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Zero‐shift thimble ionization chamber
Author(s) -
Tessier Frédéric,
Hooten Brian D.,
McEwen Malcolm R.
Publication year - 2010
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 - 10.1118/1.3314072
Subject(s) - ionization chamber , ionization , zero (linguistics) , physics , atomic physics , optics , nuclear physics , materials science , medical physics , nuclear medicine , nuclear magnetic resonance , ion , medicine , quantum mechanics , linguistics , philosophy
Purpose: Verify experimentally the theoretical prediction of F. Tessier and I. Kawrakow [Med. Phys. 37, 96–107 (2010)] that it is possible to design a thimble ionization chamber with no shift in its effective point of measurement (EPOM), i.e., a chamber that provides a measure of the dose to the medium at the location of its central axis. Methods: Measure dose from a 25 MV photon beam incident on water with an Exradin A1SL ionization chamber inside a thin sleeve (as a means of effectively increasing the thimble wall thickness). The depth‐dose curve is compared to that obtained using a well‐characterized PTW Roos parallel‐plate chamber. Results: With an appropriate increase in thimble wall thickness, the EPOM shift of the Exradin A1SL vanishes. Further increase of the wall thickness yields a chamber with a positive (downstream) shift in its point of measurement. Conclusions: It is possible to design a thimble ionization chamber with a zero EPOM shift by adjusting the wall thickness.