Introduction of a novel dose saving acquisition mode for the PortalVision aS500 EPID to facilitate on-line patient setup verification

In external beam radiotherapy, electronic portal imaging becomes more and more an indispensable tool for the verification of the patient setup. For the safe clinical introduction of high dose conformal radiotherapy like intensity modulated radiation therapy, on-line patient setup verification is a prerequisite to ensure that the planned dosimetric coverage of the tumor volume is actually realized in the patient. Since the direction of setup fields often deviates from the direction of the treatment beams, extra dose is delivered to the patient during the acquisition of these portal images which may reach clinical relevance. The aim of this work was to develop a new acquisition mode for the PortalVision aS500 electronic portal imaging device from Varian Medical Systems that allows one to take portal images with reduced dose while keeping good image quality. The new acquisition mode, called RadMode, selectively enables and disables beam pulses during image acquisition allowing one to stop wasting valuable dose during the initial acquisition of "reset frames." Images of excellent quality can be taken with 1 MU only. This low dose per image facilitates daily setup verification with considerably reduced extra dose.

Synergy-inducing chemokines enhance CCR2 ligand activities on monocytes

The migration of monocytes to sites of inflammation is largely determined by their response to chemokines. Although the chemokine specificities and expression patterns of chemokine receptors are well defined, it is still a matter of debate how cells integrate the messages provided by different chemokines that are concomitantly produced in physiological or pathological situations in vivo. We present evidence for one regulatory mechanism of human monocyte trafficking. Monocytes can integrate stimuli provided by inflammatory chemokines in the presence of homeostatic chemokines. In particular, migration and cell responses could occur at much lower concentrations of the CCR2 agonists, in the presence of chemokines (CCL19 and CCL21) that per se do not act on monocytes. Binding studies on CCR2(+) cells showed that CCL19 and CCL21 do not compete with the CCR2 agonist CCL2. Furthermore, the presence of CCL19 or CCL21 could influence the degradation of CCL2 and CCL7 on cells expressing the decoy receptor D6. These findings disclose a new scenario to further comprehend the complexity of chemokine-based monocyte trafficking in a vast variety of human inflammatory disorders.

VMC++ versus BEAMnrc: a comparison of simulated linear accelerator heads for photon beams

BEAMnrc, a code for simulating medical linear accelerators based on EGSnrc, has been bench-marked and used extensively in the scientific literature and is therefore often considered to be the gold standard for Monte Carlo simulations for radiotherapy applications. However, its long computation times make it too slow for the clinical routine and often even for research purposes without a large investment in computing resources. VMC++ is a much faster code thanks to the intensive use of variance reduction techniques and a much faster implementation of the condensed history technique for charged particle transport. A research version of this code is also capable of simulating the full head of linear accelerators operated in photon mode (excluding multileaf collimators, hard and dynamic wedges). In this work, a validation of the full head simulation at 6 and 18 MV is performed, simulating with VMC++ and BEAMnrc the addition of one head component at a time and comparing the resulting phase space files. For the comparison, photon and electron fluence, photon energy fluence, mean energy, and photon spectra are considered. The largest absolute differences are found in the energy fluences. For all the simulations of the different head components, a very good agreement (differences in energy fluences between VMC++ and BEAMnrc <1%) is obtained. Only a particular case at 6 MV shows a somewhat larger energy fluence difference of 1.4%. Dosimetrically, these phase space differences imply an agreement between both codes at the <1% level, making VMC++ head module suitable for full head simulations with considerable gain in efficiency and without loss of accuracy.

