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.
Glendinning
A G
AG
Department of Medical Physics, University Hospitals of Leicester NHS Trust, The Leicester Royal Infirmary, UK. agg2@le.ac.uk
Hunt
S G
SG
Bonnett
D E
DE
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