First tests of a liquid ionization chamber to monitor intensity modulated radiation beams

Abstract

First measurements with a prototype ionization chamber are described to be applied in online monitoring of modulated fields in radiation therapy. The liquids isooctane, isononane (TMP) and tetramethylsilane (TMS) are used in a high purity grade in order to realize high current signals for electronic read-out in parallel at frequencies exceeding 10 Hz. Signals of more than a factor 4 with respect to isooctane, analysis grade, are obtained. With an electrode structure of 400 pads, a uniformity in efficiency within 1.2% has been measured. The penumbra of a multileaf collimator could be resolved. Theoretical examination verifies that the free electrons in the liquids cause higher signals when the measured currents are compared with expectation for ion transport only.

Development and clinical characterization of a novel 2041 liquid‐filled ionization chambers array for high‐resolution verification of radiotherapy treatments

“…LICto-water stopping power ratio for commonly used liquids is quite constant over the range of energies typically used in radiotherapy, minimizing the energy dependence caused by the ionization medium (although materials composing the frame of the device can affect its energy dependence). Several multipixel LIC prototypes have been developed, [24][25][26] and the OCTAVIUS 1000 SRS and the LA48 are commercial devices based on this technology.…”

Characterization of tetramethylsilane for liquid-filled ionization dosimeters: Ion mobilities, free-ion yield and general recombination

“…However, they do affect the limit given by Eq. (5). For a TMS-filled microLion-like LIC operating at voltages ranging from 300 to 900 V, such limits range from 16.0 to 5.3 ms, Eq.…”

“…Research in LICs for radiotherapy has grown in the last two decades due to the good characteristics that they present for dosimetry, namely a near water-equivalent response, and the attainable high spatial resolution due to the high density of the ionization medium (when compared to air), which is especially important in the verification of small and/or high gradient fields such as those present in many advanced radiotherapy techniques. Several prototypes and commercial devices, as well as dosimetry methods, have been developed and characterized [1][2][3][4][5][6][7][8][9][10][11]. Isooctane (2,2,4-trimethylpentane, C 8 H 18 ) is the liquid most commonly used in LICs due to its good physico-chemical properties.…”

Development of Two-dimensional Fiber-optic Radiation Sensor for High Energy Photon Beam Therapy Dosimetry

“…1) Small sized dosimeters for radiotherapy use such as ion chambers, silicon photodiodes, diamond detectors, and liquid ion chamber have been developed and used for dose measurements. [2][3][4][5] However, they have some problems as a rather large sensitive volume, dose rate dependence, complicated construction and high cost. 6) And it is difficult to measure depth dose curves and beam profiles with conventional detectors due to the loss of lateral electronic equilibrium and volume averaging.…”