bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐342‐04: An Update On Computer‐Aided Diagnosis (CAD): What's Next?
Authors: Jiang Y
Published: July 2008

Computer‐aided diagnosis (CAD) has been developed over the last few decades as a tool to improve diagnostic performance. Computer‐aided detection (CADe) promises to help radiologists detect some of the subtle cancers that radiologists tend to miss. After CADe systems are introduced into clinical practice, many clinical studies have been conducted to assess the clinical effect of CADe. Like laboratory observer studies, many of these clinical studies show that CADe helps radiologists detect more cancers. However, all clinical studies do not agree. Controversies have recently arisen that question whether CADe helps radiologists detect more cancers or does more harm by increasing the number of false positives. While laboratory observer studies are very good at controlling biases, potential biases in clinical studies are far less understood and could fundamentally influence the clinical evaluation of CADe. In this presentation, we will review the concept of CAD and summarize laboratory and clinical studies of CADe. We will discuss the pros and cons of various types of clinical studies and discuss their limitations. We will identify some pitfalls that must be overcome to determine the true clinical effect of CAD.

Educational Objectives:

1. Understand the basic concept of CAD.

2. Understand the common types of laboratory and clinical studies of CADe.

3. Understand the limitations of current clinical studies.

Conflict of Interest Statement: Y Jiang receives research funding from Hologic (Bedford, MA).
TH‐C‐352‐02: From Licensing to QA, How to Implement HDR Brachytherapy Into Your Clinic
Authors: Prisciandaro J
Published: July 2008

Brachytherapy has been utilized as a modality for treating cancer since shortly after the discovery of radium by Madame Curie in the early 1900's. Although radium was the workhorse for brachytherapy treatments in the first half of the 21st century, alternative sources began to emerge in the 1950's as mechanisms to produce radioactive isotopes were discovered. Cesium‐137, and a number of other low dose rate (LDR) sources were soon utilized clinically. However, it was not until the 1980's that high dose rate (HDR) brachytherapy emerged as a possible alterative to LDR treatments. Although HDR had the advantage of delivering dose in a shorter time frame, there were several concerns regarding this transition, such as the radiological response of HDR versus LDR treatments, and staff safety. Prior to the era of HDR units, most sources were loaded manually resulting in occupational dose to staff participating in LDR procedures. However, before HDR programs could be utilized clinically, alternatives for manual loading were necessary as the resulting exposure to staff would be prohibitively high. In response, remote afterloading HDR units emerged, allowing sources to be delivered to patients remotely. However, along with this advancement in technology came increasing regulatory and quality assurance requirements.

Although there are a number of similarities between LDR and HDR treatments, there are substantial differences in the clinical implementations of these treatment programs. During this presentation, we will discuss relevant federal regulatory requirements, NRC licensing, AAPM recommendations and task group reports, available HDR equipment, and logistical planning in order to develop a successful HDR program.

Educational Objectives:

1. Discuss the necessary steps to prepare for the clinical implementation of a HDR brachytherapy program.

a. NRC licensing

b. Equipment purchase

c. Room design and shielding

d. Acceptance testing and commissioning

e. Quality assurance

2. Discuss logistics for HDR workflow.
TH‐D‐350‐05: Remote Real‐Time Teaching and Learning (RRTL) in Medical Physics — An Update
Authors: Woo M , Ng K
Published: July 2008

