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Poster — Thur Eve — 57: Use of a Micro Liquid Ionization Chamber for Commissioning of Radiosurgery Beams
Author(s) -
Patrocinio H,
Evans M,
Ruo R,
Soisson E,
AlDahlawi I,
Seuntjens J
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 - 10.1118/1.3476162
Subject(s) - ionization chamber , collimator , electrometer , radiosurgery , dosimetry , beam (structure) , materials science , optics , linear particle accelerator , nuclear medicine , percentage depth dose curve , physics , ionization , ion , radiation therapy , medicine , quantum mechanics
A commercially available liquid ionization chamber (PTW, Freiburg, Germany) was used in the commissioning of stereotactic radiosurgery beams for a Novalis Tx linear accelerator. The chamber has a small collecting volume (0.002cm 3 ) yet providing a relatively high signal for its size. The chamber was attached to a solitary electrometer for output measurements, and to a water scanning system for PDD and beam profile measurements. The commissioning set consisted of output factors, percentage depth doses and off‐axis beam profiles for six collimator sizes ranging from 4mm to 15mm in diameter. The measured data was compared to both Gafchromic film dosimetry measurements and to data from the literature. Output factors measured with the liquid ion chamber are in good agreement with film measurements (<2% difference, except for 3.8% difference for the 4mm collimator). Similar overall agreement was found with a recent publication by Fan et al.,(2009). Beam profile measurements were found to be in very good agreement with Gafchromic film measurements. Our PDD data was equally in reasonable agreement with data from a recent publication by Chang et al., (2008) with discrepancies of 2–3% observed. A comparison of TMRs calculated from our PDD data and from direct measurement revealed larger differences, increasing with depth, that have yet to be resolved. The liquid ion chamber was easy to use required only a brief pre‐irradiation to provide a stable signal. Our preliminary results suggest this high spatial resolution chamber has usefulness in small field measurements.