A technique for the fast calculation of three-dimensional photon dose distributions using the superposition model

Techniques for reducing computation time in 3D photon dose calculations are addressed with specific emphasis given to the convolution/superposition approach. A single polyenergetic superposition model calculating absorbed dose per incident photon fluence (Gy cm2) was developed in terms of TERMA and a total energy deposition kernel (a total point spread function). A novel approach was devised for reducing calculation time. The method, named the CF method, was based on the use of a conventional, fast model (here a modified power-law method was used) for the generation of 3D dose distributions on a fine dose matrix. Superposition calculations were carried out on a coarse matrix and calculation speed was increased simply by reducing the number of calculations. A set of correction factors was derived on the coarse grid from the ratio of the dose values from superposition to those from the conventional algorithm. These were interpolated onto the fine matrix and used to modify the dose calculation from the conventional algorithm. The method was tested in a worst-case example where large dose gradients were present and in a clinically relevant irradiation geometry. It is shown that the time required for the generation of a 3D matrix with superposition can be reduced by at least a factor of 100 with no significant loss in accuracy.     

MR-cholangiopancreatography using three-dimensional Fourier transfer fast asymmetric spin-echo method (3DFT-FASE)--clinical evaluation

MR-cholangiopancreatography (MRCP) is a new and non-invasive method. With the three-dimensional Fourier transform fast asymmetric spin-echo (3DFT-FASE) method that allows data collection as volume and three-dimensional expression, a higher spatial resolution can be obtained in the direction of both slab thickness and in-plane. In this method, analysis by multi planar reconstruction (MPR) and observation from various angle by maximum intensity projection (MIP) are available. Although further studies are required to shorten the imaging time to stop breathing only once, to use the respiratory gating or navigator echo, clinically useful diagnosis are possible utilizing by the advantages of the 3DFT method.     

An efficient method for small field treatment dose calculation for stereotactic radiosurgery using a LINAC

The normal procedure for a physician-physicist team designing a treatment plan for multiarc stereotactic radiosurgery is the trial-and-error approach of changing the collimator size and the location of the isocenter of radiation and viewing the isodose curves on two-dimensional computed tomography (CT) or magnetic resonance imaging (MRI) image planes. Automatic optimization procedures have also been used to optimize beam weight or beam size. However, either process is very time consuming. To improve the speed of the dose calculation, a random sampling method has been proposed. Unfortunately, the sampled values of an objective function are different from one sample to another. Such a sampling method cannot be used in automatic optimization because the next move in an optimization process is based on the current and past objective function values. To this end, an adaptive method based on the size of the collimators is proposed and used to determine a small volume in the shape of a hollow sphere for which the dose is calculated. With an appropriate choice of an adaptive hollow sphere, the objective function calculated based on such a hollow sphere is the same as that calculated with the traditional three-dimensional (3-D) cube matrix. However, with the new adaptive method, the speed of calculating a dose can be improved by a factor of 4 to a factor of 100. Because of the improvement in the speed of calculating a treatment dose, the new adaptive hollow sphere method for calculating a treatment dose can be used routinely in designing a treatment plan.     

Calculating dose and output factors for wedged photon radiotherapy fields using a convolution/superposition method

To account for clinical divergent and polychromatic photon beams, we have developed kernel tilting and kernel hardening correction methods for convolution dose calculation algorithms. The new correction methods were validated by Monte Carlo simulation. The accuracy and computation time of the our kernel tilting and kernel hardening correction methods were also compared to the existing approaches including terma divergence correction, dose divergence correction methods, and the effective mean kernel method with no kernel hardening correction. Treatment fields of 10 x 10-40 x 40 cm2 (field size at source to axis distance (SAD)) with source to source distances (SSDs) of 60, 80, and 100 cm, and photon energies of 6, 10, and 18 MV have been studied. Our results showed that based on the relative dose errors at a depth of 15 cm along the central axis, the terma divergence correction may be used for fields smaller than 10 x 10 cm2 with a SSD larger than 80 cm; the dose divergence correction with an additional kernel hardening correction can reduce dose error and may be more applicable than the terma divergence correction. For both these methods, the dose error increased linearly with the depth in the phantom; the 90% isodose lines at the depth of 15 cm were shifted by about 2%-5% of the field width due to significant underestimation of the penumbra dose. The kernel hardening effect was less prominent than the kernel tilting effect for clinical photon beams. The dose error by using nonhardening corrected kernel is less than 2.0% at a depth of 15 cm along the central axis, yet it increased with a smaller field size and lower photon energy. The kernel hardening correction could be more important to compute dose in the fields with beam modifiers such as wedges when beam hardening is more significant. The kernel tilting correction and kernel hardening correction increased computation time by about 3 times, and 0.5-1 times, respectively. This can be justified by more accurate dose calculations for the majority of clinical treatments.     

