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A Beam Model Accuracy Comparison of Small, Medium, and Large Segments for IMRT Treatment Plans

K Fischer*, J Rembish, S Stathakis, UT Health San Antonio, San Antonio, TX

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To compare the accuracy of beam models as complexity of treatment increases and determine if a specific treatment system’s model results in a better treatment for complex plans.

Methods: A control case was developed in Pinnacle Treatment Planning System (TPS) that consisted of seven 10cm x 10cm fields, labeled A-G. Each field delivered 20 MUs, but differed in the number of control points used. The complexity of the fields increased from 1 control point (A) to 40 control points (G). The fields created in Pinnacle TPS were then exported to Monaco TPS and recalculated. The seven beams were delivered at one angle with an Elekta VersaHD using an energy of 6 MV. The beams were measured using the PTW Octavius4D system with the 1500 2D detector array. The measured beams were then compared with the planned treatment using gamma analysis in Verisoft. The gamma analysis was performed using 3%/3mm, 3%/2mm, 3%/1mm, 2%/2mm, and 1%/1mm dose difference and distance-to-agreement, respectively.

Results: When analyzing the Pinnacle plans using 3%/2mm dose difference and distance-to-agreement the gamma results range from 98.7% (A) to 52.7% (G). The average pixel gamma value increased from 0.318 (A) to 1.337 (G). When analyzing the Monaco plan the gamma results range from 98.9% (A) to 50.1% (G). The average pixel gamma value increased from 0.365 (A) to 1.904 (G).

Conclusion: The results indicate that as complexity increases for treatments, the gamma analysis decreases while the average pixel gamma value increases. It may be necessary to evaluate improvements to Treatment Planning Systems as more stringent criteria are used to evaluate complex treatment fields to ensure better agreement between planned and delivered dose distributions.

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