bluuebunny/crossref_metadata_2025 huggingface dataset:
Collective and Family Agriculture in Socialist Economies
Authors: Dong Nguyen Huu
Published: August 2010

summary This article analyses existing theories concerning the relationship between private and collective agricultural sectors in socialist economies with special reference to Vietnam. Dong argues that the household sector retains its vitality within socialist agriculture since it is a distinct and historically necessary mode of mobilising surplus labour and should be seen as playing a developmentally desirable role in both the rural reproduction process and surplus accumulation.

Resumen La agricultura colectiva y familiar en economies socialistas

Mediante este articulo se analizan las teorias actuales concernientes a la relación entre los sectores agricoles privados y colectivos dentro de economias socialistas, con referencia especiai al Vietnam. Dong argumenta que el sector familiar retiene su vitalidad dentro de la agricultura socialista, puesto que constituye un modo distinto e históricamente necesario, de movilizar la mano de obra excedente y deberia interpretarse como emprendedor de una misión deseable en cuanto al desarrollo, tanto dentro del proceso rural de reproducción como en la acumulación de excedentes.

Résumé L'agriculture familiale et collective dans les économies socialistes

Cet article analyse les théories actuelles concernant les relations entre les secteurs agricoles privés et collectifs dans les économies socialistes avec une référence spéciale au Vietnam. Dong démontre que le secteur familial conserve sa vitalité au sein de l'agriculture socialiste dès lors que c'est un mode distinct et historiquement nécessaire de mobilisation de surplus de main‐d'oeuvre et qu'il devrait être considéré comme ayant un rôle désirable à jouer dans le développement à la fois du processus de reproduction rurale et de surplus d'accumulation.
Soviet Agriculture since Khrushchev – Decentralisation and Dirigisme
Authors: Dyker D. A.
Published: August 2010

summary This article studies the efforts of the Soviet Government to redress the balance of developmental policies which favoured industry at the expense of agriculture. Particular attention is paid to the search for more flexible forms of organisation within the collective farm, as a basis for improved operational and motivational efficiency. The experience of the last 15 years indicates that better remuneration and increased investment flows are not enough in themselves to produce a radical upward shift in agricultural performance.

Resumen La agricultura soviética desde Khruschev — descentralizaciön y dirigismo

En este articulo se someten a estudio los esfuerzos del Gobierno Soviético para modificar el equilibrio de las politicas de desarrollo que favorecian a la industrie a expensas de la agricultura. Se dedica atención especial a la búsqueda de medios más flexibles de organización dentro de la granja, como base para mejorar el rendimiento de operaciones y motivaciones. La experiencia de los últimos 15 años revela que la mejor remuneración y el incrementado flujo de inversiones no resultan suficientes de por si para provocar un desplazamiento radical ascendente en el rendimiento agricola.

Résumé L'agriculture soviétique depuis Kroutchev — décentralisation et dirigisme

Cet article étudie les efforts du gouvernement soviétique pour redresser la balance des politiques de développement qui ont favorisé l'industrie au détriment de l'agriculture. Il attache une importance particulière à la recherche de formes d'organisation plus flexibles au sein de la ferme qui permettraient l'amélioration d'une efficacité motivée opérationnelle. L'expérience de ces 15 dernières années indique qu'une meilleure rémunération et une augmentation des volumes d'investissements ne sont pas des facteurs suffisants en eux‐mêmes pour provoquer une remontée radicale des performances agricoles.
Suspect novel adverse drug reactions to trimethoprim‐sulphonamide combinations in horses: A case series
Authors: STACK A. , SCHOTT II H. C.
Published: August 2010

Adverse drug reactions to trimethoprim‐sulphonamide combinations are common in many species, manifesting as gastrointestinal tract disorders, dermatopathies and blood dyscrasias. In this case series, neurological abnormalities in 4 horses being treated with trimethoprim‐sulphonamide combinations at normal dosages and in one foal that received an overdose are described. The horses developed hypermetric gait, agitation and erratic behaviour. All signs resolved once medication was withdrawn, and no horse had residual deficits. No other cause for observed neurological deficits could be determined. These clinical signs appear to represent a novel adverse drug reaction to some commonly used antimicrobial combinations.
Effect of Upstream Shear on Flow and Heat (Mass) Transfer Over a Flat Plate—Part I: Velocity Measurements
Authors: Ghosh K. , Goldstein R. J.
Published: August 2010

A parametric study investigates the effects of wall shear on a two-dimensional turbulent boundary layer. A belt translating along the direction of the flow imparts the shear. Velocity measurements are performed at 12 streamwise locations with four surface-to-freestream velocity ratios (0, 0.38, 0.52, and 0.65) and a momentum-based Reynolds number between 770 and 1776. The velocity data indicate that the location of the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt with increasing surface velocity. The highest belt velocity ratio (0.65) results in the removal of the “inner” region of the boundary layer. Measurements of the streamwise turbulent kinetic energy show an inner scaling at locations upstream and downstream of the belt, and the formation of a new self-similar structure on the moving surface itself. Good agreement is observed for the variation in the shape factor (H) and the skin friction coefficient (cf) with the previous studies. The distribution of the energy spectrum downstream of the belt indicates peak values concentrated around 1 kHz for the stationary belt case in the near wall region (30<y+<50). However, with increasing belt velocity, this central peak plateaus over a wide frequency range (0.9–4 kHz).
Molecular Dynamics Simulation of Phonon Scattering at Silicon/Germanium Interfaces
Authors: Sun Lin , Murthy Jayathi Y.
Published: August 2010

