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Initial Single Institution Experience of the Testing of the IAEA-AAPM Code of Practice for Small Field Dosimetry

M Huq

M Huq*, Y Zhang , M Hwang , P Teo , K Fallon , c Ozhasoglu , S Jang , r Lalonde , University of Pittsburgh Cancer Institute, Pittsburgh, PA


SU-K-205-11 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 205

Purpose: The International Atomic Energy Agency (IAEA) and AAPM have jointly developed a new code of practice (CoP), TRS 483, for the dosimetry of small static photon fields. Procedures and data are provided for reference dosimetry in non-standard machine-specific reference (msr) fields. Consensus data on correction factors for use in conjunction with measured, detector-specific field output factors are also provided. This work presents the results of testing of the recommendations of this CoP.

Methods: Measurements were made for GammaKnife®, CyberKnife®, and TrueBeam™ STx machines. The recommendations of TRS483 were also followed for selection of detectors. Five ionization chambers were used for reference dosimetry measurements and seven diodes and two ionization chambers for field output factor measurements. For field output factor measurements, fourteen field sizes were measured for TrueBeam™ STx (0.5cm2 to 10cm2) and twelve for CyberKnife® (0.5cm to 6.0cm cones). Beam energies used for TrueBeam™ STx are: 6X, 6XFFF, 10X, 10XFFF. Where appropriate, results were compared with those obtained from the recommendations of TG51 addendum.

Results: For GammaKnife® reference dosimetry, measurements with different detectors agreed to within 0.7% of each other; TRS483 and TG51 addendum results agreed to within 0.4%. For CyberKnife® reference dosimetry, measurements with different detectors agree to within 0.9%; TRS483 and TG51 addendum results agree to within 0.3%; field output factor data agree to within 1.4% down to 0.75cm cone. The largest difference of 5% from the mean value of the output factor was observed for the 0.5cm cone. For TrueBeam™ STx msr dosimetry, the agreement among all chamber measurements for TRS483 dosimetry and between TRS483 and TG51 addendum are within 0.5% for all beam energies.

Conclusion: Initial testing of the implementation of TRS483 has not shown any major issues and confirms the consistency of its recommendations for relative and msr dosimetry in all three platforms investigated.

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