A method for controlling image acquisition in electronic portal imaging devices.
Certain types of camera-based electronic portal imaging devices (EPIDs) which initiate image acquisition based on sensing a change in video level have been observed to trigger unreliably at the beginning of dynamic multileaf collimation sequences. A simple, novel means of controlling image acquisition with an Elekta linear accelerator (Elekta Oncology Systems, Crawley, UK) is proposed which is based on illumination of a photodetector (ORP-12, Silonex Inc., Plattsburgh, NY, USA) by the electron gun of the accelerator. By incorporating a simple trigger circuit it is possible to derive a beam on/off status signal which changes at least 100 ms before any dose is measured by the accelerator. The status signal does not return to the beam-off state until all dose has been delivered and is suitable for accelerator pulse repetition frequencies of 50-400 Hz. The status signal is thus a reliable means of indicating the initiation and termination of radiation exposure, and thus controlling image acquisition of such EPIDs for this application.
Department of Medical Physics, University Hospitals of Leicester NHS Trust, The Leicester Royal Infirmary, UK. agg2@le.ac.uk
A G
AG
Glendinning
S G
SG
Hunt
D E
DE
Bonnett
D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D010315:Particle Accelerators; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D011882:Radiotherapy, High-Energy