Abstract
Purpose: To demonstrate the suitability of the use of alanine dosimeters as a supplement or alternative to TG51 as an acceptable secondary calibration method for high energy photons beams from a medical linear accelerator. Methods: Alanine dosimiters were irradiated at three radiation treatment facilities and compared to dose/mu determined by TG51 using ionization chambers calibrated at ADCL. The ionization chamber was positioned in a Scanditronix Wellhoffer water phantom with dimensions 42 cm × 36 cm × 36 cm and at a dept of 5.0 cm. The volume of the ionization chamber was 0.6 cc. A polystyrene holder containing two alanine dosimeters was placed at the same point. Each alanine dosimeter is cylindrical in shape with a diameter of 5 mm and a length of 3 mm (volume = 0.25 cc). Ten sets of alanine detectors (20) were irradiated to 20 Gy in sequential exposures. An independent ionization chamber was used to normalize the exposures for any variation in accelerator output for every measurement. For one beam energy the alanine detectors were returned to a national standards laboratory for conversion to dose based on the same primary standard used for ionization chambers. The remaining dosimeters was evaluated on a Bruker EMX EPR spectrometer at the Armed Forces Radiobiology Research Institute which is directly traceable to NIST based on calibrated alanine dosimeters. Results: The average normalized dose per mu for all data is within expected experimental uncertainty. The uncertainty of each measurement technique is believed to be approximately 2% and will be discussed in detail. Conclusion: Analysis of the intercomparison measurements establishes that the alanine dosimeters are a valid method to establish the dose per mu for a medical linear accelerator that is traceable to the primary standard at a national standards laboratory in the same manner as used in TG51.
Published Version
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