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A Quantitative Metric Analysis Tool for Region-Specific Beam Modeling

T Roth1*, N Nguyen2 , R Rodgers3 , M Belley1 , (1) Alpert Medical School of Brown University, Providence, RI, (2) Yale New Haven Hospital, Cromwell, CT, (3) Vanderbilt University Medical Center, Nashville, TN


(Sunday, 7/29/2018) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 4

Purpose: Develop an aggregate method using gamma analysis to identify beam model parameters requiring adjustment to improve agreement between measured and computed distributions.

Methods: A 1-D gamma analysis tool was developed to compare measured and computed scans exported from RayStation to summarize agreement per user-defined criteria. Users may dynamically display the passing criteria across any field size for Percent Depth Dose (PDD) curves and/or depths for profiles. PDDs were analyzed in two regions (build-up and fall-off) and profiles in three (infield, penumbra, and out-of-field). Due to the efficiency of this process, succinctness of data presentation, as well as information provided regarding regional failure, appropriate beam model parameters that required adjustment were quickly determined.

Results: Pivot tables allowed for a condensed comparison of over two hundred (measured and computed) scans into five tables per photon energy. The following metrics were attained: Greater than 95% pass rate criteria at a 1-D gamma of 0.5%/1mm for PDDs in the fall-off region, greater than 95% pass rate for the in-field region of the profiles at 1%/1mm, the penumbra region exceeded 95% pass rate at 2%/2mm, and the out-of-field region exceeded 95% pass rate at 3%/3mm. No parameters were adjusted per validation measurements.

Conclusion: These metrics served as a benchmark during beam modeling as well as validation when matching beam models across machines. The pivot tables displaying the pass rates of the 1-D gamma index provide the physicist with an immediate and efficient way of detecting regions requiring improvement for PDDs and profiles. Provided one has knowledge of the beam model parameters affecting the regions of the PDDs and profiles, fine tuning of the parameters to improve fit can be achieved. Future work will aim to correlate passing criteria to diode-array measurements to support the 1-D gamma analysis method as a beam modeling endpoint.


Commissioning, Modeling, Treatment Planning


TH- External beam- photons: Development (new technology and techniques)

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