Detailed phonon transport at Si/Ge interfaces is studied using the molecular dynamics wave-packet method. Three types of interfaces are investigated: A smooth interface, an interface with random roughness, and an interface with a regularly patterned roughness. The phonon transmissivity for each case is calculated as a function of phonon frequency, roughness characteristic length, and atomic structure. For a smooth interface, the transmissivities predicted by the MD simulations agree well with the acoustic mismatch model based on the continuum assumption. The rough interface simulation results indicate that random roughness is the source of incoherent phonon scattering and decreases the phonon transmission. Periodic structures such as the regularly patterned roughness employed in this paper cause strong phonon wave interference and may restore phonon transmission as the layer thickness increases.
SU‐DD‐A1‐02: The X's and O's of 3D Dosimetry Phantoms
Authors: Nelms B , Feygelman V
Published: August 2010

Purpose: As rotational radiation therapy becomes more prevalent, the need grows for new methodologies of per‐patient dose QA. An approach commonly used for static‐field IMRT QA (per‐beam planar dose normal to the beam axis) is less relevant for rotating beams; thus, more attention has turned to composite dose in a 3D phantom. In this work, two commercial 3D dosimetry phantoms are studied under identical conditions (TPS, delivery) for rotational plans. Materials and Methods: The Delta4 (ScandiDos) and ArcCHECK (Sun Nuclear Corporation) devices were each entered into the TPS as QA phantoms for the transference of VMAT plans produced by the Pinnacle TPS (Philips). The sensitivity to the angular discretizing of a rotational plan into 2, 4, and 6 degree sub‐arcs was studied. In addition, small errors were introduced into the TPS calculation (MLC shifts, transmission changes) to assay each device's sensitivity to those errors. Results: The ArcCHECK's peripheral detector geometry was far more sensitive to TPS angular discretization of the dose calculation; however, the impact of the difference in 2‐degree and 4‐degree sub‐arcs was very small in the high dose central/target regions, as evidenced by the high passing rates of the Delta4. Both devices showed insensitivity to small errors induced in MLC position and transmission, but both were sensitive (D4 at 3%/3mm and 2%/2mm, AC at 2%/2mm) to MLC shifts of 0.9 mm. Comparison results between Delta4 and ArcCHECK trended similarly, but passing rates were not the same. Conclusions: The design of the detectors' locations in 3D space is critical to understanding the behavior of a 3D dosimetry phantom. Dose QA results measured by one system are not interchangeable with another's if the detector geometries are not identical. Ideally, it would be useful to correlate these phantom dose QA results to their impact to patient dose/DVH on a per‐patient basis.
SU‐DD‐A1‐03: On Rotational Measurements with the ArcCHECK 3D Diode Array
Authors: Feygelman V , Zhang G , Stevens C , Nelms B
Published: August 2010

Purpose: The ArcCHECK 3D diode array dosimeter (Sun Nuclear Corporation) represents a novel approach to detector placement. We investigate the effects this design can have on the rotational measurements' accuracy and suggest correction factors that could sometimes improve it. Method and Materials: The ArcCHECK design places 1386 0.8×0.8mm2 diodes arranged on a 1×1cm helical grid on a cylindrical surface 21cm in diameter inside a doughnut‐shaped phantom.. Beam arrangements tested in this work include single static beams, simple open arcs, and VMAT plans based on the AAPM TG1 19 test suite. Field size dependence, angular dependence, phantom inhomogeneity effects, and calculation angular‐discretization effects were investigated separately.Results: Unlike an existing device using the same diodes (MapCHECK), ArcCHECK exhibits non‐negligible field size dependence in detector response, likely due to the increased phantom volume. Angular‐dependent detector response is also shown, evidenced by measured beam profiles deviating from the calculations and ion chamber measurements by more than 2% for field widths exceeding approximately 15 cm. The issue is being addressed by the manufacturer. There is an additional small disagreement between measured and calculated exit doses (1.5%) due to the inhomogeneous phantom structure. Simple arc measurements demonstrate strong influence of the small changes in field width (e.g. 9%/mm at 2cm), while the isocenter dose is essentially unchanged. This is inherent and expected given the device design. The average gamma analysis passing rates for a well‐commissioned VMAT system were 98.4 and 92.9% at the 3%/3mm and 2%/2mm error thresholds, respectively. They improved to 98.7 and 94.2%, respectively, after manual application of the field size correction factor. Conclusion: Despite hypersensitivity to field width in the simple arc geometry, the VMAT gamma analysis results are in line with expectations based on independent dosimetry measurements. Introduction of correction factors for angular and field‐size dependence would further improve measurement accuracy.
SU‐DD‐A2‐03: Can the Linear Quadratic (LQ) Model Predict the Biological Response of Cells to Simple Dose Heterogeneity for Single and Multiple Fraction Irradiation?
Authors: Bromley R , Oliver L , Davey R , Harvie R , Baldock C
Published: August 2010

