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PubMed1990

A new method for calculating the distribution of radioactivity in man measured with a whole-body counter.

A whole-body counter with a scanning bed and two opposite (antero-posterior) probes was used to obtain profiles of count rates of radioactivity held in the whole body. The distribution of the activity in the patient was calculated by solving an overdetermined system (more equations than unknowns) of linear equations with the Chebyshev method, the least-squares method, and an iterative method. The iterative method gave the best results, especially in the case of distributions with peaks of radioactivity. Some in-vivo applications of the method are presented.

Diphosphonates↗

PubMed1991

A local area network for controlling the ordering and purchasing of radioactive material.

Efficient control over the purchase and receipt of radioactive material is a necessary part of any radiation safety program. We describe a novel computerized method for monitoring the flow of radioactive material within a large broad-licensed medical research complex. The Local Area Network (LAN) described interfaces the radiation safety office with radionuclide receiving, the authorized user, grants and contracts, special accounts, and purchasing. Task-specific software enables the authorized user to place an order and allows the monitoring of possession/ordering limits, personnel, date of order, and time of receipt via the screen. The resultant data base is easily annexed for specific information. The system is user-friendly and adaptable to any set of circumstances.

Academic Medical Centers↗

PubMed1994

A rapid method for modeling the kinetics of radioactive progeny applied to thorium in the lungs.

A general method for solving first-order compartmental models (recycling and nonrecycling) with any number of radioactive progeny is described and a heuristic proof of the method is provided. The method can be applied to any system where the progeny are assumed to behave isokinetically with the parent, as is the case with the biokinetic models currently recommended by the ICRP. The method is simple to apply, and its application to the modeling of radioactive progeny in the lungs following inhalation of thorium oxides is illustrated. The new ICRP respiratory tract model is used for this illustration.

Humans↗

PubMed1995

A method for computing the decision level for samples containing radioactivity in the presence of background.

It is often necessary to make a decision whether or not a sample contains radioactivity in excess of background. The most common procedure is a deterministic approach that compares the result from each sample against a critical level, Lc. Originally Lc was derived from the case where each sample is paired with a blank or control that is known not to contain excess radioactivity. However, most analytic laboratories do not process a blank with each and every sample. Another approach computes Lc using a collection of measurements to form a "well defined" background. This paper presents a method for determining a decision level, L delta, that includes the uncertainties in both the mean and variance of background and how these combine to form uncertainties in estimating the tails of the background distribution. The values of L delta are greater than Lc for a given Type I error. It can be applied whenever the true distribution of background is either normal or log normal. The process is not restricted to counting statistics and is valid for identifying excess contamination of any type providing that unknown samples are processed identically to background samples.

Biological Assay↗

PubMed1998

The need for better methods to determine release criteria for patients administered radioactive material.

In current NRC regulations, three options exist that may be used to determine release criteria for patients administered radioactive materials. Absorbed dose estimates may be based on administered activity, measured dose rate, or on patient-specific calculations. All of these methods proposed by the NRC can lead to overestimation of the dose equivalent to others due to their oversimplified nature. The primary oversimplifications are the use of a point source methodology and using the measured surface entrance dose rate to determine whole body dose. In order to show the inaccuracy of these oversimplifications for 131I, results using Monte Carlo radiation transport analysis with simplified anthropomorphic mathematical phantoms were determined. These results were then compared to actual patient measurements and the results of point source analysis. The measurement data were taken from 49 131I radioimmunotherapy patients. The point source calculations were performed using well established methodologies and using the same assumptions as in the NRC regulations for patient release criteria. Monte Carlo results were obtained by implementing two simplified 70 kg anthropomorphic phantoms and performing radiation transport simulation. The activity in the "patient" phantom was assumed to be localized in the abdominal region to correspond to the activity localization seen in the radioimmunotherapy patients who were measured. Dose equivalents per unit cumulated activities were determined for 131I using the various methods. The relationship between measured dose equivalent per unit cumulated activity and whole body dose equivalent per unit cumulated activity was also investigated using Monte Carlo analysis. The point source method as implemented by the NRC yields an estimated dose equivalent per unit cumulated activity of 1.6 x 10(-8) mSv MBq(-1) s(-1) at 1 m (2.2 x 10(-4) rem mCi(-1) h(-1) at 1 m), and the Monte Carlo based method yielded a whole body dose equivalent per unit cumulated activity in the target phantom of 6.8 x 10(-9) mSv MBq(-1) s(-1)(9.0 x 10(-5) rem mCi(-1) h(-1)) for abdominal localization of activity in the source phantom. The measurements of the radioimmunotherapy patients yielded an average result of 1.0 x 10(-8) mSv MBq(-1) s(-1) (13 x 10(-4) rem mCi(-1) h(-1)). When corrected for the difference between measured surface dose equivalent and whole body dose equivalent as determined by Monte Carlo analysis, these measurements represent a whole body dose equivalent per unit cumulated activity of about 6.2 x 10(-9) mSv MBq(-1) s(-1) (8.1 x 10(-5) rem mCi(-1) h(-1)). Based on these results, the current NRC dose-based methodology for the release of patients administered radioactive materials significantly overestimates the dose equivalent to others from 131I therapy patients.