Testing the GlaaS algorithm for dose measurements on low- and high-energy photon beams using an amorphous silicon portal imager

The GLAaS algorithm for pretreatment intensity modulation radiation therapy absolute dose verification based on the use of amorphous silicon detectors, as described in Nicolini et al. [G. Nicolini, A. Fogliata, E. Vanetti, A. Clivio, and L. Cozzi, Med. Phys. 33, 2839-2851 (2006)], was tested under a variety of experimental conditions to investigate its robustness, the possibility of using it in different clinics and its performance. GLAaS was therefore tested on a low-energy Varian Clinac (6 MV) equipped with an amorphous silicon Portal Vision PV-aS500 with electronic readout IAS2 and on a high-energy Clinac (6 and 15 MV) equipped with a PV-aS1000 and IAS3 electronics. Tests were performed for three calibration conditions: A: adding buildup on the top of the cassette such that SDD-SSD = d(max) and comparing measurements with corresponding doses computed at d(max), B: without adding any buildup on the top of the cassette and considering only the intrinsic water-equivalent thickness of the electronic portal imaging devices device (0.8 cm), and C: without adding any buildup on the top of the cassette but comparing measurements against doses computed at d(max). This procedure is similar to that usually applied when in vivo dosimetry is performed with solid state diodes without sufficient buildup material. Quantitatively, the gamma index (gamma), as described by Low et al. [D. A. Low, W. B. Harms, S. Mutic, and J. A. Purdy, Med. Phys. 25, 656-660 (1998)], was assessed. The gamma index was computed for a distance to agreement (DTA) of 3 mm. The dose difference deltaD was considered as 2%, 3%, and 4%. As a measure of the quality of results, the fraction of field area with gamma larger than 1 (%FA) was scored. Results over a set of 50 test samples (including fields from head and neck, breast, prostate, anal canal, and brain cases) and from the long-term routine usage, demonstrated the robustness and stability of GLAaS. In general, the mean values of %FA remain below 3% for deltaD equal or larger than 3%, while they are slightly larger for deltaD = 2% with %FA in the range from 3% to 8%. Since its introduction in routine practice, 1453 fields have been verified with GLAaS at the authors' institute (6 MV beam). Using a DTA of 3 mm and a deltaD of 4% the authors obtained %FA = 0.9 +/- 1.1 for the entire data set while, stratifying according to the dose calculation algorithm, they observed: %FA = 0.7 +/- 0.9 for fields computed with the analytical anisotropic algorithm and %FA = 2.4 +/- 1.3 for pencil-beam based fields with a statistically significant difference between the two groups. If data are stratified according to field splitting, they observed %FA = 0.8 +/- 1.0 for split fields and 1.0 +/- 1.2 for nonsplit fields without any significant difference.

Electronic properties of zig-zag carbon nanotubes : a first-principles study

Carbon nanotube (CNT) is a one dimensional (1-D) nanostructured material, which has been the focal point of research over the past decade for intriguing applications ranging from nanoelectronics to chemical and biological sensors. Using a first-principles gradient corrected density functional approach, we present a comprehensive study of the geometry and energy band gap in zig-zag semi-conducting (n,0) carbon nanotubes (CNT) to resolve some of the conflicting findings. Our calculations confirm that the single wall (n,0) CNTs fall into two distinct classes depending upon n mod 3 equal to 1 (smaller band gaps) or 2 (larger gaps). The effect of longitudinal strain on the band gap further confirms the existence of two distinct classes: for n mod 3 = 1 or 2, changing Eg by ~ ±110 meV for 1% strain in each case. We also present our findings for the origin of metallicity in multiwall CNTs.

Hermitian curve interpolation for CT-data re-sampling

Purpose: Development of an interpolation algorithm for re‐sampling spatially distributed CT‐data with the following features: global and local integral conservation, avoidance of negative interpolation values for positively defined datasets and the ability to control re‐sampling artifacts. Method and Materials: The interpolation can be separated into two steps: first, the discrete CT‐data has to be continuously distributed by an analytic function considering the boundary conditions. Generally, this function is determined by piecewise interpolation. Instead of using linear or high order polynomialinterpolations, which do not fulfill all the above mentioned features, a special form of Hermitian curve interpolation is used to solve the interpolation problem with respect to the required boundary conditions. A single parameter is determined, by which the behavior of the interpolation function is controlled. Second, the interpolated data have to be re‐distributed with respect to the requested grid. Results: The new algorithm was compared with commonly used interpolation functions based on linear and second order polynomial. It is demonstrated that these interpolation functions may over‐ or underestimate the source data by about 10%–20% while the parameter of the new algorithm can be adjusted in order to significantly reduce these interpolation errors. Finally, the performance and accuracy of the algorithm was tested by re‐gridding a series of X‐ray CT‐images. Conclusion: Inaccurate sampling values may occur due to the lack of integral conservation. Re‐sampling algorithms using high order polynomialinterpolation functions may result in significant artifacts of the re‐sampled data. Such artifacts can be avoided by using the new algorithm based on Hermitian curve interpolation

