Impact of patient centering in CT on organ dose and the effect of using a positioning compensation system: Evidence from OSLD measurements in postmortem subjects

Abstract

The purpose of this study was to investigate the frequency and impact of vertical mis‐centering on organ doses in computed tomography (CT) exams and evaluate the effect of a commercially available positioning compensation system (PCS). Mis‐centering frequency and magnitude was retrospectively measured in 300 patients examined with chest‐abdomen‐pelvis CT. Organ doses were measured in three postmortem subjects scanned on a CT scanner at nine different vertical table positions (maximum shift ± 4 cm). Organ doses were measured with optically stimulated luminescent dosimeters inserted within organs. Regression analysis was performed to determine the correlation between organ doses and mis‐centering. Methods were repeated using a PCS that automatically detects the table offset to adjust tube current output accordingly. Clinical mis‐centering was >1 cm in 53% and 21% of patients in the vertical and lateral directions, respectively. The 1‐cm table shifts resulted in organ dose differences up to 8%, while 4‐cm shifts resulted in organ dose differences up to 35%. Organ doses increased linearly with superior table shifts for the lung, colon, uterus, ovaries, and skin (R2 = 0.73–0.99, P < 0.005). When the PCS was utilized, organ doses decreased with superior table shifts and dose differences were lower (average 5%, maximum 18%) than scans performed without PCS (average 9%, maximum 35%) at all table shifts. Mis‐centering occurs frequently in the clinic and has a significant effect on patient dose. While accurate patient positioning remains important for maintaining optimal imaging conditions, a PCS has been shown to reduce the effects of patient mis‐centering.

Heart‐centered positioning and tailored beam‐shaping filtration for reduced radiation dose in coronary artery calcium imaging: A Multi‐Ethnic Study of Atherosclerosis (MESA) Study

“…By decreasing the X‐ray fluence to peripheral, less attenuating regions of the body, these filters reduce dose and equalize image quality throughout the field‐of‐view (FOV) 10–13 . Incorrect patient positioning is known to increase radiation dose 14 and, consequently, vendors have sought to improve the process by developing automated, camera‐based patient position detection, 15,16 and moving tables 17 …”

“…[10][11][12][13] Incorrect patient positioning is known to increase radiation dose 14 and, consequently, vendors have sought to improve the process by developing automated, camera-based patient position detection, 15,16 and moving tables. 17 The conventional design of beam-shaping filters and a body-centered patient positioning strategy does not take into account the fact that clinical interest in cardiac imaging is limited to the heart: an off-center subsection of the larger chest cavity. While the entire patient cross-section must be imaged to avoid limited FOV artifacts, 18,19 it has been shown that significant dose reductions can be achieved by limiting higher X-ray fluence to a smaller subregion.…”

Accuracy and reproducibility of effective atomic number and electron density measurements from sequential dual energy CT

“…The shift test was used to test the effect of off‐centering the phantom. It has been shown that patients can be routinely off‐center from isocenter by as much as 3 cm 33 . Measurements were repeated on a phantom that was off‐centered by increments of 1 cm up to 3 cm in four directions: up, down, left, and right.…”

Heart-centered positioning and tailored beam-shaping filtration for reduced radiation dose in coronary artery calcium imaging: a MESA study

“…[10][11][12][13] Incorrect patient positioning is known to increase radiation dose 14 and, consequently, vendors have sought to improve the process by developing automated, camera-based patient position detection 15,16 and moving tables. 17 The conventional design of beam-shaping filters and a body-centered patient positioning strategy does not take into account the fact that clinical interest in cardiac imaging is limited to the heart: an off-center subsection of the larger chest cavity. While the entire patient cross-section must be imaged to avoid limited FOV artifacts, 18,19 it has been shown that significant dose reductions can be achieved by limiting higher X-ray fluence to a smaller subregion.…”