Comparison of entrance surface air kerma to eye lens in head computed tomography protocols between 32-MDCT and 64-MDCT on an anthropomorphic phantom

Abstract

Background: Brain multi-detector computed tomography (MDCT) is commonly performed for diagnosis of traumatic or non-traumatic brain injury cases. During brain CT scan, the eye lens is highly sensitive to radiation and may cause radiation-induced cataracts irradiated by CT primary beam. Objectives: This study aimed to determine and compare entrance surface air kerma (ESAK) to the eye lens in clinical routine head protocols between 32-MDCT and 64-MDCT using an anthropomorphic phantom. Materials and methods: A PBU-60 head phantom was scanned by 32-MDCT and 64-MDCT in helical, axial, and tilted axial modes used in clinical routine head protocols with tube voltage of 120 kVp, tube current of 108-150 mAs for 32-MDCT, and 200-310 mAs for 64-MDCT. The NanodotTM optically stimulated luminescent dosimeters (OSLDs) was used to measure ESAK to eye lens. Dose length product (DLP), normalized volume CT dose index (nCTDIvol), and normalized mean ESAK were compared between two CT scanners. Results: The ranges of mean normalized ESAK to the eye lens in each scanning mode was found from 0.41±0.01 to 0.51±0.01 mGy/100 mAs for 32-MDCT and 0.30±0.01 to 0.40±0.01 mGy/100 mAs for 64-MDCT. The normalized ESAKs obtained from 64-MDCT were lower than 32-MDCT by 21.57-37.50%. The lowest normalized ESAK of 0.30±0.01 mGy/100 mAs was obtained in tilted axial scanning mode in 64-MDCT with the difference of 37.50% compared to 32-MDCT of using identical scanning mode. Conclusion: This study demonstrated that normalized mean ESAK to the eye lens for 64-MDCT in all brain scanning protocols was lower compared to 32-MDCT. In addition, using tilting gantry in axial scanning mode as well as using an automatic tube current modulation system could be beneficial for reducing radiation dose to eye lens during brain CT in clinical routine