bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐D‐330A‐02: Optical‐Computed‐and Emmission Tomography: Applications in Cancer Research
Authors: Oldham M , Sakhalkar H , Oliver T , Dewhirst M
Published: July 2006

Purpose: This work explores the potential of optical‐computed and emission‐tomography (OCT/OET), when coupled with optical clearing techniques, for imaging aspects of biological structure and function for cancer research. OCT/OET are the optical analogues to x‐ray‐CT and SPECT respectively, and can yield high resolution high contrast 3D images of a variety of inherent or applied absorbing and fluorescing stains. Materials and Methods Several methods of staining tissue have been explored and applied to a range of tissue types. Xenograph tumor microvasculature was labeled with both passive absorbing stain and fluorescing active probes (e.g. lectin conjugated with FITC) by tail vein injection. Murine vasculature in major organs (lung, heart, brain) were stained with absorbing dye in a similar manner. OCT/OET imaging was performed using an in‐house custom built scanner. Isotropic 3D transmision and emission data were reconstructed using tomographic algorithms from equiangularly spaced projection images. Results: Isotropic high resolution 3D image data of the xenograph tumor showed extensive peripheral microvasculature with the occasional larger vessels penetrating to the tumor core. High‐quality 3D images of the lungs were achieved showing clear differences in perfusion between irradiated and unirradiated lung regions. Exquisite high contrast images were acquired of the vasculature and myocardial perfusion of the murine heart. Conclusion Primary advantages of OCT/OET include the preservation of tissue structure in 3D (tissue sectioning is not required), and the ability to acquire co‐registered images of both structure (e.g.micro‐vasculature) and function (e.g. perfusion, gene expression). Higher spatial resolution and higher contrast is achieved when compared with alternative modalities like micro‐CT and micro‐MRI. The techniques are versatile as imaging can be performed on a wide variety of absorbing and fluorescing stains.
Sci‐Thur PM Therapy‐04: Comparison of treatment planning system and Monte Carlo calculated dose distributions in an extreme water‐lung interface phantom
Authors: Gagne I , Zavgorodni S
Published: July 2006

The study compares the performance of the analytical anisotropic algorithm (AAA), a new superposition‐convolution algorithm recently implemented in Eclipse™ Integrated Treatment Planning System (TPS), to that of the pencil beam convolution (PBC) algorithm for a variety of clinical beam configurations at nominal beam energies of 6 MV and 18 MV, respectively in an extreme water‐lung interface phantom using Monte Carlo (MC) calculated dose distributions as benchmarks. Dose profiles at specific depths, 2‐D dose difference (TPS — MC) maps and histograms as well as first order statistics were used to quantify the accuracy of both photon dose calculation algorithms. For each open beam configuration, the AAA algorithm yielded smaller means, standard deviations and confidence limits. On average, the standard deviation of the dose differences was reduced by half with the AAA dose calculation model. Confidence limits for the PBC algorithm were ⩾ 3%, ranging from 3.0% for the 6 MV, 10×10 cm2 beam to 11.2% for the 18 MV, 4×4 cm2 beam while for the AAA algorithm they were ⩽ 4% for all beam configurations. The worst agreement of AAA algorithm with MC results was observed for the highest energy and smallest field combination (18 MV, 4×4 cm2). The standard deviation of the differences (2.4%) and confidence limit (4.0%) were however right between the standard deviations and confidence limits provided by the current clinical PBC model of the 6MV 4×4 and 10×10 cm2 beams.
Sci‐Thur PM Therapy‐09: Investigation of a 3D MR Distortion Correction Protocol
Authors: Stanescu T , Jans H , Fallone BG
Published: July 2006

Magnetic Resonance Imaging is the imaging modality of choice for target volume delineation required by radiotherapy planning (RTP) due to its superior soft‐tissue contrast. However, MR images are affected by distortions that alter the image spatial accuracy which is crucial for RTP. In the present work, we investigate a complete 3D phantom‐based protocol that determines and corrects both geometrical and object‐induced distortions. A 3D oil‐filled phantom consisting of parallel plastic grid sheets equally distributed inside the phantom was scanned on a 3T MR unit and CT (spatially accurate reference dataset). To determine the geometrical distortions we developed a novel automatic procedure. This allows us to accurately identify and register the MR and CT control points and to determine iteratively the 3D distortion field. To correct the sample‐induced effects we applied a standard method as per Chang and Fitzpatrick [1]. For the entire field of view the control points were located accurately within one pixel resolution. We found that the total distortion in the transverse plane is approximately 7 mm and the z‐distortion is around 4 mm for a 15×15×15 cm3 volume. The MR images are corrected by applying a spatial and a pixel intensity 3D interpolation procedure, the residual distortion after applying these transformations being under one pixel resolution. We investigated a procedure that relies on a new system distortion correction technique and a standard sample‐induced correction method to successfully rectify the MR images required by Treatment Planning.
Po‐Thur Eve General‐02: Set‐up error simulations for head and neck IMRT
Authors: Ploquin N , Kay I , Rangel‐Baltazar A , Lau H , Dunscombe P , Baker Tom
Published: July 2006

