Radiation protection measurements in clinical practice - Dosimetry with NaCl pellets

Abstract: Within the field of medical radiation protection, radiation safety and personal dosimetry, there is a constant pursuit for improving existing methods and evaluating new approaches for measuring and quantifying the radiation doses that hospital staff may be exposed to in their clinical work. There are numerous ways of determining what doses the staff are being exposed to and the most commonly used is based on thermoluminescent dosemeters (TLD) with e.g. chips of lithium fluoride. However, these traditional TLDs tend to be expensive which limit the possibilities of having many simultaneous measuring points on the same occasions in clinical practice. Furthermore, the TLDs based on lithium fluoride are toxic and have a limited lifetime, both physically and in terms of calibration. Ordinary sodium chloride (NaCl) has, in many studies, been found to possess good properties for quantifying exposure to ionizing radiation, making it a good candidate as a potential dosemeter in clinical applications. NaCl is cheap, non-toxic and the use of NaCl for dosimetry is based on one-time usage of the dosemeters with an individual calibration directly after reading the signal. These factors in combination with the read out of the signal is based on optical stimulation rather than thermal, provides for potentially high accuracy in the dose determinations as well as lower detection limits. The aims of this study have been to investigate the potential of ordinary household salt, in the form of NaCl pellets, for radiation dose assessments in a variety of clinical applications: to determine “hand doses”, “body doses” and to perform dose mapping of laboratory premises. In the study it was also evaluated what advantages and disadvantages salt pellets has as a potential dosemeter within these clinical applications as well as investigating which what type of packaging technique that are beneficial in order to keep the NaCl pellets protected and easy to handle, and what possible improvements that might be needed. The project has shown that a good packaging technique, sufficient to keep the NaCl pellets protected from both light exposure and mechanical stress during use in clinical work, is necessary. An initial layer of ordinary household plastic followed by 4 layers of aluminum foil was determined to be optimal. The study further showed that the equivalent dose to the treating physicians hand surface, during low-dose-rate (LDR) brachytherapy, was between 0-0.33 mSv using 96 measuring points evenly distributed over the hands. It also showed that the nurse, during the same treatment and with the same amount of measuring points, received between 0- 0.27 mSv over the hand surface. Furthermore, using the NaCl pellets it was shown that the equivalent dose to the hand surface, of the staff working with 18F-FDG synthetization, was between 1.04-15.10 mSv for a 30-minutes session. The staff working with Ammonia synthetization received a dose to the hand surface between 0.9-5.2 mGy per preparation. All measurements of hand surface doses thus showed a large diversity in terms of dose magnitude and how the dose is distributed over the hands. Also, the premises where 18F-FDG and Ammonia synthetization takes place, were measured for 7 days and showed large variation in the room depending on where the “sources” were placed and handled during the measurement period. In addition, prolonged measurements were performed during 6 weeks at office premises close to patient administration rooms (18F-FDG), which showed a mean dose rate of 0.032 uSv/h i.e. well under the normal background level of 0.16 uSv/h. All together, these results show potential for optimization of the various clinical practices and may be used when educating the personal for planning and conducting their work. The NaCl pellet results also opens for more elaborate assessments in other routine and complex clinical irradiation geometries. ‘