A comparison between LiF, Al2O3 and NaCl pellets for luminescence dosimetry based on clinical and laboratory measurements

Abstract: Radiation protection is of importance for the general public, patients and personnel in many different situations: rare accidents involving ionizing radiation, medical examinations or work tasks in the medical clinic or nuclear industry to name a few. Optimization in radiation protection and limitation of radiation doses are essential to prevent overexposure and for reducing negative health consequences. Therefore, research in the field of dosimetry is needed, to improve existing methods for dose monitoring and develop new ones. In luminescence dosimetry, thermoluminescence (TL) and optically stimulated luminescence (OSL) are examples of techniques used for quantifying radiation absorbed doses using passive dosemeters made from e.g. lithium fluoride (LiF) or carbon-doped aluminum oxide (Al2O3:C). OSL dosimetry studies are also conducted on newer materials. One such promising OSL material is household salt (NaCl) that has shown many beneficial dosimetric characteristics. Thus, it is of relevance to investigate whether household salt is a suitable choice for luminescence dosimetry, in relation to commercial alternatives. The purpose of this project was to further investigate NaCl pellets as a potential passive personal dosemeter and specifically to compare NaCl pellets (OSL) to commercial detectors, such as LiF chips (TL) and Al2O3 discs (OSL). The three detector materials were positioned together in identical exposure geometries after which the absorbed doses to the various materials were estimated and compared. Possible effects due to differences in positioning, unit of calibration, and differences in energy dependence were taken into account. Both laboratory simulations and clinical experiments were conducted for the assessment of radiation doses in different nuclear medicine (NM) applications. These measurements were based on concerns and interests of staff members in the NM department, regarding the elution, preparation and handling of radiopharmaceuticals, the handling of patients, and radioactive waste. Experiments were carried out using radionuclides with photon energies relevant for the nuclear medicine clinic (140 keV and 662 keV). The results presented in this project confirm previous results in terms of dose linearity and fading. Results show comparable dose estimations between the three types of detectors when studied under controlled conditions in the laboratory. For the experiments conducted in the clinic, the dose estimations show larger uncertainties compared to the laboratory simulations due to the low doses during the limited exposure times and consequently low signals in the various detector materials. Thus, the results for the Al2O3 discs during the preparation and elution of radiopharmaceuticals, as well as a couple other experiments were excluded as the signals appeared below detection limits. To conclude, the obtained results provide dose estimations in reasonably good agreement between the three detector materials for a limited number of measurements, considering the energies involved and the duration of the measurements. Thus, NaCl has a strong potential to be utilized as an alternative point- and personal dosemeter. To improve the accuracy on the dose estimations, longer measurements are required in the clinic, and further measurements between NaCl and other commercial alternatives are necessary.