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Impact of Effective Target Spot Size and Beam Data Field Size Range On the Agreement Between Measured Small Field PDDs and Profiles and Those Predicted by Acuros Beam Model of Version 13

Y Wang*, X Wu , T Mutanga , G Zeng , M Nielsen , Trillium Health Partners/the Credit Valley Hospita, Mississauga, ON


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: An Acuros XB beam model focusing on small field for SRS/SBRT techniques had been created for 6XFFF beam in Eclipse version 11 and been found to agree well with the measurement. However, after upgrade to version 13, the predicted PDDs were found to deviate from the measured data by up to 1.5%. This work was to demonstrate the solutions to resume good agreement between the Acuros beam model to the measurement.

Methods: Multiple Acuros models were created with various combinations of effective target spot sizes and beamdata in different sized ranges,ie, PDDs and profiles from 2x2 to 40x40cm. The spot size X from 0 to 1.5 and Y from 0 to 1mm. The beam data of 2x2 was measured using a microDiamond, and the rest was from Varian representative data. The model predicted PDDs and profiles were compared to the measured.

Results: When beamdata of 2 to 15cm was used to build the model, as the spot size X setting increased from 1 to 1.5mm, the PDD agreement improved to 0.5-0.6% from 1-2%, but the profile agreement worsened at 1.5mm. When beamdata included large fields up to 40x40, PDD disagreement reduced to 0.6-0.7% with the spot size X set to 1mm.

Conclusion: Version upgrade of Acuros algorithm can result in significant dose disagreement, for example PDD differed by up to 1.5%. Both effective target spot size setting and field size range of the beamdata can individually impact the predicted PDDs and affect the agreement with the measurement. The combination of spot size x at 1mm and y at 0.5mm with the beam data ranging from 3 to 40cm were found to have the best agreement in version 13.


Small Fields, Dose


TH- External beam- photons: dose computation engines- deterministic

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