Electron beam quality control using an amorphous silicon EPID
- North Western Medical Physics, Christie Hospital NHS Foundation Trust, Withington, Manchester M20 4BX (United Kingdom)
An amorphous silicon EPID has been investigated to determine whether it is capable of quality control constancy measurements for linear accelerator electron beams. The EPID grayscale response was found to be extremely linear with dose over a wide dose range and, more specifically, for exposures of 95-100 MU. Small discrepancies of up to 0.8% in linearity were found at 6 MeV (8-15 MeV showed better agreement). The shape of the beam profile was found to be significantly altered by scatter in air over the approximately 60 cm gap between the end of the applicator and the EPID. Nevertheless, relative changes in EPID-measured profile flatness and symmetry were linearly related to changes in these parameters at 95 cm focus to surface distance (FSD) measured using a 2D diode array. Similar results were obtained at 90 deg. and 270 deg. gantry angles. Six months of daily images were acquired and analyzed to determine whether the device is suitable as a constancy checker. EPID output measurements agreed well with daily ion chamber measurements, with a 0.8% standard deviation in the difference between the two measurement sets. When compared to weekly parallel plate chamber measurements, this figure dropped to 0.5%. A Monte Carlo (MC) model of the EPID was created and demonstrated excellent agreement between MC-calculated profiles in water and the EPID at 95 and 157 cm FSD. Good agreement was also found with measured EPID profiles, demonstrating that the EPID provides an accurate measurement of electron profiles. The EPID was thus shown to be an effective method for performing electron beam daily constancy checks.
- OSTI ID:
- 22100516
- Journal Information:
- Medical Physics, Vol. 36, Issue 5; Other Information: (c) 2009 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
Similar Records
Daily QA of linear accelerators using only EPID and OBI
Development of an accurate EPID-based output measurement and dosimetric verification tool for electron beam therapy
Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
BEAM PROFILES
ELECTRON BEAMS
ELECTRONS
IONIZATION CHAMBERS
LINEAR ACCELERATORS
MEV RANGE 01-10
MEV RANGE 10-100
MONTE CARLO METHOD
QUALITY CONTROL
RADIOTHERAPY
SEMICONDUCTOR MATERIALS
SI SEMICONDUCTOR DETECTORS