Organ Dose Estimation for CT Localizer Images

Purpose: Current radiation dose estimation for CT localizer exams report a single CTDIvol value. Localizer exams with the same CTDIvol can be acquired as AP, PA, or lateral geometries, each of which carry different radiation burdens. The Purpose of this study was to quantify radiation burden from different CT localizer geometries using Monte-Carlo Methods to estimate organ dose for a population of patients. Methods: Fifty-seven adult computational phantoms (XCAT) and a previously validated Monte-Carlo simulation (PENELOPE) of a commercial CT system (Siemens SOMATOM Flash) were used to estimate organ dose. Clinically relevant chest localizer protocols were simulated with the x-ray tube in AP, right lateral, and PA positions. Organ doses were estimated and normalized by mAs. Breast and lung dose were compared across different views and calculated as a percentage of organ dose for chest CT scans. Results: Breast dose from AP localizers was the highest with an average value of 9.24 mGy/100 mAs compared with 4.75 mGy/100 mAs for right lateral and 1.59 mGy/100 mAs for PA. Lung dose was also the highest for AP localizers with an average value of 8.27 mGy/100 mAs compared with 6.14 mGy/100 mAs for right lateral and 6.76 mGy/100 mAs for PA. For typical CT chest examinations, the CTDIvol of the localizer is about 3% of the actual scan (0.13 mGy vs 4.09 mGy). As an example organ dose comparison, the average breast dose was 0.12 0.02 mGy for the AP localizer (3% CT breast dose) and 0.020 0.006 mGy (0.4% CT breast dose) for PA localizer. Conclusion: Localizer exams can be acquired using protocol specific views to keep radiation dose to sensitive organs as low as reasonably achievable. Future reporting of organ dose in CT should include the localizer scan acquisition to more fully represent the total radiation burden associated with CT imaging.

Duke Scholars

Author Ehsan Abadi Radiology

Author Ehsan Samei Radiology