Monte Carlo study of electron dose distributions produced by the elekta precise linear accelerator

Abstract

Background

Monte Carlo simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation and has ability to reduce the uncertainty in the calculated dose to a few percent.

Aims

(1) To study the efficacy of the MCNP4C Monte Carlo code to simulate the dose distribution in a homogeneous medium produced by electron beams from the Elekta Precise linear accelerator. (2) To quantify the effect of introduction of various components to the simulated geometry for the above machine.

Materials/Methods

Full Monte Carlo simulation of the detailed geometry of the Precise treatment head for 8 and 15 MeV energies and 10×10 applicator was performed. Experimental depth dose and lateral profiles at 2cm depth were measured using a P-type diode detector with a 2.5 mm diameter. To quantify the effects of different parts of the treatment head, seven cases were simulated for a 15 MeV beam to reflect increasing levels of complexity, by step-wise introduction of beam divergence, primary and secondary scattering foils, secondary collimators, applicator, Mirror and Mylar screen.

Results

The discrepancy between measured and calculated data is within 2%/2 mm at both 8 and 15 MeV. In terms of the mean and most probable energies at the surface, the difference was <0.2 MeV for the majority of cases and the maximum deviation was no more than 0.3 MeV.

Conclusions

The results obtained with MCNP4C agree well with measured electron dose distributions. Inclusion of all the main components of the treatment head in the simulated geometry is necessary to avoid discrepancies of about 5% compared to measurements.