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Comparison of Electron Monte Carlo and Pencil-Beam Algorithms in Clinical Electron Beam Radiation Dosimetry

Z Liu

Z Liu*, I Hargrove, A Tazi, J Barrett, Watson Clinic, Lakeland, FL

MO-D-108-7 Monday 2:00PM - 3:50PM Room: 108

Purpose: Electron Monte Carlo (eMC) and Pencil-Beam (PB) algorithms are both used clinically for electron beam radiation dosimetry. The purpose of this study is to evaluate the two calculation algorithms with reference to the standard electron beam dosimetry parameters and isodose distributions in practical clinical applications.

Methods: eMC and PB algorithms were both commissioned in Eclipse treatment planning system. Standard radiation dosimetry parameters --including percent depth dose, beam profile width, and output factors--were calculated in homogeneous water phantom for various combinations of electron energy and cone applicators. The calculation results were compared with the measured data. The two algorithms were also compared in clinical situation. A phantom simulating chest wall and lung was created and used for dose calculation. A 9 MeV electron beam with a customized cutout on the 20x20 cone was used at fixed SSD of 100cm. The calculation setting for eMC was 1% precision, 1.5-mm grid, and strong Gaussian smoothing. For PB, 2.5mm grid was used for dose calculation.

Results: The difference between measured and calculated depths of R100, R90, R80, and R50 for both algorithms is less than 1mm for all combinations of energies and cone applicators. For the field width and output factors, eMC affords slightly better agreement with measurement than PB does. For practical phantom calculations with both surface irregularity and heterogeneity, eMC shows a more reasonable isodose distribution. Comparing to eMC, PB algorithm tends to overestimate the dose neighboring the air cavity and underestimate the dose past the air cavity in a water phantom. For surface irregularity, eMC and PB show similar results though.

Conclusion: eMC and PB algorithms are accurate in the calculation of standard electron dosimetry parameters. Both eMC and PB can handle the surface irregularity very well. eMC is superior to PB in terms of heterogeneity.

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