| dc.description.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 increased
with 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 the
high-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. | sv |