Investigation of surface water/groundwater relationships in a rural watershed in Southern Honduras

Despite failed attempts at obtaining a potable water system, the village of El Caracol in Southern Honduras remains committed to improving access to water resources. To assist in this endeavor, an investigation of the hydrogeological characteristics of the local watershed was conducted. Daily precipitation was recorded to examine the relationship between precipitation and approximated river and spring discharges. A Thornthwaite Mather Water Balance Model was used to predict monthly discharges for comparison with observed values, and to infer the percentage of topographic watersheds contributing to the respective discharges. As aquifer porosity in this region is thought to be primarily secondary (i.e., fractures), field observed lineaments were compared with those interpreted from remote sensing imagery in an attempt to determine the usefulness of these interpretations in locating potential water sources for a future project.

The Quantitve Measurement of Amalgamation

Mercury has been known since ancient times. In fact, one mine, the "Almaden" in Spain, has been worked continuously since Roman times. It has been used during all this time for the recovery of free gold from gold concentrates, and from black sand and galena in concentrates from placer work.

The Amplifier - v. 8,(a-12) no. 12

In this issue...Ingersoll-Rand Company, Joseph Weindl, Sports Staff, M Club, Mother's Tea, religious history, Al Huizanga, Photo Club, mining engineering

The Bison: 1950

This digital object was funded in part through a grant from the Andrew W. Mellon Foundation. The digitalization of this object was part of a collaborative effort with the Washington Research Library Consortium and George Washington University.

Intra-abdominal pressure development after different temporary abdominal closure techniques in a porcine model

BACKGROUND: Decompressive laparotomy followed by temporary abdominal closure (TAC) is an established prophylaxis and treatment for abdominal compartment syndrome. The herein presented study aimed at the comparison of volume reserve capacity and development of intra-abdominal hypertension after forced primary abdominal closure and different TAC techniques in a porcine model. METHODS: Eight anesthesized and mechanically ventilated domestic pigs underwent a standardized midline laparotomy. A bag was placed into the abdominal cavity. Before abdominal closure, the bag was prefilled with 3,000 mL water to simulate increased intra-abdominal volume. The intra-abdominal pressure (IAP) was then increased in 2 mm Hg steps up to 30 mm Hg by adding volume (volume reserve capacity) to the intra-abdominal bag. Volume reserve capacity with the corresponding IAP were analyzed and compared for primary abdominal closure, bag silo closure, a zipper system, and vacuum-assisted closure (VAC) with different negative pressures (-50, -100, and -150 mm Hg). Hemodynamic and pulmonary parameters were monitored throughout the experiment. RESULTS: Volume reserve capacity was the highest for bag silo closure followed by the zipper system and VAC with primary abdominal closure providing the least volume reserve capacity in the whole IAP range. Of interest, VAC -50 mm Hg resulted in a lower volume reserve capacity when compared with VAC -100 and -150 mm Hg. Pulmonary and hemodynamic parameters demonstrated no significant differences between primary abdominal closure and the evaluated TAC techniques at all IAP levels. CONCLUSIONS: The present experimental in vivo study indicates that bag silo closure and zipper systems may be favorable TAC techniques after decompressive laparotomy. In contrast, the VAC techniques resulted in lower volume reserve capacity and therefore may bear an increased risk for recurrent intra-abdominal hypertension in the initial phase after decompressive laparotomy.