Comparison of the recommendations of the AAPM TG‐51 and TG‐51 addendum reference dosimetry protocols

This work quantified differences between recommendations of the TG‐51 and TG‐51 addendum reference dosimetry protocols. Reference dosimetry was performed for flattened photon beams with nominal energies of 6, 10, 15, and 23 MV, as well as flattening‐filter free (FFF) beam energies of 6 and 10 MV, following the recommendations of both the TG‐51 and TG‐51 addendum protocols using both a Farmer(®) ionization chamber and a scanning ionization chamber with calibration coefficients traceable to absorbed dose‐to‐water (D (w)) standards. Differences in D (w) determined by the two protocols were 0.1%–0.3% for beam energies with a flattening filter, and up to 0.2% and 0.8% for FFF beams measured with the scanning and Farmer(®) ionization chambers, respectively, due to k(Q) determination, volume‐averaging correction, and collimator jaw setting. Combined uncertainty was between 0.91% and 1.2% (k = 1), varying by protocol and detector.