Frantisek Gabris

Re-evaluation of correction factors of a primary standard graphite calorimeter in 60Co gamma ray beams as a basis for the appointment of the BEV absorbed dose rate to water reference value

The graphite calorimeter of the Federal Office of Metrology and Surveying (BEV-Bundesamt für Eich- und Vermessungswesen) was established in the 1980s as the primary standard for the absorbed dose to water for (60)Co gamma ray beams. To maintain the primary standard at an international level the graphite calorimeter and its corresponding components had to undergo a refurbishment and modernisation process. The correction factors of the graphite calorimeter were re-evaluated with Monte Carlo and experimental methods to obtain improved values. These are the correction for the effect of the gaps (1.0061), the scaling correction (0.9998), the correction for the difference in air attenuation (0.9971) and the corrections for the effective measurement depths in the graphite phantom for the graphite calorimeter (0.9886) and the CC01-105 ionisation chamber (0.9913). Consequently, it was necessary to change the reference value for the absorbed dose rate to water of the (60)Co teletherapy unit used for the calibration of secondary standard dosemeters.

A Joint Research Project to improve the accuracy in dosimetry of brachytherapy treatments in the framework of the European Metrology Research Programme.

This paper outlines the joint research project “Increasing cancer treatment efficacy using 3D brachytherapy” co-funded in the FP7, according to the iMERA-Plus Grant Agreement No. 217257 between the EC and EURAMET e. V. (European Association of National Metrology Institutes). The project brings together the capabilities of ten major European National Metrology Institutes in the ionizing radiation field and it is focused on the targeted programme “Health”. It aims at establishing across Europe a more accurate metrological basis in brachytherapy by developing methods for the direct measurement of the quantity absorbed dose to water in brachytherapy dosimetry with an uncertainty on the dose delivered to the target volume less than 5% (k=1) at clinical level. In fact, in the current brachytherapy practice, the procedures to determine the absorbed dose imparted to the patient are affected by an uncertainty that could reduce the treatment success. Most of this uncertainty is due to a lacking metrology. No absorbed-dose primary standards are so far available to assure direct traceability in dosimetry of brachytherapy sources. In order to optimize the brachytherapy treatments there is also a need for more accurate dosimetry with high spatial resolution. The present research project is expected to increase the accuracy of brachytherapy to a level comparable to that typical of radiotherapy with external accelerator beams.

Exploitation of secondary standard for calibration in units of Dw,1 cm and assessment of several HDR brachytherapy planning systems*

A secondary standard of the BEV, calibrated at the PTB in terms of Dw,1 cm, was used for calibration of the well-type chamber-based measuring systems used in clinics. In addition to the calibration, we tried to employ it for assessment of treatment planning systems (TPS) used for each particular afterloader. The dose to water at 1 cm distance from the source position was calculated by the TPS, using reference data from the source producer certificate. The values were compared directly with the dose measured at the same distance from the source.The comparison has been carried out for GammaMed Plus and MicroSelectron HDR sources. Differences of secondary standard measurements and TPS calculations were lower than ±5%, which is below the achievable uncertainty of both dose measurement and dose determination by the TPS. Nevertheless, it is higher than generally accepted in the case of external beam radiotherapy. Additional direct measurements in terms of Dw,1 cm may improve the safety and reliability of patient treatment.

Comparison of the standards for absorbed dose to water of the BEV, Austria, and the BIPM for 60Co gamma radiation

A comparison of the standards for absorbed dose to water of the Bundesamt f?r Eich- und Vermessungswesen (BEV), Austria, and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co radiation beam of the BIPM in March 2009 under the auspices of the key comparison BIPM.RI(I)-K4. The comparison result, based on the calibration coefficients measured for two transfer standards and expressed as a ratio of the BEV and the BIPM standards for absorbed dose to water, is 0.9996(37). This result replaces the 1994 BEV value of 0.9990(43) in this key comparison. The degrees of equivalence between the BEV and the other participants in this comparison have been calculated and the results are given in the form of a matrix for the ten national metrology institutes (NMIs) that have published results in this ongoing comparison for absorbed dose to water. A graphical presentation is also given. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Corrigendum: Experimental determination of the dose rate constant for selected 125I- and 192Ir-brachytherapy sources (2012 Metrologia 49 S219–22)

The consensus value for Λ reported in the last column of table 2 should be Λ = 1.012 × 104 not Λ = 1.021 × 104.

Comparison of the standards for air kerma of the BEV and the BIPM for 137Cs gamma radiation

A direct comparison of the standards for air kerma of the Bundesamt fur Eich- und Vermessungswesen (BEV), Austria, and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 137Cs radiation beam of the BIPM in March 2009. The result, expressed as ratios of the BEV and the BIPM standards for air kerma, is 1.0041 with a combined standard uncertainty of 3.1 × 10−3. The result of the earlier direct comparison in 137Cs γ rays, made in 1995, was 0.9961 (28); taking into account the changes made recently to both standards, the 1995 result becomes 1.0035 (24), in agreement with the present comparison result. The degrees of equivalence between the BEV and the other participants in the key comparison have been calculated and the results are presented in the form of a matrix. A graphical presentation is also given. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).