SU‐FF‐T‐76: Analysis of a Novel Method of IMRT QA Using EPID‐Acquired QA Planes

Purpose: To assess the efficacy and quantify the accuracy of a novel method for IMRT QA in which the measured dose plane is derived from an EPID image. Method and Materials: aSi EPID data was acquired and converted using a novel method based on a machine‐specific beam model to estimate QA dose planes from mega voltage (MV) EPID images. Dose planes were calculated in a homogeneous, water‐equivalent QA phantom using the model and an acquired MV EPID image with no additional buildup required on the EPID. Specific parameters, such as field size output dependency, dose redistribution kernel, potential off‐axis corrections and absolute dose calibration, were measured to create the model that is based on the raw EPID files. QA dose planes were compared to ion chamber measurements, MapCHECK® measurements, and planar fluences generated by ADAC Pinnacle³® TPS. MapCHECK® and ion chamber (IC) measurements were taken at multiple depths at a source to detector distance (SDD) of 100cm. Dose planes in homogenous media were estimated using EPID images acquired at a distance of 140cm SDD. Data was collected for both 6 MV and 10 MV energies to determine the accuracy of the model for these two energies. Results: Preliminary sample analysis demonstrates that the dose planes estimated by the model using EPID images of complex IMRT fields result in >98% pass rate of all point measurements from MapCHECK®, employing a 3% dose or a 2mm distance to agreement criterion. Agreement between MapCHECK® and IC measurements were within 1%. Conclusion: This novel method shows promise as a tool for IMRT QA with reasonable accuracy. Setup, acquisition and analysis can be performed in a more time efficient manner than is possible with current methods of IMRT QA. Conflict of Interest: This work was partially funded by Sun‐Nuclear Co.® and Canis Lupus LLC.