exceed the DRLs established by other countries.

Effects of the Use of Automatic Tube Current Modulation on Patient Dose and Image Quality in Computed Tomography

Objectives: The frequency of abdominal computed tomography examinations is increasing, leading to a significant level of patient dose. This study aims to quantify and evaluate the effects of automatic tube current modulation (ATCM) technique on patient dose and image quality in contrast-enhanced biphasic abdominal examinations. Methods: Two different scan protocols, based on constant tube current and ATCM technique, were used on 64 patients who visited our radiology department periodically. For three patient groups with different patient size, results from two protocols were compared with respect to patient dose and image quality. Dosimetric evaluations were based on the Computed Tomography Dose Index, dose length product, and effective dose. For the comparison of image qualities between two protocols, Noise Index (NI) and Contrast to Noise Ratio (CNR) values were determined for each image. Additionally, the quality of each image was evaluated subjectively by an experienced radiologist, and the results were compared between the two protocols. Results: Dose reductions of 31% and 21% were achieved by the ATCM protocol in the arterial and portal phases, respectively. On the other hand, NI exhibited an increase between 9% and 46% for liver, fat and aorta. CNR values were observed to decrease between 5% and 19%. All images were evaluated by a radiologist, and no obstacle limiting a reliable diagnostic evaluation was found in any image obtained by either technique. Conclusion: These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.

Size-specific dose estimates in chest, abdomen, and pelvis CT examinations of pediatric patients.

PURPOSE: Size-specific dose estimates (SSDEs) are the latest focus of interest among medical physicists studying radiation dose to the patient in computed tomography (CT). This study aims to make conversions from CTDIvol to SSDE and investigate the relationship between mean SSDE (SSDE) and central SSDE (SSDEcenter) values for pediatric patients of different age groups undergoing chest, abdomen, and pelvis scans. METHODS: In this retrospective study, we examined 105 consecutive pediatric CT exams of chest, abdomen, and pelvis (CAP) classified in 3 separate groups according to age: 0-5 years, 6-10 years, and 11-16 years. A MATLAB program was developed to determine SSDE values for each patient along 6 subregions: chest, abdomen, pelvis, chest and abdomen, abdomen and pelvis, and CAP. SSDE values derived over the slice at the center of each scan range (SSDEcenter) were also recorded. SSDE and corresponding SSDEcenter results were compared for each age group. RESULTS: Root mean square differences (RMSD) between SSDE and SSDEcenter values ranged between 0.13 mGy and 2.1 mGy through all groups and subregions, corresponding to 1.2% and 11%, respectively. CONCLUSION: In pediatric CT exams involving CAP region, CTDIvol and the water equivalent diameter at the middle of the scan range can be used to provide a reasonable estimate of mean SSDE with an RMSD of 11% at most.