Purpose: Monte Carlo methods for electron treatment planning systems were commercially implemented in the early 21st century. However, Monte Carlo’s known complexity due to inherent scattering from inhomogeneous densities within the treatment field as well as lengthy calculation times have made adoption in the clinic a more recent phenomenon. Heterogeneity of the dose distribution creates high dose regions (hot-spots) in the treated volume, which is a concern for electron therapy planning. The purpose of this study is to evaluate the planning algorithm results on an electron patient to determine an optimal plan for treatment.
Methods: Two commercial Monte Carlo treatment planning systems, Varian Eclipse and Raystation, are compared. Two electron plans for a patient’s left ear were created using a custom cutout with 12MeV selected for depth. One plan was generated with a 1mm margin on the body while a second plan used a 5mm margin on the body. This margin was generated to aid in setup reproducibility. Dot-decimal software, which contains a pencil beam algorithm was used to create the tissue equivalent material (bolus). Plans and bolus were exported to both Eclipse and Raystation to be calculated and evaluated.
Results: The isodose distributions are calculated by Eclipse, Raystation and dot-decimal. Hot-spots were found to be 109.5%, 115%, and 123.8% respectively. By changing the distance from 1mm to 5mm between skin-to-bolus the hot-spot isodoses were found to be 112%, 121%, and 137.6% respectively, which also revealed deeper penetration of the dose into the patient.
Conclusion: Although Eclipse and Raystation are using Monte Carlo algorithms for dose calculation, the hot-spots found from each of them were different by 5% for 1mm skin-to-bolus distance and 8% for 5mm skin-to-bolus distance. Interestingly, isodose distributions calculated by Raystation and dot-decimal were in agreement within 7-13% for different skin-to-bolus distance.
Not Applicable / None Entered.