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J Med Phys. 2019 Oct-Dec;44(4):246-253. doi: 10.4103/jmp.JMP_60_19. Epub 2019 Dec 11.

Experimental Determination of Radial Dose Function and Anisotropy Function of GammaMed Plus 192Ir High-Dose-Rate Brachytherapy Source in a Bounded Water Phantom and its Comparison with egs_brachy Monte Carlo Simulation.

Author information

1
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India.
2
Department of Radiotherapy, Sri Shankara Cancer Hospital and Research Centre, Bengaluru, Karnataka, India.
3
Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, ON, Canada.

Abstract

Objective:

The aim of the present study is to experimentally measure the radial dose function g(r) and anisotropy function F(r,θ) of GammaMed Plus 192Ir high-dose-rate source in a bounded water phantom using thermoluminescent dosimeter (TLD) and film dosimetry and compare the obtained results with egs_brachy Monte Carlo (MC)-calculated values for the same geometry.

Materials and Methods:

The recently developed egs_brachy is a fast Electron Gamma Shower National Research Council of Canada MC application which is intended for brachytherapy applications. The dosimetric dataset recommended by Task Group 43 update (TG43U1) is calculated using egs_brachy for an unbounded phantom. Subsequently, radial dose function g(r) and anisotropy function F(r,θ) are measured experimentally in a bounded water phantom using TLD-100 and Gafchromic EBT2 film.

Results:

The TG43U1 dosimetric parameters were determined using the egs_brachy MC calculation and compared with published data which are found to be in good agreement within 2%. The experimentally measured g(r) and F(r,θ) and its egs_brachy MC code-calculated values for a bounded phantom geometry are found to be good in agreement within the acceptable experimental uncertainties of 3%.

Conclusion:

Our experimental phantom size represents the average patient width of 30 cm; hence, results are closer to scattering conditions in clinical situations. The experimentally measured g(r) and F(r,θ) and egs_brachy MC calculations for bounded geometry are well in agreement within experimental uncertainties. Further, the confidence level of our comparative study is enhanced by validating the egs_brachy MC code for the unbounded phantom with respect to consensus data.

KEYWORDS:

192 Ir source; Monte Carlo; anisotropy function; radial dose function

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