Room: Exhibit Hall
Purpose: This study sought to determine k-factors for adults who undergoing chest CT with TCM using Monte Carlo simulation method and tube current data of clinic cases.
Methods: 60 Chest CT scan cases were selected in this study, based on the water-equivalent diameter (Dw) patients were divided into three groups (thin, moderate, and fat). Either automatic current selection (ACS) or ACS+ dynamic dose modulation (DOM) were performed by 64-MDCT scanner Neuviz 16 1.1, Dw and mAs data of each of each patient were obtained from their CT images. Normalized Organ doses per mAs of each CT scan rotation were simulated by Monte Carlo method, combined with mAs data on a slice-by-slice basis and corrected using D w, the patient organ doses of a CT protocol were finally calculated. Moreover, ED was calculated using tissue-weighting factors defined in ICRP Publication 103, and k-factor for each patient were determined by their scanner-reported DLP.
Results: The mean conversion factors of thin, moderate and fat patients for chest TCM scan were calculated as follows: 0.0263, 0.0229, 0.0187 mSvï¹’mGy-1cm-1, for the ACS, and 0.0259, 0.0246, 0.0198 mSvï¹’mGy-1cm-1 for the ACS+DOM, which indicate that the k-factor decreases with the increasing size of patients. Using the chest k-factor listed on ICRP publication 102 may underestimate ED by an average of 37 %, 39% for ACS, and ACS+DOM.
Conclusion: The k-factors varies from patient to patient according their size, and the TCM k-factors for all patients are considerably higher than the k-factor currently used to estimate ED of fixed tube current studies, suggesting that radiation doses from fixed tube current have been significantly and systematically underestimated