Page 15

ISRRT | Book Of Abstracts

13 5.13. Practical approach to minimize off focal radiation dose to patient during general radiography Presenter: Vitharana Gamage Wimalasena, Sri Lanka School of Radiography, The National Hospital of Sri Lanka, Colombo 10, Sri Lanka Author: V.G.Wimalasena Introduction: We consider that the patient is adequately protected when the x-ray beam is collimated with the LBD. But it is not true. The light beam diaphragms are not standardized and the x-ray beam collimators are not very much effective in removing the extra focal radiation. The amount of extra focal radiation present is variable from equipment to equipment. During radiography of, specially the abdominal and thoracic areas the tissues outside the collimated area receive and absorb this unnecessary radiation and increase the dose. We cannot say that this will not produce any after effect on the patient. The effect of extra focal radiation is not always visible on the images (except on the posterior side of lateral lumbar spine or dorsal spine images) and is neglected. In case of Lumbar spine and dorsal spine laterals the percentage of extra focal radiation is vey high and they will increase the radiation dose to the more radiation sensitive tissues such as intestine, gonads and the breast. These doses will contribute to the cumulative dose to increase if these patients may undergo further investigations later. Therefore it is high time that we take necessary precautions to prevent this unnecessary radiation reaching the patient if we are really concerned about the minimization of radiation dose to the patient. This experiment shows a pre-patient collimation (using at least 2 mm lead) close to the patient’s body can do this. Methods: The skull phantom was exposed with the beam collimated just to cover the region, lead four numbers place just outside the collimated margins. It was repeated with a lead mask with an opening equal to the collimated area kept above the phantom. Conclusions: On the processed first film, the area outside the collimated margins were dark due to the exposure to extra focal radiation. . This results in unnecessary radiation dose to patient even if we collimate the beam. The present day collimators are not effective in removing this extra focal radiation. The second film did not show this effect. That means the extra focal radiation fall on patient can be minimized by using additional shielding (collimation) just above the upper surface of the patient. 5.14. Dose optimization in hip joint axio-lateral projection with air gap Presenter: Susanne Kivistö, Oulu University Hospital, Finland Authors: Susanne Kivistö, Anja Henner, Seija Mattila Introduction: The quantity of scattered radiation in x-ray beam reaching a receptor can be reduced by separating the patient's body and receptor surface, known as an air gap. Scattered radiation leaving a patient's body is more divergent than the primary x-ray beam. Therefore, scattered radiation spreads out of the primary beam area. The reduction of scattered radiation in proportion to primary radiation increases with airgap distance 30 cm. The use of an air gap introduces magnification. Therefore, a larger receptor size is required to obtain the same patient area coverage but the magnification can be reduced by smaller focus size as well as by increasing the focus-to-receptor distance. Also, increasing the separation distance between the patient and the receptor, increases focal spot blurring. It is usually necessary to use relatively small focal spots with an air-gap technique. This technique is most used in mammography but it is also useful in hip axiolateral projection. When using air gap the mistakes and dose increase caused by grid can be avoided (tilted grid, grid lines). Methods: The data of hip joint axio-lateral projection was collected in emergency x-ray department with Fuji FDR Acselerate and wireless flat panel detector. Focus to receptor distance varied from 160 cm to 193 cm (Mean 166 cm). Results: Patient doses with air gap varied from 1,68 dGycm2 to 10,049 dGycm2 (mean 3,57 dGycm2 ). Mean of the S-value was 509. It shows significant decrease in patient dose compared those with anti-scatter grid. Patient doses can be decreased with air gap instead of anti-scatter grid. In 2009 patient data collected in Health Center showed that with air gap dose decrease can be with air gap even 2/3 compared with gird in hip joint axiolateral projection. 5.15. Posterior-anterior radiograph of lower extremity to reduce radiation exposure to gonad and effective dose Presenter: Jina Shim, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea Authors: Jina Shim Introduction: A standard full-length standing anteroposterior (AP) radiograph of the lower extremity is the most widely used imaging technique in orthopedic measurements for leg-length discrepancy or alignment of lower limbs. Even though the reproduction system is included in the direct x-ray beam exposure in this examination, radiation protection for gonad is not routinely applied. The aim of our study was to determine the advantage of posteroanterior (PA) projection of the lower extremity regarding reduction of radiation exposure to gonad, and determine the effective dose compared to AP projection. In the phantom study, surface doses at the gonad were measured to compare AP, PA, and AP with gonad protection. In this 182 patients study, we calculated the measured dose area product, effective dose and gonad dose using the PCXMC program. There was a problem due to magnification in the study, there were differences between AP and PA projections of the femur and tibia and there was a fundamental matter in the x-ray 2D image. The study showed that gonad and effective doses in PA radiograph for a full-length lower extremity were much lower compared to the standard AP radiograph. Methods: Radiation exposure to gonad was measured at the testicles in AP both with and without protection and PA without using a humanoid phantom. 182 patients were enrolled to determine the AP and PA of gonad dose and effective dose using PCXMC program. Results: In the phantom study, the mean value of surface radiation dose to the location of gonads in PA projection without gonad protection was lower than that in AP projection, both with and without protection (p<0.05). In this 182 patients study, effective doses decreased by 47%, testicles and ovaries decreased by 93%, 21%, respectively in the PA radiograph. The gonad and effective doses in the PA radiograph of fulllength lower extremity was much lower than a standard AP radiograph. 5.16. Abdominal Examination in KNH using 16 multi slice CT scan: Review of ALARA practice in managing patient dose Presenter: Catherine Muchuki, Kenyatta National Hospital, Kenya Author: C.W Muchuki Introduction: Objective of the study: To assess the justification of abdominal CT examinations carried out, quantify radiation dose and evaluate the optimization of scanning parameters that contribute to radiation dose determination within the ALARA principle in comparison to international standards. Methods: A retrospective study of 76 patients aged between 30 and 80 years of age referred for abdominal CT scanning at KNH, s department of diagnostic radiology during the period between April to December 2013 using the new protocol. Conclucions: MDCT as a new and useful technology in medical imaging is providing technical challenges to end users that compromise optimization in reducing patient dose, from Kenyatta National hospitals experience. Local protocol practice was shown not only to have had an impact on the dose but also to have influenced the diagnostic yield of the examinations. Further quality assurance practices are ongoing. 5.17. Evaluation of radiation dose received by patients during dental X-ray imaging in Japan Presenter: Shoichi Suzuki, Faculty of Radiological Technology,School of Health Sciences,Fujita Health University Authors: Yuta Matsunaga, Ai Kawaguchi, Masanao Kobayashi, Yumi Kataoka Objective: Although dental X-ray imaging is increasingly being digitized, and the use of cone-beam computed tomography (CBCT), a device specifically for dental imaging, is spreading at dizzying speed, methods utilizing diagnostic X-ray CT devices that are not designed specifically for dental use are also under consideration. In this study, we compared the radiation dose received under imaging conditions obtained from basic studies by dentists in terms of the doses received by patients when conventional panoramic dental imaging, CBCT, 64-row CT, and 320-row CT were used. There have been few reports of relative comparisons between these devices, even internationally. We therefore evaluated the radiation


ISRRT | Book Of Abstracts
To see the actual publication please follow the link above