Government Agencies↗

PubMed1999

Unwanted radioactive sources in the public domain: a historical perspective.

In the 1920's, reports of radium sources entering the public domain in an uncontrolled manner began to appear in the press and in the literature. Additionally, gold jewelry was made from depleted radon gold seeds which, in some cases, resulted in radiation injuries to the persons wearing the jewelry. Such jewelry was made as early as 1910. For many years, radium was distributed and used largely without regulatory oversight for safety. In the 1950's, increasing concern over the radiation hazards associated with the inadequate use, control, and disposal of radium sources resulted in increased regulatory oversight by the States, with significant assistance from the U.S. Public Health Service. In 1958, the U.S. Atomic Energy Commission staff proposed extension of the general license concept to include measuring, gauging, and controlling devices. Since then, more than 1.8 million radioactive devices have been distributed under the general licenses in 10 CFR Part 31.5 and equivalent Agreement State regulations. These devices are typically used with minimal regulatory oversight. In recent years there has been an increasing number of reports of radioactive sources and devices appearing in the public domain as a result of inadequate control and disposal of these items with attendant risk of environmental contamination and radiation exposure. As a result of concerns over these developments there have been calls for increased regulatory oversight of general licensees. It is ironic that the present problems are the result of a program that was established about the time that States were increasing regulatory oversight over radium to address similar problems with radium.

Conservation of Natural Resources↗

PubMed2000

Design and development of a radioactive gas monitoring system in the positron emission tomography center.

This paper presents experiences in developing a simple, inexpensive radioactive gas monitoring system that proved to be practical and useful at a clinical and research Positron Emission Tomography (PET) Center. The system is described from four key aspects: (1) design of radiation detectors and calibrations; (2) use of an existing PC-based hospital-wide facility management network; (3) placement and oversight of real-time PC monitor stations; and (4) modification of a ventilation system in the PET center. The radiation safety oversight efficacy of a real-time PC-based radioactive gas monitoring system in the academic PET center also is discussed.

Calibration↗

PubMed2003

A proposed method to determine the decision level for radioactivity measurements.

When measuring radioactivity, the problem rises of deciding whether or not a sample contains radioactivity in excess of background and above which value the result is meaningful. This decision process is why the notion of decision level was introduced. Whereas there is unanimity about its definition, this is not the case for its calculation, and many expressions have been proposed. This article contains a comparison of several decision level models by means of the calculation of actual false positive probability. First, three models are compared for the case of a well-known background, then a proposed model is developed and the four models are compared for the case of a poorly-known background. It appears from this study that, in order to be valid, the formula of the decision level must verify three conditions. First, the counting times have to appear symmetrically in the formula of the decision level; second, for long background counting times, the expression has to be equivalent to the one obtained with the corrected normal distribution corresponding to the Poisson law for the case of a well-known background; and, third, for large background, the expression has to be equivalent to those given by the three former models. It will be demonstrated that only the proposed model fulfills these requirements.

Algorithms↗

PubMed2004

The use of autoradiography for investigating the distribution of radioactivity in lung counter calibration sources.

This paper shows that autoradiography is a useful technique for investigating radioactivity distributions in lung phantoms and planar sources. It was applied to a sliced lung phantom that had activity homogeneously distributed throughout the tissue substitute material and to laminated planar sources in an attempt to answer three questions: 1) Was the activity distribution the same in each slice of the sliced homogeneous lung set? 2) Was the activity distribution the same for each of the laminated planar sources? and 3) Were the activity distributions the same between slices and planar sources? The activity distribution, including identification of some locations of elevated activity in the sliced homogeneous lungs, was easily obtained using autoradiography. This study demonstrates that neither the sliced homogeneous lung sets nor the laminated planar sources had a homogeneous distribution of radioactivity, as had been previously thought.

Autoradiography↗

PubMed1996

MR-based correction of brain PET measurements for heterogeneous gray matter radioactivity distribution.

