Dosimetric characteristics of a liquid-filled electronic portal imaging device
- Netherlands Cancer Institute, Amsterdam (Netherlands); and others
The purpose of this investigation was to determine the characteristics of a commercial electronic portal imaging device (EPID), based on a two-dimensional matrix of liquid-filled ionization chambers, for transmission dose measurements during patient treatment. Electronic portal imaging device measurements were performed in a cobalt-60 beam and two accelerator x-ray beams, and compared with measurements performed with a Farmer-type ionization chamber in air in a miniphantom and in an extended water phantom. The warming up time of the EPID is about 1 h. The long-term stability of the detector is better than 1% under reference conditions for a period of about 3 months. The signal of the ionization chambers follows approximately the square root of the dose rate, although the relation becomes more linear for larger (> 1 Gy/min) dose rates. The signal can be transformed to dose rate with an accuracy of 0.6% (1 SD). The short-term influence of integrated dose on the sensitivity of the ionization chambers is small. The sensitivity increases about 0.5% for all ionization chambers after an absorbed dose of 8 Gy and returns to its original value in less than 5 min after stopping the irradiation. This small increase in sensitivity can be ascribed to the electrode distance of the ionization chambers in commercial EPIDs, which is 0.8 {plus_minus} 0.1 mm. The sensitivity increase depends on the electrode distance and is 4% for a 1.4 mm electrode distance. The scattering properties of the EPID ionization chambers were between those of an ionization chamber in a miniphantom and in a water phantom. The matrix ionization chamber EPID has characteristics that make it very suitable for dose rate measurements. It is therefore a very promising device for in vivo dosimetry purposes. 17 refs., 5 figs.
- OSTI ID:
- 447712
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 33, Issue 5; Other Information: PBD: 1 Dec 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Accurate two-dimensional IMRT verification using a back-projection EPID dosimetry method
SU-F-T-263: Dosimetric Characteristics of the Cine Acquisition Mode of An A-Si EPID