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SU‐EE‐A2‐06: The Measurement of KQ Factor for the FC65‐G Water Proof Chamber in 6, 10 and 18 MV Photon Beams
Author(s) -
Amin M,
Norrlinger B,
Heaton 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 - 10.1118/1.3468017
Subject(s) - reproducibility , ionization chamber , beam (structure) , linear particle accelerator , monitor unit , imaging phantom , materials science , analytical chemistry (journal) , photon , dosimetry , physics , nuclear medicine , optics , chemistry , ion , medicine , chromatography , quantum mechanics , ionization
Purpose : The beam quality conversion coefficient k Q is one of the factors needed to determine the absorbed dose to water of a linac following the guideline prescribed by TG‐51 and TRS‐398. In this study k Q values were determined for a farmer type IBA FC65‐G chamber in a 6, 10 and 18 MV photon beams (beam qualities %dd (10) X of 67.5, 73.55 and 79.7 respectively) using a solid water phantom. FC65‐G is a 0.65cc water proof graphite chamber for which the published measured k Q values are not widely available. Methods and Materials : The k Q measurement was performed on an Elekta Synergy linear accelerator and a cobalt unit. Corrections for beam stability were performed using down stream monitoring detectors. The k Q of five NE2571 chambers have been checked to validate the methodology, as well as the stability and the sensitivity of our system. Reproducibility of k Q measurements for a single chamber and variability across multiple chambers of the same type were investigated. Results : The average k Q values measured for the five FC65‐G chambers in the 6, 10 and 18 MV photon beams are 0.9928±0.0006, 0.9833±0.0007 and 0.9738±0.0006 respectively. These k Q values are within ±0.02%, ±0.03% and ±0.04% respectively of those reported in TG‐51 for chambers of similar construction. The measurement reproducibility of 0.02% and 0.03% were determined for NE2571 and FC65‐G chambers respectively. Conclusion : The k Q has been directly determined for both NE2571 and FC65‐G chambers and found to be consistent with values provided in TG‐51 and TRS‐398. The TG‐51 recommendation to use k Q for chambers of similar construction was found to be good within measurement uncertainly in this case.