Published in:
01-07-2017 | Original Article
Changes in deviation of absorbed dose to water among users by chamber calibration shift
Published in: Japanese Journal of Radiology | Issue 7/2017
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Purpose
The JSMP01 dosimetry protocol had adopted the provisional 60Co calibration coefficient \(N_{{{\text{D,w,Q}}_{ 0} }}^{{}}\), namely, the product of exposure calibration coefficient N
C and conversion coefficient k
D,X. After that, the absorbed dose to water D
w standard was established, and the JSMP12 protocol adopted the \(N_{{{\text{D,w,Q}}_{ 0} }}^{{}}\) calibration. In this study, the influence of the calibration shift on the measurement of D
w among users was analyzed.
Materials and methods
The intercomparison of the D
w using an ionization chamber was annually performed by visiting related hospitals. Intercomparison results before and after the calibration shift were analyzed, the deviation of D
w among users was re-evaluated, and the cause of deviation was estimated.
Results
As a result, the stability of LINAC, calibration of the thermometer and barometer, and collection method of ion recombination were confirmed. The statistical significance of standard deviation of D
w was not observed, but that of difference of D
w among users was observed between N
C and \(N_{{{\text{D,w,Q}}_{ 0} }}^{{}}\) calibration.
Conclusion
Uncertainty due to chamber-to-chamber variation was reduced by the calibration shift, consequently reducing the uncertainty among users regarding D
w. The result also pointed out uncertainty might be reduced by accurate and detailed instructions on the setup of an ionization chamber.