We have compared four computational methods for quantifying the effect of set‐up error and uncertainty on delivered doses to targets and organs at risk in the IMRT treatment of head and neck cancer. These four methods were direct simulation, simple convolution plus two modified convolution approaches: the corrected convolution and the truncated convolution proposed by our group. Discrepancies of up to 20% in the Equivalent Uniform Dose (EUD) between direct simulation and simple convolution were estimated for the relatively superficial parotid gland at a systematic set‐up error of 6mm standard deviation and a random uncertainty of 2mm standard deviation. Truncated convolution agreed with direct simulation to within 6% for all situations studied. However, of the four methods, only direct simulation can quantify the range of outcomes (EUD) associated with a finite number of courses and fractions. Our results are particularly relevant to the design of dose escalation studies in head and neck cancer.
Po‐Thur Eve General‐11: Data for Intensity Modulated Radiotherapy Planning with Pinnacle for a 6MV Siemens Primus Beam
Authors: Ozard S
Published: July 2006

Background and purpose: Intensity‐modulated radiation therapy (IMRT) with a Siemens Primus linear accelerator and the Pinnacle V7.6c (IMRT V2.0) treatment planning system requires additional measurements and quality assurance (QA). This study presents the small field data for a 6MV beam and results of the additional QA for small monitor unit (MU) fields and the multi‐leaf collimator (MLC).

Materials and methods: Beam measurements included relative output factors, MLC transmission and MLC interleaf transmission, percentage depth doses, and dose profiles. Beam modeling in Pinnacle is discussed. QA measurements included MU linearity and stability, MLC leaf position and abutment, and small MU field symmetry and flatness.

Results and discussion: For field sizes 2×2cm2 and larger, ROFs for the two linacs were well within 0.6% of one another. MLC transmission and MLC interleaf transmission agreed with published values. The penumbral width was larger for the upper Y jaws compared to the lower MLC collimator by 1.4mm for the 2×2cm2 field. The Pinnacle model parameters that were adjusted to improve the fit to measured data were C2, K and ECD10×10, as well as the source size. MU linearity was adjusted to reduce the linearity error introduced for small MU IMRT segments. MLC leaf abutment test results are consistent with results at other centres with the same MLC.

Conclusions: MU stability and MLC leaf position calibration have an important influence over the accuracy of the delivered dose for small MU segments. Field flatness in the inplane direction will also degrade dose accuracy for small MU segments.
Po‐Thur Eve General‐23: 3He MRI Phenotypes of Lung in Phantoms and Healthy Volunteers
Authors: McKay S , McCormack D , Etemad‐Rezai R , Lam W , Ouriadov A , Santyr G , Parraga G
Published: July 2006

Chronic Obstructive Pulmonary Disease (COPD) is the most common chronic lung disease in North America and is the fourth leading cause of death in the US, Canada and Europe. We believe that the paucity of new mechanistic insights and disease treatments based on this information is due in part to the lack of non‐invasive, sensitive and specific tests for pulmonary structure and function. Our goal is to validate MRI‐derived biomarkers in phantoms and healthy volunteers laying the foundation for the study of lung disease progression in subject volunteers. Our overarching objective is to validate the use of MRI in the detection of early and novel phenotypes and biomarkers of respiratory disease including COPD. Here we report the first results of phantom and human studies with images acquired at 3Tesla. Ten healthy volunteers were scanned under protocol as well as a single pig lung phantom scanned twice within a single week. 3He MRI image‐derived measurements of ventilated volumes of the porcine phantom and subject volunteer images were made three times by a single observer. Using Image J, ventilated volumes were measured (excluding the airways) on the basis of manual outlining of contrast within lung each three times. Four different subject's images were reviewed providing a range of size and age of subjects. One subject was scanned twice on the same day (003) and one was scanned twice within a period of 2 weeks (008). Intra‐observer variability (ICC = 0.99) for all images was assessed.
Po‐Thur Eve General‐24: Non‐Invasive Imaging Phenotypes of Carotid Atherosclerosis in Subjects: MRI, B‐mode and 3D Ultrasound Measurements
Authors: Egger M , Blake C , Vidal A , Kost J , Spence JD , Rutt B , Fenster A , House A , Parraga G
Published: July 2006

Atherosclerosis is a chronic inflammatory disease, characterized by the accumulation of lipids and fibrous elements within the inner‐most layer of the artery wall. Vulnerable atherosclerotic plaques may eventually rupture, resulting in emboli that can obstruct blood flow and result in stroke or myocardial infarction. Direct measurements of atherosclerosis include non‐invasive imaging phenotypes such as MRI and 3DUS derived plaque and wall volume measurements and B‐mode US measurements of the intima media thickness (IMT). Here we report the first comparison of IMT with 3D Ultrasound and MRI‐derived atherosclerosis phenotypes measured in five subjects with moderate carotid atherosclerosis. Five research subjects with carotid plaque area ⩾ 0.5 cm2 were studied and all subjects were undergoing treatment for hyperlipidemia. Mean age was 66 yrs with no significant difference between males and females. Subjects underwent MRI, 3DUS and 2D B‐mode US of the left and right carotid arteries. A single observer carried out 3DUS vessel wall volume measurements (VWV) in 10 subject images at both time points, a second observer measured MRI vessel wall volume; a third observer measured IMT. Both 3DUS VWV and MRI VWV measurements were repeated five times to determine intra‐observer variability and variability between time points. At baseline 3DUS and MRI VWV measurements were not significantly different. No significant differences was observed for mean 3DUS VWV and MRI VWV at test and retest. No significant difference between mean IMT at test and retest was found. IMT measurements had the highest intra‐class correlation coefficients and the lowest coefficient of variation values.
Po‐Thur Eve General‐29: Clinical Implementation of Helical Tomotherapy
Authors: MacPherson M , Gerig L , Malone S , MacRae R , Fox G , Carty K , Montgomery L , Clark B
Published: July 2006