Partial volume and mixed tissue sampling errors can cause significant inaccuracy in quantitative positron emission tomographic (PET) measurements. We previously described a method of correcting PET data for the effects of partial volume averaging on gray matter (GM) quantitation; however, this method may incompletely correct GM structures when local tissue concentrations are highly heterogeneous. We have extended this three-compartment algorithm to include a fourth compartment: a GM volume of interest (VOI) that can be delineated on magnetic resonance (MR) imaging. Computer simulations of PET images created from human MR data demonstrated errors of up to 120% in assigned activity values in small brain structures in uncorrected data. Four-compartment correction achieved full recovery of a wide range of coded activity in GM VOIs such as the amygdala, caudate, and thalamus. Further validation was performed in an agarose brain phantom in actual PET acquisitions. Implementation of this partial volume correction approach in [18F]fluorodeoxyglucose and [11C]-carfentanil PET data acquired in a healthy elderly human subject was also performed. This newly developed MR-based partial volume correction algorithm permits the accurate determination of the true radioactivity concentration in specific structures that can be defined by MR by accounting for the influence of heterogeneity of GM radioactivity.

Aged↗

PubMed1984

Differential radioactivity monitor for noninvasive detection of ocular melanoma.

A novel instrument for the noninvasive diagnosis of ocular melanoma was evaluated with 67Ga in patients with pathologically confirmed tumours. The decision to enucleate was based on the results of standard ophthalmic diagnostic modalities including the 32P uptake test. The differences in the ocular radioactivity at 48-72 h predicted the presence of ocular abnormality. A positive differential result was found for tumours having a volume of greater than 600 mm3. Smaller tumours indicated lower retention of 67Ga in the eye with the tumour, whereas control subjects showed less than 2% differences in the radioactivity present in either eye.

Choroid Neoplasms↗

PubMed1989

A review of the secretion of radioactivity in human breast milk: data, quantitative analysis and recommendations.

A general method is given to quantify the radioactivity ingested by a breast-fed infant following maternal radiopharmaceutical administration, and to derive the period to interrupt feeding which reduces the corresponding effective dose equivalent to below 1 mSv. Results are presented from applying the method to all available measurements of radioactivity secreted in breast milk. This review includes some hitherto unpublished data, takes more account of the scarcity of the available data, and has resulted in modifications to the guidance for interrupting breast feeding. Recommendations for interrupting feeding with mature milk have been expanded into four categories: (1) interruption not essential; (2) interruption for a fixed period of time; (3) interruption until measurements indicate feeding can be resumed; and (4) cease breast feeding. Changes to the earlier guidance are that 99Tcm-pertechnetate, (99Tcm) erythrocytes, 125I-OIH and 131I-OIH have been moved to the third category, and that recommendations have been included for 99Tcm-DMSA, 99Tcm-glucoheptonate, 99Tcm-HDP, 99Tcm-HMDP, 123I-iodide and 123I-OIH. Before recommendations (1) and (2) can be issued to a mother, quality control measurements must be made of the radiopharmaceutical administered. Recommendations (3) or (4) only should be issued to mothers secreting colostrum. If there are changes in the recommended dosimetry in the future, the calculated fractional ingested activities can be used as a basis to refine the recommendations.

Breast Feeding↗

PubMed1991

Radiological protection guidance for radioactive patients--new data for therapeutic 131I.

Patients leaving hospital after 131I treatment for thyrotoxicosis face restrictions on their contact with other members of the public. These restrictions depend on the level of residual body radioactivity which for practical purposes can be taken to be almost entirely in the thyroid gland. This study provides an appropriate data base from which to draw advice to patients consistent with current radiological protection requirements in terms of the duration of these restrictions. Thyroidal retention of 131I was measured in 77 thyrotoxic patients over a period of 1-50 days after a first therapeutic administration of the radionuclide. Mean 131I activity in the gland (+/- S.D.) at 1 day was 56.1 +/- 11.1% of the administered dose activity and thereafter retention followed a single exponential decay pattern with a mean effective half-life (+/- S.E.M.) of 6.35 +/- 0.14 days. In patients who required further 131I therapy, there was evidence that retention could be markedly reduced if there was virtual ablation of thyroid tissue. It is proposed that these retention data can be used to determine body radioactivity at any interval after the administration of 131I for treatment of thyrotoxicosis, thus obviating the need for serial measurements in every individual patient.

Adult↗

PubMed2000

Radioactive contamination of contact lenses during radioiodine therapy.

