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The yellowed archives of yellowcake.

Extensive historical documentation of exposures and releases at government-owned energy facilities is a unique and valuable resource for analyzing and communicating health risks. Facilities at all stages of the atomic fuel cycle were the subject of numerous industrial hygiene, occupational health, and environmental assessments during the Cold War period. Uranium mines and mills on the Colorado Plateau were investigated as early as the 1940s. One such facility was the mill in Monticello, Utah, which began operation as a vanadium extraction plant in 1943 and was later adapted to recover uranium from carnotite ores. The mill ceased operation in 1960. The site was added to the federal Superfund list in 1986. ATSDR held public availability sessions in 1993 as part of its public health assessment process, at which several former mill workers voiced health concerns. An extensive literature search yielded several industrial hygiene evaluations of the Monticello mill and health studies that included Monticello workers, only two of which had been published in the peer-reviewed literature. In combination with the broader scientific literature, these historical reports provide a partial basis for responding to mill workers' contemporary health concerns. The strengths and limitations of the available exposure data for analytical epidemiologic studies and dose reconstruction are discussed. As an interim measure, the available historical documentation may be especially helpful in communicating about health risks with workers and communities in ways that acknowledge the historical context of their experience.

Chronic Disease↗

Chernobyl accident: reconstruction of thyroid dose for inhabitants of the Republic of Belarus.

The Chernobyl accident in April 1986 resulted in widespread contamination of the environment with radioactive materials, including (131)I and other radioiodines. This environmental contamination led to substantial radiation doses in the thyroids of many inhabitants of the Republic of Belarus. The reconstruction of thyroid doses received by Belarussians is based primarily on exposure rates measured against the neck of more than 200,000 people in the more contaminated territories; these measurements were carried out within a few weeks after the accident and before the decay of (131)I to negligible levels. Preliminary estimates of thyroid dose have been divided into 3 classes: Class 1 ("measured" doses), Class 2 (doses "derived by affinity"), and Class 3 ("empirically-derived" doses). Class 1 doses are estimated directly from the measured thyroidal (131)I content of the person considered, plus information on lifestyle and dietary habits. Such estimates are available for about 130,000 individuals from the contaminated areas of the Gomel and Mogilev Oblasts and from the city of Minsk. Maximum individual doses are estimated to range up to about 60 Gy. For every village with a sufficient number of residents with Class 1 doses, individual thyroid dose distributions are determined for several age groups and levels of milk consumption. These data are used to derive Class 2 thyroid dose estimates for unmeasured inhabitants of these villages. For any village where the number of residents with Class 1 thyroid doses is small or equal to zero, individual thyroid doses of Class 3 are derived from the relationship obtained between the mean adult thyroid dose and the deposition density of (131)I or 137Cs in villages with Class 2 thyroid doses presenting characteristics similar to those of the village considered. In order to improve the reliability of the Class 3 thyroid doses, an extensive program of measurement of (129)I in soils is envisaged.

Adolescent↗

Optical CT reconstruction of 3D dose distributions using the ferrous-benzoic-xylenol (FBX) gel dosimeter.

In recent years, magnetic-resonance imaging of gelatin doped with the Fricke solution has been applied to the direct measurement of three-dimensional (3D) radiation dose distributions. However, the 3D dose distribution can also be imaged more economically and efficiently using the method of optical absorption computed tomography. This is accomplished by first preparing a gelatin matrix containing a radiochromic dye and mapping the radiation-induced local change in the optical absorption coefficient. Ferrous-Benzoic-Xylenol (FBX) was the dye of choice for this investigation. The complex formed by Fe3+ and xylenol orange exhibits a linear change in optical attenuation (cm-1) with radiation dose in the range between 0 and 1000 cGy, and the local concentration of this complex can be probed using a green laser light (lambda = 543.5 nm). An optical computed tomography (CT) scanner was constructed analogous to a first-generation x-ray CT scanner, using a He-Ne laser, photodiodes, and rotation-translation stages controlled by a personal computer. The optical CT scanner itself can reconstruct attenuation coefficients to a baseline accuracy of < 2% while yielding dose images accurate to within 5% when other uncertainties are taken into account. Optical tomography is complicated by the reflection and refraction of light rays in the phantom materials, producing a blind spot in the transmission profiles which, results in a significant dose artifact in the reconstructed images. In this report we develop corrections used to reduce this artifact and yield accurate dosimetric maps. We also report the chemical reaction kinetics, the dose sensitivity and spatial resolution (< 1 mm3) obtained by optical absorption computed tomography. The article concludes with sample dose distributions produced by "cross-field" 6 MV x-ray beams, including a radiosurgery example.

