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Validation of Photon Dose Calculation Using Mobius3D System Compared to AAA and Acuros XB Systems

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L Majithia

L Majithia*, D DiCostanzo, M Weldon, N Gupta, Y Rong, Ohio State Univ, Columbus, OH

SU-E-T-564 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To study the Collapsed Cone Convolution/Superposition algorithm in Mobius 3D system for dose calculations in comparison to Acuros XB and AAA dose calculation algorithms in Eclipse treatment planning system.

Methods:
Dose modeling or correction at density heterogeneity (lung/tissue or bone/tissue interfaces) remains an area of maximum discord amongst treatment planning systems. Thus, four phantoms were constructed and CT scanned with both horizontal and vertical density heterogeneity interfaces. Treatment plans were created with varying field sizes (3x3 cm², 5x5 cm², and 10x10 cm²) and energies (6FFF, 6MV, and 15 MV). All plans were created in Eclipse TPS with one single AP field, 100 cm SSD, 1 mm grid size for improved resolution, and 200 MU. Plans were calculated with AAA and Acuros XB algorithms and exported to Mobius3D for recalculation and comparison. Percent depth dose (PDD) and horizontal profiles at multiple depths through density heterogeneity interfaces were compared and analyzed. RPC Lung phantom was also used for complex plan (3DCRT and IMRT) dose comparisons.

Results:
Examination of PDD and horizontal dose profiles were reported graphically and numerically. Highest conformality was noted between AcurosXB and Mobius3D in homogenous sites. CCC in Mobius3D generally matches closer with AcurosXB, especially for large field sizes, compared to AAA. In PDDs, Mobius3D tends to under-predict dose compared to AcurosXB at the tissue-to-water interface up to 3%, while over-predicting dose in and beyond the lung-to-tissue interface compared to AcurosXB up to 7%. In 10x10 profiles with vertical heterogeneity interface, Mobius3D agrees with AcurosXB within 3%/3mm for 6MV and 15MV, but higher difference was seen for 6X-FFF.

Conclusion:
The recently released Mobius3D program offers physicist and physician ease in evaluation, rapid plan review, and dose second check to TPS calculations. Future research directions include confirmatory clinical dose calculations and additional evaluation with patient geometry.

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