Purpose: This is an update on the Remote Real‐time Teaching and Learning (RRTL) project. The purpose of the project is to conduct real‐time lectures to Medical Physics students over the Internet. Method and Materials: Since 2002 there has been ongoing collaboration between the University of Toronto and the University of Malaya, with lecturers in Toronto conducting lectures for Medical Physics students in Malaysia over the Internet. Another project has started this year between the University of Toronto and the University of Wuhan in China. Students at the University of Wuhan view Power Point slides as they are presented by the lecturer in Toronto. They could see a live video image of the lecturer, while listening to the live audio feed. Various typing and drawing tools allow the lecturer and the students to interact directly. The lectures could also be recorded and viewed at a later date. Guest lecturers as well as students can be included from multiple sites. The software platform Microsoft LiveMeeting is used as the main tool. Results: Some initial technical difficulties had to be addressed, but the system has attained a stable condition to allow the lectures to be carried out smoothly. The software platform is already a standard feature at our institution so the cost is minimal. The project is interesting enough to attract guest lecturers who have been generous to donate their time for a worthy course. Students find the experience very comparable to a traditional classroom environment, and the ability to interact directly with experts in the field highly valuable and rewarding. Conclusion: With the advent and ubiquity of the Internet, remote real‐time teaching/learning is an extremely cost‐effective way to deliver quality education, especially to locations where the profession is developing rapidly and there is high demand for training. It should be actively promoted.
TH‐D‐AUD A‐02: Measurement of Neutron Spectrum and Ambient Dose Equivalent Around a Mini‐Phantom at a Proton Therapy Facility
Authors: Wang Z , Kry S , Burgett E , Howell R , Tailor R , Oliver J , Followill D , Smith A , Salehpour M
Published: July 2008

Purpose: To determine neutron spectra and ambient dose equivalents (H*(10)) for out‐of‐field and in‐field‐out‐of‐range locations around a mini‐phantom irradiated by proton beams. Method and Materials: A dual‐activation foil‐based Bonner sphere (BS) and BS extension (BSE) system was used to determine the neutron spectral fluence in conditions typical for treatment of pediatric patients with proton beams. Proton beams with nominal energies of 120 MeV and 180 MeV were modulated to generate in water 5.0‐cm Spread‐Out‐Bragg‐Peak (SOBP)/5.5‐cm range and 15.0‐cm SOBP/15.5 cm range, respectively. Brass apertures were placed in the large snout at the end of the treatment nozzle to project a 5×5 cm2 field at isocenter. Lucite blocks with a cross‐section of 6×6 cm2 and thicknesses of 5.7 cm and 14.7 cm were used for the 120‐ and 180‐MeV beam irradiations, respectively. Neutron H*(10) was calculated using the fluence‐to‐ambient dose equivalent coefficients from ICRU report 57. Results: The H*(10) was determined at three locations around the mini‐phantom: 25 cm from the isocenter perpendicular to the beam axis (L1), 25 cm from the isocenter along the axis downstream (L3), and 35.4 cm from the isocenter along 45° downstream (L2). The H7*(10) for the 180‐MeV irradiation were 6.89, 4.07, and 4.60 mSv/Gy at L1, L2, and L3, respectively, and was 6.18 mSv/Gy at L1 when the mini‐phantom was removed. For the 120‐MeV irradiation, the H*(10) were 1.21, 0.774, and 0.919 mSv/Gy at L1, L2, and L3, respectively, and was 1.06 mSv/Gy at L1when the mini‐phantom was removed. Conclusion: The neutron spectrum near the isocenter has a two‐peak structure, with peaks near 1 MeV for both energies and a peak near 110 MeV for the 180‐MeV and near 80 MeV for the 120‐MeV proton irradiations. Neutrons below 100 keV contribute less than 2% of the ambient dose equivalent.
TH‐D‐AUD A‐03: Central Axis Neutron Production Determination for a Double Scatterer Passive System
Authors: Perez‐Andujar A , Newhauser W , DeLuca P
Published: July 2008

Purpose: The purpose of this work was to determine which components along the central axis of a passive beam delivery system for proton therapy contributes the most to the production of secondary neutrons. Method and Materials: In this work a passive beam delivery system was modeled based on the MD Anderson Cancer Center treatment nozzle. We performed Monte Carlo simulations with Los Alamos code MCNPX. In these simulations a 200 MeV proton beam is shaped by a rotational modulator wheel (RMW), a secondary scatterer and by a collimating system including a variable snout. Cylindrical volumes were placed along the beam central axis to determine the radial distribution of the neutrons produced. The volumes were made of concentric cylinders with radius ranging from 50 mm to 20 mm. The volumes were placed after the RMW, the secondary scatterer, before and after the snout. The neutron flux and energy spectra were determined for each volume radii and for three treatment volumes. Results: After the RMW the neutron flux was higher for all treatment volumes diminishing as the distance along the central axis increased. The flux increased slightly just before the final snout for the smaller field sizes indicating a backscatter contribution as the proton beam is finally collimated. At the end of the nozzle the flux was lower than after the RMW. The larger neutron flux with energies ranging from 130 MeV to almost 200 MeV was found at smaller radii. As the radial distance increased the flux of energetic neutrons diminished. Conclusion: We found that the RMW was the major source of neutrons in the treatment nozzle. The flux diminished as the distance increased indicating a 1/r2 dependency. The other shaping components contribute to the neutron production but it is difficult to differentiate between contributors after the RMW.
SU‐GG‐J‐53: Comparison of Dosimetric Consequences of Intrafraction Prostate Motion Between IMRT and IMPT
Authors: Li H , Foster R , Chetty I , Dempsey J , Solberg T
Published: July 2008