In March 2005 The Ottawa Hospital Regional Cancer Center took delivery of a helical TomoTherapy Hi‐Art machine. We report our experience for installation, commissioning and training for tomotherapy relative to a conventional single energy linac as well as our experiences regarding throughput, process change and implementation of a radically different staffing model. Tomotherapy implementation was faster than a conventional single energy linac (23 vs. 31 days), but additional training requirements for tomotherapy made the overall times comparable (28 vs. 31 days). Presently, the tomotherapy team includes two physicists and two physicians, and dedicates three therapists to tomotherapy per 8 hour shift. The therapists are given responsibility for data transfer, structure contouring, planning and delivery. Mean total effort for treatment preparation per patient is 8.9 hours (median 6.6, range 3.4 to 33). We find daily machine QA for tomotherapy is more demanding than for a conventional linac, requiring approximately 1 hour for machine warm‐up, safety system testing and CT detector calibration. In addition we require approximately 45 minutes of physics time to establish output, energy, and geometric consistency. Overall system performance is verified by a daily delivery QA. The mean overall time for patient setup, MVCT, registration and treatment is 26.5 minutes (median 25.0). Eliminating the MVCT and registration reduces the mean to 18 minutes. For an 8 hour shift we anticipate that a single team (3 therapists) can maintain a patient load of at least 16 patients with daily MVCT and 24 patients with weekly MVCT.
Po‐Thur Eve General‐34: Normalized data for the estimation of fetal radiation dose from radiotherapy of the breast
Authors: Osei E , Bradley B , Fleck A , Darko J
Published: July 2006

There can be several reasons why a pregnant patient may receive a radiological examination. It could have been a planned exposure or may have resulted from an emergency when a thorough evaluation of pregnancy was impractical or the pregnancy was unsuspected during the examination. With younger women being diagnosed with breast cancer, the likelihood of the later will increase in the radiotherapy departments. Whatever the reason, when presented with a pregnant patient who has been exposed to ionizing radiation, the dose to the fetus should be assessed. However, a major source of uncertainty in the estimation of fetal dose is the influence of fetal size and position as these changes with gestational age. We have investigated doses to the fetus from radiotherapy of the breast of a pregnant patient using an anthropomorphic phantom. Data for estimating fetal dose that takes into account the size and depth within the maternal abdomen for different treatment techniques have been provided. The data indicate that fetal dose is dependent on both depth and gestational age and hence these factors should always be considered when estimating dose. The data shows that dose can be underestimated up to about 10% or overestimated up to about 30% if the dose to the uterus is assumed instead of the actual fetal dose. It can also be underestimated up to about 23% or overestimated up to about 12% if a mean depth of 9cm is assumed, instead of using the actual depth of the fetus within the maternal abdomen.
Po‐Thur Eve General‐35: Official statistics generated using a commercial R&V system in the Canadian context
Authors: Gelinas D , Tanguay M
Published: July 2006

In Quebec every radiotherapy department has to present official statistics to the government known has technical units. All actions taken by therapists generate technical units roughly related to the amount of time needed to complete the task. Technical units are defined per category and task by the officials.

A commercial record and verify system, VARiS version 7.2 from Varian Medical Systems, has successfully been configured to automatically capture the required technical units in Quebec. VARiS is normally installed preconfigured to collect charges in the United States using Medicare codes and charges through the application Activity Capture. This program interacts with other applications of the R&V system to greatly ease the process of confirming chargeable activities as they are completed. Replacing the Medicare codes with the Quebec codes in the administration module was the most demanding task.

At treatment machines, a window will automatically appear when a treatment session is completed to confirm the activity to be charged. The application will suggest the same codes that were completed the last time. In the case portal images were acquired, the configured code will be suggested even though the code was not used in the prior session.

