Patient absorbed dose comparison in CT and Stereoradiography (EOS) imaging during lower limb torsion evaluation using in-vivo and in-vitro dosimetry methods

Introduction: Accurate evaluation of femoral and tibial torsion is essential for children or adult with legs deformity, becuse incorrect legs morphogenesis can lead to pathological situation. CT scan is commonly used for the measurement of skeletal bone parameters. But, disability in imaging from standing and sitting posture and absorb dose of patients are deficits of this method. EOS method overcome this dificits. Likewise some paper have reported decrease of EOS dose rather than dose level in CT, this project aim to measure amount of dose reduction and to verify reduction of EOS dose level in compare to CT. Materials and Methods: For EOS and CT invitro dosimetry, a pencil ionization chamber was used. Computed tomography dose index volume (CTDIvol) was mesuered, using this dosimeter and standard tissue equivalent CT phantom. DLP of both imaging methods was compared for acquisition of adult hip. With radiothermoluminescent detectors (TLD) in vivo dosimetry enterans skin dose for 30 patients was measuered, which 15 of them were underwented CT scan and the other were underwented EOS imaging. Results: The reading of dosimeters level and therefor enterans skin doses, in EOS system was significantly lower than CT scan. Patient dose in AP, RT and LT fields of CT scan was respectively 24, 41.5 and 9 times more than EOS. Enterans skin dose in CT scan was 18 times more than EOS on average. Also, in invitro dosimetry CT scan dose was 47 times more than EOS dose. Conclusion: Elimination of scatter radiation and high quantum efficiency of detector lead to minimum dose for an optimum qulity scan with EOS system than CT scan. Stereoradiography imaging modality will impose less doses of CT scan imaging modality in similar imaging views from the lower limbs.