Comparison of Megavoltage Electron Dosimetry Beams in Radiation Therapy Using Different Protocols

Background: International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) have introduced new protocols for the dosimetry of megavoltage electron and photon beams, increasing them to more than five protocols at the beginning of the new decade. Selecting a protocol by medical physicists and acquiring skills for using reference conditions and recommended formulation by each protocol necessitates the recognition of various dosimetry protocols. This study aimed to compare the protocols TRS-277, TRS-381, and TRS-398 of IAEA for megavoltage electron beams used in radiation therapy. Methods: The comparison of TRS-398 with other protocols was done as follows: 1. Measurement and estimation of the absorbed dose of a 6 MeV Neptun 10 linear accelerator through an ionization chamber with parallel NACP plates in water phantom and acrylic. 2- Measurement of the absorbed dose in a 17 MeV Saturn 20 linear accelerator through an ionization chamber with parallel NACP plates in a water phantom. Results: The results indicated that the differences observed between the protocols compared to protocol TRS-398 ranged between -4.9% and 0.2%; the highest difference was related to the 17 MeV electron beam using protocol TRS-277. Conclusion: According to the results, the considerable difference observed in 17 MeV electrons was related to TRS-277 and TRS388 protocols. Given that the calibration ratio of the absorbed dose in the air is used in protocol TRS-277, the difference obtained was related to the application of secondary calibration used in this study.