Purpose: To compare the dosimetric impact of intrafraction prostate motion in IMRT and intensity modulated proton therapy (IMPT), with an emphasis on determining the necessary CTV‐to‐PTV margins to compensate for the motion in these two modalities. Method and Materials: Intrafraction prostate motion of 35 patients was tracked in real‐time using the Calypso System. Data were categorized into three groups according to the treatment intervention performed in response to the motion: (1) if motion larger than 3 mm was observed for 30 seconds during a fraction, dose delivery was interrupted and the patient was re‐aligned; (2) as above, but with motion threshold of 5 mm for 30 seconds; (3) no treatment intervention performed regardless of the motion amplitude. Dose delivered in presence of motion was evaluated by convolving the static dose distribution matrix with the motion probability density matrix. IMRT and IMPT plans for the same patient data were constructed with Pinnacle and UFORT planning systems respectively, using CTV‐PTV margins from zero to 11 mm. Results: For single fractions with the largest average motion in groups (1) to (3), CTV‐PTV margins of 2, 5, and 11 mm for IMRT, and 3, 7, 11 mm for IMPT, are necessary to maintain minimum CTV doses above 95% of nominal dose respectively. In the individual patient with the largest average motion over an entire treatment course (37 fractions), the necessary CTV‐PTV margin was 2 and 3 mm for IMRT and IMPT respectively. Using these margins, any compromise in CTV DVH and the generalized equivalent uniform dose (gEUD) under the corresponding motion was insignificant. Conclusion: The required CTV‐PTV margin for IMPT is slightly larger than that for IMRT, due largely to the sharper penumbra of proton beam relative to photons. However, IMPT resulted in superior sparing of the urinary bladder and rectum compared with IMRT.
Sci‐Fri AM: YIS‐03: Simulated annealing optimization of the pre‐target electron beam in Monte Carlo virtual linac models
Authors: Bush K , Zavgorodni S , Beckham W
Published: July 2008

The purpose of this study is to develop a method for determining the initial parameters of the pre‐target electron beam within a Monte Carlo (MC) accelerator model able to produce accurate 18 MV 40×40 cm2 photon field profiles. We have developed a novel method by which the electron beam intensity distribution can be reverse engineered to reproduce measured dose distributions. The method begins from a cylindrically symmetric pre‐target electron beam (radius 0.5 cm) of uniform intensity. This beam is subdivided into annular regions of fluence for which each region is individually transported through the accelerator head and into a water phantom. A simulated annealing search is then performed to determine the optimal combination of weights of the annular fluences that provide a best match between measured dose distributions and the weighted sum of annular dose distributions. Remarkably, the intensity distribution converges to a solution that is predominantly Gaussian, with a FWHM=1.1mm. In addition, the solution contains an important secondary “extra focal halo” on the order of 10% of the maximum Gaussian intensity. Agreement of the 40×40 cm2 photon field profiles with measurement was within 0.5%. The method greatly reduces the effort required to commission a MC accelerator model for clinical use and has achieved better agreement with measurement than other methods described in the literature. Our derived value of the electron beam FWHM agrees with that measured by Jaffray et al, 1993, and the “extra focal halo” is in qualitative agreement with their measurements of extra focal radiation.
Sci‐Fri AM: YIS‐09: The effect of magnetic interference on a coupled MR‐linac system: Optimization of 3D FEM linac model
Authors: St. Aubin J , Steciw S , Carlone M , Fallone BG
Published: July 2008

