Experimental analysis of general ion recombination in a liquid‐filled ionization chamber in high‐energy photon beams

Abstract

This work suggests an empirical method to correct for differences in general ion recombination of a LIC between different radiation fields. More work is needed to quantitatively explain the LIC general ion recombination behavior in pulsed beams generated from linear accelerators.

Determination of small field output factors in 6 and 10 MV flattening filter free photon beams using various detectors

“…Most of all filed sizes, microLion shows mostly higher value of output factor and it was only one to use highest voltage and concern about ion recombination effect in FFF beams as shown by Stephanie L [10] and Eunah C [11]. In addition, the output factor values were closed to the values of EDGE for all field sizes down to 1.0×1.0 cm 2 within 1.5% which agrees with the result of Shin H J [12].…”

Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements

“…changes were calculated from the per-plan changes in pass rates. et al 8 The magnitude of the slope of the 6 MV linear fits was 4.44%/(mGy/pulse) for 360 Hz (600 MU/min). The slope was close to the manufacturer quoted values of 3.79%/(mGy/pulse) compared to previous publications that found slopes closer to 10.0%/(mGy/pulse) for the 1000 SRS.…”

“…Chung et al described the difference in the ion recombination slopes between, pulsed and continues beams. 8 The slopes of the continuous beams were steeper than the pulsed slopes. This was due to the buildup of free charge in the chamber, which will increase general recombination, resulting in a higher ion recombination effect.…”

“…5,6 However, there is a tradeoff-the liquid reduces ion mobility, leading to ion collection times that are approximately 100 times larger than air-filled chambers, which increases ion recombination effects. [7][8][9][10][11][12][13] Ion recombination effects have been studied in LICs and found to be proportional to the frequency and dose of the pulses delivered to the detector, among other parameters that are typically constant during a measurement. The dose and frequency of the pulses at each detector will vary during an IMRT delivery due to the changing multileaf collimator (MLC) aperture and changing machine dose rate (MU/min), respectively.…”

Development and clinical evaluation of an ionization chamber array with 3.5 mm pixel pitch for quality assurance in advanced radiotherapy techniques

“…19,20 A disadvantage of liquid filled ionization chambers is their dependence of sensitivity on dose per pulse, which makes them not ideal for dose measurements in stereotactic beams. 19,21 Detectors based on diode technology have sensors with a small sensitive volume, but they may show dose per pulse dependence as well as photon energy dependence. 22,23 Moreover, silicon sensors may show a pronounced dependence of sensitivity on accumulated dose, although modern manufacturing technology has significantly reduced this weakness.…”