Technical units generated elsewhere, for example in dosimetry, are computed using a single predefined template attached to every patient. The therapist searches the template for the proper code and manually completes it so that it is taken in to account in the patient's statistics.
Sci‐Fri AM General‐02: Planning and automatic delivery of energy modulated electron therapy (EMET): a novel technique
Authors: Al‐Yahya K , Verhaegen F , Seuntjens J
Published: July 2006

Energy modulated electron therapy (EMET) with conventional clinical accelerators has lagged behind photon intensity modulated therapy (IMRT) despite the potential of the former modality to achieve highly conformal dose distributions tailored to superficial targets which are inherently difficult to plan with IMRT. The main reason for this lag is the lack of an automated collimating device that allows sequential beam shaping of a series of variable field openings. In this study, we present a novel technique to deliver EMET using a prototype of a “few leaf electron collimator” (FLEC) that consists of four motor‐driven leaves fit in a standard clinical applicator. An inverse treatment planning procedure was developed using a Monte Carlo‐based optimization algorithm that makes use of patient‐specific dose kernels. With this procedure optimal plans of three clinical sites were compared to 3D‐conformal radiation therapy and IMRT. Output measurements using radiochromic film and ionization chambers were obtained to validate the Monte Carlo calculations. Further comparisons of 2D dose distributions were also performed using gamma‐index analysis. The FLEC was CAD designed and constructed after optimizing its physical configurations based on Monte Carlo studies. Treatment planning Monte Carlo studies also showed that EMET, delivered using FLEC, is able to provide conformal dose to the superficially located targets, reduce dose to organs at risk, and lower whole body dose without significant perturbation of the dose homogeneity in the target. Comparisons between Monte Carlo calculations and measurements of complex delivery maps show an overall agreement within 3%.
Sci‐Fri AM General‐05: Measurement of daily interfraction prostate motion with tomotherapy MVCT images
Authors: Rivest R , Riauka T , Murtha A , Fallone B
Published: July 2006

It is well known that the interfraction motion of the prostate gland can have a significant impact on the efficacy of radiotherapy in the treatment of prostate cancer. As we move towards more complex treatment protocols involving dose escalation and adaptive therapy, accurate daily prostate localization will increase in importance. In this work, the daily interfraction prostate motion has been measured for research patients receiving prostate treatment on the Cross Cancer Institute's TomoTherapy Hi*Art unit. An automated rigid registration algorithm designed to overlay the rigid bony anatomy was used to align the daily on‐line MVCT images with their respective planning CT images. The position of the prostate in the MVCT images was achieved using a prostate localization algorithm based on mutual information registration that only requires prostate delineation on the planning CT image. A multi‐start optimization approach was employed to reduce registration uncertainty and eliminate any gross miss‐registrations. The technique was validated with kVCT and MVCT images of two patients with localization seeds implanted in their prostates. Accurate convergence could only be achieved when assuming translations only, thus neglecting any prostate rotation. The maximum interfraction motion observed in the anterior‐posterior, superior‐inferior, and lateral directions was 5.7mm, 5.2mm, and 2.0mm, respectively. Mean and standard deviation values were −1.1mm, 0.4mm, and 0.3mm, and 1.7mm, 2.4mm, and 0.7mm, respectively.
Sci‐Fri AM General‐08: Image Fusion for Catheter Tracking in MR‐Guided Endovascular Therapy
Authors: Draper JN , Sabati M , Lauzon ML , Frayne R
Published: July 2006

Endovascular therapy describes a class of minimally invasive treatments for certain vascular diseases, including the placement of stents to correct arterial stenoses, and the administration of intra‐arterial thrombolysis for ischemic stroke. Our objective is to develop a real‐time system to guide interventional endovascular procedures with MR imaging. Our approach in developing this system is to mimic, where appropriate and possible, the functionality of current clinical x‐ray fluoroscopy systems. Our endovascular MR system is comprised of two major components: a data acquisition module and an image reconstruction module. Data acquisition was performed using a 3‐tesla MR scanner (Signa VH/i; General Electric Healthcare; Waukesha, WI). Image reconstruction was performed on a separate dedicated workstation (2.2‐GHz Athlon processor‐equipped workstation running Windows XP). We achieved catheter visualization by filling catheters with MR contrast and imaging using a multi‐cycle projection dephaser to suppress the background signal. We used image‐processing filters available in the VTK library to isolate the catheter in the background‐suppressed images. The output of this image‐filtering pipeline was then used as a mask for an anatomical roadmap image. The image fusion process described herein has successfully been used to combine background‐suppressed in vivo images of a catheter with anatomical roadmap images. The fusion process removed most of the noise and residual background signal from the background‐suppressed image, leaving the catheter with improved conspicuity. Our endovascular MR system functions in a similar manner to x‐ray fluoroscopic systems and has applications in the treatment of stroke and other vascular diseases.
Sci‐Fri PM Imaging‐03: Avalanche multiplication in diagnostic x‐ray imaging
Authors: Hunt D , Tanioka K , Rowlands J
Published: July 2006

The state‐of‐the‐art detector for digital radiography, the flat‐panel detector (also know as the active matrix flat‐panel imager), requires more gain to improve its performance at typical fluoroscopy — real time x‐ray imaging — exposure rates. It has been shown that avalanche multiplication gain in amorphous selenium (a‐Se) can provide the necessary amplification. This amplification, however, must also make little or no contribution to the noise. To achieve this using avalanche gain the intrinsic noise of avalanche multiplication must be reduced. Theoretical calculations and experiments examining the noise properties of an imaging system implementing avalanche multiplication in a layer of a‐Se are presented. The results indicated that avalanche multiplication in a‐Se can have the potential to improve the performance of flat‐panel detectors in fluoroscopy.
Sci‐Fri PM Imaging‐07: The feasibility of using FBP to reconstruct electron densities from attenuation corrected scatter sinograms
Authors: Alpuche Aviles JE , Pistorius S
Published: July 2006

