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The properties of the ultramicrocylindrical ionization chamber for small field used in stereotactic radiosurgery
Author(s) -
Vahc Young W.,
Chung Won K.,
Park Kyung R.,
Lee Jong Y.,
Lee Yong H.,
Kwon Ohyun,
Kim Sookil
Publication year - 2001
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 - 10.1118/1.1350437
Subject(s) - ionization chamber , dosimetry , dose profile , materials science , imaging phantom , absorbed dose , percentage depth dose curve , radiosurgery , thermoluminescent dosimetry , thermoluminescent dosimeter , optics , detector , beam (structure) , linear particle accelerator , nuclear medicine , physics , dosimeter , ionization , ion , radiation therapy , medicine , quantum mechanics
Accurate dosimetry of small‐field photon beams tends to be difficult to perform due to the presence of lateral electronic disequilibrium and steep dose gradients. In stereotactic radiosurgery (SRS), small fields of 6–30 mm in diameter are used. Generally thermoluminescence dosimetry chips, Farmer, Thimble ion chamber, and film dosimetry are not adequate to measure dose in SRS beams. These techniques generally do not provide the required precision due to their energy dependence and/or poor resolution. It is necessary to construct a small, accurate detector with high spatial resolution for the small fields used in SRS. The ultramicrocylindrical ionization chamber (UCIC) with a gold wall of 2.2 mm in diameter and 4.0 mm in length has dual sensitive volumes of air (8.0 mm 3 ) and borosilicate (2.6 mm 3 ) cavity. Reproducibility, linearity, and radiation damage with respect to absorbed dose, beam profile of small beam, and independence of dose rate of the UCIC are tested by the dose measurements in high energy photon (5, 15 MV) and electron (9 MeV) beams. The UCIC with a unique supporting system in the polystyrene phantom is demonstrated to be a suitable detector for the dose measurements in a small beam size.