title: Incident air kerma to absorbed organ dose conversion factors for breast and lung in PA thorax radiography: The effect of patient thickness and radiation quality.
abstract: OBJECTIVE
  Converting the measurable quantities to patient organ doses in projection radiography is usually based on a standard-sized patient model and a specific radiation quality, which are likely to differ from the real situation. Large inaccuracies can therefore be obtained in organ doses, because organ doses are dependent on the exposure parameters, exposure geometry and patient anatomy. In this study, the effect of radiation quality and patient thickness on the organ dose conversion factors were determined.
  
  
  METHODS
  In this study, the posterior-anterior projection radiograph of the thorax was selected in order to determine the effect of radiation quality (tube voltages of 70-130kV and total filtrations of 3mmAl to 4mmAl+0.2 mmCu) and patient thickness (anterior-posterior thicknesses of 19.4-30.8cm) on the breast and lung dose conversion factors. For this purpose, Monte Carlo simulation programs ImpactMC and PCXMC were used with computed tomography examination data of adult male and female patients and mathematical hermaphrodite phantoms, respectively.
  
  
  RESULTS
  Compared to the reference beam quality and patient thickness, the relative variation range in organ dose conversion factors was up to 74% for different radiation qualities and 122% for different patient thicknesses.
  
  
  CONCLUSIONS
  Conversion factors should only be used with comprehensive understanding of the exposure conditions, considering the exposure parameters, exposure geometry and patient anatomy they are valid for. This study demonstrates that patient thickness-specific and radiation quality-specific conversion factors are needed in projection radiography.
authors.affiliation: STUK - Radiation and Nuclear Safety Authority, Laippatie 4, P.O. Box 14, FI-00881 Helsinki, Finland; HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, PO Box 340, FI-00290 Helsinki, Finland; Department of Physics, University of Helsinki, P.O. Box 64, Helsinki FI-00014, Finland. Electronic address: anna.kelaranta@alumni.helsinki.fi.
authors.forename: A
authors.initials: A
authors.lastname: Kelaranta
authors.affiliation: STUK - Radiation and Nuclear Safety Authority, Laippatie 4, P.O. Box 14, FI-00881 Helsinki, Finland; Inselspital University Hospital, Freiburgstrasse 10, CH-3010 Bern, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Toroi
authors.affiliation: Inselspital University Hospital, Freiburgstrasse 10, CH-3010 Bern, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Vock
mesh_terms: D065638:Absorption, Radiation; D000328:Adult; D049628:Body Size; D001940:Breast / Q000000981:diagnostic imaging / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008297:Male; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D013902:Radiography, Thoracic / Q000379:methods*; D035501:Uncertainty
keywords: Conversion factor; Organ dose; Patient thickness; Radiation quality; Thorax X-ray examination