Purpose: Can the α and β values derived from uniform irradiation be used in the Summed Dose Method to predict cell survival for single or multiple fraction irradiation with a heterogeneous dose distribution? Method and Materials: A549 non‐small cell lung cancer cells were investigated by clonogenic assay in a NUNC 6‐well plate using single and multiple fractions up to 10Gy. The plate contains two uniformly irradiated wells and two heterogeneously irradiated wells. The α and β values measured in the uniformly irradiated wells were used to predict the survival for a sharp and shallow dose distribution. The experimental survival was compared with that predicted by the Summed Dose Method. Results: The Summed Dose Method cannot predict in the total well survival of A549 cells for either dose distribution at single fraction doses. The total well survival cannot be predicted for the sharp distribution at fraction 4 and 5, for any fraction in the irradiated region, for the shallow dose distribution at fractions 3 and 5 in the unirradiated region or any fraction in the irradiated region or total well. The Summed Dose Method can predict the survival of the sharp distribution at all single fraction doses in the unirradiated region and up to 2 Gy in the irradiated. The survival can be predicted at 5 Gy in the unirradiated region and 1 and 5 Gy in the irradiated for the shallow dose distribution. The survival is predicted at fractions 1, 2 and 4 in the unirradiated regions for the shallow dose distribution and is predicted for the sharp distribution at all multiple fractions in the unirradiated region, and fractions 1 to 3 in the total well. Conclusion: The Summed Dose Method is still limited in predicting cell survival for single or multiple fraction irradiation with a heterogeneous dose distribution.
SU‐DD‐A2‐04: Functional Relationships between Imaging and Biological Markers for the Purpose of Dose Painting Using the Example of FLT‐PET and the Ki‐67 Labeling Index
Authors: Keller H , Lakshman M , Vines D , Dunne M , Bristow R
Published: August 2010

Purpose: To develop a Monte Carlo simulation based parameter estimation procedure to obtain and assess functional relationships between imaging data and an underlying biological property that are necessary for dose prescription strategies such as dose painting. Method and Materials: An example of such a relationship is the correlation of FLT tracer uptake in the tumor and the fraction of proliferating cells as measured by the labeling index (LI) of the Ki‐67 protein. Lung tumor xenografts (H520) in 6 mice were irradiated on a small animal irradiator and FLT‐PET/CT imaged pre‐and 24 hours post‐irradiation. Tumors were harvested after the second imaging session, processed and stained for Ki‐67. The post‐irradiation FLT uptake distributions were analyzed within the boundary of the tumors as segmented on the CT images. For 4/6 tumors 2 ROIs each and corresponding uptake distributions were identified, resulting in a total of 10 FLT distributions and associated Ki‐67 LI. For every FLT uptake distribution a test statistic and its probability density function (pdf) was computed that mimicks the measurement of the LI using 4 non‐overlapping fields. A likelihood function from the test statistics of each tumor ROI was maximized to obtain the parameters of an assumed linear relationship between FLT uptake in units of %ID/g and the LI. Results: A linear relationship is compatible with the measured LI, however the likelihood function demonstrates a broad maximum if the pdfs are generated from purely random samples within the ROIs. More samples and additional information about the location of the sample fields narrows the width of the pdfs and enhances the maximum likelihood. Conclusion: The advantage of the proposed parameter estimation is that it simulates the LI analysis process and does not rely on any summary metric of the FLT uptake distributions, such as the maximum or a tail‐mean value.
SU‐DD‐A2‐06: Effect and Optimization of Beam Delivery Sequence for Consistent Biological Effective Dose Realization in Stereotactic Radiosurgery Treatments
Authors: Ma L , Hu W , Sahgal A , Larson DA
Published: August 2010

Purpose: Intracranial radiosurgery commonly employs many isocenters or beams to deliver dose distributions over an extended treatment time (30–100 minutes or more). In this study, we investigate whether the sequential order of delivering these isocenters or beams would significantly influence the biological effectiveness of the treatment and how to optimize a delivery sequence based on such considerations. Method and Materials: A group of patient cases treated with Gamma Knife Perfexion at our institution were analyzed All permutation possibilities of the delivery sequence were reconstructed for each patient. For each possibility, the time‐sequence of 3D dose accumulation within the target and the surrounding normal structures was computed. Then the equivalent uniform dose (EUD) based on a generalized linear‐quadratic model formula was calculated for each possible delivery sequence. Variations in the EUD values from all combinations were calculated. Dependence of EUD values for the alpha‐beta ratios ranging from 2 to 20 was also investigated for each case in order to determine its effect on the results. Results: The maximum EUD and minimum EUD values varied approximately 10–15%, or 1–2 Gy for different order of delivery sequences depending on the target size and the target peripheral dose. The effect was found to be dependent on the total number of isocenters and dose interference among them. Furthermore, discrepancy in the EUD values was found to increase with decreasing alpha‐beta values, suggesting the effect being most relevant for treating lesions such as large AVM, where alpha‐beta ratio is supposedly low and a high number of isocenters are typically used. Conclusion: Optimizing sequential order of beam delivery based on biological considerations is important in minimizing treatment‐related EUD variations and ensuring consistency in treatment dosimetry.
SU‐DD‐A3‐02: The Impact of Cone‐Beam Computed Tomography (CBCT) Artifacts on Deformable Image Registration Algorithms
Authors: Ueda U , Hu W , Pouliot J , Yom S , Quivey J , Aubin M , Chen J
Published: August 2010

