title: Comparison of measured and estimated maximum skin doses during CT fluoroscopy lung biopsies.
abstract: OBJECTIVE
  To measure patient-specific maximum skin dose (MSD) associated with CT fluoroscopy (CTF) lung biopsies and to compare measured MSD with the MSD estimated from phantom measurements, as well as with the CTDIvol of patient examinations.
  
  
  METHODS
  Data from 50 patients with lung lesions who underwent a CT fluoroscopy-guided biopsy were collected. The CT protocol consisted of a low-kilovoltage (80 kV) protocol used in combination with an algorithm for dose reduction to the radiology staff during the interventional procedure, HandCare (HC). MSD was assessed during each intervention using EBT2 gafchromic films positioned on patient skin. Lesion size, position, total fluoroscopy time, and patient-effective diameter were registered for each patient. Dose rates were also estimated at the surface of a normal-size anthropomorphic thorax phantom using a 10 cm pencil ionization chamber placed at every 30°, for a full rotation, with and without HC. Measured MSD was compared with MSD values estimated from the phantom measurements and with the cumulative CTDIvol of the procedure.
  
  
  RESULTS
  The median measured MSD was 141 mGy (range 38-410 mGy) while the median cumulative CTDIvol was 72 mGy (range 24-262 mGy). The ratio between the MSD estimated from phantom measurements and the measured MSD was 0.87 (range 0.12-4.1) on average. In 72% of cases the estimated MSD underestimated the measured MSD, while in 28% of the cases it overestimated it. The same trend was observed for the ratio of cumulative CTDIvol and measured MSD. No trend was observed as a function of patient size.
  
  
  CONCLUSIONS
  On average, estimated MSD from dose rate measurements on phantom as well as from CTDIvol of patient examinations underestimates the measured value of MSD. This can be attributed to deviations of the patient's body habitus from the standard phantom size and to patient positioning in the gantry during the procedure.
authors.affiliation: Department of Radiology, Leuven University Center of Medical Physics in Radiology, UZ Leuven, Herestraat 49, 3000 Leuven, Belgium and Imaging and Pathology Department, UZ Leuven, Herestraat 49, Box 7003 3000 Leuven, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Zanca
authors.affiliation: Department of Radiology, Leuven University Center of Medical Physics in Radiology, UZ Leuven, Herestraat 49, 3000 Leuven, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Jacobs
authors.affiliation: Department of Radiotherapy, UZ Leuven, Herestraat 49, 3000 Leuven, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Crijns
authors.affiliation: Imaging and Pathology Department, UZ Leuven, Herestraat 49, Box 7003 3000 Leuven, Belgium and Department of Radiology, UZ Leuven, Herestraat 49, 3000 Leuven, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: De Wever
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002648:Child; D002675:Child, Preschool; D005260:Female; D005471:Fluoroscopy / Q000009:adverse effects / Q000295:instrumentation; D006801:Humans; D061705:Image-Guided Biopsy / Q000009:adverse effects; D008168:Lung / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D012867:Skin / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed / Q000009:adverse effects / Q000295:instrumentation; D055815:Young Adult