Abstract
Introduction IMRT and VMAT has become a standard for radiation treatments with highly conformal dose distributions. Because of the high complexity of IMRT and VMAT treatment plans, patient-specific Quality Control (QC) is a necessary prerequisite for patient treatment. In recent years much interest has been shown in the use of a Portal-Vision™ system for such measurements. The aim of this study was to demonstrate the efficiency and convenience of portal dosimetry IMRT and VMAT QC by comparing the QC done with a Varian Portal-Vision™ to that done with a 2D array and a 4D Octavius phantom. The time taken to do the QC, the accuracy of the system as well as the plan analysis results was compared. Methods and Materials For evaluation purposes 5 IMRT and 25 RapidArc treatment verification plans were generated using the Eclipse treatment planning system (TPS). QC of all these plans was done at the Linear Accelerator. The resulting dose fluences were evaluated by comparing the measured dose fluences to the TPS calculated dose fluences. The final evaluation was carried out using a gamma agreement index (GAI) scoring modulated area with γ < 1 ; the threshold dose difference was set to 3% and the distance to agreement was set to 3 mm. Results The QC of plans evaluated with the portal dosimetry system was completed notably faster than when compared to the other measurement systems used. This included set up and measurement time. The GAI varied between (94.7–98.7)% and (96.6–99.9)% for the Octavius and portal dosimetry respectively. Conclusion Portal dosimetry simplifies the pre-treatment QC process, as it is quick and provides reliable and accurate results. IMRT and VMAT has become a standard for radiation treatments with highly conformal dose distributions. Because of the high complexity of IMRT and VMAT treatment plans, patient-specific Quality Control (QC) is a necessary prerequisite for patient treatment. In recent years much interest has been shown in the use of a Portal-Vision™ system for such measurements. The aim of this study was to demonstrate the efficiency and convenience of portal dosimetry IMRT and VMAT QC by comparing the QC done with a Varian Portal-Vision™ to that done with a 2D array and a 4D Octavius phantom. The time taken to do the QC, the accuracy of the system as well as the plan analysis results was compared. For evaluation purposes 5 IMRT and 25 RapidArc treatment verification plans were generated using the Eclipse treatment planning system (TPS). QC of all these plans was done at the Linear Accelerator. The resulting dose fluences were evaluated by comparing the measured dose fluences to the TPS calculated dose fluences. The final evaluation was carried out using a gamma agreement index (GAI) scoring modulated area with γ < 1 ; the threshold dose difference was set to 3% and the distance to agreement was set to 3 mm. The QC of plans evaluated with the portal dosimetry system was completed notably faster than when compared to the other measurement systems used. This included set up and measurement time. The GAI varied between (94.7–98.7)% and (96.6–99.9)% for the Octavius and portal dosimetry respectively. Portal dosimetry simplifies the pre-treatment QC process, as it is quick and provides reliable and accurate results.
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