146 research outputs found
Development of Proficiency Testing for Detection of Irradiated Food: Project E01068. Results of First Round PSL Trials, September 2005
Rotational IMRT techniques compared to fixed gantry IMRT and Tomotherapy: multi-institutional planning study for head-and-neck cases
<p>Abstract</p> <p>Background</p> <p>Recent developments enable to deliver rotational IMRT with standard C-arm gantry based linear accelerators. This upcoming treatment technique was benchmarked in a multi-center treatment planning study against static gantry IMRT and rotational IMRT based on a ring gantry for a complex parotid gland sparing head-and-neck technique.</p> <p>Methods</p> <p>Treatment plans were created for 10 patients with head-and-neck tumours (oropharynx, hypopharynx, larynx) using the following treatment planning systems (TPS) for rotational IMRT: Monaco (ELEKTA VMAT solution), Eclipse (Varian RapidArc solution) and HiArt for the helical tomotherapy (Tomotherapy). Planning of static gantry IMRT was performed with KonRad, Pinnacle and Panther DAO based on step&shoot IMRT delivery and Eclipse for sliding window IMRT. The prescribed doses for the high dose PTVs were 65.1Gy or 60.9Gy and for the low dose PTVs 55.8Gy or 52.5Gy dependend on resection status. Plan evaluation was based on target coverage, conformity and homogeneity, DVHs of OARs and the volume of normal tissue receiving more than 5Gy (V<sub>5Gy</sub>). Additionally, the cumulative monitor units (MUs) and treatment times of the different technologies were compared. All evaluation parameters were averaged over all 10 patients for each technique and planning modality.</p> <p>Results</p> <p>Depending on IMRT technique and TPS, the mean CI values of all patients ranged from 1.17 to 2.82; and mean HI values varied from 0.05 to 0.10. The mean values of the median doses of the spared parotid were 26.5Gy for RapidArc and 23Gy for VMAT, 14.1Gy for Tomo. For fixed gantry techniques 21Gy was achieved for step&shoot+KonRad, 17.0Gy for step&shoot+Panther DAO, 23.3Gy for step&shoot+Pinnacle and 18.6Gy for sliding window.</p> <p>V<sub>5Gy </sub>values were lowest for the sliding window IMRT technique (3499 ccm) and largest for RapidArc (5480 ccm). The lowest mean MU value of 408 was achieved by Panther DAO, compared to 1140 for sliding window IMRT.</p> <p>Conclusions</p> <p>All IMRT delivery technologies with their associated TPS provide plans with satisfying target coverage while at the same time respecting the defined OAR criteria. Sliding window IMRT, RapidArc and Tomo techniques resulted in better target dose homogeneity compared to VMAT and step&shoot IMRT. Rotational IMRT based on C-arm linacs and Tomotherapy seem to be advantageous with respect to OAR sparing and treatment delivery efficiency, at the cost of higher dose delivered to normal tissues. The overall treatment plan quality using Tomo seems to be better than the other TPS technology combinations.</p
Development of Proficiency Testing for Detection of Irradiated Food: Project E01068. Results of Second Round PSL and TL Trials, September 2006
Measurement of E2 Transitions in the Coulomb Dissociation of 8B
In an effort to understand the implications of Coulomb dissociation
experiments for the determination of the 7Be(p,gamma)8B reaction rate,
longitudinal momentum distributions of 7Be fragments produced in the Coulomb
dissociation of 44 and 81 MeV/nucleon 8B beams on a Pb target were measured.
These distributions are characterized by asymmetries interpreted as the result
of interference between E1 and E2 transition amplitudes in the Coulomb breakup.
