Dosimetry for Low Energy X-rays: Efficiency of the Alanine Pellet Dosimeter

Research output: Book/ReportPh.D. thesisResearch

Abstract

kilovoltage (kV) x-rays are used extensively in several aspects of radiation processing and radiotherapy. For applications, such as irradiation of blood products before transfusion, where irradiators using the radionuclide cesium-137 has traditionally been used, a demand for replacement with small self-shielded low energy x-ray irradiators has occurred in recent years. However, the response of commonly used routine dosimeters, such as alanine pellets, show an increasing energy dependence for low energy x-rays.
The present work investigates the energy dependence of the alanine pellet dosimeter. The alanine/electron paramagnetic resonance (EPR) dosimetry system is commonly used for reference and routine dosimetry, typically with traceability to national standards through calibration in a cobalt-60 reference field. Here the relative response, and efficiency, of the alanine pellet dosimeter is experimentally determined for irradiation at different kV x-ray qualities. The dependence of the relative efficiency of the dosimeter on spectral distribution of the x-ray beam is investigated using a microdosimetric one-hit detector model (OHDM). The results indicate that for medium energy x-rays there is little variation in the relative efficiency for a specific effective energy, while a more significant variation is observed for low energies.
Based on the conclusions from the application of the microdosimetric OHDM a general approach for determining quality correction factors, from literature data on the relative response, for cobalt-60 based calibrations is proposed.
Finally, the microbicidal effectiveness of kV x-rays is investigated using a specially designed test piece comprised of spores of Bacillus pumilus. The radiation response for irradiation with a 150 kV x-ray beam has been measured, and the response is shown to be identical to the radiation response for irradiation in cobalt-60, high energy x-ray, and low and high energy electron beams.
Original languageEnglish
PublisherDTU Health Technology
Number of pages174
Publication statusPublished - 2021

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