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Effect of Dose Calculation Grid Size On Proton Dose Calculation


L Zhao

L Zhao1*, (1) Procure Proton Therapy Center in Oklahoma City, OK

SU-E-T-579 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
The effect of dose calculation grid size for highly conformal proton planning is evaluated for the first time. Our goal is to find the optimal dose calculation grid size for different cases to increase the treatment planning efficiency while maintaining the dose calculation accuracy within clinical tolerance.

Methods:
Four clinical head& neck, prostate, lung and CSI cases are studied and calculated at three different calculation grid sizes (1 mm, 3 mm, 5 mm). To further understand the dose accuracy, a phantom simulating lung treatment with small fields and large fields is measured with EBT films. The measured results are compared with the calculated results in the form of point dose and dose profiles in regions of low and high dose gradients, dosimetric parameters, DVHs, and gamma analysis. The calculation time difference is investigated against the grid resolution as well.

Results:
There is no significant difference in pass rate of gamma analysis with 3 mm/3% acceptance criteria. The grid size effect is observed more clearly for small field size in inhomogeneous media. When comparing varying calculation grid sizes and measurements, the variation of the dose difference histogram is insignificant, but a local effect is observed in the dose difference map and point dose comparisons.

Conclusion:
The effect of calculation grid size on proton dose calculation can be clinically significant, depending on the disease sites, patient anatomy and treatment target volume and organ at risk. Small grid sizes (1 or 2mm) are necessary for small structures in and near inhomogeneous geometries such as in the head and neck regions.

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