Evaluation of Effective Dose from chest CT scanning in women with and without Automatic Exposure Control (AEC)

Background and goal: Chest CT in women allocates higher Effective Dose (ED) due to being breasts in radiation field relative to men. There are various techniques inorder to optimize radiation dose to the patients in chest CT scanning. One of these methods is the use of Automatic Exposure Control (AEC) during the scanning that modulate mA according to patient’s weight and shape. So the goal of this study was evaluates ED from common chest CT scan, with and without AEC system and investigate possibility of changing clinical protocols in routine chest protocol. Method: Total of 54 female patients (25 patients with AEC and 29 patients without AEC) were investigate in this study. Computed Tomography Dose Index (CTDI) in two situations was measured with a calibrated ionization chamber with active length of 100mm at the center and peripheral of 32cm PMMA body phantom. Weighted CTDI (CTDIw) was calculated according to following formula: . Effective Doses were evaluated with CT-Expo, CT dose calculation software according to ICRP report no.103 tissue weighting factor. Also noise in a conventional water phantom was measured with average clinical parameters, both for patients whom scan with and without AEC system. All measurements were performing on Siemens Emotion 6 CT scanner. Results: With AEC: Calculated CTDIw and evaluated ED were 9.94±0.75mGy and 5.4±1.2 mSv respectively. Max amount of organ doses were related to breast (13.1±1.8), esophagus (12.3±3), lungs (12.5±2.5) and thymus (12.3±3.1). Without AEC: Calculated CTDIw and evaluated ED were 12.46±0.90mGy and 6.3±1.7mSv respectively. Max amount of organ doses were related to breast (15.3±1.1), esophagus (14.3±2.1), lungs (14.6±2.7) and thymus (14.3±2.4). Discussion and conclusion: Measurements show the decrease of 15 percent in dose with use of AEC systems. Also organ doses were less in patients whom scanned with AEC system. However Dose reduction is associated with an increase in noise by 11 percent (4.20±0.3 to 4.74±0.3), this amount of increase is negligible.

کلیدواژه ها:

Automatic Exposure Control (AEC) ، Chest CT ، Effective Dose ، Noise