Electron dose calculation using multiple-scattering theory: a new theory of multiple scattering

Starting from the Boltzmann-Fokker-Planck transport equation, we have developed a new theory of multiple scattering which incorporates the advances already made with our Gaussian multiple-scattering theory for electron dose calculation. This incorporation has been accomplished in a natural way, by modifying the scattering power T and by adding a convolution term to the distribution-function equation of the Gaussian theory. Our previous results concerning increasing the accuracy of the small-angle approximation used and dealing with localized tissue inhomogeneities have thus been maintained, and we have arrived at a complete distribution function in both transverse spatial and angular variables. When integrated over the transverse angular variables, for a first-order small-angle approximation this distribution function for a pencil beam is essentially the same as the Moliere multiple-scattering distribution, which includes large-angle single scattering. For a water phantom, we have used comparisons with EGS4 Monte Carlo calculations to demonstrate the greatly increased accuracy of our new multiple-scattering theory over the Gaussian theory, which includes the usual Fermi-Eyges theory. We have also presented a fairly accurate Gaussian approximation to the pencil-beam dose profiles given by our new theory, which can be used in order to maintain the mathematical simplicity of the predictions of the Fermi-Eyges theory.     

Establishing isostructural metal substitution in metalloproteins using 1H NMR, circular dichroism, and Fourier transform infrared spectroscopy

Far-UV CD, 1H-NMR, and Fourier transform infrared (FTIR) spectroscopy are three of the most commonly used methods for the determination of protein secondary structure composition. These methods are compared and evaluated as a means of establishing isostructural metal substitution in metalloproteins, using the crystallographically defined rubredoxin from Desulfovibrio gigas and its well-characterized cadmium derivative as a model system. It is concluded that analysis of the FTIR spectrum of the protein amide I resonance represents the most facile and generally applicable method of determining whether the overall structure of a metalloprotein has been altered upon metal reconstitution. This technique requires relatively little biological material (ca. 300 micrograms total protein) and, unlike either CD or 1H-NMR spectroscopy, is unaffected by the presence of different metal ions, thus allowing the direct comparison of FTIR spectra before and after metal substitution.     

Influence of ADP, AMP-PNP and of depletion of nucleotides on the structural properties of F1ATPase: a Fourier transform infrared spectroscopic study

Mitochondrial F1ATPase from beef heart was treated with different buffers in order to modulate the nucleotide content of the enzyme and then analysed by FT-IR spectroscopy. Treatment of F1ATPase with a buffer lacking nucleotides and glycerol led to the formation of two fractions consisting of an inactive aggregated enzyme deprived almost completely of bound nucleotides and of an active enzyme containing ATP only in the tight sites and having a structure largely accessible to the solvent and a low thermal stability. Treatment of F1ATPase with saturating ADP, which induced the hysteretic inhibition during turnover, or AMP-PNP did not affect remarkably the secondary structure of the enzyme complex but significantly increased its compactness and thermal stability. It was hypothesised that the formation of the inactive aggregated enzyme was mainly due to the destabilisation of the alpha-subunits of F1ATPase and that the induction of the hysteretic inhibition is related to a particular conformation of the enzyme, which during turnover becomes unable to sustain catalysis.     

Peptides from the conserved ends of the rod domain of desmin disassemble intermediate filaments and reveal unexpected structural features: a circular dichroism, Fourier transform infrared, and electron microscopic study

Synthetic peptides representing the conserved ends of the rod domain of desmin are shown to disassemble preformed desmin filaments when added in moderate molar excess. This argues for a similar importance of both ends of the rod for filament stability. Recent structural models of intermediate filaments suggest close proximity of the ends and perhaps even an interaction (N. Geisler, J. Schünemann, and K. Weber, 1992, Eur. J. Biochem. 206, 841-852; P. M. Steinert, L. N. Marekov, R. D. B. Fraser, and D. A. D. Parry, 1993, J. Mol. Biol. 230, 436-452). Since the disassembling activity of the peptides, in addition to their sequences, should be related in some way to their secondary structure, we have investigated the structures of a number of related peptides which all arise from the ends of the rod using electron microscopic and spectroscopic methods. All peptides showed the expected alpha-helical structure at low concentrations in the presence of trifluoroethanol, as revealed by circular dichroism. At higher concentrations the peptides showed extensive self-aggregation into various types of filaments. The filaments contain the peptides in beta-sheet conformation as shown by Fourier transform infrared spectroscopy.     