Benzoic Acid↗

Dose-guided radiation therapy with megavoltage cone-beam CT.

Recent advances in fractionated external beam radiation therapy have increased our ability to deliver radiation doses that conform more tightly to the tumour volume. The steeper dose gradients delivered in these treatments make it increasingly important to set precisely the positions of the patient and the internal organs. For this reason, considerable research now focuses on methods using three-dimensional images of the patient on the treatment table to adapt either the patient position or the treatment plan, to account for variable organ locations. In this article, we briefly review the different adaptive methods being explored and discuss a proposed dose-guided radiation therapy strategy that adapts the treatment for future fractions to compensate for dosimetric errors from past fractions. The main component of this strategy is a procedure to reconstruct the dose delivered to the patient based on treatment-time portal images and pre-treatment megavoltage cone-beam computed tomography (MV CBCT) images of the patient. We describe the work to date performed to develop our dose reconstruction procedure, including the implementation of a MV CBCT system for clinical use, experiments performed to calibrate MV CBCT for electron density and to use the calibrated MV CBCT for dose calculations, and the dosimetric calibration of the portal imager. We also present an example of a reconstructed patient dose using a preliminary reconstruction program and discuss the technical challenges that remain to full implementation of dose reconstruction and dose-guided therapy.

Calibration↗

Immediate breast reconstruction and high-dose chemotherapy.

BACKGROUND: Immediate breast reconstruction (IBR) is considered as a safe procedure nowadays, and it can be proposed in the majority of patients requiring a mastectomy. In fact, recent studies have demonstrated that immediate breast reconstruction is not detrimental also to patients with locally advanced breast cancers. However, IBR should be reevaluated in case of locally advanced breast cancer requiring high-dose chemotherapy (HDCT). The aim of this study is to evaluate both the risk of chemotherapy delay due to surgical complications and the risk of late surgical complications related to the association with HDCT. We considered 3 series of 23, 67, and 15 patients requiring a mastectomy at the European Institute of Oncology in Milan. After mastectomy, these groups respectively received an IBR and HDCT, an IBR and conventional chemotherapy, and only HDCT with no IBR. METHODS: Files of 105 patients who were admitted to our department from October 1999 to January 2002 were reviewed. Twenty-three patients underwent a mastectomy, followed by IBR and HDCT; 67 underwent a mastectomy plus IBR plus conventional CT; and, finally, 15 underwent a mastectomy alone followed by HDCT. The reconstructive techniques performed were 72 permanent prosthesis and 18 temporary expanders. We excluded all patients with IBR by flap (latissimus dorsi or pedicled rectus abdominis) to improve the homogeneity of the sample. RESULTS: All patients who underwent IBR started high-dose chemotherapy without any delay; the time elapsed between surgery and HDCT is not significantly different for patients with and without IBR (54 versus 60 days, P = 0.13). The early complication rate (before CT) was 2.9% (2 patients with infection). The late complication rate (after CT) was higher for the group that underwent IBR followed by HDCT (39% versus 20%). CONCLUSION: We did not observe any delay for the administration of high-dose chemotherapy after mastectomy with IBR surgery. The complication rate before HDCT is similar to the complication rates published in the literature. On the contrary, we observed a higher rate of infections (13% versus 0%, P = 0,014) after HDCT than after conventional CT, which can be related to the association with high-dose chemotherapy, inducing a decrease of the immune defenses. These results seems to demonstrate that the association of IBR with HDCT is not detrimental to patients from the oncological point of view, but the impact of HDCT on the reconstruction is more negative. Further studies are needed to verify if this risk exists, although lower, in the association with conventional CT. However, a careful evaluation of the risk of infections should be considered preoperatively, and perioperative contaminations should be carefully prevented.

Adult↗

[Effective in vivo radiation dose with image reconstruction controlled pedicle instrumentation vs. CT-based navigation].

