EVALUATION OF RADIATION DOSES USING CONE BEAM COMPUTED TOMOGRAPHY IN ENDOVASCULAR AORTIC REPAIR AND SCOLIOSIS PROCEDURES

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Abstract: Purpose: The study includes the two areas, vascular surgery and orthopedics, and focuses on endovascular aortic aneurysm repair (EVAR) and scoliosis procedures. EVAR procedures contribute to a high radiation dose to the patient and for scoliosis procedures, it is often young girls that are undergoing surgery. It is therefore important to keep the radiation doses as low as possible. The aim of this project was to evaluate the radiation dose when cone beam CT (CBCT) is used in interventional fluoroscopy and operating rooms (OR), for protocols used in EVAR and scoliosis procedures, ahead of optimization. Theory: Ionizing radiation may be an important tool during surgery, for instance, to guide instruments through the patient blood vessels. In interventional fluoroscopy and angiography, two-dimensional (2D) imaging is widely used. However, to avoid overlay of the patient anatomy and improve visualization a CBCT can be performed, which gives a three-dimensional (3D) image of the patient. CBCT uses a cone beam shaped radiation field and can be performed during surgery using the interventional x-ray equipment. One advantage with this method is that a 3D image of the patient can be received without having to move the patient to a computed tomography (CT) room. CBCT and CT are imaging methods that give a relatively high radiation dose, which makes it important to evaluate differences between the two modalities. Method: Two phantoms were used to evaluate the radiation doses, a polymethyl methacrylate(PMMA) phantom and an abdominal phantom. Dose area product (DAP), absorbed dose rate and incident air kerma (IAK) in the reference point (skin dose received from DICOM data) were collected for different protocols and settings on three modalities, Artis Q, Pheno and Zeego. Effective dose and absorbed organ doses were also calculated using PCXMC20Rotation. Image quality was evaluated using the high resolution module in Catphan and the number of line pairs per cm was calculated. CT scans were performed and effective doses and equivalent doses were calculated using CT-Expo. 2D-fluoroscopy and exposure were performed with the abdominal phantom to evaluate DAP at 2D-3D-fusion. Personnel radiation dose was estimated using the real-time personal radiation dosimetry system, Dose Aware. Measurements were made at different distances from the patient center, on all modalities and for all protocols. Also, measurements with thermoluminescent dosimeters (TLD) was performed on both phantoms for one modality, Artis Q.Result: The maximum difference, comparing the protocols giving the highest and lowest effective doses, was a factor of 16. Using collimation and zoom decreases the effective dose compared to the default setting. However, IAK in the reference point increasedwith both collimation and zoom. The quotient of effective dose for the scoliosis protocols, for the normal dose protocols compared to the low dose protocols, was a factor 1.3 and 1.8, on Artis Pheno and Artis Zeego, respectively. For the two high radiation dose protocols used for EVAR procedures, on all modalities, CBCT gave a higher effective dose than CT, when using the same scan range. The two low radiation dose CBCT protocols, used for EVAR, gave a lower effective dose than the CT protocol with the same scan range. The CBCT protocols for scoliosis, on both modalities Artis Pheno and Artis Zeego, gave a higher effective dose than the CT scan using the same scan range, except for the protocols, 4sRygg Low dose 3D and CT Low dose 4s R15P85, compared to the CT protocol Full back (automatic). Evaluating thehigh-resolution image quality on all protocols, for both EVAR and scoliosis, gave 8-9 lp/cm, except for the scoliosis protocol CT Low dose 4s R15P85 on Artis Zeego which had a decreased resolution with 4 lp/cm. With 2D-3D-fusion a factor 10 lower DAP was received, when comparing six seconds fluoroscopy with the lowest dose protocol, FL Low, with the CBCT protocol 5sDR Body Care on Artis Q. Using an increased distance to the patient, and settings such as collimation and zoom, decreased the estimated personnel radiation dose.

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