(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To investigate the use of the multiple diode-array detector (MapCHECK2) for dose verification in the commissioning process and plan quality assurance for electron Monte Carlo dose calculation algorithm (EMC) in the Eclipse treatment planning system.
Methods: Plans using open fields determined by electron cones 6x6, 10x10, 15x15, 20x20, and 25cmx25cm in combination of energies of 6, 9, 12, 16, and 20 MeV and source-to-surface distances of 104cm and 110cm were calculated in a solid-water phantom using the EMC dose calculation algorithm in the Eclipse treatment planning system. The calculated dose distributions were compared with the corresponding two-dimensional dose distributions measured with MapCHECK2 where dose delivery was performed using a Varian Trilogy Linac. The gamma test with dose difference of 5% and distance-to-agreement of 5mm were used for dose evaluation similar to photon IMRT plans.
Results: The measured dose distributions agreed well mostly with the corresponding dose distributions of the plans calculated with EMC. The calculated dose distributions passed a gamma test (5%, 5mm) with a rate greater than 90% in comparison with MapCHECK2 measurements. The low passing rates of the electron plans resulted from the deviations between the measured and calculated doses in the penumbra region where the measured dose distributions showed higher dose gradients. Additionally, discrepancies between the measured and calculated dose distributions outside of the treatment field were found, where EMC stopped dose calculations in the umbra region. These dose deviations in penumbra and umbra were mainly due to uncertainties in the EMC-algorithm.
Conclusion: This study demonstrates feasibility of use of measurements with MapCHECK2 for dose verification and quality-assurance of electron therapy plans calculated with the EMC-algorithm in Eclipse treatment planning system particularly in the flat dose region around central-axis. In the penumbra and umbra regions, large dose deviations between the calculated and measured doses were found.
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