UNLABELLED: There is a rapid increase of computer-assisted surgery (CAS) in the spine for insertion of pedicle screws. In contrast to the traditional technique using fluoroscopy, CT is the primary source for surgical navigation systems. PURPOSE OF THE STUDY: To compare organ and effective doses of fluoroscopy-controlled versus computer-assisted pedicle screw insertion under the aspect of risk reduction and number needed to treat. MATERIALS AND METHODS: In 20 consecutive cases of traditional pedicle screw instrumentation under fluoroscopic control the effective doses were recorded in vivo and the organ doses then calculated. Simulating a spiral CT necessary for the 3-D-model for navigation we defined a spiral CT protocol for the instrumented levels and calculated organ and effective doses from Monte Carlo Results from CT examinations. RESULTS: Organ doses were clearly higher for the CT model than in any of the fluoroscopic procedures in vivo. The mean effective dose for the CT model was fifteen times higher than the fluoroscopic dose: 7.27 mSv versus 0.48 mSv. CONCLUSIONS: In experienced hands open pedicle screw insertion in the thoracic and lumbar spine using fluoroscopy-control requires a fifteen times lower radiation dose than do CT scans necessary for computer-assisted surgery. Regarding the published small percentage of neurological complications in traditional screw insertion technique the use of computer-assisted surgery in pedicle screw insertion using CT scan should be limited to carefully chosen indications. The development of navigation systems based on other data sources than CT should be encouraged.

Adolescent↗

[Clinical and radiation physics studies on the influence of mandibular reconstruction plates on the dose distribution of ultrahard photons].

The effect of mandibular reconstruction plates on the dose distribution of megavoltage photons was analysed. All treated patients showed the normal reactions expected from radiation therapy regardless the modification of dose distribution by the metal plates. For dose estimation measurements were done in a phantom with photons of the energy 60Co to 42 MV and different material.

Alveolar Process↗

The reconstruction and dose-rate calculation of radium needle implants.

A comprehensive computer program has been developed for carrying out the various tasks associated with radium needle implants. Data input for the program are obtained by digitizing an orthogonal pair of radiographs with an analogue tracing system. Corresponding needles in the two radiographs are automatically located, and the implant may be rotated to any desired position in three dimensional space, at the same time presenting a view of the rotation on a storage oscilloscope. Automatic determination of the mean plane of a planar implant is possible, and the dose-rate distribution may be calculated in any specified plane. A Paterson--Parker exposure rate calculation may be performed with a biological dose and treatment time correction incorporated. The program is written in Fortran and runs on a small interactive computer system.

Computers↗

Angular correction in reconstruction of electron spectra from depth dose distributions.

Techniques for reconstruction of electron spectra from the depth-dose curves used to date have ignored the angular distribution of incident electrons scattered at large angles. The approximation adopted is to employ a database of monoenergetic depth-dose curves generated for normal incidence of electrons at the surface. This approximation is acceptable for direct electrons with small angular spread. However, electrons scattered from the treatment head and collimating system may have large average angles of incidence which affects the depth-dose distribution significantly at shallow depths by increasing energy deposition close to the surface. We show that ignoring the electron incident angular distribution leads to systematic errors in the low energy region of reconstructed electron spectra. We propose a simple 1-D model to correct for these systematic errors using only electron angular distribution at the central beam axis. This model provides reconstructed spectra in excellent agreement with Monte Carlo simulation in the low energy region.

Algorithms↗

Penalized weighted least-squares image reconstruction for dual energy X-ray transmission tomography.

We present a dual-energy (DE) transmission computed tomography (CT) reconstruction method. It is statistically motivated and features nonnegativity constraints in the density domain. A penalized weighted least squares (PWLS) objective function has been chosen to handle the non-Poisson noise added by amorphous silicon (aSi:H) detectors. A Gauss-Seidel algorithm has been used to minimize the objective function. The behavior of the method in terms of bias/standard deviation tradeoff has been compared to that of a DE method that is based on filtered back projection (FBP). The advantages of the DE PWLS method are largest for high noise and/or low flux cases. Qualitative results suggest this as well. Also, the reconstructed images of an object with opaque regions are presented. Possible applications of the method are: attenuation correction for positron emission tomography (PET) images, various quantitative computed tomography (QCT) methods such as bone mineral densitometry (BMD), and the removal of metal streak artifacts.

