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Med Phys. 2011 Mar;38(3):1627-34.

A novel lateral disequilibrium inclusive (LDI) pencil-beam based dose calculation algorithm: evaluation in inhomogeneous phantoms and comparison with Monte Carlo calculations.

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Department of Radiation Oncology, Mannheim Medical Centre, University of Heidelberg, 68167 Mannheim, Germany.



Pencil-beam (PB) based dose calculation for treatment planning is limited by inaccuracies in regions of tissue inhomogeneities, particularly in situations with lateral electron disequilibrium as is present at tissue/lung interfaces. To overcome these limitations, a new "lateral disequilibrium inclusive" (LDI) PB based calculation algorithm was introduced. In this study, the authors evaluated the accuracy of the new model by film and ionization chamber measurements and Monte Carlo simulations.


To validate the performance of the new LDI algorithm implemented in Corvus 09, eight test plans were generated on inhomogeneous thorax and pelvis phantoms. In addition, three plans were calculated with a simple effective path length (EPL) algorithm on the inhomogeneous thorax phantom. To simulate homogeneous tissues, four test plans were evaluated in homogeneous phantoms (homogeneous dose calculation).


The mean pixel pass rates and standard deviations of the gamma 4%/4 mm test for the film measurements were (96 +/- 3)% for the plans calculated with LDI, (70 +/- 5)% for the plans calculated with EPL, and (99 +/- 1)% for the homogeneous plans. Ionization chamber measurements and Monte Carlo simulations confirmed the high accuracy of the new algorithm (dose deviations < or = 4%; gamma 3%/3 mm > or = 96%).


LDI represents an accurate and fast dose calculation algorithm for treatment planning.

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