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Dosimetric Verification of Elekta Agility in Brainlab IPlan RT Dose

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M Florijn

MA Florijn*, IK Russel, J van Egmond, RGJ Wiggenraad, JPC van Santvoort, AL Petoukhova. Haaglanden Medical Centre, The Hague, The Netherlands


SU-I-GPD-T-581 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The study aim was to verify the accuracy of Pencil Beam (PB) and Monte Carlo (MC) dose calculations in iPlan RT Dose (v4.5.4, Brainlab) for the Elekta Agility, with emphasis on small fields.

Methods: Depth dose curves, dose profiles and output factors were calculated with PB and MC in iPlan and compared to water phantom measurements. Additionally the dose distribution of three clinical plans (dynamic conformal arcs) was measured with Gafchromic EBT3 films, inside the IMRT verification phantom, calibrated and analyzed using DoseLab software. PTVs ranged from 0.077 to 7.44cm³. Measurements were performed with 6MV photon beams on an Elekta Versa HD linac with Agility MLC. PB is calculated with 2mm spatial resolution and MC with 2mm spatial resolution and 1% variance. The measurements were evaluated with gamma criteria 2%/1mm.

Results: The PDDs/profiles at various depths calculated with PB and MC both agree very well for the 100x100mm² field. MC performs better on 6x6mm² and 10x10mm² compared to PB calculation. For 6x6mm² some negative effects of the 2mm resolution are visible. The output factors are also in good agreement. Only, the 5x5 off axis and 6x6mm² fields show larger deviations where MC performs better. Dose distributions measured with film gave an average pass rate of 84.6% (MC) and 67.2% (PB). The absolute dose measurements show good agreement with MC calculations even measured with large table rotations, and deviations are mainly outside the PTV (in low dose region).

Conclusion: Based on the measurements performed on an Elekta Versa HD with Agility MLC, we conclude that in homogeneous media the MC dose calculations in iPlan agree better with the measurements for fields between 6x6 and 10x10mm² than the PB dose calculations. For fields larger than 10x10mm², the PB and MC dose calculations are comparable.

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