Cloning of Mix-related homeodomain proteins using fast retrieval of gel shift activities, (FROGS), a technique for the isolation of DNA-binding proteins

We have developed a technique, fast retrieval of gel shift activities (FROGS), that allows for the rapid isolation of proteins that interact with DNA. Using this technique, we have isolated two proteins that are structurally similar to Mix.1, a PAX class homeodomain protein with ventralizing activity in Xenopus. The Mix family of proteins are expressed during late blastula and gastrula stages of Xenopus development. During gastrulation, these genes are expressed at high levels in distinct, yet overlapping regions in mesoderm and endoderm. The members of the Mix family heterodimerize with each other and overexpression of each results in severe axial abnormalities. Mix.3 and Mix.4 can directly induce primitive ectoderm to become endoderm whereas Mix.1 cannot. Injection of Mix.3 or Mix.4 RNA in the whole embryo results in extensive ectopic endodermin mRNA expression. The expression of the Mix family homeoproteins is differentially regulated by activin, Vg1, BMP-4, and fibroblast growth factor, supporting a model in which the Mix homeoproteins are downstream effectors of growth factor signaling during endoderm and ventral mesoderm formation.     

Repeatability of patellar cartilage thickness patterns in the living, using a fat-suppressed magnetic resonance imaging sequence with short acquisition time and three-dimensional data processing

Twenty-two patients with large nonossifying fibromas (NOFs) in weight-bearing bones were studied to evaluate risk of pathologic fracture. Previous reports suggest an absolute size threshold for NOFs beyond which there is a reasonable chance of impending fracture. In this series, 13 (59%) large NOFs had not had pathologic fracture despite exceeding the previously established size threshold. Four of the patients had fractures of the long bone in which the NOF was located without the fracture involving the lesion. In the nine (41%) patients in whom pathologic fracture occurred, healing was uneventful after closed reduction and cast immobilization. Whereas absolute size parameters may be useful in predicting pathologic fracture rate, they do not imply a requirement for prophylactic curettage and bone grafting. The majority of patients with large NOFs can be monitored without surgical intervention, and fractures can be successfully managed with nonoperative treatment.     

Moderate dose escalation for advanced stage Hodgkin's disease using the bleomycin, etoposide, adriamycin, cyclophosphamide, vincristine, procarbazine, and prednisone scheme and adjuvant radiotherapy: a study of the German Hodgkin's Lymphoma Study Group

The BEACOPP (bleomycin, etoposide, adriamycin, cyclophosphamide, vincristine, procarbazine, and prednisone) regimen, a rearranged and accelerated version of the standard COPP/adriamycin, bleomycin, vinblastine, and dacarbazine (ABVD) chemotherapy, has been shown to be effective and safe in a previous pilot study for advanced stage Hodgkin's disease (HD). The present study aimed to determine a maximum practicable dose of three drugs, ie, etoposide, adriamycin, and cyclophosphamide, for which acute toxicities were acceptable and to assess the feasibility of the escalated scheme. Sixty untreated patients with advanced stage HD were enrolled in this study. Radiotherapy was given in 44 patients (73%) after chemotherapy to initial bulk lesions and residual disease. Granulocyte-colony stimulating factor (G-CSF) was given from day 8 to prevent prolonged neutrocytopenia and severe infections. The intended doses of adriamycin, etoposide, and cyclophosphamide in the BEACOPP schedule could be substantially escalated: adriamycin from 25 to 35, cyclophosphamide from 650 to 1,200, and etoposide from 100 to 200 mg/m2. The major toxicities were leukocytopenia and thrombocytopenia with considerable heterogeneity between individual patients. Of 60 patients, 56 (93%) achieved a complete remission (CR). At a median observation of 32 months, the rates of survival and freedom from treatment failure (FFTF) were estimated to be 91% (95% confidence interval 83% to 99%) and 90% (82% to 98%). These results show that a moderate dose escalation of adriamycin, cyclophosphamide, and etoposide of the baseline BEACOPP regimen is feasible. The escalated BEACOPP regimen shows very encouraging results in advanced stage HD and is now being compared in a randomized phase III study with BEACOPP at baseline dose level.     

An accurate determination of human growth hormone content in different pituitary extracts, using a radioimmunoassay with polyacrylamide gel electrophoresis as a bound-free separation system

Human growth hormone was extrated and purified according to the method of Roos et al. (Roos, P., Fevold, H.R. and Gemzell, C.A. (1963) Biochim. Biophys. Acta 74, 525). A first control of its purification and integrity was performed through molecular weight determination by gel filtration on Sephadex G-100 and on polyacrylamide gel electrophoresis (PAGE). Its biological activity was confirmed by the growth promoted in non-hypophysectomized rats at plateau. The main object, however, was the setting up of accurate, reproducible method tha could furnish the more absolute and comparable values of radioimmunoassayable HGH content in perfect agreement with the results obtained by other laboratories. This was accomplished through a radioimmunoassay system that uses HGH labelled with 125I, where separation of the bound from the free antigen is achieved on polyacrylamide gel electrophoresis, by a modification introduced in the original method of Davis. The resulting values, extremely close to that stated by the KABI-Laboratories (Stockolm), though obtained in quite different conditions of incubation, antibody concentration and with no use of second antibody, represent a confident approach to a comparable measure of this hormone in extracts, which can also be applied to plasma determinations.     

