Introduction: X-ray imaging of the lumbar spine is the most common examination in general radiography, in which the patient has a relatively high dose of ionizing radiation. The dose of ionizing radiation recieved by the patient from the lateral projection of the lumbar spine is described as the equivalent of 50 chest imaging. Purpose: The purpose of this diploma work was to determine how the distance of the patient from the image reciever affects the dose recieved by the patient in lateral imaging of the lumbar spine, in the horizontal course of the central beam. Methods: The research was conducted in two parts. In the first part of the thesis, doses were measured on two anthropomorphic lumbar spine phantoms PBU 60 and RS-113T with different attenuation coefficients in three different positions. In the second part of the task, the doses of ionizing radiation were compared according to different attenuation coefficients of the previously mentioned phantoms, and it was determined whether the dose changes according to proximity of the image reciever to the patient or to the phantom. Measured dose and surface area (DAP) values were read on both phantoms. We also calculated the input skin dose (VKD), effective dose (E), SNR, CNR and dose of ionizing radiation to the organs. Results: In the study, we demonstrated statistically significant differences in the dose of ionizing radiation in the imaging of the lumbar spine in all three positions with both anthropomorfic phantoms PBU 60 and RS-113T. The values of DAP, VKD and effective dose were the lowest in both phantoms PBU 60 and RS-113T in the position where the image reciever is by the table, the phantom next to the image reciever (position 3), and the highest in the position where the image reciever is in the basic position, phantom in the middle of the examination table (position 1). The difference in DAP between theese two positions in the PBU 60 phantom is 25.15 µGy m2, and in the RS-113T phantom 122.97 µGy m2. The difference in VKD between theese two positions in the PBU 60 phantom is 5.21 mGy, and in the RS-113T phantom 11.98 mGy. The difference in effective dose between theese two positions in the phantom PBU 60 is 42.72 µSv, and in the phantom RS-113T 144.76 µSv. Discussion and conclusion: In our study, we demonstrated that the distance of the patient from the image reciever effects the dose of ionizing radiation. The mean difference in phantom PBU 60 between position 3 and position 1 for DAP is 23.1 %, for VKD 62.5 % and for effective dose 25.0 %. The mean difference in phantom RS-113T between position 3 and position 1 for DAP is 45.4 %, for VKD 75.2 % and for effective dose 47.4 %. For further research in the future, we recommend optimization of exposition protocol at each positions and the measure performance on patients.
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