Tano, Jolan E.Yasuda, HiroshiGonzales, Chryzel Angelica B.
11页
查看更多>>摘要：The potential confounding influence of heat on the electron spin resonance (ESR) spectra of fingernails has been studied in irradiated and unirradiated samples. The samples were heated at different temperatures between 20 and 160 ? for 1 h. The experimental temperature range was selected considering that the fingernails may be accidentally exposed to heat during normal daily activities or in a certain working environment. Changes in the overall visual shape of the ESR spectra were observed in the gamma-ray irradiated and unirradiated samples heated above 100 ?, thereby showing that a heat-induced signal was present in the fingernail spectrum. The effect of heating showed an evident bulge in the spectra (between g = 2.014 and 2.024), which was more pronounced in both the irradiated and unirradiated samples heated at higher temperatures, with reduced peak-to-peak intensities and broadened spectra. The heat-induced signal was unstable, decayed for about a few days, and was easily removed upon treatment with water. While the radiation-induced signal (RIS) was stable up to 160 ?, our results also suggest that heating up to 160 ? did not affect the sensitivity of the RIS, but the heat-induced signal was still observed after irradiation. Similar thermal stability was also found in both the irradiated and unirradiated samples, suggesting that the heat-induced signal and RIS were overlapped, but probably independent. Overall, these findings will be useful to obtain a more reliable radiation dose assessment using fingernails that
查看更多>>摘要：& nbsp;The objective of this work is to demonstrate that MgB4O7:Ce,Li, a new optically stimulated luminescence (OSL) dosimetric material, shows improved response for proton therapy dosimetry, with less reduction in luminescence detector efficiency with the particle linear energy transfer (LET). MgB4O7:Ce,Li was synthesized and its luminescence efficiency as a function of LET was characterized for dose-averaged LET values from 0.73 keV/mu m up to 74.9 keV/mu m using proton, He-4, and C-12 ion beams. Commercial Al2O3:C OSLDs were also used for comparison. Monte Carlo simulations were used to predict the material's response in pristine and spread-out Bragg peaks (SOBP), suggesting the MgB4O7:Ce,Li would offer minimum quenching in proton beams of energies relevant to radiotherapy. This prediction was confirmed by irradiations of MgB4O7:Ce,Li and Al2O3:C along SOBPs from proton beams. The results demonstrate that new OSL materials optimized for proton dosimetry can be developed using their dose response to low-LET radiation as a guide during material development.
查看更多>>摘要：Whole-body counters (WBC) are used to detect potential intake of radioisotopes in the human body. To achieve a precise measurement of an incorporated activity, a WBC needs to be properly characterized and calibrated. However, due to technical limitations, not every geometry can be calibrated using adequate physical phantoms. To extend the use of a standard calibration to other geometries, we performed GEANT4 Monte Carlo (MC) simulations characterizing the WBC at the Spiez Laboratory, Switzerland. The aim of our project was threefold: (1) to validate our MC model against an experimental model, (2) to study the impact of a person's size on the detection efficiency of the WBC and (3) to study the impact of intake scenarios on the estimation of whole-body activity. First, we simulated the calibration of the WBC with the IGOR phantoms. Then, we computed the detection efficiency of the WBC for homogenous whole-body contamination using ICRP adult voxel phantoms scaled to sizes. We computed the bias of the activity that would be measured by the WBC relative to the activity contained in the body in case of inhalation, modeled by the ICRP biokinetic models. Our computed detection efficiency obtained with the IGOR phantoms agreed within 5% with the calibration measurements. We found that WBC efficiency depends on the weight over height ratio (w/h). We proposed a criterion for the calibration curve selection adequate for any person, and we validated this criterion using ICRP pediatric phantoms. We estimated that the precision of a whole-body activity measurement in the case of a homogeneous activity distribution is at the level of 20%. Finally, for a non-homogenous contamination of the body by inhalation, we showed that the WBC measurements can overestimate intake up to 40-80% depending on the absorption type of the substance into the blood, and the size of the scanned person. In conclusion, our study confirms the need of using phantoms with different sizes to calibrate a WBC and shows that in case of a highly non-homogenous distribution of the radioisotope in the body, the WBC may significantly overestimate the whole-body activity. To limit this bias, we recommend scanning the entire body with the detectors instead of setting them at fixed positions or increasing the distance between the detectors and the phantom.
NSTL
Elsevier