Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms

Zhang, Di; Savandi, Ali S.; DeMarco, John J.; Cagnon, Chris H.; Angel, Erin; Turner, Adam C.; Cody, Dianna D.; Stevens, David B.; Primak, Andrew N.; McCollough, Cynthia H.; McNitt‐Gray, Michael F.

doi:10.1118/1.3078053

Cited by 49 publications

(41 citation statements)

References 18 publications

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“…This results in dose variation along the z-axis. Since the tube start-position could not be controlled, it was not possible to perform multiple scans using the exact same start angle (11) . A significant reduction in organ dose could be achieved if the option to choose the start angle were provided (12) .…”

Section: Resultsmentioning

confidence: 99%

Implications of Patient Centring on Organ Dose in Computed Tomography

Kataria

Sandborg

Althén

2016

Radiat Prot Dosimetry

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Automatic exposure control (AEC) in Computed Tomography (CT) facilitates optimization of dose absorbed by the patient. The use of AEC requires appropriate "patient centering" within the gantry, since positioning the patient off-center may affect both image quality and absorbed dose. The aim of this experimental study was to measure the variation in organ and abdominal surface dose during CT examinations of the head, neck/thorax and abdomen. The dose was compared at the isocenter with two off-center positions -ventral and dorsal to the isocenter.Measurements were made with anthropomorphic adult phantom and thermoluminescent dosemeters (TLDs). Organs and surfaces for ventral regions received lesser dose (5.6% -39.0%) than the isocenter when the phantom was positioned +3cm off-center. Similarly, organ and surface doses for dorsal regions were reduced by 5.0% -21.0% at ˗5 cm off-center.Therefore correct vertical positioning of the patient at the gantry isocenter is important to maintain optimal imaging conditions.

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Section: Resultsmentioning

confidence: 99%

Implications of Patient Centring on Organ Dose in Computed Tomography

Kataria

Sandborg

Althén

2016

Radiat Prot Dosimetry

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“…In radiation transport calculations, it is impossible to define the geometry of the beam-shaping filter, which rotates along with the x-ray tube. Thus, a weighting factor (wgt) was given to each emitted particle with consideration of photon attenuation through the beam-shaping filter in a radiation transport calculation, as in previous studies Zhang et al 2009;Li et al 2010;Lee et al 2011). In this study, aluminum was always considered for the material of a hypothesized beam-shaping filter that could give the measured dose profile.…”

Section: Methodsmentioning

confidence: 99%

“…Then a source model was defined with consideration of photon attenuation at the hypothesized beam-shaping filter to reproduce the measured dose profile. CTDI 100 was measured for a condition by rotating the x-ray tube in the gantry for some MDCT devices to check the validity of the source model for each device Zhang et al 2009;Lee et al 2011). The tube currenttime product was set to 200 mAs.…”

Section: Methodsmentioning

confidence: 99%

Numerical Analysis of Organ Doses Delivered During Computed Tomography Examinations Using Japanese Adult Phantoms with the WAZA-ARI Dosimetry System

Takahashi¹,

Sato²,

Endo³

et al. 2015

Health Physics

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A dosimetry system for computed tomography (CT) examinations, named WAZA-ARI, is being developed to accurately assess radiation doses to patients in Japan. For dose calculations in WAZA-ARI, organ doses were numerically analyzed using average adult Japanese male (JM) and female (JF) phantoms with the Particle and Heavy Ion Transport code System (PHITS). Experimental studies clarified the photon energy distribution of emitted photons and dose profiles on the table for some multi-detector row CT (MDCT) devices. Numerical analyses using a source model in PHITS could specifically take into account emissions of x rays from the tube to the table with attenuation of photons through a beam-shaping filter for each MDCT device based on the experiment results. The source model was validated by measuring the CT dose index (CTDI). Numerical analyses with PHITS revealed a concordance of organ doses with body sizes of the JM and JF phantoms. The organ doses in the JM phantoms were compared with data obtained using previously developed systems. In addition, the dose calculations in WAZA-ARI were verified with previously reported results by realistic NUBAS phantoms and radiation dose measurement using a physical Japanese model (THRA1 phantom). The results imply that numerical analyses using the Japanese phantoms and specified source models can give reasonable estimates of dose for MDCT devices for typical Japanese adults.

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“…Dramatic dose variation near the periphery of a scanned volume, which was caused by different tube starting angles alone, has also been reported in the literature. 22,23,43 This characteristic of the helical CT scans created a random factor into our point dose measurements.…”

Section: Discussionmentioning

confidence: 99%

In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans

Zhang

Padole

et al. 2014

Medical Physics

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Purpose: To present a study of radiation dose measurements with a human cadaver scanned on a clinical CT scanner. Methods: Multiple point dose measurements were obtained with high-accuracy Thimble ionization chambers placed inside the stomach, liver, paravertebral gutter, ascending colon, left kidney, and urinary bladder of a human cadaver (183 cm in height and 67.5 kg in weight) whose abdomen/pelvis region was scanned repeatedly with a multidetector row CT. The flat energy response and precision of the dosimeters were verified, and the slight differences in each dosimeter's response were evaluated and corrected to attain high accuracy. In addition, skin doses were measured for radiosensitive organs outside the scanned region with OSL dosimeters: the right eye, thyroid, both nipples, and the right testicle. Three scan protocols were used, which shared most scan parameters but had different kVp and mA settings: 120-kVp automA, 120-kVp 300 mA, and 100-kVp 300 mA. For each protocol three repeated scans were performed. Results: The tube starting angle (TSA) was found to randomly vary around two major conditions, which caused large fluctuations in the repeated point dose measurements: for the 120-kVp 300 mA protocol this angle changed from approximately 110• to 290• , and caused 8% − 25% difference in the point dose measured at the stomach, liver, colon, and urinary bladder. When the fluctuations of the TSA were small (within 5• ), the maximum coefficient of variance was approximately 3.3%. The soft tissue absorbed doses averaged from four locations near the center of the scanned region were 27.2 ± 3.3 and 16.5 ± 2.7 mGy for the 120 and 100-kVp fixed-mA scans, respectively. These values were consistent with the corresponding size specific dose estimates within 4%. The comparison of the per-100-mAs tissue doses from the three protocols revealed that: (1) dose levels at nonsuperficial locations in the TCM scans could not be accurately deduced by simply scaling the fix-mA doses with local mA values; (2) the general power law relationship between dose and kVp varied from location to location, with the power index ranged between 2.7 and 3.5. The averaged dose measurements at both nipples, which were about 0.6 cm outside the prescribed scan region, ranged from 23 to 27 mGy at the left nipple, and varied from 3 to 20 mGy at the right nipple over the three scan protocols. Large fluctuations over repeated scans were also observed, as a combined result of helical scans of large pitch (1.375) and small active areas of the skin dosimeters. In addition, the averaged skin dose fell off drastically with the distance to the nearest boundary of the scanned region. Conclusions: This study revealed the complexity of CT dose fluctuation and variation with a human cadaver.

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Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms

Cited by 49 publications

References 18 publications

Implications of Patient Centring on Organ Dose in Computed Tomography

Implications of Patient Centring on Organ Dose in Computed Tomography

Numerical Analysis of Organ Doses Delivered During Computed Tomography Examinations Using Japanese Adult Phantoms with the WAZA-ARI Dosimetry System

In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans

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