Absorbed Dose

In radionuclide therapy, absorbed dose is calculated by convolution of a three-dimensional activity matrix with a three-dimensional dose point kernel. A technique employing the fast Hartley Transform (FHT) has been developed to perform this calculation. An important part of that development was the indexing scheme for 3D data. The results of this new FHT convolution technique were compared to direct convolution. A cube was convolved with itself by these two techniques. The results differed by less than 2 percent. In an effort to show the practical applicability of 3D convolution, a three-dimensional activity matrix from a I-131-labeled 16.88 monoclonal antibody patient was convolved with beta and photon dose point kernels using direct convolution. Isodose contours were then generated from the calculated absorbed dose matrix and overlaid on a CT image of the patient

Background: Nnewi town has undergone a marked increase in industrialization over the years. Considering the continuous disposal of automotive and hospital wastes in dumpsites within the town there is a need to ascertain the background radiation level of some of its dumpsites. Objective: To evaluate the level of background radiation in some selected dumpsites in Nnewi and compare the background radiation dose levels with the worldwide recommended average natural dose of 2.4mSv/yr to humans. Methods: The levels of background radiation in these dumpsites were estimated using a well-calibrated International Medicom CRM-100 Digital Radiation Monitor (survey meter). A cross-sectional survey was adopted for this study. Following the standard procedure, the radiation monitor was held at a distance of 1.0 meters above the ground and three readings are taken at each location and the mean recorded. The Annual Absorbed Dose Rate (ADR), Absorbed Dose Rate (AD) and the Annual Equivalent Dose Rate (AEDR) were calculated. Descriptive statistics were used to summarize the data using Statistical Package for Social Sciences SPSS version 20. Results: The mean of the calculated Annual Absorbed Dose Rates recorded at 21 and 24 meters was marginally greater than the accepted exposure rate for the public with the values of 1.5 mSv/year respectively. At 12 and 27 meters, the values were 1.5 mSv/year for Bank Road dumpsite respectively. Other distances were below the limit of 1mSv/year for the public and also below the dose limit of 20mSv/year for radiation workers as recommended by the ICRP. Conclusion: The radiation levels emitted from the study area were within permissible limits for the general population. Therefore there is little risk of instantaneous radiation hazard with an estimated safety zone at 6 meters from the dumpsites.

Radiation damage restricts the useful lifetime for macromolecular crystals in the X-ray beam, even at cryotemperatures. With the development of structural genomics pipelines, it will be essential to incorporate projected crystal lifetime information into the automated data collection software routines. As a first step towards this goal, a computer program,RADDOSE, is presented which is designed for use by crystallographers in optimizing the amount of data that can be obtained from a particular cryo-cooled crystal at synchrotron beamlines. The program uses the composition of the crystal and buffer constituents, as well as the beam energy, flux and dimensions, to compute the absorption coefficients and hence the theoretical time taken to reach an absorbed dose of 2 × 10^7 Gy, the so-called `Henderson limit'. At this dose, the intensity of the diffraction pattern is predicted to be halved. A `diffraction–dose efficiency' quantity is introduced, for the convenient comparison of ...

Benzene (C6H6) is a highly flammable, colorless liquid. Ubiquitous exposures result from its presence in gasoline vapors, cigarette smoke, and industrial processes. Benzene increases the incidence of leukemia in humans when they are exposed to high doses for extended periods; however, leukemia risks in humans at low exposures are uncertain. The exposure-dose-response relationship of benzene in humans is expected to be nonlinear because benzene undergoes a series of metabolic transformations, detoxifying and activating, in the liver, resulting in multiple metabolites that exert toxic effects on the bone marrow. We developed a physiologically based pharmacokinetic model for the uptake and elimination of benzene in mice to relate the concentration of inhaled and orally administered benzene to the tissue doses of benzene and its key metabolites, benzene oxide, phenol, and hydroquinone. As many parameter values as possible were taken from the literature; in particular, metabolic parameters obtained from in vitro studies with mouse liver were used since comparable parameters are also available for humans. Parameters estimated by fitting the model to published data were first-order rate constants for pathways lacking in vitro data and the concentrations of microsomal and cytosolic protein, which effectively alter overall enzyme activity. The model was constrained by using the in vitro metabolic parameters (maximum velocities, first-order rate constants, and saturation parameters), and data from multiple laboratories and experiments were used. Despite these constraints and sources of variability, the model simulations matched the data reasonably well in most cases, showing that in vitro metabolic constants can be successfully extrapolated to predict in vivo data for benzene metabolism and dosimetry. Therefore in vitro metabolic constants for humans can subsequently be extrapolated to predict the dosimetry of benzene and its metabolites in humans. This will allow us to better estimate the risks of adverse effects from low-level benzene exposures.

Image-guided techniques for radiation therapy have improved the precision of radiation delivery by sparing normal tissues. Cone-beam computed tomography (CBCT) has emerged as a key technique for patient positioning and target localization in radiotherapy. Here, we investigated the imaging radiation dose delivered to radiosensitive organs of a patient during CBCT scan. The 4D extended cardiac-torso (XCAT) phantom and Geant4 Application for Tomographic Emission (GATE) Monte Carlo (MC) simulation tool were used for the study. A computed tomography dose index (CTDI) standard polymethyl methacrylate (PMMA) phantom was used to validate the MC-based dosimetric evaluation. We implemented an MC model of a clinical on-board imager integrated with the Trilogy accelerator. The MC model's accuracy was validated by comparing its weighted CTDI (CTDIw) values with those of previous studies, which revealed good agreement. We calculated the absorbed doses of various human organs at different trea...

