title: Clinical reference dosimetry: comparison between AAPM TG-21 and TG-51 protocols.
abstract: We compare the results of absorbed dose determined at reference conditions according to the AAPM TG-21 dose calibration protocol and the new AAPM TG-51 protocol. The AAPM TG-21 protocol for absorbed dose calibration is based on ionization chambers having exposure calibration factors for 60Co gamma rays, N(x). The new AAPM TG-51 dosimetry protocol for absorbed dose calibration is based on ionization chambers having 60Co absorbed dose-to-water calibration factor, N60Co(D,w). This study shows that the dose changes are within 1% for a cobalt beam, 0.5% for photon energies of 6 and 18 MV, and 2%-3% for electron beams with energies of 6 to 20 MeV. The chamber primary calibration factors, Nx and N60Co(D,w), are traceable to the Canadian primary standards laboratory (NRCC). We also present estimated dose changes between the two protocols when calibration factors are traceable to NIST in the United States.
authors.affiliation: Fraser Valley Cancer Centre, British Columbia Cancer Agency, Surrey, Canada. gding@bccancer.bc.ca
authors.forename: G X
authors.initials: GX
authors.lastname: Ding
authors.forename: J E
authors.initials: JE
authors.lastname: Cygler
authors.forename: C B
authors.initials: CB
authors.lastname: Kwok
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002985:Clinical Protocols; D003037:Cobalt Radioisotopes; D004583:Electrons; D005720:Gamma Rays; D006801:Humans; D017785:Photons; D011874:Radiometry / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D011882:Radiotherapy, High-Energy; D012015:Reference Standards; D012958:Societies, Scientific; D014481:United States; D014867:Water
chemical_list: D003037:Cobalt Radioisotopes; D014867:Water