The Method Of Estimation Size-Specific Radiation Dose Of Patient In CT Examinations

Medical exposure had been the largest source of man-made radiation, computed tomography (CT) is the biggest contribution in medical exposure. As the numbers of CT examinations and the scope of applications increased, radiation dose from CT examinations has caused more and more attention. CTDIvol and DLP are common used to estimate organ dose and effective dose, but their conversion factor are both based on stylized phantom and tissue weight factors of ICRP 60. Especially the conversion factors were not size-specific, this would cause a great uncertainty. The aim of this dissertation is to suggest and assess a method for accurately estimation size-specific organ dose and effective dose in CT examinations. The research task included:(1)research the influenced factors of radiation dose from CT examinations.(2)estimate radiation dose based on CTDIvol and DLP.(3)estimate radiation dose based on SSDE. The method of this study is:(1) use the VirtualDoseTM software and tissue weight factors of ICRP 103 to computer organ dose and effective dose.(2) use AAPM 204 and 220 report to computer SSDE. This research have gained many results, (1)the radiation dose and conversion coefficients are proportion to tube voltage,and inverse proportion to the width of beam collimation, with the different of beam collimation, CTDIvol-normalized-organ dose and DLP-normalized effective dose have changed less than 10%. Using the body bow tie filter substitute for head bow tie filter, it would increase organ dose, and CTDIvol-normalized-organ dose and DLP-normalizedeffective dose increased up to twice. The overrangging of sprial scan great influence the radiation dose of organ near the edge of scanning range, owing to anatomical position and radiosensitivity of the organs. The efficiency of CTDI more influence effective dose of adult in body CT examinations than child, this is correlate with scanning length. (2)I have researched estimation radiation dose based on CTDIvol and DLP. Investigated the scanning parameters how to affect the eye lens dose, then calculated the CTDIvol-normalized-eye lens dose to estimate eye lens dose. Based on the tissue weight of ICRP 103 and voxel phantoms, calculate the conversion factors from DLP to effective dose of child, teenager and adult with different BMI (Body Mass Index) to rapidly and accurately estimate effective dose. (3) I have researched to estimate organ dose based on SSDE, calculate the conversion factors from SSDE to organ dose for child,teenage and adult.when we not considered the scan range to affect the conversion factors, and calculated the conversion coefficients to estimate effective dose of adult in body CT examinations. Considered the influence of scan range and obese, I have proposed a new method to estimate effective dose in body CT scanning based on obese and height, then computed the conversion factors of effective dose. The conclusions included:this doctoral dissertation established a method for estimate size-specific radiation dose form CT examinations, it can reduce the uncertainty from the size of patient to estimate radiation dose. We have found a solution to optimize the CT scanning plan,and the derivations many conversion factors based on CTDIvol, DLP and SSDE to estimate organ dose and effective dose, radiological technologist can use them to rapidly and accurately estimate organ dose and effective dose.