SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm

Authors


Abstract

Purpose:

To evaluate the accuracy of the Raystation electron Monte Carlo algorithm for bone and air inhomogeneity.

Methods:

A solid water phantom slab was drilled to contain two openings of 1.3cm diameter, 0.6cm apart. The center of the opening is at 1cm depth from the surface. Two Teflon rods of exact same diameter were inserted to investigate bone inhomogeneity. Slab is 2cm total in thickness and was placed on top of 10cm solid water. Plans were created in Raystation with clinical settings previously established for 6, 9, 12, 15 and 18MeV Elekta Infinity beams. Coronal profiles were extracted posteriorly to the inhomogeneity. EBT3 films were irradiated under the same conditions and analyzed using FilmQAPro using the red channel. Calibration films were used for all energies. Same plans and films were performed for a Varian accelerator with same energies and Eclipse Monte Carlo.

Results:

Air Inhomogeneities: For lower energies, Raystation- Film agreement is less than 1% for the regions of the air cavity. In the lateral interface border, Raystation underestimates dose by approximately 2%. Eclipse results are similar. For higher energies, Raystation-Film agreement remains the same across the air cavity and interface. Eclipse-Film difference increases with energy up to 5% for 18MeV, with Eclipse calculating higher doses than the film at the interface. Bone Inhomogeneities: For lower energies, Raystation underestimates the dose behind the bone up to 12%. Eclipse underestimates the dose in the same area up to 18%. For higher energies, the dose difference behind the bone decreases to 1% for Raystation and 3% for Eclipse. At the lateral interface, Raystation underestimates the dose by 2.2% and Eclipse underestimates the dose by 5%.

Conclusion:

Raystation prediction for air and bone is acceptable. Maximum deviations are consistent with algorithm limitations. Differences between calculations and measurement are closer for Raystation than for Eclipse.

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