Breast CT is an emerging modality which aims to generate high quality 3D images. At these energies a large number of the incident x‐ray photons are scattered, resulting in a reduced contrast to noise ratio. As the reduction of dose and the detection of blurred calcifications and other poorly visible lesions are diagnostically important, we have developed an approach which uses both the primary and scattered photons to obtain low‐dose conventional CT and electron density (ρe) images. In the absence of attenuation and for a spherical detector, electron densities can be reconstructed using a mono‐energetic pencil beam and conventional Filtered Back Projection (FBP). In place of a spherical detector we have simulated a more practical detector ring with an angular width of 5 degrees and capable of measuring both scattered and primary photons. In practice, attenuation cannot be neglected and Attenuation Correction Factors (ACF) were calculated for each detector using an initial estimate of the electron density based on reconstructed linear attenuation coefficients. The corrected measurements were summed at each rotation and translation of the x‐ray beam to yield a scatter sinogram. This sinogram was processed using FBP to yield an image which provides, in an iterative manner, a new estimate of the electron density. This approach has shown that we are capable of reconstructing electron densities in simple geometries with errors ranging from 2 to 4%. Polyenergetic beam hardening and multiple scattering corrections are being investigated, for future incorporation into the algorithm.
Sci‐Fri PM Imaging‐08: Development of Micro‐Strip Coils and “Direct” Method for Bilateral Breast Imaging
Authors: Wang J , Plewes D
Published: July 2006

In this work, we present a position‐independent decoupling method using micro‐strip transmission line coils. Micro‐strip transmission line coils consist of a grounded back plane together with the conductive strip bonded to either side of a low‐loss, high permittivity material. This two‐part structure exhibits the shielding decoupling properties and excellent decoupling over a range of geometries. Its asymmetrical signal response operates so that signals from each individual breast originate primarily from the coil facing the breast. In this work we also present a parallel imaging method similar to Partially Parallel Imaging with Localized Sensitivities (PILS) method for bilateral breast MRI by taking advantage of the isolation properties of micro‐strip coils to allow independent imaging of both breasts in the time usually required to scan a single breast without resorting to traditional SENSE techniques.
Sci‐Fri PM Imaging‐09: Robust MR‐DSC Perfusion using a Patient Motion Correction Scheme
Authors: Kosior R , Kosior J , Frayne R
Published: July 2006

Stroke is a leading cause of death in North America and results when blood supply to the brain is reduced, which compromises nutrient exchange to and waste product removal from brain cells. Ischemic stroke is the most common type of stroke and results when blood flow in an artery supplying blood to brain tissue is reduced due to a thrombus or embolism. Magnetic resonance (MR) dynamic susceptibility contrast (DSC) perfusion‐weighted imaging (PWI) shows great utility in assessing blood flow characteristics in brain tissue, and thus for potentially assessing tissue status in ischemic stroke. Quantitative cerebral blood flow (qCBF) maps can be generated from the 4D perfusion data and may be useful for defining perfusion thresholds to better determine tissue status. The accuracy of quantitative perfusion maps depends on the tracking of the same tissue location within the brain over the course of the image series; the consistency of this location tracking is compromised by patient motion during the scan. Patient motion blends the temporal signals of adjacent tissue locations in the brain, yielding erroneous perfusion measurements. Using a digital brain phantom and patient data, we investigated the effect of motion on qCBF maps and evaluated the efficacy of a realignment scheme for motion correction. Results show that qCBF maps are sensitive to motion and that that rigid‐body registration (realignment) is a robust scheme for correcting patient motion to improve the accuracy of qCBF maps.
Sci‐Fri PM Imaging‐11: Evaluation of SPECT/CT for Regenerative Medicine Applications: Tracking Transplanted Cells in a Large Animal Model
Authors: Stodilka R , Blackwood K , Prato F
Published: July 2006

Introduction: The purpose of this study was to characterize the performance of dual‐radionuclide SPECT/CT in quantitative tasks associated with tracking transplanted cells in vivo. Previous studies identified matters of hardware design, whereas we focus on biological variables impacting performance such as non‐specific uptake of radiolabels, and radiolabel dilution with cell colony growth. Methods: Using experimental SPECT/CT data, a canine digital phantom was developed of in vitro ‐radiolabeled stem cells, transfected with a reporter gene, transplanted into canine infarcted myocardium, and interrogated post‐transplantation using a peripherally‐injected ‐radiolabeled reporter probe. Single‐ and dual‐head SPECT/CT acquisitions were simulated. Simulations included physical effects of radionuclide‐specific attenuation, scatter, resolution, and dual‐radionuclide crosstalk. CT data was used to simulate photon attenuation. Performance was characterized using an estimation task, incorporating the statistical properties of SPECT imaging, where the precision of parameter estimates ( and radiolabel quantity, cell colony size and location, and background) was tracked as the phantom evolved to simulate ‐label efflux, cell colony growth, and improved reporter probe specificity. Results: In vitro pre‐labeling of transplanted cells with improved precision of parameter estimates via a priori size and location information. Precision of radiolabel quantity estimates improved with cell colony growth, despite radiolabel dilution; size and location parameters were influenced little. Precision of radiolabel quantity estimates improved with reduced reporter probe non‐specific uptake. Conclusion: The performance of SPECT/CT in cell tracking is influenced strongly by biological variables. These should be considered when planning experiments or developing SPECT/CT technology for cell tracking.
Sci‐Sat AM (1) General‐02: Experiences with the Quality Assurance Testing of the Restitu Ultrasound System
Authors: Drever L , Hilts M
Published: July 2006

