Introduction: Radiography of lumbar and thoracic spine are classified as examinations which cause the greatest radiation burden in classical radiography. By the optimal usage of collimator according to the instructions given in the professional literature it's possible to greatly influence the reduction of the patients dose load. Purpose: The purpose of the research is to determine the influence of the optimal usage of collimator on patient irradiation and the image quality. Methods: The study was performed on 110 patients that were referred to the lumbar spine radiography and 84 patients that were referred to the thoracic spine radiography. For the first part of the study, half of the patients were imaged with the current collimation protocol used in the General Hospital Dubrovnik. For the second part of the study, the other half of the patients were imaged with the collimation protocol mentioned in the professional literature. For each patient DAP, image field size, exposure condtions, weight and height (for calculating the body mass index) were measured. From that data using the PCXMC program the effective dose and the absorbed organ doses were calculated. At the end, the image quality was evaluated by two radiologist and one radiologic technologist. Results and discussion: With the optimal use of the collimatior for the lumbal spine radiography we found out that the size of the primary field for the AP projection was reduced by 35,5 % and the LAT projection by 40,3 %. As a consequence, DAP value was reduced by 45,7 % and the effective dose by 47,7 % for AP projection. Regarding the LAT projection we did not find statistically different results between the groups in the DAP and the effective dose measurements which was caused by the incorrect positioning of the central beam before the optimization of collimation. The absorbed dose to selected radiosensitive organs decreased in the AP projection by an average of 40,9 % and in the LAT projection by 9,5 %. With the optimal usage of collimator in the imaging of the thoracic spine we found that the size of the primary field in the AP projection was reduced by 45,4 % and in the LAT projection by 40,7 %. The study also showed reduced values of DAP for AP projection by 33,5 % and for LAT projection by 23,3 %. The effective dose was reduced by 53,8 % for AP projection and 29,2 % for LAT projection. The mean absorbed dose to the selected organs decreased by 25,7 % in the AP projection and 28,4 % in the LAT projection. In addition, in all projections, except for the AP projection of the lumbar spine, it was found that the optimal usage of collimator improves the image quality. Conclusion: By carrying out the research we have demonstrated that optimal usage of collimator in lumbar and thoracic spine imaging has an influence on patient exposure to radiation. It also affects the image quality, which is not only preseved but rather improved.
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