At the lower beam energy, both the asymmetries and the measured cross sections
are well reproduced by perturbation theory calculations, allowing a
determination of the E2 strength.Comment: 8 pages, 3 figure
Robust signatures of solar neutrino oscillation solutions
With the goal of identifying signatures that select specific neutrino
oscillation parameters, we test the robustness of global oscillation solutions
that fit all the available solar and reactor experimental data. We use three
global analysis strategies previously applied by different authors and also
determine the sensitivity of the oscillation solutions to the critical nuclear
fusion cross section, S_{17}(0), for the production of 8B. The favored
solutions are LMA, LOW, and VAC in order of g.o.f. The neutral current to
charged current ratio for SNO is predicted to be 3.5 +- 0.6 (1 sigma), which is
separated from the no-oscillation value of 1.0 by much more than the expected
experimental error. The predicted range of the day-night difference in charged
current rates is (8.2 +- 5.2)% and is strongly correlated with the day-night
effect for neutrino-electron scattering. A measurement by SNO of either a NC to
CC ratio > 3.3 or a day-night difference > 10%, would favor a small region of
the currently allowed LMA neutrino parameter space. The global oscillation
solutions predict a 7Be neutrino-electron scattering rate in BOREXINO and
KamLAND in the range 0.66 +- 0.04 of the BP00 standard solar model rate, a
prediction which can be used to test both the solar model and the neutrino
oscillation theory. Only the LOW solution predicts a large day-night effect(<
42%) in BOREXINO and KamLAND. For the KamLAND reactor experiment, the LMA
solution predicts 0.44 of the standard model rate; we evaluate 1 sigma and 3
sigma uncertainties and the first and second moments of the energy spectrum.Comment: Included predictions for KamLAND reactor experiment and updated to
include 1496 days of Super-Kamiokande observation
Low-lying continuum structures in B8 and Li8 in a microscopic model
We search for low-lying resonances in the B8 and Li8 nuclei using a
microscopic cluster model and a variational scattering method, which is
analytically continued to complex energies. After fine-tuning the
nucleon-nucleon interaction to get the known 1+ state of B8 at the right
energy, we reproduce the known spectra of the studied nuclei. In addition, our
model predicts a 1+ state at 1.3 MeV in B8, relative to the Be7+p threshold,
whose corresponding pair is situated right at the Li7+n threshold in Li8.
Lacking any experimental evidence for the existence of such states, it is
presently uncertain whether these structures really exist or they are spurious
resonances in our model. We demonstrate that the predicted state in B8, if it
exists, would have important consequences for the understanding of the
astrophysically important Be7(p,gamma)B8 reaction.Comment: 6 pages with 1 figure. The postscript file and more information are
available at http://nova.elte.hu/~csot
Determination of the sign of screw dislocations viewed end-on by weak-beam diffraction contrast
Interatomic potentials for atomistic simulations of the Ti-Al system
Semi-empirical interatomic potentials have been developed for Al, alpha-Ti,
and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large
database of experimental as well as ab-initio data. The ab-initio calculations
were performed by the linear augmented plane wave (LAPW) method within the
density functional theory to obtain the equations of state for a number of
crystal structures of the Ti-Al system. Some of the calculated LAPW energies
were used for fitting the potentials while others for examining their quality.
The potentials correctly predict the equilibrium crystal structures of the
phases and accurately reproduce their basic lattice properties. The potentials
are applied to calculate the energies of point defects, surfaces, planar faults
in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al
system, the proposed potentials provide reasonable description of the lattice
thermal expansion, demonstrating their usefulness in the molecular dynamics or
Monte Carlo studies at high temperatures. The energy along the tetragonal
deformation path (Bain transformation) in gamma-TiAl calculated with the EAM
potential is in a fairly good agreement with LAPW calculations. Equilibrium
point defect concentrations in gamma-TiAl are studied using the EAM potential.
It is found that antisite defects strongly dominate over vacancies at all
compositions around stoichiometry, indicating that gamm-TiAl is an antisite
disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press
A Q-TWiST analysis comparing panitumumab plus best supportive care (BSC) with BSC alone in patients with wild-type KRAS metastatic colorectal cancer
DR6 as a Diagnostic and Predictive Biomarker in Adult Sarcoma
The Death Receptor 6 (DR6) protein is elevated in the serum of ovarian cancer patients. We tested DR6 serum protein levels as a diagnostic/predictive biomarker in several epithelial tumors and sarcomas.DR6 gene expression profiles were screened in publically available arrays of solid tumors. A quantitative immunofluorescent western blot analysis was developed to test the serum of healthy controls and patients with sarcoma, uterine carcinosarcoma, bladder, liver, and pancreatic carcinomas. Change in DR6 serum levels was used to assay the ability of DR6 to predict the response to therapy of sarcoma patients.DR6 mRNA is highly expressed in all tumor types assayed. Western blot analysis of serum DR6 protein demonstrated high reproducibility (r = 0.97). Compared to healthy donor controls, DR6 serum levels were not elevated in patients with uterine carcinosarcoma, bladder, liver, or pancreatic cancers. Serum DR6 protein levels from adult sarcoma patients were significantly elevated (p<0.001). This was most evident for patients with synovial sarcoma. Change in serum DR6 levels during therapy correlated with clinical benefit from therapy (sensitivity 75%, and positive predictive value 87%).DR6 may be a clinically useful diagnostic and predictive serum biomarker for some adult sarcoma subtypes.Diagnosis of sarcoma can be difficult and can lead to improper management of these cancers. DR6 serum protein may be a tool to aid in the diagnosis of some sarcomatous tumors to improve treatment planning. For patients with advanced disease, rising DR6 levels predict non-response to therapy and may expedite therapeutic decision making and reduce reliance on radiologic imaging
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