Purpose: Deformable image registration algorithms capable of rapidly contouring kV and MV cone‐beam computed tomography (CBCT) images would greatly facilitate new adaptive radiotherapy techniques. However, the CBCT imaging geometry produces well‐known image artifacts. The goal of this study is to quantify the impact of these artifacts on a commercially available deformable image registration algorithm and suggest maximum acceptable artifact levels. Method and Materials: In‐house programs were used to modify conventional CT images of several head‐and‐neck radiotherapy patients to simulate common, previously reported CBCT artifacts such as noise, global shifts in Hounsfield units (HU), and reduction in bone contrast. The contours drawn on the original CTs were deformed to the modified CTs using the MIM software suite's deformable registration algorithm (Mimvista, Cleveland, OH). Dice similarity indices (DSI), the volume of the contours' overlap divided by their average volume, were calculated and used to determine the impact of CBCT artifacts on contour deformation accuracy. Results: The addition of moderate levels of noise had little effect on accuracy. Brainstem and temporal lobe contours were most affected with DSI values of ∼0.9 for a 70 HU noise level (1 standard deviation). Global shifts in HU created large discrepancies in the deformed contours. Large deviations were observed for a global shift of −75 HU for the parotids (DSI ∼ 0.77), brainstem (DSI ∼ 0.68) and especially the temporal lobe (DSI ∼ 0.57). Suppression of the bone CT numbers from 900 HU to 151 HU had marked effects on the deformed contours of the cochleae (DSI∼0.48), mandible (DSI∼0.63), and TMJs (DSI∼0.57). Conclusions: Additional noise in CBCT images has a small effect on the accuracy of a commercial deformable registration algorithm. However, global shifts in CT number and the suppression of bone CT numbers can produce significant errors depending on the magnitude of the change in HU.
SU‐EE‐A2‐02: Present Status of IAEA/AAPM Recommendations on Small and Composite Field Dosimetry
Authors: Alfonso R , Andreo P , Noy R Capote , Huq M , Izewska J , Johansson J , Kilby W , Mackie T , Meghzifene A , Palmans H , Rosser K , Seuntjens J , Ullrich W
Published: August 2010

Purpose: An international IAEA/AAPM working group is preparing recommendations for reference dosimetry in small fields and composite fields. A proposed formalism for dosimetry in small and composite fields was published that introduces machine specific reference (msr) fields for static small fields and plan‐class specific reference (pcsr) fields for composite fields such as an IMRT sequence. The status of present activities, based on the proposed formalism, will be reviewed. Method and Materials: For msr fields a literature review is conducted and for some modalities experiments and Monte Carlo simulations are performed. For composite fields various routes are explored to arrive at suitable pcsr fields. Some of these start from clinical plans and try to distil most representative reference deliveries, while others start from treatment unit specific features to arrive at relevant modulated plans. Experiments and Monte Carlo simulations are performed as well to determine correction factors for ionisation chambers in pcsr fields and to evaluate their suitability to represent a class of clinical plans. One idea being explored is that for a composite field where full charged particle equilibrium is established, the overall correction factor equals the reciprocal of the gradient correction factor in the conventional reference field. Results: State‐of‐the‐art results on the correction factors for msr and pcsr fields will be reviewed. Experimental work performed on pcsr fields in TomoTherapy and step‐and‐shoot prostate plans indicates that correction factors for suitably sized ion chambers are not more than 1% different from unity. Monte Carlo simulations confirm this. Studies are underway to test the sensitivity of the correction factors to characteristics of the pcsr field. Conclusion: Results indicate that reference dosimetry in msr and pcsr fields is feasible with acceptably small corrections. A working document on static small field dosimetry is aimed for by the end of this year.
SU‐EE‐A2‐04: Traceability to National Measurement Standards for Electronic Brachytherapy Calibrations
Authors: Mitch M , O'Brien M , Tosh R , Seltzer S , McClelland M , Eardley D
Published: August 2010

Purpose: To establish a primary air‐kerma standard for the Xoft miniature x‐ray brachytherapy source. Method and Materials: A new calibration facility has been designed at the National Institute of Standards and Technology (NIST) to directly realize air kerma from electronic brachytherapy sources operated up to 50 kV. The previously established primary x‐ray standard, the Lamperti free‐air ionization chamber, has been dedicated for this measurement capability. The spectrum emergent from the source is measured with a high‐purity germanium spectrometer. To account for possible anisotropy of emissions from the source, both the free‐air chamber and the spectrometer are rotated about the long axis of the source. Well‐chamber measurements are also performed to study the variability in the ratio of well‐chamber current to air‐kerma rate in anticipation of developing a method for transferring the NIST standard to secondary calibration laboratories and/or therapy clinics. Results: Comparisons of the air‐kerma rate realized by two NIST x‐ray primary standards, the Lamperti free‐air chamber (10 kV to 60 kV) and the Ritz free‐air chamber (20 kV to 100 kV), were in agreement to better than 1% as is typical for well‐established primary x‐ray standards. This comparison validated the use of the Lamperti chamber in establishing the measurement techniques required for the determination of air kerma. Conclusion: NIST has designed, constructed, and validated the experimental apparatus necessary for the measurement of air‐kerma from an x‐ray brachytherapy source using a primary standard. NIST acknowledges the support of Xoft, Inc., in this project.
SU‐EE‐A2‐05: Central Electrode Correction Factor, Pcel, for Steel and Wire Electrodes
Authors: Muir B , Rogers D
Published: August 2010

