Preliminary study of Varian Halcyon linear accelerator machine performance with 6 MV FFF photon beam

Abstract

A new development of a linear accelerator machine has been installed in Indonesia for the first time. There is no dosimetric protocol specifically discussing the measurement of absorbed dose to water in the Halcyon linac. But, few global dosimetric protocols determine the measurement of absorbed dose for linac machine which at the same substance. This paper describes the measurement of the dosimetry parameter for a 6 MV flattening filter-free (FFF) photon beam produced from a new model Varian Halcyon linac using IAEA TRS No. 483 protocols. The measurement data presented in this paper were primary data obtained after the machine was installed at the hospital and secondary data from Varian bunker before the machine was sent to Indonesia. Measurement has been performed using 0.016 cm3 model Pinpoint 3D and 0.6 cm3 model TW30013 ionization chambers. Measurement of percentage depth dose and absorbed dose to water calculation was based on IAEA TRS No. 483. The measurement of percentage depth dose was done also using 1 mm lead foil (Pb). The result obtained shows that the percentage dose at maximum depth, Dmax was in a good agreement with the manufacture specification with deviation 0.3 %, while the absorbed dose to water rate for the machine-specific reference field of the Varian Halcyon was in a good agreement within ±0.05 % against 1 cGy = 1 MU after calibration. The measurement of the absorbed dose rate to water can be done using IAEA TRS No. 483. The determination of the value of the radiation quality factor (kQ) of the photon beam using two methods from the IAEA dosimetry protocol TRS-483 (TPR20,10) and TRS-483 %dd(10,10))x get a good match.