Algorithms↗

A revised probabilistic estimate of the maternal methyl mercury intake dose corresponding to a measured cord blood mercury concentration.

In 2001, the U.S. Environmental Protection Agency (EPA) adopted a revised reference dose (RfD) for methyl mercury (MeHg) of 0.1 microg/kg/day. The RfD is based on neurologic developmental effects measured in children associated with exposure in utero to MeHg from the maternal diet. The RfD derivation proceeded from a point of departure based on measured concentration of mercury in fetal cord blood (micrograms per liter). The RfD, however, is a maternal dose (micrograms per kilogram per day). Reconstruction of the maternal dose corresponding to this cord blood concentration, including the variability around this estimate, is a critical step in the RfD derivation. The dose reconstruction employed by the U.S. EPA using the one-compartment pharmacokinetic model contains two areas of significant uncertainty: It does not directly account for the influence of the ratio of cord blood: maternal blood Hg concentration, and it does not resolve uncertainty regarding the most appropriate central tendency estimates for pregnancy and third-trimester-specific model parameters. A probabilistic reassessment of this dose reconstruction was undertaken to address these areas of uncertainty and generally to reconsider the specification of model input parameters. On the basis of a thorough review of the literature and recalculation of the one-compartment model including sensitivity analyses, I estimated that the 95th and 99th percentiles (i.e., the lower 5th and 1st percentiles) of the maternal intake dose corresponding to a fetal cord blood Hg concentration of 58 microg/L are 0.3 and 0.2 microg/kg/day, respectively. For the 99th percentile, this is half the value previously estimated by the U.S. EPA.

Environmental Monitoring↗

Enhanced bremsstrahlung spectrum reconstruction from depth-dose gradients.

We present a technique to significantly improve the accuracy of bremsstrahlung spectra reconstructed from central-axis depth-dose data using inverse methods. While typical approaches directly use the measured depth-dose data, we show the advantage of using the gradient of these data for reconstruction. The inverse problem in terms of gradients is shown to be markedly less ill-conditioned than the usual inverse problem. In each case, a regularization is introduced to alleviate the effects of noise due to measurement and computation. The error in taking derivatives of depth-dose data is demonstrated to be sufficiently controllable as not to overtake the improvements in the conditioning of the inverse problem in a pair of simulated examples.

Algorithms↗

Artefacts of electron paramagnetic resonance dosimetry caused by a mechanical effect on samples of tooth enamel.

It has been ascertained that in the process of the mechanical preparation of tooth enamel, two types of paramagnetic centres are formed. The centres of one type, the long-lived ones, occurred in the process of friction of dental borers against the enamel. Their number grew with an increase of the treated surface area and the rotation rate of the borers. The electron paramagnetic resonance signal of such radicals looked like a symmetric singlet with the width deltaHpp=0.094 mT and g=2.0029. The other, short-lived centres, occurred when tooth enamel was crushed into small granules, which caused an increase in the background signal intensity. The mechanism of formation of paramagnetic centres in enamel during the process of teeth treatment and prepartion has been considered. The estimation of an increase in the reconstructed absorbed dose due to the contribution from the mechanically induced signal has been made. Contamination of tooth enamel samples with diamond crumb during diamond borer preparation has been shown to lead to an imaginary increase in radiation-induced signal intensity and, consequently, to an increase in the reconstructed dose.

Artifacts↗

Delivery verification in sequential and helical tomotherapy.

