SU-E-T-527: Assessment of Field-Junction Dosimetry: Pinnacle V9.0 versus Film (EBT2)

Medical Physics
A MelanconR Tailor

Abstract

To investigate dose agreement of Pinnacle V9.0 with measurements across the junction between abutting photon and electron fields. Photon-photon, photon-electron, and electron-electron field junctions of energies 6 MV and 9 MeV were evaluated with 0, 5, and 10 mm gaps between the field edges at depths of 2, 15, and 30 mm with Gafchromic film (EBT2). Photon and electron fields (10×10 cm) were setup to deliver 300 cGy in their field centers to 30 mm depth. Film optical density was measured every millimeter across the field-junction with a densitometer (light beam 2 mm). Optical Density to dose conversion was accomplished using a calibration curve specific to the batch of this film. For comparison, all field combinations were generated in Pinnacle, and doses were calculated with collapsed-cone convolution algorithm employing calculation-grid sizes 2, 3, and 4 mm. Measured doses at junction are as much as 20% different than Pinnacle calculation. 3 profiles with zero gap, 1 profile with 0.5 cm gap, and 0 profiles with 1.0 cm gap showed a disagreement greater than 12%. Measurement showed a bias towards higher dose in the junction when compared to Pinnacle calculation. With dose-calculation grid reduced below 4 mm, Pinnacle calculation...Continue Reading

Citations

Aug 21, 2018·The American Statistician·Alexander SibleyKouros Owzar

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