Purpose: Beam quality conversion factors, kQ, are required for use with the TG‐51 clinical dosimetry protocol. TG‐51 values of kQ are calculated using the ratio of several correction factors including the central electrode correction factor, Pcel, which is known for ion chambers with aluminum or graphite electrodes. This study calculates Pcel values in photon beams for more recent chambers that use electrodes composed of high‐Z materials. Method and Materials: Monte Carlo simulations using the EGSnrc user‐code egs_chamber are used to calculate the absorbed dose to the gas in an ion chamber with and without the central electrode. The ratio of the two doses gives Pcel. Manufacturers' blueprints and user's manuals are used to model the ion chambers. The source is modeled as a collimated point source from tabulated spectra for Cobalt‐60 and linear accelerator photon beams. Spectra used include some linear accelerators without flattening filters to investigate the value of Pcel in ‘soft’ beams. Results: For small volume ion chambers with electrodes composed of high‐Z materials the central electrode effect is unlike that of aluminum electrodes in standard Farmer‐like chambers. This results in kQ factors which are up to 1.5% larger for clinical beams than those used in current dosimetry protocols. For standard Farmer‐like chambers, Pcel does not depend on the degree of filtration in the beam but for chambers with high‐Z electrodes Pcel is different by up to 1.5% in lightly‐filtered beams compared to values in typical clinical beams. Conclusion: Calculations of the central electrode correction factor in photon beams have shown that ion chambers with electrodes made of high‐Z materials have significantly larger electrode effects (1 to 2.5%) than those with aluminum electrodes (<0.8%). It would be best to avoid such high‐Z electrode materials.
SU‐EE‐A2‐06: The Measurement of KQ Factor for the FC65‐G Water Proof Chamber in 6, 10 and 18 MV Photon Beams
Authors: Amin M , Norrlinger B , Heaton R
Published: August 2010

Purpose: The beam quality conversion coefficient kQ is one of the factors needed to determine the absorbed dose to water of a linac following the guideline prescribed by TG‐51 and TRS‐398. In this study kQ values were determined for a farmer type IBA FC65‐G chamber in a 6, 10 and 18 MV photon beams (beam qualities %dd(10)X of 67.5, 73.55 and 79.7 respectively) using a solid water phantom. FC65‐G is a 0.65cc water proof graphite chamber for which the published measured kQ values are not widely available. Methods and Materials: The kQ measurement was performed on an Elekta Synergy linear accelerator and a cobalt unit. Corrections for beam stability were performed using down stream monitoring detectors. The kQ of five NE2571 chambers have been checked to validate the methodology, as well as the stability and the sensitivity of our system. Reproducibility of kQ measurements for a single chamber and variability across multiple chambers of the same type were investigated. Results: The average kQ values measured for the five FC65‐G chambers in the 6, 10 and 18 MV photon beams are 0.9928±0.0006, 0.9833±0.0007 and 0.9738±0.0006 respectively. These kQ values are within ±0.02%, ±0.03% and ±0.04% respectively of those reported in TG‐51 for chambers of similar construction. The measurement reproducibility of 0.02% and 0.03% were determined for NE2571 and FC65‐G chambers respectively. Conclusion: The kQ has been directly determined for both NE2571 and FC65‐G chambers and found to be consistent with values provided in TG‐51 and TRS‐398. The TG‐51 recommendation to use kQ for chambers of similar construction was found to be good within measurement uncertainly in this case.
SU‐EE‐A3‐05: Real Time Tumor Motion Monitoring during IGRT Based on Manifold Learning and Dynamic Registration between 4DCT and Fluoroscopy
Authors: Chen T , Jabbour S , Goyal S , Zhou J , Haffty B , Yue N
Published: August 2010

