1.
Adolfsson, Emelie, 1985-
(author)
Lithium formate EPR dosimetry for accurate measurements of absorbed dose in radiotherapy
2014
Doctoral thesis (other academic/artistic) abstract
Lithium formate has shown to be a material with properties suitable for electron paramagnetic resonance (EPR) dosimetry, among them up to 7 times higher sensitivity compared to alanine, which is a well-established EPR detector material for dose determinations in radiotherapy.The aim of this thesis was to further investigate the properties of lithium formate and develop the dosimetry system towards applications in radiotherapy. The intrinsic efficiency for energies of relevance to brachytherapy and the signal stability were investigated. The dosimetry system was expanded to include a smaller dosimeter model, suitable for measurements in dose gradient regions. An individual sensitivity correction method was applied to the smaller dosimeters to be able to perform dose determinations with the same precision as for the larger ones. EPR dosimetry in general is time consuming and effort was spent to optimize the signal readout procedure regarding measurement time and measurement precision.The system was applied in two clinical applications chosen for their high demands on the dosimetry system: 1) a dosimetry audit for external photon beam therapy and 2) dose verification measurements around a low energy HDR brachytherapy source.The conclusions drawn from this thesis were: dose determinations can be performed with a standard uncertainty of 1.8-2.5% using both the original size dosimeters and the new developed smaller ones. The dosimetry system is robust and useful for applications when high measurement precision and accuracy is prioritized. It is a good candidate for dosimetry audits, both in external beam therapy and brachytherapy.
2.
Israelsson, Axel
(author)
Chewing gum and human hair as retrospective dosimeters
2014
Doctoral thesis (other academic/artistic) abstract
Retrospective dosimeters are sometimes needed after radiological/nuclear (RN) exposures to determine the doses to individuals. Conventional dosimeters may not be at hand or may not be applicable calling for alternative materials.The possible exposure situations can be divided into external and internal; the radiation field stems either from outside the body or from a source within. This thesis investigates the possibility to use chewing gum and hair as retrospective dosimeters. The chewing gum would be used after an unexpected radiation event of external type whereas human hair is examined after chronic intake of uranium. Chewing gum containing xylitol and sorbitol was analyzed using electron paramagnetic resonance (EPR) and the hair was analyzed by alphaspectrometry following radiochemistry and by synchrotron radiation microbeam x-ray fluorescence (SR μ-XRF).Xylitol and chewing gum (in this particular case, V6) are in the present work found to be valuable dosimeters after unexpected radiation events. The xylitol signal linearity with dose in the interval 0-10 Gy was confirmed (r2=1.00). The doses to the coating of the chewing gums were determined 4-6 days after irradiation with an uncertainty of less than 0.2 Gy (1 SD). Spectral dependence with time after exposure was found, but was, however, minimal between 4-8 days.Hair was evaluated and compared with urine as biodosimeter after ingestion and inhalation intake of uranium. Concentrations of 234U and 238U and their activity ratios were measured in the hair, urine and drinking water sampled from 24 drilled bedrock well water users in Östergötland, Sweden, as well as among 8 workers at a nuclear fuel fabrication factory, Westinghouse Electric Sweden. The results show that there is a stronger correlation between the uranium concentrations in the drinking water of the well water and the users’ hair (r2 = 0.50) than with their urine (r2 = 0.21). There is also a stronger correlation between the 234U/238U activity ratios of water and hair (r2 = 0.91) than between water and urine (r2 = 0.56). The individual absorbed fraction of uranium, the ƒ value, calculated as the ratio between the excreted amount of uranium in urine and hair per day and the daily drinking water intake of uranium stretched from 0.002 to 0.10 with a median of 0.023. The uranium concentrations of the fuel factory workers’ hair and urine were also obtained as well as that of personal air sampler (PAS) filters for the determination of inhaled uranium activity. A large day-to-day variation (7-70 Bq d-1) of the inhaled 234U activity was seen over a 6 week period. Over a 12 week period the 234U activity concentration in urine was similarly seen to vary from 2 to 50 mBq kg-1. Four hair samples from the same subject and period showed less variation (100-240 mBq g-1). The uranium inhalation to urine and hair factors finh,u and finh,h were found to be 0.0014 and 0.0002 respectively given by calculations based on the measured PAS, urine and hair data from two individuals. The SR μ-XRF measurements showed that uranium is present in an outer layer of the hair shaft, about 10-15 μm wide. The measurements also revealed particles containing uranium being present on the surface of unwashed hair shafts. However, the washed hair shafts showed few, if any, particles.This thesis concludes that chewing gum and hair can be used as retrospective dosimeters after external radiation and after intake of uranium respectively.
