Radiation doses, cancer risks and optimization process of routine computed tomography (CT) exminations in Johor

Abstract

ABSTRACT The concerns towards radiation–induced cancer from Computed Tomography (CT) examinations have led to the encouragement of CT dose monitoring and further optimization of the scanning parameters. Therefore, in this study, radiation dose from CT scan and its related risks to the patients from current CT practice were analysed. In the first stage, this thesis started the discussion on the level of current knowledge among radiology personnel towards CT radiation risk and its optimization. There is no significant difference of the current knowledge of CT optimization between the two professions of interest herein, the medical and the allied health groups. A CT dose survey was conducted in 8 CT facilities for a 6-month period, encompassing data for 1024 patients with various CT examinations that included regions of the abdomen, brain and thorax. CT-EXPO (Version 2.3.1, Germany) software was used to validate the dose information such as CT Dose Index (CTDI) and dose-length product (DLP). The proposed Diagnostic Reference Levels (DRLs) were indicated by rounding off the third quartiles (Q3s) of whole dose distributions for weighted CTDI (CTDIw) (in mGy), volume CTDI (CTDIvol) (in mGy) and DLP (in mGy.cm) and their values were; 16, 17, and 650 respectively for CT abdomen; 70, 70, and 1030 respectively for CT Brain and 15, 16, and 670 respectively for CT thorax. In the second stage, the cancer risks of the CT examinations were estimated and the calculation was based on International Commission on Radiation Protection (ICRP) Publication 103 Report and Biological Effects of Ionizing Radiation (BEIR) VII Report. Based on BEIR VII recommendation, the study discovered that the lifetime attributable risks (LARs) of 100,000 populations who underwent abdominal CT examinations for stomach cancer were 2.3 for male and 1.0 for female; while for colon cancer the LARs were 2.3 for male and 0.7 for female. The effectiveness of optimization of CT parameters and application of shielding in routine CT procedures were evaluated. Of 7 protocols (P1 – P7), the k factors were constant for all protocols and decreased by ~8% compared to the universal k factor. It is of interest that k factors from CT-EXPO were found to vary between 0.010 for protocol P5 and 0.015 for protocol P3 due to inconsistency in tube potential and pitch factor. The application of breast shielding to routine CT thorax protocols reduced by 14% the breast’s equivalent dose. Hence, this study supports the importance of initiating protection and optimization processes of routine CT examinations in order to offer safer imaging practices.