Purpose: To develop a real time tumor respiratory motion monitoring methodology for thoracic cancer IGRT by integrating manifold learning and dynamical registration of 4DCT and fluoroscopy technique during the radiation treatment.Method and Materials: 10‐phases retrospective 4DCT have been acquired from 6 patients (5 lung, 1 pancreas) with audio coaching. During their gated radiation treatment, fluoroscopy videos were collected with the same audio coaching. A radiation oncologist delineated the contours including the GTV in the 50% phase 4DCT. The methodology is divided into three steps. First an object‐constrained registration has been used to register 4DCT at other phases to the reference 50% phase in order to build a spatial‐temporal tumor motion model. Then the 4D motion model has been used as the constraint in the spatial registration and temporal matching of the 4DCT with the fluoroscopy. An Isomap based manifold learning has been used to establish a global matching scheme between the 4DCT phases and fluoroscopy frames. In the last step, the GTV in newly acquired fluoroscopy frames were monitored in real time based on the fast registration between the frame and the DRR of the corresponding 4DCT phase using the global constraint and local image information.Results: The registration between 4DCT phases is within 30 minutes. The 4DCT to fluoroscopy registration and tumor motion monitoring are close to real time. After registration and training, for all 6 patients, the tumor (GTV) in an arbitrary fluoroscopy frame can be tracked with motion error less than 2mm, based on comparison between manually delineated contours in the fluoroscopy and the deformed GTV. Conclusion: The proposed tumor monitoring approach can achieve real time efficiency as well as satisfactory accuracy and precision and has the potential to be used in IGRT to improve setup and tumor tracking accuracy to achieve desired dose coverage.
SU‐GG‐E‐03: Current Status of Medical Physics Undergraduation Courses in Brazil
Authors: Costa P , Terini R , Freitas M , Watanabe E
Published: August 2010

PURPOSE Medical Physics teaching in Brazil differs of other countries, since there are a number of undergraduation courses providing this background for bachelor's students. A survey was performed by Brazilian Association of Physicist in Medicine (ABFM) and a Workshop on Medical Physics Education and Training was organized in order to understand the state‐of‐the‐art of the current teaching methods. METHODS AND MATERIAL During 2009, electronic forms were sent to Medical Physics courses coordinators in order to obtain information regarding the status of each University. The requested information included: year of starting the offer of Medical Physics undergraduation, number of students accepted per year, modality of students' selection, and others. During the Workshop (February 4–5th, 2010), the current educational methods and ideal profile bachelors in Medical Physics were discussed at roundtables and testimonies of employers, ex‐students and graduation and residency program supervisors. RESULTS The survey collected data from 8 out of 13 courses and it showed that Medical Physics courses open at least 360 places per year and have duration of 4–5 years. Around 120 students had concluded their undergraduation courses in the last year, totalizing approximately 550 students graduated until 2008. As a result of the Workshop, the need for attention on improving the clinical experience during the undergraduation period appears as the main topic to be reinforced by the course coordinators. Hospital training after to conclude the undergratuation course is an important part of the education‐training. CONCLUSION The data survey and Workshop showed that undergraduate courses have accelerated the formation of staff for the Medical Physics. Differences on the provided scientific background for the students of different Medical Physics courses must be harmonized in order to provide similar information and resources in each University. It should be done without interference in the main characteristics and natural specialization of each school.
SU‐GG‐I‐02: A Simple Technique for Generating Respiratory Signals with Lasers in Radiotherapy
Authors: Prabhakar R , Rath G
Published: August 2010

One of the challenging problems in radiotherapy is the treatment of mobile tumors. The usual method is to give a large clinical target volume (CTV) to planning target volume (PTV) margin to accommodate the movement of the tumor within the treatment field. In recent years, several new concepts such as tracking, gating, breath‐hold techniques have been developed to combat the movement of tumor during treatment which are very useful in the treatment of mobile tumors such as lung, liver, breast, pancreas etc., Most of these methods uses respiratory signal generated by different methods. In this study, a simple technique has been devised to generate the respiratory signal pattern with the help of lasers. Two lasers, red and green are mounted on the collimator head of a Clinac 2300 C/D linac along with the camera for generating the respiratory signal pattern. A software written in visual basic 2005 .net was developed to read the images from a 12‐megapixel camera mounted below the collimator. The projection of the laser images on the chest of a subject was acquired during breathing. Multiple frames of laser images are acquired from the camera mounted on the collimator head and each frame was analyzed with the SSDLas software to generate the respiratory signal. As the patient breathes, the separation between the projected lasers on the skin surface also changes. The changes in the lasers separation are converted to produce a respiratory signal with the SSDLas software. The technique described for generating the respiratory signals using lasers is cost effective and easy to implement. The generated respiratory signal based on the laser position on the patient surface will be useful for acquiring 4D images and also for treating mobile tumors.
SU‐GG‐I‐08: Optimize Pediatric Abdominal CT Protocols Based on Circumferences
Authors: Dong F , Davros W
Published: August 2010

