SU‐E‐T‐204: Comparison of Absorbed‐Dose to Water in High‐Energy Photon Beams Based On Addendum AAPM TG‐51, IAEA TRS‐398, and JSMP 12

Purpose: Several clinical reference dosimetry protocols for absorbed-dose to water have recently been published: The American Association of Physicists in Medicine (AAPM) published an Addendum to the AAPM’s TG-51 (Addendum TG-51) in April 2014, and the Japan Society of Medical Physics (JSMP) published the Japan Society of Medical Physics 12 (JSMP12), a clinical reference dosimetry protocol, in September 2012. This investigation compared and evaluated the absorbed-dose to water of high-energy photon beams according to Addendum TG-51, International Atomic Energy Agency Technical Report Series No. 398 (TRS-398), and JSMP12. Methods: Differences in the respective beam quality conversion factors with Addendum TG-51, TRS-398, and JSMP12 were analyzed and the absorbed-dose to water using 6- and 10-MV photon beams was measured according to the protocols recommended in Addendum TG-51, TRS-398, and JSMP12. The measurements were conducted using two Farmer-type ionization chambers, Exradin A12 and PTW 30013. Results: The beam quality conversion factors for both the 6- and 10-MV photon beams with Addendum TG-51 were within 0.6%, in agreement with the beam quality conversion factors with TRS-398 and JSMP12. The Exradin A12 provided an absorbed-dose to water ratio from 1.003 to 1.006 with TRS-398 / Addendum TG-51 and from 1.004 to 1.005 with JSMP 12 / Addendum TG-51, whereas the PTW 30013 provided a ratio of 1.001 with TRS-398 / Addendum TG-51 and a range from 0.997 to 0.999 with JSMP 12 / Addendum TG-51. Conclusion: Despite differences in the beam quality conversion factor, no major differences were seen in the absorbed-dose to water with Addendum TG-51, TRS-398, and JSMP12. However, Addendum TG-51 provides the most recent data for beam quality conversion factors based on Monte Carlo simulation and greater detail for the measurement protocol. Therefore, the absorbed-dose to water measured with Addendum TG-51 is an estimate with less uncertainty.