Landauer (United States)

A cohort mortality study was conducted of 123,401 industrial radiographers in the United States to estimate risks following protracted radiation exposures. The cohort was constructed from the Nuclear Regulatory Commission Radiation Exposure Information Reporting System and the Landauer, Inc. dosimetry databases. Workers were monitored between 1939 and 2011 and were exposed mainly to external gamma radiation from 192Ir and 60Co. Causes of death were obtained from the National Death Index and state mortality files with follow-up through 2019. The mean duration of follow-up was 27.7 years. Nearly 19% of workers were monitored for more than 10 years. There were 30,617 (24.8%) who worked at shipyards and 5,071 (4.1%) at nuclear power plants with the potential for asbestos exposure. The mean radiation dose to the red bone marrow (RBM) was 15.2 mGy (maximum 1.24 Gy; percent >100 mGy was 3.6%), 17.2 mGy to lung, 18.1 mGy to colon, 11.9 mGy to brain, and 18.1 mGy to heart. Overall, 30,560 deaths occurred; the Standardized Mortality Ratio and 95% confidence interval for all-cause mortality was 0.92 95% CI (0.91, 0.93); for all solid cancers 1.01 (0.99, 1.03; n = 7,734); for ischemic heart disease (IHD) 0.83 (0.81, 0.85; n = 5,820); for cerebrovascular disease (CeVD) 0.88 (0.83, 0.93; n = 1,257); for mesothelioma 6.08 (5.35, 6.89; n = 248); and for asbestosis 13.4 (11.2, 15.9; n = 134). The Cox linear excess relative risk (ERR) per 100 mGy (95% CI) for leukemia (excluding CLL) was 0.45 (0.05, 0.85) and for non-Hodgkin lymphoma (NHL) was 0.33 (0.04, 0.62). For all solid cancers it was 0.06 (0.02, 0.10); lung cancer 0.11 (0.04, 0.19); all solid cancers excluding lung cancer and mesothelioma 0.02 (-0.03, 0.07); Parkinson's disease 0.24 (-0.13, 0.61); IHD -0.03 (-0.06, 0.01); and CeVD 0.05 (-0.08, 0.17). The ERR per 100 mGy for chronic obstructive pulmonary disease (COPD) was 0.19 (0.08, 0.30) and was similar in magnitude to that for lung cancer. This finding suggests that residual confounding by smoking may have influenced the results, warranting cautious interpretations. No significant association was found between cumulative radiation exposure and all solid cancers after excluding lung cancer and mesothelioma, nor for IHD or CeVD. The marginally non-significant increased risk of Parkinson's disease, also seen in other Million Person Study cohorts, requires further investigation. Early workers monitored entirely before 1979 had the same linear ERR per 100 mGy for solid cancers [0.06 (0.00, 0.12) n = 3,587] as for all other more contemporary workers monitored after 1978 [0.07 (0.01,0.13) n = 4,150]. This report provides convincing evidence that low-dose and low-dose-rate exposures over time significantly increases the risk of leukemia (excluding CLL) following cumulative doses up to 200 mGy while also providing information on early versus contemporary workers.

IntroductionGold nanoparticles (AuNPs) are visualized and quantified in a human‐sized phantom with a clinical MDCT scanner.MethodsExperiments were conducted with AuNPs between 0.00171 and 200 mgAu/mL. CT images were acquired at 80, 100, 120, and 140 kVp in a 33‐cm phantom. Image contrast due to AuNPs was experimentally determined from regions of interest (ROIs) and effective linear attenuation coefficients were calculated from CT x‐ray spectra with consideration of tissue attenuation.ResultsThe typical 12‐bit dynamic range of CT images was exceeded for AuNPs at 150 mgAu/mL. A threshold concentration of 0.3–1.4 mgAu/mL was determined for human visualization in 1‐mm images at a typical diagnostic CTDIvol of 23.6 mGy. Optimal image contrast was also achieved at 120 kVp and verified by calculation.ConclusionsWe have shown that scanners capable of reconstructing images with extended Hounsfield scales are required for distinguishing any contrast differences above 150 mgAu/mL. We have also shown that AuNPs result in optimal image contrast at 120 kVp in a human‐sized phantom due to gold’s 80.7 keV k‐edge and the attenuation of x‐rays by tissue. Typical CT contrast agents, like iodine, require the use of lower kVps for optimal visualization, but lower kVps are more difficult to implement in the clinic because of elevated noise levels, elongated scan times, and/or beam‐hardening artifacts. This indicates another significant advantage of AuNPs over iodine not yet discussed in the literature.

During brachytherapy for cancer of uterine cervix using 192 Ir, organ doses should be managed. In the clinical treatment, the absorbed doses are calculated by a therapeutic planning system, but actual doses are not measured. In order to measure the amount of radiation the rectum is exposed to we have developed a new rectum dosimeter using an optically stimulated luminescence (OSL) sheet. In this study, we aim to propose a calibration procedure. First, we fabricated a novel phantom which consisted of water and acrylic; a radioactive source and an area in which our rectum dosimeter can be inserted. Second, a clinically used therapeutic system was used to calibrate the rectum dosimeter; namely, the doses related to the dosimeters were calibrated using precise calculations. At this time, to obtain a three-dimensional image from the system, a one-beam computed tomography (CT) system was used. In addition, a Monte-Carlo simulation was performed to consider the difference between ideal conditions (100% water used in the therapeutic planning system) and realistic phantoms. Then, an experiment to calibrate the actual rectum dosimeter was carried out. As the results show, a calibration curve can be determined in the dose region of 0.1-10 Gy with an accuracy of 15%. Furthermore, absorbed dose of impact of distance between radioactive source and dosimeters was estimated using Monte-Carlo simulation.

Background The reconstruction of lifetime radiation doses for medical workers presents special challenges not commonly encountered for the other worker cohorts comprising the Million Worker Study. Methods The selection of approximately 175,000 medical radiation workers relies on using estimates of lifetime and annual personal monitoring results collected since 1977. Approaches have been created to adjust the monitoring results so that mean organ absorbed doses can be estimated. Results Changes in medical technology and practices have altered the radiation exposure environments to which a worker may have been exposed during their career. Other temporal factors include shifts in regulatory requirements that influenced the conduct of radiation monitoring and the changes in the measured dose quantities. Conclusions The use of leaded aprons during exposure to lower energy X rays encountered in fluoroscopically based radiology adds complexity to account for the shielding of the organs located in the torso when dosimeters were worn over leaded aprons. Estimating doses to unshielded tissues such as the brain and lens of the eye become less challenging when dosimeters are worn at the collar above the apron. The absence of leaded aprons in the higher energy photon settings lead to a more straightforward process of relating dosimeter results to mean organ doses.

Presented is the first accumulating capacitive radiation sensor for low-dose, long-term exposures observed in occupational dosimetry. The sensor's capacitance-voltage curve undergoes a semi-permanent negative shift due to ionizing radiation. By measuring the change in capacitance at a given voltage in the depletion region, the ionizing radiation that has been present on the sensor can be extracted. In order to achieve the low dose resolution required (less than 100 μGy) for occupational dosimetry, parameters such as the oxide thickness and annealing conditions are optimized. The result for a 2 mm × 2 mm sensor is 1.6 fF per 100 μGy, a capacitance shift detectable with commercial electronics.