Purpose: There is an increasing demand on lowering the radiation dose in pediatric CT to reduce the long‐term cancer risks. In this study, pediatric CT protocols are optimized based on “equivalent abdominal circumference (EAC)” by varying both kVp and effective mAs (mA*exposure_time/pitch). Methods and Materials: All measurements were taken using a 16‐row CT scanner. To mimic the shape of the pediatric abdomen, a saline bag was placed on each side of 10cm and 16cm‐diameter, circular cylindrical phantoms. Dose was measured using a 100 mm pencil probe ion chamber. Noise was measured by recording the standard deviation near the center of selected images while kVp, mAs and phantom diameter were varied in turn. Dose was collected at four available kVp settings. At each kVp, measurements were taken at five different mAs. For CNR measurement, iodine contrast was diluted to match clinically relevant CT number of ∼300 HU and this diluted contrast was injected into the center holes of the CTDI phantoms. Distilled water was also injected to one of the peripheral holes as reference. The contrast was measured based on the difference of CT number between iodine and water. Results: Optimal scan techniques are selected for each EAC range based on the clinical noise tolerance < 20HU and CTDIvol < 2.5cGy. For the smallest patient (< 30 cm EAC), scan technique of 80kVp and <100 mAs can be used; for 50 cm EAC, 100 kVp and <60 mAs. The signal‐to‐noise ratio measurement indicated lower kVp can effectively enhance the iodine contrast and increase CNR under the same dose with higher kVp. Conclusions: For pediatric CT, the most effective way to strike the balance between image quality and radiation dose is to adjust dose according to patient abdominal circumference. The EAC‐based technique optimization curve can be used to optimize kVp and mAs.
SU‐GG‐I‐136: Theoretical Limits to System Performance of High Efficiency, Direct Detection, Megavoltage Active Matrix Flat‐Panel Imagers Based on Polycrystalline Mercuric Iodide
Authors: Zhao Q , Liu L , El‐Mohri Y , Antonuk L , Jiang H , Koniczek M
Published: August 2010

Purpose: Megavoltage active matrix, flat‐panel imagers (MV AMFPIs), in which a phosphor screen/copper plate serves as the x‐ray detector, are the de facto gold standard in portal imaging. Nevertheless, the poor efficiency of conventional MV AMFPIs, which detect only ∼2% of the incident radiation at 6 MV, has stimulated efforts to develop more efficient detectors, potentially facilitating high‐contrast tomographic imaging at low, clinically practical doses. In one approach, multiple thick layers of polycrystalline mercuric iodide (HgI2) photoconductor replace the phosphor screen to increase x‐ray detection efficiency. In this presentation, theoretical limits to MTF and DQE for this approach are examined through variation of photoconductor thickness and the composition and thickness of the metal plate. Method and Materials: Monte Carlo simulations of the interaction of a 6 MV beam with various photoconductor/metal plate combinations were performed. From the resulting MTF and NPS for HgI2 (in the form of particle‐in‐binder, PIB) up to 6 mm thick, in combination with metal plates up to 3 mm thick, DQE was determined. Results: Various trends are apparent. Increasing the thickness of the PIB layer results in lower MTF and higher DQE, as expected. However, for a given thickness of PIB, MTF is observed to decrease with increasing plate thicknesses — with this effect becoming less pronounced as PIB thickness increases. Moreover, increasing plate thickness enhances DQE at low spatial frequencies while diminishing it at higher spatial frequencies — with the absolute changes in DQE becoming greater as PIB thickness increases. Conclusion: As thicker PIB detectors exhibiting good mechanical and signal properties are developed, the composition and thickness of the overlying metal plate (which also serves to absorb scattered radiation) will require optimization, based on considerations such as the trade‐off of DQE at low spatial frequencies against DQE at high spatial frequencies.
SU‐GG‐I‐137: Study of the Perception of Microcalcification Clusters in Stack‐Mode Digital Breast Tomosynthesis
Authors: Yang A , Carton A‐K , Bakic P , Kundel H , Nodine C , Maidment A
Published: August 2010

Purpose: To observe human performance in viewing Digital Breast Tomosynthesis (DBT) images of microcalcification clusters (MCs) in stack‐mode. Method and Materials: A GUI program was created to simulate the presentation of DBT images in stack‐mode. The background consisted of either a uniform gray screen, a gray screen with varying amounts of Poisson noise, or simulated breast images. Each image had an average intensity value of 128, and was displayed for a total of 6 seconds. After the first 4 seconds, a MC at a specified radius from the center was shown for 1 second. The MCs were simulated after those found in the ACR mammography accreditation phantom. The radii used were: 540, 360, and 180 pixels. Contrast differences between the MC and the background were chosen randomly from a set range of about 10–35 gray values. Three test subjects were asked to look at the center of the screen, and to click where they saw a MC in their periphery after the images were displayed. The angular error of the response was calculated, and served as a measure of detection accuracy. A monotonic fit was applied to the data. Results: As contrast of the MC increases, the probability of detection increases, and the angular error decreases. With increasing radius from the center, the threshold contrast for detection increases. Similarly, as the Poisson noise in the image increases from a factor of 1 to 4, the threshold contrast for detection increases. Abnormalities that appear in the right and left sides of the screen have a lower angular error than those that appear in the top and bottom of the screen. Conclusion: These data provide insight into how radiologists perceive MCs while viewing DBT images in stack‐mode. Findings about peripheral vision may suggest a more optimal way of displaying DBT images.
SU‐GG‐I‐140: Maximum Intensity Projection (MIP) Imaging Using Multi‐Slice Cine MRI
Authors: Adamson J , Chang Z , Wang Z , Yin F , Cai J
Published: August 2010