Effects of benzodiazepine receptor ligands on the ingestion of sucrose, intralipid, and maltodextrin: An investigation using a microstructural analysis of licking behavior in a brief contact test.

Microstructural analysis of licking behavior in the rat was conducted (a) to describe in detail the characteristics of benzodiazopine-induced changes in ingestion and (b) to determine if the changes are consistent with an alteration in palatability. The effects of the benzodiazepine receptor (BZR) agonist midazolam (0.3–3 mg/kg), and the partial inverse agonist Ro 15-4513 (0.3–3 mg/kg), on licking for several concentrations of sucrose, Intralipid, and maltodextrin in a brief contact test were investigated. Midazolam increased the total number of licks for all 3 fluids; conversely, Ro 15-4513 decreased the total number of licks. Midazolam increased mean bout duration for sucrose and maltodextrin drinking and there was a trend toward a similar effect with Intralipid drinking. Ro 15-4513 reduced mean bout duration for all 3 test fluids. These data are discussed in terms of bidirectional changes in fluid palatability by drug actions at BZRs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Treatment with the anti-tumor drugs, cis-platin and mafosfamide, does not affect the structure of prekinetochores in a human breast cancer cell line. An immunofluorescence study using human anti-centromere autoantibodies

The goal of the present article was to determine whether a nuclear parameter, centromere structure of interphase cells, could serve as an indicator to assess cellular damage caused by anti-tumor drugs. These were cis-platin and mafosfamide, which are widely used for the management of solid tumors. To visualize the centromeres, we probed treated and untreated cells of a human breast cancer cell line, MX-1, with a human anti-centromere serum. The serum was obtained from a scleroderma patient and detects antigens associated with prekinetochores of the decondensed chromosomes. The DNA was simultaneously displayed by a specific fluorescent dye. The cells were grown on coverslips, incubated for 1 h in a drug-containing medium, transferred into a drug-free medium and observed 24 h later. Since the efficiency of many anti-tumor drugs increases with the temperature, two different temperatures, 37 and 42 degrees C, were used. The analysis revealed that the treatment did not visibly alter the labeling pattern. We conclude that chromosome structure remains largely intact and is not suitable for the cytological evaluation of the efficiency of anti-tumor drugs. This is in contrast with, for example, the microtubular cytoskeleton and mitochondria, which were extensively damaged under the conditions applied here (compare Wolf et al. 1995). Independent of the drug and the temperature selected, the nuclear lumen of mononucleated and multinucleated cells contained small fluorescent spots. Double dots corresponding to the sister centromeres in the G2 phase of the cell cycle were rare. In addition to the voluminous nuclei, some cells possessed micronuclei in the lateral cytoplasm and these were regularly labeled by the autoantibodies. A small subset of the mononucleated MX-1 cells had unusually large nuclei. It is reasonable to assume that they are polyploid. The fluorescent spots marking the prekinetochores were very large in these cells. This may indicate that the chromosomes remain associated after replication.     

Can one predict protein stability? An attempt to do so for residue 133 of T4 lysozyme using a combination of free energy derivatives, PROFEC, and free energy perturbation methods

Free energy derivatives, pictorial representation of free energy changes (PROFEC) and free energy perturbation methods were employed to suggest the modifications that may improve the stability of a mutant T4 lysozyme with a S-2-amino-3-cyclopentylpropanoic acid residue (Cpe) at position 133. The free energy derivatives and PROFEC methods were used to locate promising sites where modifications may be introduced. The effects of several candidate modifications on the enzyme's stability were analyzed by the free energy perturbation method. We found that this scheme is able to effectively suggest modifications that may increase the enzyme's stability. The modifications investigated are the introduction of a methyl, a tert-butyl or a trifluoromethyl group at the Cepsilon2 position and a cyclopropyl group between the Cdelta2 and Cepsilon2 position on the cyclopentyl ring. The stereochemistry of the introduced groups (in the alpha or beta configurations) was studied. Our calculations predict that the introduction of a methyl group in the alpha configuration or a cyclopropyl group in the beta configuration will increase the stability of the enzyme; the introduction of the two groups in the other configurations and the other modifications will decrease the stability of the enzyme. The results indicate that packing interactions can strongly influence the stability of the enzyme.