Although the secretion of radioiodine in tears is not unexpected, there are only few investigations in that field. We report the measurement of 131I in disposable contact lenses for daily use during radioiodine treatment. After administration of 740 MBq 131I, all contact lenses of a 59-year-old female used the day before and 5 days after radioiodine therapy were collected and measured in a gamma counter. Activities of 124 Bq (right) and 139 Bq (left) were measured in the contact lenses used during the first day after administration of radioiodine. The activity in the contact lenses of the following days was significantly lower. An initial dose rate of approximately 0.31 microSv x h(-1) was caused by the radioactivity resulting in a total dose of 13 microSv to the patient's eye lens. That dose is negligible compared to the dose caused by the incorporated radioactivity.

Contact Lenses, Hydrophilic↗

PubMed2004

Delivery and collection of radioactive packages to and from UK hospital nuclear medicine departments.

Under radiation protection legislation in the UK, employers have a duty to maintain appropriate records to account for radioactive materials in their possession and to ensure security of these materials. This applies to radioactive packages, containing items such as technetium generators, which are regularly delivered to hospital nuclear medicine departments. It also applies to the collection of packages, such as those containing used generators for return to the supplier. This article has been written by the professional bodies representing nuclear medicine in the UK in order to provide guidance to hospitals on appropriate procedures that will comply with the legislation. General principles, which should be met by any acceptable protocol, are stated, and practical guidance on how these may be implemented is given. Some example scenarios are outlined.

Laboratories↗

PubMed1976

Multiple myeloma on polycythemia vera following radioactive phosphorus therapy.

A 74-year-old white man with established polycythemia vera was treated with radioactive phosphorus after phlebotomies alone failed to control his disease. About 2 3/4 years later he died of multiple myeloma. The mutagenic effect of radioactive phosphorus may have caused or possibly accelerated preexisting myeloma. Basic nonmalignant disease deserves careful consideration before radiation or radiomimetic agents are used. One might consider a probably less mutagenic drug such as hydroxyurea in patients with polycythemia vera when phlebotomy alone does not give good control of red cell mass and thrombocytosis.

Aged↗

PubMed2005

In situ gamma spectrometry measurements and Monte Carlo computations for the detection of radioactive sources in scrap metal.

A very limited number of field experiments have been performed to assess the relative radiation detection sensitivities of commercially available equipment used to detect radioactive sources in recycled metal scrap. Such experiments require the cooperation and commitment of considerable resources on the part of vendors of the radiation detection systems and the cooperation of a steel mill or scrap processing facility. The results will unavoidably be specific to the equipment tested at the time, the characteristics of the scrap metal involved in the tests, and to the specific configurations of the scrap containers. Given these limitations, the use of computer simulation for this purpose would be a desirable alternative. With this in mind, this study sought to determine whether Monte Carlo simulation of photon flux energy distributions resulting from a radiation source in metal scrap would be realistic. In the present work, experimental and simulated photon flux energy distributions in the outer part of a truck due to the presence of embedded radioactive sources in the scrap metal load are compared. The experimental photon fluxes are deduced by in situ gamma spectrometry measurements with portable Ge detector and the calculated ones by Monte Carlo simulations with the MCNP code. The good agreement between simulated and measured photon flux energy distributions indicate that the results obtained by the Monte Carlo simulations are realistic.

Computer Simulation↗

PubMed2006

Radioactive rock phosphate: the feed stock of phosphate fertilizers used in Pakistan.

The existence of natural radioactivity in phosphate fertilizers originates from the rock phosphate that is used as a feed stock for the manufacturing of various types of phosphate fertilizers. Gamma ray activity mass concentrations have been determined in phosphate rock and fertilizer samples collected from different fertilizer manufacturing factories and suppliers in Pakistan. The technique of gamma ray spectrometry was applied using a HPGe (high purity germanium) gamma ray detector coupled with a personal computer (PC) based multichannel analyzer (MCA). The specific activity values of 40K, 226Ra, and 232Th were widely distributed in the rock and fertilizer samples. Activity mass concentrations of 238U (226Ra) in the rock phosphate from Jordan and Pakistan were 428 +/- 11 and 799 +/- 10 Bq kg(-1), respectively, and that in the triple-superphosphate fertilizer was 701 +/- 21 (-1), which was greater than the average values of 238U (226Ra) for other types of fertilizers under study. The concentrations of 40K and 232Th were of the order of background level on the Earth's crust. Chemical analysis for concentration of different constituents in rock phosphate was also carried out. The higher the concentrations of P2O5 and K2O were, the higher the specific activities of 226Ra and 40K were, respectively, in the rocks under study. The amount of radioactivity in the rock phosphate is a source of continuous exposure to radiation, which varies widely depending upon the origin and grade of rock; therefore, radiation dose rate has been estimated. The values of dose rate and other derived quantities were many folds larger than the limits specified for those quantities.

Fertilizers↗