Development of EPID-based real-time dosimetry and geometry in radiation therapy

A real-time EPID-based dosimetric and geometric verification system is proposed. The system enables detection of gross treatment delivery errors prior to delivery of substantial radiation to the patient in IMRT treatment. A sophisticated physics-based model is utilized to generate an image stream of predicted cine EPID images as a reference dataset, and it then compares these to measured EPID images acquired during treatment. A new method that combines both geometrical and dosimetric comparison is used for synchronisation. In addition, jaw position and collimator angle are detected and verified in the beginning of treatment (approximately first 5 seconds). The system was simulated using MATLAB/SIMULINK. The synchronisation is shown to agree within 2 control points (~1% of the total dose delivered). In real-time dosimetry, two case studies were simulated: 1) Gross dose delivery error and 2) MLC leaf failure; the real-time dosimetry system was able to detect both of these errors in real-time (within 0.1 sec). In real-time geometry, jaw positioning and collimator angle were tested, and an average 0.5 mm error for jaw positioning and less than 0.5 degrees for collimator angle are shown in the tests. MLC leaf verification uses the advantageous result of synchronisation to monitor the MLC leaf motion behaviour during the treatment. A real-time verification system can prevent many of the major mistreatments that have recently occurred in radiation therapy. The system design is fast and can be easily applied in a clinical environment.