The BC Cancer Agency — Vancouver Island Centre recently acquired the new Restitu three‐dimensional ultrasound (US) system (Resonant Medical, Montreal) for performing prostate image‐guided radiation therapy. The system consists of an US assembly, with a free hand US probe and an optical tracking device, installed in both the CT simulation room (US Sim) and the linac suite (US Guide). Daily prostate misalignments are determined by comparing US images acquired at US Guide to US images acquired at time of planning CT.

This work presents preliminary results from our on‐going quality assurance (QA) program to monitor performance of the Restitu system. Weekly and monthly tests use a QA phantom supplied by Resonant Medical with an embedded spherical target, rods and wires. Setup and imaging of the phantom is found to be highly reproducible with a standard deviation (SD) of < 0.5 mm for measures of target position. Deviations of measured target position relative to predicted position have all been < 2.1 mm (SD = 0.8 mm), misalignments between US Sim and US Guide < 2.5mm (SD = 1.2 mm) and re‐positioning errors < 1.5mm (SD = 0.6 mm). Deviations from predicted values of > 2 mm have only been measured once and 2 mm is recommended as the tolerance for system re‐calibration. Additionally, a phantom with a single embedded ellipsoid target has been constructed in‐house for daily QA purposes. Results indicate this inexpensive phantom is simple to use and provides a reliable means of testing daily for consistency of target position.
Sci‐Sat AM (1) General‐08: Study of Characteristics of a New Liquid Ionization Chamber
Authors: Elliott A , Stewart K , Seuntjens J
Published: July 2006

Liquid ionization chambers (LICs) have characteristics that can remedy some of the drawbacks of air‐filled ionization chamber dosimetry: large sensitive volumes, fluence perturbations, and energy dependence over the clinical range of beam qualities. However, there are significant problems in liquid chambers. High ionization density and low ion mobility leads to high ion recombination rates. In this work, extensive experimental work has been performed to investigate properties of a new liquid chamber, including chamber stability over time, chamber reproducibility, and establishing recombination corrections. The new chamber is called the GLIC‐03 (Guarded Liquid Ionization Chamber), and is filled with isooctane. The sensitive volume is 0.7 mm3. We used the 18 MV beam of a Varian Clinac 21EX linear accelerator. The lowest pulse rate setting was used in order to minimize ion recombination. Measurements were taken in solid water at 15 cm depth, with various field sizes and SSDs. Boag's theory for general collection efficiency for parallel‐plate gas ionization chambers, applied to isooctane in pulsed radiation, was used for recombination corrections. The GLIC‐03 response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. The collection efficiency decreased with increasing dose per pulse due to general recombination of ions from a larger number of ionizing particle tracks. Recombination corrections were within 1% for low dose rates and high electric field strengths. The establishment of these characteristics in the present work allows us to perform accurate measurements in high gradient non‐equilibrium fields.
Sci‐Sat AM (2) Therapy‐04: Evaluation of Ultrasound‐Based 3D Positioning System (Restitu by Resonant Medical) for Localizing and Delineating Prostate Targets for Image‐Guided Radiation Treatment: Phantom Study and Estimates of Distortions in US Images of a Patient
Authors: Szpala S , Morton G , Tirona R , O'Brien P
Published: July 2006

3D‐Ultrasound (US) promises to be a noninvasive alternative to the portal imaging of surgically implanted gold seeds for positioning the prostate before radiation treatment. In this work we have evaluated a new US system, the Restitu, manufactured by Resonant Medical (Montréal). Using a prostate phantom we have measured the base‐line reproducibility of couch shifts calculated with the Restitu software algorithms. We have also attempted to estimate the influence of US image artifacts on the calculated prostate position. Unlike similar early systems (e.g. BAT), Restitu uses 3D‐US to 3D‐US image registration to determine the prostate position relative to the position during the planning CT. If the internal organs remain stationary and the movement of the US probe is invariant during each fraction then we would expect that the calculated results would be immune to US image distortions. However, due primarily to variations in bladder filling, second‐order US artifacts need to be considered. Using 3D‐US images collected on a sample patient with a full and a half‐empty bladder, we have found the error caused by variations in the time of travel of the sound wave to be about −0.8 mm, and the error caused by sound wave refraction at tissue‐urine interfaces to be about 2.1 mm. The combined error, 2.2 mm, is close to the quoted system tolerance of ±2 mm, but may vary due to anatomical differences. These errors can be reduced under consistent full‐bladder operation.
Sci‐Sat AM (2) Therapy‐05: Early Experience with a Clinical TomoTherapy Unit
Authors: Gerig L , MacPherson M , Malone S , MacRae R , Carty K , Montgomery L , Fox G , Clark B
Published: July 2006

