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Sci‐Sat AM (1) General‐08: Study of Characteristics of a New Liquid Ionization Chamber
Author(s) -
Elliott A,
Stewart K,
Seuntjens J
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2244695
Subject(s) - ionization chamber , ionization , dosimetry , ion , range (aeronautics) , beam (structure) , atomic physics , fluence , materials science , electric field , physics , optics , nuclear medicine , medicine , quantum mechanics , composite material
Liquid ionization chambers (LICs) have characteristics that can remedy some of the drawbacks of air‐filled ionization chamber dosimetry: large sensitive volumes, fluence perturbations, and energy dependence over the clinical range of beam qualities. However, there are significant problems in liquid chambers. High ionization density and low ion mobility leads to high ion recombination rates. In this work, extensive experimental work has been performed to investigate properties of a new liquid chamber, including chamber stability over time, chamber reproducibility, and establishing recombination corrections. The new chamber is called the GLIC‐03 (Guarded Liquid Ionization Chamber), and is filled with isooctane. The sensitive volume is 0.7 mm 3 . We used the 18 MV beam of a Varian Clinac 21EX linear accelerator. The lowest pulse rate setting was used in order to minimize ion recombination. Measurements were taken in solid water at 15 cm depth, with various field sizes and SSDs. Boag's theory for general collection efficiency for parallel‐plate gas ionization chambers, applied to isooctane in pulsed radiation, was used for recombination corrections. The GLIC‐03 response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. The collection efficiency decreased with increasing dose per pulse due to general recombination of ions from a larger number of ionizing particle tracks. Recombination corrections were within 1% for low dose rates and high electric field strengths. The establishment of these characteristics in the present work allows us to perform accurate measurements in high gradient non‐equilibrium fields.