Representation and illustration of the initial parameters in GATE 8.1 monte carlo simulation of an Elekta Versa-HD linear accelerator

Determination and validation of the initial beam parameters of Elekta Agility collimator head by Monte Carlo simulations

The availability of geometrical, physical, and initial beam parameters for Monte Carlo (MC) simulations of the Elekta Agility collimator head has become very difficult due to the proprietary nature of this data. This study presents strategies to independently determine the geometrical and physical properties of the components and initial beam parameters of the Agility collimator head for full beam simulations and postulates a benchmarking process using the EGSnrc MC toolkit. Target material of W (90%) and Re (10%) of 0.09 cm thickness, flattening filter of 1.77 cm thick stainless steel placed on 0.5 cm Al disc, and primary and secondary collimators of Tungsten alloy have been found to best fit the Agility head. The initial beam energy of 6.0 MeV with a radial distribution given as full-width half maxima (FWHM) of 0.301 cm (crossline) × 0.201 cm (inline) for 6 MV beam with a mean angular spread of 1.34° has been found best fitting the model. Variations of 0.29% and 0.59% have been noted in the measured and calculated values of TPR_20,10 and D₁₀ respectively. More than 90% dose points for all simulations passed the 2D gamma criteria of 3% DD, 3 mm DTA. This MC model of the Agility head can be used for dose calculation and validation of advanced treatment techniques.

Determination of dose distributions by monte-carlo simulation of 6 MV photon beam of varian vitalbeam accelerator using geant4 multithreaded code

Background:

Accuracy of dose delivery in radiation therapy is a primary requirement for effective cancer treatment. In practice, dose delivery accuracy of ±5% is desired. To achieve this accuracy level, an accurate method for calculating the dose distributions in the tumor volume is required. Monte-Carlo method is one of the methods considered to be the most accurate for calculating dose distributions.

Materials and Methods:

G4 linac-MT code was used to simulate a 6 MV photon beam. The initial electron beam parameters were tuned to validate the beam modeling from depth doses and beam profile. The dose distributions measured in water phantom were compared to the calculated dose distributions based on gamma index criterion.

Results:

The beam tuning showed the initial electron energy, sigma and full width at half maximum of 6.2 MeV, 0.8 MeV, and 1.18 mm, respectively, best match the measured dose distributions. The gamma index tests showed the calculated depth doses and beam profile were generally comparable with measurements, passing the standard acceptance criterion of 2%/2 mm. The simulated photon beam was justified by the index of beam quality, which showed excellent agreement with measured doses with a discrepancy of 0.1%.

Conclusion:

The observed agreement confirm the accuracy of the simulated 6 MV photon beam. It can therefore be used as radiation source for calculating dose distributions and further investigations aimed at improving dose delivery and planning in cancer patients.