Streamlining EPID-based IMRT quality assurance: auto-analysis and auto-report generation

Using an EPID for patient specific IMRT QA is an efficient way to verify patient plans prior to the treatment. Our centres’ current EPID dosimetry method is based on a water equivalent depth approach, where EPID images of each IMRT field are converted to dose images and compared to Treatment planning system calculated dose images using a commercial software tool. Two physicists across two sites perform the analysis for an average of 12 new IMRT patients per week. To speed up this process, an in-house program called AutoEPIDIMRTQA was developed. The program automatically performs the following tasks sequentially: reading and converting raw EPID images acquired on either a Siemens Oncor or Elekta Synergy linear accelerator, registering them with planar dose images calculated by Pinnacle (Philips) or CMS XiO (Elekta) treatment planning systems, analyzing the profiles for registered images and calculating the Gamma map. Finally an IMRT QA report is automatically generated. AutoEPIDIMRTQA was validated against commercial software. The analysis time for a typical 9-beam IMRT head-neck patient decreases from 30 minutes to 4 minutes. The total QA time was reduced by 40% using AutoEPIDIMRTQA. Thus we have demonstrated a significant reduction in the time burden for physics staff performing IMRT QA.