Purpose: To propose a novel method of acquiring Maximum Intensity Projection (MIP) images using multi‐slice cine MRI, termed as MRI‐MIP, and to evaluate its feasibility in quantifying motion magnitude. Materials and Methods: MRI‐MIP images are acquired using a modified multi‐slice cine MR sequence in which each axial slice was imaged repeatedly throughout the duration of the respiratory cycle. A maximum intensity image was then constructed for each slice using all acquired images. For this study, we used a 1.5T clinical whole body MRI scanner (Signa, GE Healthcare, WI) and a sequence of fast imaging employed steady state acquisition (FIESTA) with a six channel phased array flexible coil to acquire 15 images in 6 seconds for each slice (flip angle= 50°, matrix= 192×128, FOV= 300×300mm, slice thickness= 0.5mm, TR/TE= 3.2/1.0ms). To test feasibility, MRI‐MIP, CT‐MIP, and single slice sagittal cine‐MR images were acquired of a 66 cm3 polygonal phantom placed on an MR compatible motion platform with Superior‐Inferior motion consisting of 2 analytical (peak‐to‐peak amplitude = 2.8cm, period = 5s) and 3 patient motion trajectories from Varian RPM. We also acquired MRI‐MIP and single slice sagittal cine‐MRI images for 3 healthy volunteers and compared the areas of interest. Results: Phantom volume from MRI‐MIP was well correlated with CT‐MIP, with the mean (± standard deviation) difference from CT MIP being 0.1%±2.9% and a max difference of −4.2%. For the analytical trajectories, area from MRI‐MIP matched cine‐MRI to within ±0.3%. For patient motion trajectories, the difference in phantom area between MRI‐MIP and cine‐MRI was −10.4%, −7.4%, and −6.6%. For patient images, the difference in contoured areas was −5.5%, 2.3%, and 4.8%. Conclusion: Preliminary results on phantom and healthy volunteers suggest using multi‐slice cine MRI to generate MIP is feasible. Motion information obtained from this technique is comparable to that from 4DCT‐MIP.
SU‐GG‐I‐143: An in Vivo Study on the Enhancement of Gene Therapy with MR‐Guided Focused Ultrasound (MRgFUS)
Authors: Chen L , Mu Z , Pollack A , Ma
Published: August 2010

Purpose: The purpose of this study is to investigate the feasibility of increasing the cellular uptake of AS‐MDM2 for prostate cancer with image‐guided focused ultrasound (MRgFUS). Materials and Method: A GE/InSightec MRgFUS system was used in this experimental study. Human prostate cancer cells LNCaP (5×105) were grown orthotopically in the prostates of 28 nude mice. Animals were divided randomly into 4 Groups (n=7/group): Group 1: MRgFUS+AS‐MDM2; Group 2: MRgFUS only; Group 3: AS‐MDM2 i.v injection only; Group 4: control. For group one the tumors were treated using MRgFUS with the acoustic power of 4 W, pulse width of 0.1 sec and 300 pulses in one sonication. The focal peak was set within the target under MR guidance. Multiple sonications were used to cover the whole tumor. Immediately after the ultrasound treatment 0.1 ml of AS‐MDM2, dissolved in PBS, was given by tail vein injection at 25 mg/kg. For group 2 animals were treated with the same as for group one except for AS‐MDM2 injection. Animals in group 3 were treated with AS‐MDM2 injection only and group 4 used as control. Mice were sacrificed 6 and 24 hr after treatment. The tumors were removed and processed for assessment of protein expression by immunohistochemical staining. The expression levels of MDM2, p53 and p21 proteins were quantified using an image‐analysis system. Results: We observed blood cell extravasations on H&E staining in the MRgFUS treated tumors, as compared to the other groups. There are no significant differences between groups with and without MRgFUS treated groups both 6 hours and 24 hours after treatment. Conclusions: One single AS‐MDM injection did not knock down MDM2 or result in increases in p53 and p21. The effect of multiple MRgFUS and AS‐MDM2 treatments on the LNCaP tumor growth is warranted in future studies.
SU‐GG‐I‐145: Dependence of Signal‐To‐Noise Ratio Variance on ROI Size in Phased‐Array Coil Measurements
Authors: Shah M , Yanasak N
Published: August 2010

Purpose: The goal of this project was to determine the dependence of SNR variance measured with the phased array coil on ROI size. Method and Materials: A doped water‐filled soccer ball and GE spherical phantom were scanned using an 8‐channel phased array coil and volume coil. SNR was calculated using two different techniques; the single acquisition method and the difference method. The dependence of the estimated standard error in the mean was calculated to assess SNR measurement variability as a function of radius. Observations were made on multiple days to characterize the impact of systematic variation on SNR calculations. Comparisons were made to simulated images containing homogenous signal and noise. Results: Simulation data demonstrated that standard error of mean SNR decreases as ROI size increases, which is expected if signal and noise are homogenous throughout an image. However, this result did not hold true for phased‐array coils. Our data suggests that there is an optimal ROI size, dependent on phantom and SNR method, above which there is no decrease in SNR variance. Data from a 32‐channel phased array coil implied a lower optimal radius as compared to the 8‐channel coil, which is most likely the result of strong signal increases near array elements. This observation was true of both SNR calculation methods. Although small relative to daily SNR variance over a period of days (< 1/10th total variance), ROI size contributed some variation to SNR beyond systematic variations. This contribution is likely to be larger for phased arrays with high numbers of channels. Conclusion: Considering that signal and noise are not homogenous across an image, our data suggests there is an optimal ROI size for determining mean SNR when utilizing phased‐array coils.