Determination of the reference air kerma rate for Ir-192 and Co-60 HDR sources using three different international protocols

International Conference on Medical Physics

August 03-05, 2015 Birmingham, UK

Golam Abu Zakaria

Posters-Accepted Abstracts: J Nucl Med Radiat Ther

Abstract :

The long half-life and comparable dose distributions to Ir-192 make Co-60 sources economically attractive, especially in developing countries. Dosimetry protocols provide no guidance for verification of Co-60 source calibration by the medical physicist. The applicability of the procedures recommended for Ir-192 in three international dosimetry protocols were applied to both Co-60 and Ir- 192 sources. The reference air kerma rates of Co-60 and Ir-192 sources were measured with ionization chambers using the procedures applicability for Ir-192 in IAEATECDOC- 1274, DIN 6809-2, and AAPM Report 4. Wherever the protocols give no correction factors for Co- 60 sources, equivalent factors from literature were used. Measurements were performed with an ionization chamber in a solid phantom and free in air, and with a well chamber. The measurements were evaluated with all three protocols. The results are compared to reference air kerma rates given in the source certificates. The measured air kerma rates show deviations from the certificate values smaller than 1.2% for Ir-192 and 2.5% for Co-60-Sources. The measurements with the well chamber show the lowest deviations from the certificate value. Determination of air kerma rate for Co-60 HDR sources using the existing protocols are possible withaccuracy sufficient to verify source calibration even though the protocols are not specifically designed for Co-60 measurements. New protocols are desirable, based on measurements with ionization chambers calibrated in absorbed dose to water and providing the complete measurement procedure and correction formalism also for Co-60 sources.