Radio-Fluorogenic Gel Dosimetry with Coumarin.

Gel dosimeters are attractive detectors for radiation therapy, with properties similar to biological tissue and the potential to visualize volumetric dose distributions. Radio-fluorogenesis is the yield of fluorescent chemical products in response to energy deposition from ionizing radiation. This report shares the development of a novel radio-fluorogenic gel (RFG) dosimeter, gelatin infused with coumarin-3-carboxlyic acid (C3CA), for the quantification of imparted energy. Aqueous solutions exposed to ionizing radiation result in the production of hydroxyl free radicals through water radiolysis. Interactions between hydroxyl free radicals and coumarin-3-carboxylic acid produce a fluorescent product. 7-hydroxy-coumarin-3-carboxylic acid has a blue (445 nm) emission following ultra-violet (UV) to near UV (365⁻405 nm) excitation. Effects of C3CA concentration and pH buffers were investigated. The response of the RFG was explored with respect to strength, type, and exposure rate of high-energy radiation. Results show a linear dose response relationship independent of energy and type, with a dose-rate dependency. This report demonstrates increased photo-yield with high pH and the utility of gelatin-RFG for phantom studies of radiation dosimetry.

Uranium mobility across annual growth rings in three deciduous tree species.

Black walnut (Juglans nigra), slippery elm (Ulmus rubra), and white ash (Fraxinus americana) trees were evaluated as potential archives of past uranium (U) contamination. Like other metals, U mobility in annual growth rings of trees is dependent on the tree species. Uranium concentrations and isotopic compositions (masses 234, 235, 236, and 238) were analyzed by thermal ionization mass spectrometry to test the efficacy of using tree rings to retroactively monitor U pollution from the FFMPC, a U purification facility operating from 1951 to 1989. This study found non-natural U (depleted U and detectable 236U) in growth rings of all three tree species that pre-dated the start of operations at FFMPC and compositional trends that did not correspond with known contamination events. Therefore, the annual growth rings of these tree species cannot be used to reliably monitor the chronology of U contamination.

In vivo measurement of 241Am in the lungs confounded by activity deposited in other organs.

Radioactive material deposited in multiple organs of the body is likely to confound a result of an in vivo measurement performed over the lungs, the most frequently monitored organ for occupational exposure. The significance of this interference was evaluated by measuring anthropometric torso phantoms containing lungs, liver, skeleton, and axillary lymph nodes, each with a precisely known quantity of 241Am uniformly distributed in the organs. Arrays of multiple high-resolution germanium detectors were positioned over organs within the torso phantom containing 241Am or over proximal organs without activity to determine the degree of measurement confounding due to photons emitted from other source organs. A set of four mathematical response functions describes the measured count rate with detectors positioned over each of the relevant organs and 241Am contained in the measured organ or one of the other organs selected as a confounder. Simultaneous solution of these equations by matrix algebra, where the diagonal terms of the matrix are calibration factors for a direct measurement of activity in an organ and the off-diagonal terms reflect the contribution (i.e., interference or cross-talk) produced by 241Am in a confounding organ, yields the activity deposited in each of the relevant organs. The matrix solution described in this paper represents a method for adjusting a result of 241Am measured directly in one organ for interferences that may arise from 241Am deposited elsewhere and represents a technically valid procedure to aid in evaluating internal dose based upon in vivo measurements for those radioactive materials known to deposit in multiple organs.

Detection efficiency for measuring 241Am in axillary lymph nodes using different types and sizes of detectors.

The detection efficiency and interference susceptibility of four different types of low energy photon detectors, each with a unique geometric arrangement, were compared for direct measurement of Am deposited in the axillary lymph nodes. Although the most efficient detector was a single large 23,226 mm square phoswich detector, it was also the most susceptible to confounding depositions from activity deposited in adjacent organs. The array of two 2,800 mm high purity germanium detectors exhibited the highest efficiency per unit detector area with some resistance to confounding from activity deposited in the lungs. The array of two 4,560 mm NaI(Tl) detectors was the least susceptible to confounding and nearly as efficient per square millimeter as the high purity germanium detector array. Thus, selection of a detector system for in vivo measurement of activity deposited in the axillary lymph nodes should consider whether there is a likelihood for activity deposited in other organs, such as the lungs, skeleton, or liver, to create an interference that will confound the measurement result.