In March 2005 The Ottawa Hospital Regional Cancer Center received a helical TomoTherapy Hi‐Art machine, beginning treatment September 2005. The delivery and planning systems were subjected to rigorous daily QA. Herein we report our geometric, dosimetric and uptime analysis. Daily dosimetric QA comprises output and energy checks as well as the geometric consistency of the integrated laser and couch drive systems. At least one patient treatment plan per day is delivered to a phantom for delivery quality assurance, thereby checking all integrated tomotherapy subsystems (e.g. gantry rotation speed, couch speed, dose rate, MLC, jaw calibration and modeling within the planning system). Over the first 130 treatment days the mean output was 0.5% above reference and varied about the mean with a SD of 0.32%. Approximately 1.5% (2 of 132) of output measurements exceeded our tolerance of 2% requiring the calibration to be modified twice prior to the resumption of clinical service. The beam energy was measured by the PDD at 10 and 20 cm. We found these to vary about their expectation values with standard deviations of 0.52% and 0.59% respectively. Single point doses for the Delivery QA were normally distributed with a standard deviation of 2.4%, where 92% of all points were within 3% and 97% of all points were within 5% of expected. All coronal plane film measurements had a distance to agreement of less than 3 mm. We experienced a total of 4.5 days of downtime, 2 of which are attributed to delay in parts delivery.
Sci‐Sat AM (2) Therapy‐06: Clinical experience with adaptive radiation therapy for lung cancer with tomotherapy
Authors: Yartsev S , Bauman G , Yu E , Dar R , Rodrigues G , Chen J , Battista J , Van Dyk J
Published: July 2006

Helical tomotherapy (TomoTherapy Inc., Madison, WI) is a new form of image‐guided radiation therapy that combines features of a linear accelerator and a helical CT scanner. Helical tomotherapy allows megavoltage computer tomography (MVCT) imaging of the patient immediately prior to treatment. The MVCT images are compared to the treatment planning (kilovoltage) CT images at the operator station in order to ensure correct alignment to the planning target volume and critical structures. We report clinical experience with our technique for adaptive therapy in two lung cancer cases where the delivery fluence modifications were considered imperative due to concerns regarding changes in patient anatomy. Daily MVCT imaging with helical tomotherapy co‐registered with the planning kVCT study can provide feedback allowing correction of patient position due to systematic or random error or organ motion. In the case of lung cancer, the gross tumour volume is clearly visible on MVCT due to high tissue contrast in the lung facilitating daily positioning correction for small setup or organ location variations. If the target has dramatically changed in its shape or location and/or other major anatomy changes occur, the MVCT study can be used for re‐calculation of the expected dose distribution which is then compared to the originally planned one. If the difference is considered clinically significant, a repeat kVCT study can be performed and a new plan is developed for further treatment, thus allowing the patient specific adaptive radiotherapy to account for anatomic changes during treatment.
Sci‐Sat AM (2) Therapy‐09: Quality Audits of a Medical Physics QA Program
Authors: Mason D , Baillie A , Wolters J
Published: July 2006

Documented radiation incidents world‐wide illustrate the importance of a rigorous physics quality assurance (QA) program. Since the QA program is such an important part of a radiotherapy operation, it should itself be subject to quality audits to ensure its effectiveness. We have been tracking QA activities in a custom database application, and since 2000, have been auditing our QA activities every six months. The audit produces quality indicators of equipment QA and physicist chart‐checking. The compliance rate and effectiveness of our tests are tracked and the information is used to improve our processes. Attention to these indicators has led to improvements in on‐time compliance, which is now typically greater than 95% for QA tests and QA review. Chart‐check activities show a rate of potentially significant problems found of about 3%, which has remained consistent through changes in workload and through major changes in treatment planning software and processes.

In this paper we will share some of the observations of QA performance data, and discuss how this data has been used to improve our QA program. We will present some general lessons to be learned about the effectiveness of QA programs, and the human psychology of doing this kind of activity well.
Electronic Control of Friction in Silicon pn Junctions
Authors: Park Jeong Young , Ogletree D. F. , Thiel P. A. , Salmeron M.
Published: July 2006

A remarkable dependence of the friction force on carrier concentration was found on doped silicon substrates. The sample was a nearly intrinsic n-type Si(100) wafer patterned with 2-micrometer-wide stripes of highly B-doped p-type material. The counter surface was the tip of an atomic force microscope coated with conductive titanium nitride. The local carrier concentration was controlled through application of forward or reverse bias voltages between the tip and the sample in the p and the n regions. Charge depletion or accumulation resulted in substantial differences in friction force. The results demonstrate the capability to electronically control friction in semiconductor devices, with potential applications in nanoscale machines containing moving parts.
Ca
2+
Entry Through Plasma Membrane IP
3
Receptors
Authors: Dellis Olivier , Dedos Skarlatos G. , Tovey Stephen C. , Taufiq-Ur-Rahman  , Dubel Stefan J. , Taylor Colin W.
Published: July 2006

