Room: Exhibit Hall
Purpose: This study aims to establish a calibration method for the novel two dimensions (2D) detectors. These 2D parallel-plate ionization chambers (PPICs) could evaluate the relative dose distribution for on-line beam characteristics testing. And we would show the preliminary measurements and Monte Carlo simulations in Co-60, 30 MeV or therapeutic-energy protons fields.
Methods: A series of NRSL/INER homemade ionization chambers had been performed to determine Co-60 primary standards and the relevant international traceability had been accomplished through international comparisons. In response to the novel PPIC developed to map real-time 2D beam profiles, NE 2571 and PTW 31006 pinpoint ionization chambers were assigned with an automated system of the modified HIWIN electromagnetic force control platform to measure lateral dose distribution. For Monte Carlo simulations, the FLUKA, GEANT4 and MCNPX/MCNP6 codes were used for photon and proton transport calculations.
Results: Dose profile of Co-60 calibration field was measured by NE2571, PTW 31006, EBT film detectors and by 25 cm x 25 cm double layered strip PPIC. At 3 cm from the central axis, the strip PPIC output declines approximately 4% to 5% and that in the penumbra appears long tailing compared to other detectors. The accurate lateral scatter corrections should be considered. While 4.5 cm x 4.5 cm Pad PPIC was used to evaluate Co-60 and 30 MeV proton beams, the average beam quality conversion factor was 0.924 Â±4.6% by simulation. However, the therapeutic-energy proton beam could be characterized and predicted using FLUKA, GEANT4 and MCNPX/MCNP6 models, and the Bragg peak positions agreed within 0.01 mm (0.07%), 0.03 mm (0.17%) and 0.06 mm (0.18%) for 80, 160 and 230 MeV protons, respectively.
Conclusion: The calibration method and calibration system of 2D detector has been preliminarily studied and the details will need more experiments or Monte Carlo simulations for further evaluation.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Bureau of Standards, Metrology & Inspection M.O.E.A(R.O.C.), Atomic Energy Council(R.O.C.), Ministry of Economic Affairs, Taiwan(R.O.C.) and Chang Gung Medical Foundation. The authors express their sincerest appreciation to Prof. Kichiji Hatanaka team at RCNP, Osaka University, Japan, and to INER for providing the 60Co standard.