The purpose of this work is to investigate the consistency of determining
Nppgasand
NppDby using three independent calibration methods from the AAPM TG 39 and IAEA TRS 381 protocols: 1) calibration with a high-energy electron beam in a phantom; 2)in-phantom calibration in a
60Co beam; and 3) in-air calibration in a
60Co beam. The plane-parallel chamber considered was the PTW-Markus and the comparisons were made against a calibrated PTW cylindrical Farmer-type chamber 30001. The phantom material used for the electron beam and
60Co in-phantom methods was a solid water phantom (RW3). For the electron beam method, the nominal energies were 18 and 21MeV. An acrylic buildup of 0.5 g/cm2 thickness was used for the
60Co in-air method. For each method,
Nppgasand
NppD were obtained for the plane-parallel chamber as proposed by the AAPM TG 39 and IAEA TRS 381 protocols. The absorbed doses were measured along the central axis at a distance of 100 cm (SSD =100 cm) with 10×10 cm
2field size at the depth of the maximum for each electron beam. The values of
Nppgasby the three independent calibration methods agreed to within±0.6%. This meant that any of the methods would give a fairly good value. Similar results were obtained for
NppD In. comparing the results for the electron beam method at energies of 18 and 21 MeV, the latter gave better agreement. The ratios of
Nppgasand
NppDfor the 159three methods were in agreement within 0.7%. The results for the absorbed dose intercomparison in the AAPM TG 39 and IAEA TRS 381 protocols showed that they agreed to within±0.7% which meant that any of the calibration methods and two different protocols would give an accurate result.
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