This paper provides information on the effects of distance and attenuation in lead sheet and gypsum board of the 0.511 MeV photon produced by positron annihilation. Exposure rates are projected external to an adult injected with 185 MBq (5 mCi) of 18F in a fluorodeoxyglucose solution and for the same activity in a small unshielded container. These data have been applied to estimate the shielding requirements for the Positron Emission Tomography (PET) suite operated by the Nuclear Medicine Department of Our Lady of the Lake Regional Medical Center. To assure that exposures are as low as reasonably achievable, lead was added to the walls of the room where the 18F is stored, handled, and injected into the patients. The PET scanner is installed in a room that formerly contained a Computerized Axial Tomography scanner; the existing 1.6 mm of lead sheet was left in place even though it is not required for personnel protection. During the initial phase of operation, a shield test program w...

The objective of this study was to validate a dose-point kernel convolution technique that provides a three-dimensional (3D) distribution of absorbed dose from a 3D distribution of the radionuclide 131I. A dose-point kernel for the penetrating radiations was calculated by a Monte Carlo simulation and cast in a 3D rectangular matrix. This matrix was convolved with the 3D activity map furnished by quantitative single-photon-emission computed tomography (SPECT) to provide a 3D distribution of absorbed dose. The convolution calculation was performed using a 3D fast Fourier transform (FFT) technique, which takes less than 40 s for a 128 x 128 x 16 matrix on an Intel 486 DX2 (66 MHz) personal computer. The calculated photon absorbed dose was compared with values measured by thermoluminescent dosimeters (TLDS) inserted along the diameter of a 22 cm diameter annular source of 131I. The mean and standard deviation of the percentage difference between the measurements and the calculations were equal to -1% and 3.6%, respectively. This convolution method was also used to calculate the 3D dose distribution in an Alderson abdominal phantom containing a liver, a spleen, and a spherical tumour volume loaded with various concentrations of 131I. By averaging the dose calculated throughout the liver, spleen, and tumour the dose-point kernel approach was compared with values derived using the MIRD formalism, and found to agree to better than 15%.

Introduction: Accurate evaluation of femoral and tibial torsion is essential for children or adult with legs deformity, becuse incorrect legs morphogenesis can lead to pathological situation. CT scan is commonly used for the measurement of skeletal bone parameters. But, disability in imaging from standing and sitting posture and absorb dose of patients are deficits of this method. EOS method overcome this dificits. Likewise some paper have reported decrease of EOS dose rather than dose level in CT, this project aim to measure amount of dose reduction and to verify reduction of EOS dose level in compare to CT. Materials and Methods: For EOS and CT invitro dosimetry, a pencil ionization chamber was used. Computed tomography dose index volume (CTDIvol) was mesuered, using this dosimeter and standard tissue equivalent CT phantom. DLP of both imaging methods was compared for acquisition of adult hip. With radiothermoluminescent detectors (TLD) in vivo dosimetry enterans skin dose for 30 ...

The objective of this article was to model pharmacokinetic data from clinical diagnostic studies involving the 111In-labeled monoclonal antibody (MAb) chimeric T84.66, against carcinoembryonic antigen. Model-derived results based on the 111In-MAb blood, urine and digital imaging data were used to predict 90Y-MAb absorbed radiation doses and to guide treatment planning for future therapy trials. Fifteen patients with at least one carcinoembryonic antigen-positive lesion were evaluated. We report the kinetic parameter estimates and absorbed 111In-MAb dose and projected 90Y-MAb doses for each patient as well as describe our approach and rationale for modeling an extensive set of pharmacokinetic data. The ADAPT II software package was used to create three- and five-compartment models of uptake against time in the patient population. The "best-fit" model was identified using ordinary least squares. Areas under the curve were calculated using the modeled curves and input into MI...

The gamma spectrometric analysis of soil and essential foodstuffs, e.g., wheat, millet, potato, lentils and cauliflower, which form the main component of the daily diet of the local public, was carried out using high purity germanium (HpGe) detector coupled with a computer based high-resolution multi-channel analyzer. The activity concentration in soil samples for 226Ra, 232Th and 40K ranged from 30.0 Bq kg−1 to 81.2 Bq kg−1, 31.4 Bq kg−1 to 78.25 Bq kg−1 and 308.8 Bq kg−1 to 2177.6 Bq kg−1, with mean values of 56.2, 58.5 and 851.9 Bq kg−1, respectively. The average activity measured for 226Ra, 232Th and 40K in soil samples was found higher than the world average. The major radionuclide found in the food items studied was 40K, while 226Ra, 232Th and 137Cs were detected in very nominal amounts. The results clearly indicate that these radionuclides have no health hazard to human beings, as they are well below the annual limit of intake (ALI) for these radionuclides. The transfer factors of these radionuclides from soil to food were also studied. The mean transfer factors of 40K, 226Ra, 232Th and 137Cs from soil to food were estimated to be about 0.17, 0.07, 0.16 and 0.23, respectively. An artificial radionuclide, 137Cs, was also present in detectable amount in all samples. The internal and external hazard indices were measured and had mean values of 0.70 and 0.55, respectively. Absorbed dose rates and effective dose have been determined in the present study. Concentration of trace metals, such as Cr, Pb, Ni and Zn, was also determined in the soil samples. The concentrations of radionuclides and trace metals found in these samples during the present study were nominal and do not pose any potential health hazard to the general public.