Significant systemic therapeutic effects of high-LET immunoradiation by 212Pb-trastuzumab against prostatic tumors of androgen-independent human prostate cancer in mice.

The purpose of this study was to determine therapeutic effects and systemic toxicity of 212Pb-trastuzumab in an orthotopic model of human prostate cancer cells in nude mice. TCMC-Trastuzumab was radiolabeled with 212Pb. The 212Pb-trastuzumab generated from the procedure was intact and had high binding affinity with a dissociation constant (of 3.9±0.99 nM. PC-3MM2 cells, which expressed a lower level of HER2 both in culture and in tumors, were used in therapy studies. A single intravenous injection of 212Pb-trastuzumab reduced tumor growth by 60-80%, reduced aortic lymph node metastasis, and prolonged the survival of tumor-bearing mice. Treatment with 212Pb-trastuzumab did not cause significant changes in body weight, serum glutamic pyruvic transaminase (SGPT), blood urea nitrogen (BUN), hematological profiles, and histological morphology of several major organs of tumor-bearing mice. These findings suggest that a systemic delivery of 212Pb-trastuzumab could be an effective modality for management of advanced human prostate cancer.

The influence of bone-density on in vivo K x-ray fluorescence bone-lead measurements.

Mathematical simulations and benchmark measurements were performed to assess the impact that normal variations in human calcium content have on in vivo K x-ray fluorescence measurements of lead in bone. Four sets of cortical bone tissue simulants were fabricated containing from 20.8% to 23.8% calcium (by weight) for measurement in a surrogate (phantom) of the human leg. The net counts detected in the coherent backscatter peak at 88.034 keV using a Cd source indicate a positive trend, with a variability of up to 17% over the range of assessed calcium content. Mathematical simulations confirm this trend and also demonstrate that the contribution of 87.3 keV Pb Kß2 counts, which are unresolved in measurements, do not contribute significantly to the coherent peak at low levels of bone-lead content. Both measurements and simulations confirm that calcium is a statistically significant parameter in predicting the K-XRF response and suggest that lead levels may be over-predicted for individuals having low bone density compared to the calibration matrix. Simulations identify a 4.5% negative bias in measured lead values for each 1% increase in calcium weight percent in the bone matrix as compared to the calibration matrix. It is therefore important to accommodate this uncertainty when performing epidemiological studies of populations having a wide range of bone densities.

Monte Carlo simulation of an anthropometric phantom used for calibrating in vivo K-XRF spectroscopy measurements of stable lead in bone.

An anthropometric surrogate (phantom) of the human leg was defined in the constructs of the Monte Carlo N Particle (MCNP) code to predict the response when used in calibrating K x-ray fluorescence (K-XRF) spectrometry measurements of stable lead in bone. The predicted response compared favorably with measurements using the anthropometric phantom containing a tibia with increasing stable lead content. These benchmark measurements confirmed the validity of a modified MCNP code to accurately simulate K-XRF spectrometry measurements of stable lead in bone. A second, cylindrical leg phantom was simulated to determine whether the shape of the calibration phantom is a significant factor in evaluating K-XRF performance. Simulations of the cylindrical and anthropometric calibration phantoms suggest that a cylindrical calibration standard overestimates lead content of a human leg up to 4%. A two-way analysis of variance determined that phantom shape is a statistically significant factor in predicting the K-XRF response. These results suggest that an anthropometric phantom provides a more accurate calibration standard compared to the conventional cylindrical shape, and that a cylindrical shape introduces a 4% positive bias in measured lead values.

Population monitoring for acute exposure to 210Po.

