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

Abstract

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.