Inositol 1,4,5-trisphosphate receptors (IP
3
Rs) release calcium ions, Ca
2+
, from intracellular stores, but their roles in mediating Ca
2+
entry are unclear. IP
3
stimulated opening of very few (1.9 ± 0.2 per cell) Ca
2+
-permeable channels in whole-cell patch-clamp recording of DT40 chicken or mouse B cells. Activation of the B cell receptor (BCR) in perforated-patch recordings evoked the same response. IP
3
failed to stimulate intracellular or plasma membrane (PM) channels in cells lacking IP
3
R. Expression of IP
3
R restored both responses. Mutations within the pore affected the conductances of IP
3
-activated PM and intracellular channels similarly. An impermeant pore mutant abolished BCR-evoked Ca
2+
signals, and PM IP
3
Rs were undetectable. After introduction of an α-bungarotoxin binding site near the pore, PM IP
3
Rs were modulated by extracellular α-bungarotoxin. IP
3
Rs are unusual among endoplasmic reticulum proteins in being also functionally expressed at the PM, where very few IP
3
Rs contribute substantially to the Ca
2+
entry evoked by the BCR.
Dynamic Forces Between Two Deformable Oil Droplets in Water
Authors: Dagastine Raymond R. , Manica Rogério , Carnie Steven L. , Chan D. Y. C. , Stevens Geoffrey W. , Grieser Franz
Published: July 2006

The understanding of static interactions in colloidal suspensions is well established, whereas dynamic interactions more relevant to biological and other suspended soft-matter systems are less well understood. We present the direct force measurement and quantitative theoretical description for dynamic forces for liquid droplets in another immiscible fluid. Analysis of this system demonstrates the strong link between interfacial deformation, static surface forces, and hydrodynamic drainage, which govern dynamic droplet-droplet interactions over the length scale of nanometers and over the time scales of Brownian collisions. The results and analysis have direct bearing on the control and manipulation of suspended droplets in soft-matter systems ranging from the emulsions in shampoo to cellular interactions.
Atomic-Scale Control of Friction by Actuation of Nanometer-Sized Contacts
Authors: Socoliuc Anisoara , Gnecco Enrico , Maier Sabine , Pfeiffer Oliver , Baratoff Alexis , Bennewitz Roland , Meyer Ernst
Published: July 2006

Stiction and wear are demanding problems in nanoelectromechanical devices, because of their large surface-to-volume ratios and the inapplicability of traditional liquid lubricants. An efficient way to switch friction on and off at the atomic scale is achieved by exciting the mechanical resonances of the sliding system perpendicular to the contact plane. The resulting variations of the interaction energy reduce friction below 10 piconewtons in a finite range of excitation and load, without any noticeable wear. Without actuation, atomic stick-slip motion, which leads to dissipation, is observed in the same range. Even if the normal oscillations require energy to actuate, our technique represents a valuable way to minimize energy dissipation in nanocontacts.
Biomineralization of Gold: Biofilms on Bacterioform Gold
Authors: Reith Frank , Rogers Stephen L. , McPhail D. C. , Webb Daryl
Published: July 2006

Bacterial biofilms are associated with secondary gold grains from two sites in Australia. 16
S
ribosomal DNA clones of the genus
Ralstonia
that bear 99% similarity to the bacterium
Ralstonia metallidurans
—shown to precipitate gold from aqueous gold(III) tetrachloride—were present on all DNA-positive gold grains but were not detected in the surrounding soils. These results provide evidence for the bacterial contribution to the authigenic formation of secondary bacterioform gold grains and nuggets.
Crystal Structure of Glycoprotein B from Herpes Simplex Virus 1
Authors: Heldwein Ekaterina E. , Lou Huan , Bender Florent C. , Cohen Gary H. , Eisenberg Roselyn J. , Harrison Stephen C.
Published: July 2006

Glycoprotein B (gB) is the most conserved component of the complex cell-entry machinery of herpes viruses. A crystal structure of the gB ectodomain from herpes simplex virus type 1 reveals a multidomain trimer with unexpected homology to glycoprotein G from vesicular stomatitis virus (VSV G). An α-helical coiled-coil core relates gB to class I viral membrane fusion glycoproteins; two extended β hairpins with hydrophobic tips, homologous to fusion peptides in VSV G, relate gB to class II fusion proteins. Members of both classes accomplish fusion through a large-scale conformational change, triggered by a signal from a receptor-binding component. The domain connectivity within a gB monomer would permit such a rearrangement, including long-range translocations linked to viral and cellular membranes.
Evolution of Character Displacement in Darwin's Finches
Authors: Grant Peter R. , Grant B. Rosemary
Published: July 2006

Competitor species can have evolutionary effects on each other that result in ecological character displacement; that is, divergence in resource-exploiting traits such as jaws and beaks. Nevertheless, the process of character displacement occurring in nature, from the initial encounter of competitors to the evolutionary change in one or more of them, has not previously been investigated. Here we report that a Darwin's finch species (
Geospiza fortis
) on an undisturbed Galápagos island diverged in beak size from a competitor species (
G. magnirostris
) 22 years after the competitor's arrival, when they jointly and severely depleted the food supply. The observed evolutionary response to natural selection was the strongest recorded in 33 years of study, and close to the value predicted from the high heritability of beak size. These findings support the role of competition in models of community assembly, speciation, and adaptive radiations.