Calibration of high-energy photon and electron beams for radiotherapy using AAPM 1983 and IAEA 1987 dosimetry protocols.

To follow up on the theoretical comparison of the IAEA 1987 and AAPM 1983 protocols for dosimetry calibration of high-energy photons and electrons [Med Phys. 18, 26-35 (1991)], results of a set of dosimetric measurements made with a Farmer type PTW and Capintec ionization chambers in solid water, PMMA, and polystyrene phantoms and exposed to a 4 MV photon beam from a Varian Clinac 4S at Yale, a 10 MV photon beam and 6 and 15 MeV electron beams from a Varian Clinac 1800 at Phelps Radiation Center, University of Connecticut, and a 25 MV photon beam from a Sagittaire at Yale, are presented. Because different methods are used for the determination of electron beam energies, the values of mean electron energy determined by the two protocols are different by up to 8%. However, for dose inter-comparison, the overall agreement between the two protocols is within 1% in most cases, with a maximum discrepancy of 3.3% in one case. For photons, the IAEA results are smaller than the AAPM results by 0.7% on the average, while maximum discrepancies are in the range of -0.4%-(-1%). In the case of 15 MeV electrons, the discrepancies between the two protocols are found to be in the range of -0.1%-1% and have an average value of 0.5%. In contrast to the above, a large discrepancy is observed between the two protocols for 6 MeV electrons. Depending upon the choice of phantom and ion chamber, this discrepancy is found to be in the range of -0.1%-(-3.3%).(ABSTRACT TRUNCATED AT 250 WORDS)