TH-CD-304-10: A Method for Correcting Ion Recombination Effects in OCTAVIUS 1000 SRS Measurements

TL;DRAbstract

Purpose: PTW's Octavius 1000 SRS array performs IMRT QA measurements with liquid filled ionization chambers to allow closer detector spacing and higher resolution. Increased density of liquid relative to air, leads to increased ion recombination effects, which are proportional to dose/pulse experienced at the detectors. During IMRT QA, dose/per pulse will vary across the array, leading to varying collection efficiencies. Magnitudes of recombination effects were investigated and a method was developed to correct them in QA measurements. Methods: The OCTAVIUS 1000 SRS was used to measure different IMRT plans using varying dose/pulse and results were normalized to air filled chamber measurements to obtain collection efficiencies. Regression analysis was performed to relate collection efficiency to dose/pulse. Matlab software was developed to correct IMRT QA measurements using these correlations. Measurements were performed on a Truebeam equipped with high-definition MLC, using 6MV and 10F

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