Program Information
New Ionization Chamber Dosimetry of Absorbed Dose to Water in Diagnostic KV X-Ray Beams
F Araki1*, T Ohno2 , (1) Kumamoto University, Kumamoto, Japan, (2) Kumamota University, Kumamoto, Japan
Presentations
MO-FG-CAMPUS-IeP1-5 (Monday, August 1, 2016) 4:30 PM - 5:00 PM Room: ePoster Theater
Purpose: To develop new ionization chamber dosimetry of absorbed dose to water in diagnostic kV x-ray beams, by using a beam quality conversion factor, kQ, for Co-60 to kV x-ray and an ionization conversion factor for a water-substitute plastic phantom.
Methods: kQ was calculated for aluminum half value-layers (Al-HVLs) of 1.5 mm to 8 mm which were generated by kV x-ray beams of 50 to 120 kVp. Twenty-two energy spectra for ten effective energies (Eeff) were calculated by a SpecCalc program. Depth doses in water were calculated at 5 x 5 to 30 x 30 cm² fields. Output factors were also obtained from the dose ratio for a 10 x 10 cm² field. kQ was obtained for a PTW30013 Former ion chamber. In addition, an ionization conversion factor of the PWDT phantom to water was calculated. All calculations were performed with EGSnrc/cavity code and egs_chamber codes.
Results: The x-ray beam energies for 1.5 mm to 8 mm Al-HVLs ranged in Eeff of 25.7 to 54.3 keV. kQ for 1.5 mm to 8 mm Al-HVLs were 0.831 to 0.897, at 1 and 2 cm depths for a 10 x 10 cm2 field. Similarly, output factors for 5 x 5 to 30 x 30 cm² fields were 0.937 to 1.033 for 25.7 keV and 0.857 to 1.168 for 54.3 keV. The depth dose in a PWDT phantom decreased up to 5% compared to that in water at depth of ten percent of maximum dose for 1.5 mm Al-HVL. The ionization ratios of water/PWDT phantoms for the PTW30013 chamber were 1.012 to 1.007 for 1.5 mm to 8 mm Al-HVLs at 1 cm depth.
Conclusion: It became possible to directly measure the absorbed dose to water with the ionization chamber in diagnostic kV x-ray beams, by using kQ and the PWDT phantom.
Contact Email: