Abstract
Purpose: To evaluate the effect on skin dose and image quality when decentering in the y- and x-direction for abdominal CT scans.
Methods: Patient centering data in CT were collected retrospectively from dose management software (DoseWatch, GE Healthcare) from a single university hospital (n=4 scanners) in 2017. Deviations from the isocentre were categorized for both vertical (±1.5cm, ±3.0cm, ±4.5cm) and horizontal (±1.5cm, ±3cm) planes on 498 patients. An anthropomorphic phantom (PBU-60) was subsequently scanned using each deviation on two scanners (Toshiba Prime, GE HD750) to allow dose and image quality (noise and visual grading assessment) comparisons.
Results: Significant skin dose increases (4.3mSv/50%) were detected anteriorly for both scanners when centered above the isocenter and reductions (2.0mSv, 24%) when below the isocenter. For the HD750, dose decreased up to 8.3mSv in four locations at the -4.5 position with increases (2.0mSv) noted on the right side with horizontal deviation. With upward vertical deviation noise increased from 13HU (isocenter) to 15HU. No change in standard deviation (SD) was detected with the phantom below isocenter. With left horizontal deviation SD increased by 12HU while SD decreased by 12HU dextro-laterally. VGA-score was lowest at the largest vertical ISO-center deviation.
Conclusion: Positioning above ISO-center may increase noise and skin dose. Similarly, horizontal deviation may increase dose. Subjective image quality is negatively affected by extreme vertical ISO-center deviation.
Methods: Patient centering data in CT were collected retrospectively from dose management software (DoseWatch, GE Healthcare) from a single university hospital (n=4 scanners) in 2017. Deviations from the isocentre were categorized for both vertical (±1.5cm, ±3.0cm, ±4.5cm) and horizontal (±1.5cm, ±3cm) planes on 498 patients. An anthropomorphic phantom (PBU-60) was subsequently scanned using each deviation on two scanners (Toshiba Prime, GE HD750) to allow dose and image quality (noise and visual grading assessment) comparisons.
Results: Significant skin dose increases (4.3mSv/50%) were detected anteriorly for both scanners when centered above the isocenter and reductions (2.0mSv, 24%) when below the isocenter. For the HD750, dose decreased up to 8.3mSv in four locations at the -4.5 position with increases (2.0mSv) noted on the right side with horizontal deviation. With upward vertical deviation noise increased from 13HU (isocenter) to 15HU. No change in standard deviation (SD) was detected with the phantom below isocenter. With left horizontal deviation SD increased by 12HU while SD decreased by 12HU dextro-laterally. VGA-score was lowest at the largest vertical ISO-center deviation.
Conclusion: Positioning above ISO-center may increase noise and skin dose. Similarly, horizontal deviation may increase dose. Subjective image quality is negatively affected by extreme vertical ISO-center deviation.
| Originalsprog | Engelsk |
|---|---|
| Publikationsdato | 26 feb. 2019 |
| Status | Udgivet - 26 feb. 2019 |
| Begivenhed | European Congress of Radiology - Wien ø, Østrig Varighed: 27 feb. 2019 → 3 mar. 2019 |
Konference
| Konference | European Congress of Radiology |
|---|---|
| Land | Østrig |
| By | Wien ø |
| Periode | 27/02/19 → 03/03/19 |