Low-intensity radioactive sources emitting low-energy photons are used in the clinic for low dose-rate brachytherapy treatments of tumours. The dosimetry of these sources is based on reference air kerma rate measurements. The absorbed dose rate to water at the reference depth d0=1cm,Dw, is then obtained by a conversion procedure with a large relative standard uncertainty of about 5%. This paper describes a primary standard developed at ENEA-INMRI to directly measure due to LDR sources. The standard is based on a large-angle and variable-volume ionization chamber, embedded in a graphite phantom and operating under wall-less air chamber conditions. A set of correction and conversion factors, based on experiments and Monte Carlo simulations, are determined to obtain the value of Dw,1 cmfrom measurements of increment of ionization current with increasing chamber volume. The relative standard uncertainty on is 2.6%, which is appreciably lower than the current uncertainty. Characteristics of the standard, its associated uncertainty budget, and some experimental results are given for125I BEBIG I25.S16.C brachytherapy seeds. Finally, results of the experimental determination of the dose-rate constant Λ1 cm, traceable to the Dw,1 cmand the low-energy air kerma ENEA-INMRI standards, are given. The relative standard uncertainty on Λ1 cmis 2.9%, appreciably lower than the typical uncertainty (4.8%) of the values available in the literature. © 2012 BIPM & IOP Publishing Ltd.
All Science Journal Classification (ASJC) codes
Toni, M. P., Pimpinella, M., Pinto, M., Quini, M., Cappadozzi, G., Silvestri, C., & Bottauscio, O. (2012). Direct determination of the absorbed dose to water from. Metrologia, 49(5), -. https://doi.org/10.1088/0026-1394/49/5/S193