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MO‐FG‐CAMPUS‐IeP1‐05: New Ionization Chamber Dosimetry of Absorbed Dose to Water in Diagnostic KV X‐Ray Beams
Author(s) -
Araki F,
Ohno T
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957337
Subject(s) - ionization chamber , dosimetry , imaging phantom , absorbed dose , ionization , percentage depth dose curve , beam (structure) , atomic physics , water equivalent , materials science , physics , x ray , optics , nuclear medicine , ion , medicine , quantum mechanics , meteorology , snow
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 × 5 to 30 × 30 cm 2 fields. Output factors were also obtained from the dose ratio for a 10 × 10 cm 2 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 × 10 cm2 field. Similarly, output factors for 5 × 5 to 30 × 30 cm 2 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.