title: In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Da
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Atul
authors.initials: A
authors.lastname: Padole
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Xinhua
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Sarabjeet
authors.initials: S
authors.lastname: Singh
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Ranish Deedar Ali
authors.initials: RD
authors.lastname: Khawaja
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Diego
authors.initials: D
authors.lastname: Lira
authors.affiliation: Nuclear Engineering Program, Rensselaer Polytechnic Institute, Troy, New York 12180.
authors.forename: Tianyu
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Jim Q
authors.initials: JQ
authors.lastname: Shi
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Alexi
authors.initials: A
authors.lastname: Otrakji
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Mannudeep K
authors.initials: MK
authors.lastname: Kalra
authors.affiliation: Nuclear Engineering Program, Rensselaer Polytechnic Institute, Troy, New York 12180.
authors.forename: X George
authors.initials: XG
authors.lastname: Xu
authors.affiliation: Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Bob
authors.initials: B
authors.lastname: Liu
mesh_terms: D000369:Aged, 80 and over; D066264:Datasets as Topic; D006801:Humans; D008297:Male; D010388:Pelvis / Q000000981:diagnostic imaging*; D011860:Radiography, Abdominal / Q000379:methods*; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*