Comparison of AAPM Addendum to TG ‐51, IAEA TRS ‐398, and JSMP 12: Calibration of photon beams in water

The American Association of Physicists in Medicine ( AAPM ) Working Group on TG ‐51 published an Addendum to the AAPM 's TG ‐51 protocol (Addendum to TG ‐51) in 2014, and the Japan Society of Medical Physics ( JSMP ) published a new dosimetry protocol JSMP 12 in 2012. In this study, we compared the absorbed dose to water determined at the reference depth for high‐energy photon beams following the recommendations given in AAPM TG ‐51 and the Addendum to TG ‐51, IAEA TRS ‐398, and JSMP 12. This study was performed using measurements with flattened photon beams with nominal energies of 6 and 10 MV . Three widely used ionization chambers with different compositions, Exradin A12, PTW 30013, and IBA FC 65‐P, were employed. Fully corrected charge readings obtained for the three chambers according to AAPM TG ‐51 and the Addendum to TG ‐51, which included the correction for the radiation beam profile ( P rp ), showed variations of 0.2% and 0.3% at 6 and 10 MV , respectively, from the readings corresponding to IAEA TRS ‐398 and JSMP 12. The values for the beam quality conversion factor k Q obtained according to the three protocols agreed within 0.5%; the only exception was a 0.6% difference between the results obtained at 10 MV for Exradin A12 according to IAEA TRS ‐398 and AAPM TG ‐51 and the Addendum to TG ‐51. Consequently, the values for the absorbed dose to water obtained for the three protocols agreed within 0.4%; the only exception was a 0.6% difference between the values obtained at 10 MV for PTW 30013 according to AAPM TG ‐51 and the Addendum to TG ‐51, and JSMP 12. While the difference in the absorbed dose to water determined by the three protocols depends on the k Q and P rp values, the absorbed dose to water obtained according to the three protocols agrees within the relative uncertainties for the three protocols.