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Determination of the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams

      Highlights

      • The surface dose was determined from the air kerma and HVL measured by a semiconductor detector.
      • A semiconductor detector was calibrated using the air kerma measured by an ionization chamber.
      • The Monte Carlo method was used to obtain the ratio of surface dose (Dw,z = 0) to air kerma (Kair).
      • Dw,z = 0 /Kair determined with a semiconductor detector agreed with Monte Carlo-calculated values.

      Abstract

      Purpose

      To determine the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams.

      Methods

      An AGMS-DM+ semiconductor detector was calibrated in terms of air kerma measured with an ionization chamber. Air kerma was measured for 20 x-ray beams with tube voltages of 50–140 kVp and a half-value layer (HVL) of 2.2–9.7 mm Al for given quality index (QI) values of 0.4, 0.5, and 0.6, and converted to the surface dose. Finally, the air kerma and HVL measured by the AGMS-DM+ detector were expressed as a ratio of the surface dose for 10 × 10 and 20 × 20 cm2 fields. The ratio of both was represented as a function of HVL for the given QI values and verified by comparing it with that calculated using the Monte Carlo method.

      Results

      The air kerma calibration factor, CF, for the AGMS-DM+ detector ranged from 0.986 to 1.016 (0.9% in k = 1). The CF values were almost independent of the x-ray fluence spectra for the given QI values. The ratio of the surface dose to the air kerma determined by the PTW 30,013 chamber and the AGMS-DM+ detector was less than 1.8% for the values calculated using the Monte Carlo method, and showed a good correlation with the HVL for the given QI values.

      Conclusion

      It is possible to determine the surface dose of a water phantom from the air kerma and HVL measured by a semiconductor detector for given QI values.

      Keywords

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