OBJECTIVE: To investigate the feasibility of using single void urine samples to monitor internal radiation exposure of first responders and large populations int he event of a radiological incident involving the intentional dispersal of 210Po. METHODS: Urinary excretion of 210Po was evaluated and organ absorbed and effective doses were calculated subsequent to an acute unit intake of 210Po. RESULTS: 210Po can be detected in single void urine samples at levels sufficient to detect effective dose below recommended limits. Minimum intakes of 210Po that would result in clinically significant effects were estimated. CONCLUSIONS: Collection and analysis of single void urine samples is adequate to identify persons who may be exposed in the event of a radiological emergency involving 210Po. Also, the first responder limit appears to be sufficiently protective to prevent clinically significant deterministic effects.

Modification to the Monte Carlo N-particle code for simulating direct, in vivo measurement of stable lead in bone.

Monte Carlo N-Particle version 4C (MCNP4C) was used to simulate photon interactions associated with in vivo x-ray fluorescence (XRF) measurement of stable lead in bone. Experimental measurements, performed using a cylindrical anthropometric phantom (i.e., surrogate) of the human leg made from tissue substitutes for muscle and bone, revealed a significant difference between the intensity of the observed and predicted coherent backscatter peak. The observed difference was due to the failure of MCNP4C to simulate photon scatter associated with greater than six inverse angstroms of momentum transfer. The MCNP4C source code, photon directory, and photon library were modified to incorporate atomic form factors up to 7.1 inverse angstroms for the high Z elements defined in the K XRF simulation. The intensity of the predicted coherent photon backscatter peak at 88 keV using the modified code increased from 3.50 x 10(-9) to 8.59 x 10(-7) (roughly two orders of magnitude) and compares favorably with the experimental measurements.

Radiation exposure from work-related medical X-rays at the Portsmouth Naval Shipyard.

BACKGROUND: Previous analyses suggest that worker radiation dose may be significantly increased by routine occupational X-ray examinations. Medical exposures are investigated for 570 civilian workers employed at the Portsmouth Naval Shipyard (PNS) at Kittery, Maine. The research objective was to determine the radiation exposure contribution of work-related chest X-rays (WRX) relative to conventional workplace radiation sources. METHODS: Methods were developed to estimate absorbed doses to the active (hematopoietic) bone marrow from X-ray examinations and workplace exposures using data extracted from worker dosimetry records (8,468) and health records (2,453). Dose distributions were examined for radiation and non-radiation workers. RESULTS: Photofluorographic chest examinations resulted in 82% of the dose from medical sources. Radiation workers received 26% of their collective dose from WRX and received 66% more WRX exposure than non-radiation workers. CONCLUSIONS: WRX can result in a significant fraction of the total dose, especially for radiation workers who were more likely to be subjected to routine medical monitoring. Omission of WRX from the total dose is a likely source of bias that can lead to dose category misclassification and may skew the epidemiologic dose-response assessment for cancers induced by the workplace.

Long-term stewardship of the environmental legacy at restored sites within the Department of Energy nuclear weapons complex.

It is readily apparent, as the Department of Energy Office of Environmental Management proceeds in remediating its vast network of contaminated nuclear weapons facilities, that final cleanup at many facilities will not be performed to a level allowing unrestricted use of the facility. Instead, these facilities must rely on engineering, administrative, and institutional controls to ensure the level of cleanup performed at the site remains adequately protective of public health and the environment. In order for these controls to remain effective, however, a plan for long-term stewardship of these sites must be developed that is approved by the U.S. Congress. Although this sounds simple enough for the present, serious questions remain regarding how best to implement a program of stewardship to ensure its effectiveness over time, particularly for sites with residual contamination of radionuclides with half-lives on the order of thousands of years. Individual facilities have attempted to answer these questions at the site-specific level. However, the complexities of the issues require federal support and oversight to ensure the programs implemented at each of the facilities are consistent and effective. The Department of Energy recently submitted a report to Congress outlining the extent of long-term stewardship needs at each of its facilities. As a result, the time is ripe for forward thinking Congressional action to address the relevant issues and ensure the remedy of long-term stewardship successfully carries out its intended purpose and remains protective of public health and the environment. The regulatory elements necessary for the stewardship program to succeed can only be implemented through the plenary powers of the U.S. Congress.