Conformal and conformal avoidance radiation therapy are new therapeutic techniques that are generally characterized by high dose gradients. The success of this kind of treatment relies on quality assurance procedures in order to verify the delivery of the treatment. A delivery verification technique should consider quality assurance procedures for patient positioning and radiation delivery verification. A methodology for radiation delivery verification was developed and tested with our tomotherapy workbench. The procedure was investigated for two cases. The first treatment using a torus-shaped target was optimized for 72 beam directions and sequentially delivered as a single slice to a 33 cm diameter cylinder of homogeneous solid water. For the second treatment, a random pattern of energy fluence was helically delivered for two slices to a 9.0 cm diameter phantom containing inhomogeneities. The presented process provides the energy fluence (or a related quantity) delivered through the multileaf collimator (MLC) using the signal measured at the exit detector during the treatment delivery. As this information is created for every pulse of the accelerator, the energy fluence and state for each MLC leaf were verified on a pulse-by-pulse basis. The pulse-by-pulse results were averaged to obtain projection-by-projection information to allow for a comparison with the planned delivery. The errors between the planned and delivered energy fluences were concentrated between +/-2.0%, with none beyond +/-3.5%. In addition to accurately achieving radiation delivery verification, the process is fast, which could translate to radiation delivery verification in real time. This technique can also be extended to reconstruct the dose actually deposited in the patient or phantom (dose reconstruction).

Acrylates↗

Review of methods of dose estimation for epidemiological studies of the radiological impact of nevada test site and global fallout.

Methods to assess radiation doses from nuclear weapons test fallout have been used to estimate doses to populations and individuals in a number of studies. However, only a few epidemiology studies have relied on fallout dose estimates. Though the methods for assessing doses from local and regional compared to global fallout are similar, there are significant differences in predicted doses and contributing radionuclides depending on the source of the fallout, e.g. whether the nuclear debris originated in Nevada at the U.S. nuclear test site or whether it originated at other locations worldwide. The sparse historical measurement data available are generally sufficient to estimate external exposure doses reasonably well. However, reconstruction of doses to body organs from ingestion and inhalation of radionuclides is significantly more complex and is almost always more uncertain than are external dose estimates. Internal dose estimates are generally based on estimates of the ground deposition per unit area of specific radionuclides and subsequent transport of radionuclides through the food chain. A number of technical challenges to correctly modeling deposition of fallout under wet and dry atmospheric conditions still remain, particularly at close-in locations where sizes of deposited particles vary significantly over modest changes in distance. This paper summarizes the various methods of dose estimation from weapons test fallout and the most important dose assessment and epidemiology studies that have relied on those methods.

Body Burden↗

Low dose dextran 40 in reconstructive hip surgery patients.

Preoperative and postoperative bilateral lower extremity venography was used to evaluate the efficacy of low dose dextran 40 in prophylaxis of deep venous thrombosis in reconstructive hip surgery patients. Patients were given dextran 40 at 50 cc/hr, with 250 cc given perioperatively and 500 cc given on postoperative days two and four. Five of 227 patients had positive venograms preoperatively. Of these 227 patients, 179 met protocol requirements and had venography postoperatively. Venous thrombosis occurred in 33 (18%) of those studied postoperatively. Of these, 11 were calf clots without extension to the popliteal region. Therefore, there were 22 patients (12%) with femoral or popliteal involvement overall. There were two deaths, neither of which was secondary to pulmonary embolus or a complication of dextran. There were two wound complications. These results suggest that low dose dextran 40 administered as indicated is a safe and efficacious means of deep venous thrombosis prophylaxis in reconstructive hip surgery patients.

Arthroplasty↗

Effect of mandibular titanium reconstructive plates on radiation dose.

BACKGROUND: The effects of the mandibular titanium alloy plates on the radiation-tissue interactions are not clearly defined. Photon beam radiation may be modified after striking a metal plate used to reconstruct the mandible after oncologic surgery. The purpose of this study was to determine, in a human mandible model, the effects of a titanium alloy plate on the radiation dose received at the bone/titanium (plate and screws) interface and bone/soft tissue interface. METHODS: We used an adult male human head and neck ex vivo model. A medical grade titanium alloy 6-hole plate, 2.4 mm, was fixed in the midline of the mandible. The mandible was then irradiated using 6 MV photon beams. Thermoluminescent dosimeters were used to measure the radiation doses anterior and posterior to the mandible. The experiment was then repeated without the plate and screws. RESULTS: The difference between the average doses received by the mandible reconstructed with plate/screws and a mandible without plate/screws was +2.1% at the buccal aspect of the mandible and +3.0% at the lingual aspect; respective P values were.741 and .323. Thus, these differences were not statistically significant. CONCLUSION: In this study, we did not observe any significant influence of titanium alloy plate/screws on the radiation doses received by tissues anterior or posterior to the mandible.

Adult↗