Bilateral comparison (IRCL/GAEC-EIM and LNE-LNHB) of calibration of brachytherapy well type ionization chamber in terms of iridium 192 reference air kerma rate

Project Description

A HDR brachytherapy well type ionization chamber of type Standard Imaging HDR 1000 with a Standard Imaging CDX 2000B electrometer will be calibrated at the IRCL/GAEC-EIM and the LNE-LNHB in terms of HDR iridium 192 reference air kerma rate. The calibration coefficient and the associate uncertainties will be compared. The above instrument, referred as working standard hereafter, will be provided by the IRCL/GAEC-EIM.

Calibration at IRCL/GAEC-EIM

The HDR brachytherapy standards of the IRCL/GAEC-EIM are traceable to the LNE-LNHB. The reference transfer instrument is a well type ionization chamber and electrometer of the same, as above, type and it was calibrated at LNE-LNHB in April 2008. The working standard instrument will be calibrated against the reference transfer in a Nucletron microSelectron HDR brachytherapy remote (?) afterloading systems with an iridium 192 source, which operates in "Alexandra" hospital, Athens. The iridium 192 reference air karma rate will be determined by the reference transfer instrument. Then, measurements will be performed with the working standard instrument using the same iridium 192 source. The calibration procedures and the calculation of the calibration coefficient include

- The determination of the source position (height) in the well type chamber where the chamber response is maximum
- Corrections for air density, kPT, ion recombination ks, source radioactive decay between measurements, kdec, and leakage signal

The associate uncertainties of the calibration coefficient will be evaluated with coverage factor k=2.

Calibration at LNE-LNHB

The working standard instrument will be transported to the LNE-LNHB, where it will be calibrated against the primary standards. LNE-LNHB is using an indirect method for the determination of the iridium 192 source reference air kerma rate. A cavity ionization chamber is used, the calibration coefficient of which for iridium 192 spectrum is determined indirectly by interpolation from x-rays (250 kV) and cesium 137 calibrations. The calibration of the working standard well type ionization chamber will be performed with the same iridium 192 source inserted into the chamber.

The results process

Both partners will simultaneously send their results to the BIPM.

Transport of instrument

IRCL/GAEC-EIM will take all necessary provision for the safe transport of the instrument. Prior to shipment from GAEC and after the return of the instrument, measurements with an 241 americium source will be performed, in order to identify and deterioration or damage during transport.

The project will enable the ICRL/GAEC-EIM to test and verify its calibration methods and capabilities in order to improve the confidence of the calibration services to the Greek brachytherapy medical centers. Furthermore, the project will enable IRCL/GAEC-EIM to support the relevant Calibration and Measurement Capabilities (CMCs) to the International System (SI) at BIPM in order to compare the results with comparison reference values. Additionally, IRCL/GAEC-EIM will be able to expand its accreditation in terms of IEC/ISO 17025 to the HDR brachytherapy field.

Final Report 2011-06-08

The comparison has been completed and the results are published in the KCDB.

Ionising Radiation (IR)
Costas J. Hourdakis, IRCL/GAEC-EIM (Greece)
Coordinating Institute
Participating Partners
LNE-LNHB (France)