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1- TITRE Sorry for my bad English. I did not practice a lot in the last years. So, I will present very small doses of radiation in CT scan of the sinuses but still important in radiology exams, particularly with children. 2- CONTENTS I will present briefly the steps of our study to compare the effective doses of radiation in children and adults with navigation and non‑navigation CT scan of the sinuses. In conclusion, I will demonstrate the importance of considering these small doses. 3- INTRODUCTION • The advent of 3D navigation imaging has opened new borders to the endoscopic surgical approaches of naso-sinusal inflammatory and neoplastic diseases; • The use of navigation systems has recently gained in popularity among the pediatric population, particularly in the fields of neurosurgery and otolaryngology; • 3D navigation can be particularly useful in a very young population, in which all the anatomical structures are smaller and in whom there is an increased risk of complications; • However, the increased tissue radiation required for data acquisition associated with 3D navigation CT scans is a source of concern in the medical literature because of its potential health hazards; 4- OBJECTIVES We aimed to compare the effective doses of radiation between 3D navigation protocols and standard protocols for sinus computed tomography scans for both the adult and pediatric population. 5- METHODS We performed a retrospective cohort study through electronic chart review of all patients who underwent both navigation and non-navigation CT scans of the sinuses from May 2019 to December 2019. We collected data for both the pediatric and adult population. The scanner used for all CT exams was a Siemens Drive. The effective dose of radiation were calculated with the CT parameters, such as KV, M A S and CTDI. 6- RESULTS A total of 115 CT scans were selected for analysis, of which 47 were standard protocols and 68 were 3D navigation protocols CT scans. Among these, 31 exams were performed on children and 84 exams on adults. 7- RESULTS The scanner protocols for non-navigation and navigation scans were respectively a cut thickness 0.6 mm versus 1 mm and a current-time product 120 M A S versus 390 M A S. 8- RESULTS For the total population, mean effective dose in the non-navigation CT scans was 0.37 mSv and mean effective dose in the 3D navigation sinus CT group was 2.33 mSv. 9- RESULTS The mean difference of 1.97 mSv between the two groups was statistically significant. There was a sixfold increase in radiation with utilization of 3D navigation protocols. The ratio was practically identical when the pediatric as well as the adult subset of patients were analyzed. 10- DISCUSSION In our study, 3D navigation sinus CT confirmed a surgical indication or was utilized during a surgical procedure in 65% of pediatric patients and 49% of adult patients. The dilemma persists. On one hand, initial imaging with a 3D navigation protocol may not yield indication for surgery, which results in a non-necessary increase in irradiation for a patient. On the other hand, if one prescribes a standard sinus CT scan that reveals positive findings and criteria for endoscopic sinus surgery, the patient may need a subsequent 3D navigation protocol sinus CT scan with further radiation exposure. Judicious prescription of standard sinus CT protocols should also be advocated for primary care physicians as well as other specialists. This could play a role in improving the diagnostic yield and utility of these exams. The data has urged us to work on globally accepted dose-reduction strategies for sinus CT scanning. 11- CONCLUSION Even if an average effective dose of 2 mSv from a navigation scan remains a small dose and the associated risks for a single exam are negligible, it is of paramount importance to know the true difference in effective radiation doses between non-navigation and navigation sinus CT scans to better raise awareness among otolaryngologists. The younger age of the patient and the possibility of repeated radiological exams for sinusitis or other conditions should prompt the physician to be meticulous in his radiological prescriptions. A patient-oriented approach is suggested to determine the exact indications for navigation and non-navigation sinus scanning and its proper timing. The otolaryngologist should evaluate 3D acquisition protocols locally with radiation physicists to optimize parameters. The medical physicist must study the other technical aspects such as the clinical software applications available on the CT scan to minimize irradiation. 12- THANKS Thank you very much for your attention. I will take the questions but it is possible I will respond in French.