title: The feasibility of patient size-corrected, scanner-independent organ dose estimates for abdominal CT exams.
abstract: OBJECTIVE
  A recent work has demonstrated the feasibility of estimating the dose to individual organs from multidetector CT exams using patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients. However, the previous study only investigated organ dose to a single patient model from a full-body helical CT scan. The purpose of this work was to extend the validity of this dose estimation technique to patients of any size undergoing a common clinical exam. This was done by determining the influence of patient size on organ dose conversion coefficients generated for typical abdominal CT exams.
  
  
  METHODS
  Monte Carlo simulations of abdominal exams were performed using models of 64-slice MDCT scanners from each of the four major manufacturers to obtain dose to radiosensitive organs for eight patient models of varying size, age, and gender. The scanner-specific organ doses were normalized by corresponding CTDIvol values and averaged across scanners to obtain scanner-independent CTDIvol-to-organ-dose conversion coefficients for each patient model. In order to obtain a metric for patient size, the outer perimeter of each patient was measured at the central slice of the abdominal scan region. Then, the relationship between CTDIvol-to-organ-dose conversion coefficients and patient perimeter was investigated for organs that were directly irradiated by the abdominal scan. These included organs that were either completely ("fully irradiated") or partly ("partially irradiated") contained within the abdominal exam region. Finally, dose to organs that were not at all contained within the scan region ("nonirradiated") were compared to the doses delivered to fully irradiated organs.
  
  
  RESULTS
  CTDIvol-to-organ-dose conversion coefficients for fully irradiated abdominal organs had a strong exponential correlation with patient perimeter. Conversely, partially irradiated organs did not have a strong dependence on patient perimeter. In almost all cases, the doses delivered to nonirradiated organs were less than 5%, on average across patient models, of the mean dose of the fully irradiated organs.
  
  
  CONCLUSIONS
  This work demonstrates the feasibility of calculating patient-specific, scanner-independent CTDIvol-to-organ-dose conversion coefficients for fully irradiated organs in patients undergoing typical abdominal CT exams. A method to calculate patient-specific, scanner-specific, and exam-specific organ dose estimates that requires only knowledge of the CTDIvol for the scan protocol and the patient's perimeter is thus possible. This method will have to be extended in future studies to include organs that are partially irradiated. Finally, it was shown that, in most cases, the doses to nonirradiated organs were small compared to the dose to fully irradiated organs.
authors: Department of Biomedical Physics and Department of Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024, USA. aturner@mednet.ucla.edu
authors: Adam C
authors: AC
authors: Turner
authors: Di
authors: D
authors: Zhang
authors: Maryam
authors: M
authors: Khatonabadi
authors: Maria
authors: M
authors: Zankl
authors: John J
authors: JJ
authors: DeMarco
authors: Chris H
authors: CH
authors: Cagnon
authors: Dianna D
authors: DD
authors: Cody
authors: Donna M
authors: DM
authors: Stevens
authors: Cynthia H
authors: CH
authors: McCollough
authors: Michael F
authors: MF
authors: McNitt-Gray
mesh_terms: D000328:Adult; D049628:Body Size; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D057285:Precision Medicine; D011829:Radiation Dosage; D011860:Radiography, Abdominal / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*