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Evaluation of Eclipse Electron Monte Carlo Dose Calculation Algorithm in Inhomogeneous Medium

G Pokharel

G Pokharel1*, S Rana2, (1) USMD Cancer Centers, Fort Myers, FL, (2) ProCure Treatment Centers, Oklahoma City, OK

SU-E-T-534 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the accuracy of Eclipse electron Monte Carlo (eMC) dose calculation algorithm in inhomogeneous medium.

Methods: The PTW inhomogeneity phantom consisting of base plate and inserts of different inhomogeneous materials (bone, tissue and lung) was used in this study. The base plate can be placed on a slab with a hole drilled for PTW diode (TN600017). With the combination of these inhomogeneous inserts, solid water slabs and bolus, a number of inhomogeneous geometries were created and CT scanned with the diode in place. The image set was then imported to Eclipse TPS (version 11.1) workstation. Several treatment plans were created for the cone size of 10x10 with the prescription dose of 200cGy at the center of the diode. All of the eMC dose calculations were performed at grid size of 2 mm and accuracy level of 2%. Measurements with diode were then carried out in Varian TrueBeam machine. The bone inhomogeneity measurements were only carried out for 15, 18 and 22Mev electron energies.

Results: The measured doses agreed well within 2% with eMC calculated doses for 9, 18 and 22Mev for all the inhomogeneities considered. For 6Mev, measured dose for tissue only was 4.28% higher whereas 4.02% lower for lung inhomogeneity. In case of 12Mev, measured doses were 2.83% and 4.61% lower compared to calculated doses for tissue only and lung inhomogeneity. In case of 15Mev, measured doses were 1.47%, 4.61% and 10.5% lower compared to eMC for tissue only, lung and bone inhomogeneity.

Conclusion: This work indicates that eMC algorithm in Eclipse provides acceptable agreement with measured data for most of the clinical cases involving inhomogeneities. However, variation as high as 10.5%, was observed for 15Mev in bone inhomogeneity case. So, care must be taken if eMC is used to calculate dose for15Mev involving bone inhomogeneity.

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