Purpose: The coupling of a 0.2T bi‐planar Magnetic Resonance Imager and medical linear accelerator (linac) is proposed to provide real‐time Image Guided Radiotherapy. This coupling necessitates the linac to be within the fringe fields of the bi‐planar magnets causing magnetic interference. The design and optimization of the minimum required shielding is necessary to reduce the fringe field magnitudes to a point where a clinically useful radiation beam is produced. Method: A first step to designing shielding is the full 3D radio‐frequency modeling of the linac waveguide using the Finite Element Method. Various optimizations were performed on the linac model in order to achieve a desired resonant frequency, π/2 phase shift per cavity and other desired properties. An accelerating cavity (AC) and coupling cavity (CC) was first optimized in 3D to have identical resonant frequencies before the full 3D model was generated. Results: In order to increase the capture efficiency of the injected electrons, the electric field in the first AC was reduced by shifting the first CC towards the gun end of the linac. The input waveguide AC dimensions were adjusted to account of the additional coupling iris and the last full AC had its gap length decreased. Conclusion: This work is the first step to determining the minimum magnetic shielding required to produce a clinically useful radiation beam from a coupled MR‐Linac system. The fully optimized 3D model more accurately calculates the electric and magnetic field values since it includes the effects of coupling.
Sci‐Fri PM: Planning‐04: Dose escalation study using anatomy‐based aperture IMRT and SPECT perfusion images for lung cancer
Authors: St‐Hilaire J , Lavoie C , Beaulieu F , Dagnault A , Morin F , Gingras L , Tremblay D , Beaulieu L
Published: July 2008

In the case of non‐small cell lung cancer, doses typically prescribed (60–66 Gy) are not sufficient to ensure a satisfactory tumor control probability. Dose escalation needs to be realized, but dose to organs at risk (OARs) must be kept under widely accepted clinical thresholds. Also, lung functionality is not homogeneously distributed over all the volume: single‐photon emission computed tomography (SPECT) allows spatial characterization of perfusion, open the way to the design of treatments plans that could preferentially avoid highly‐functional lung. In this study, three cases of lung cancer were retrospectively used to assess the capacity of an anatomy‐based aperture inverse planning system to realize dose escalation while limiting dose to perfused lung. Plans were generated for four‐beam non‐coplanar configurations, mixing 6 and 23 MV photon beams. All dose calculations were performed using Pinnacle3 superposition/convolution algorithm. An increasing dose was prescribed to a subvolume of the initial planning target volume. Levels of escalation achieved for the three cases studied were 81 Gy, 111 Gy and 66 Gy to the subvolume. Escalation was limited in two cases by the dose to the esophagus and in the other case by the presence of overdosages near beam entry ports. Calculation of dose‐volume parameters for OARs shows that they respect clinical thresholds. Plans generated by the system are less complex than plans generated in beamlet‐based IMRT, because of the use of few, large segments. The approach used in this study allows important dose escalation, potentially improving treatment outcome.
Sci‐Fri PM: Planning‐06: Verification of a Monte Carlo based treatment planning system in a homogeneous water phantom
Authors: Nairz O , Cygler J , Clark B
Published: July 2008

In this abstract we present the results of the verification of the XVMC based treatment planning system “PrecisePLAN” (release 2.50; Elekta). We investigated a 6 MV photon beam from an Elekta Synergy linear accelerator in a homogeneous water phantom. Measurements of profiles, percentage depth dose curves (pdds) and relative output factors (ROFs) for square fields of sides 3, 5, 7, 10, 15, 20 and 30 cm were compared to calculations performed with PrecisePLAN and simulations with BEAMnrc and DOSXYZnrc. Following recommendations from the literature we investigated the deviations between measurements and calculations of the profiles and pdds in four regions and checked for the criterion of acceptability (given in parenthesis): the inner region (3 %, 2 % at the central axis), the penumbra (2 mm distance to agreement), the outer region (3 %) and the build up region (2 mm). The mean deviation +/− 1.5 times the standard deviation should lie within the confidence interval of the thresholds quoted above. For the ROFs we found very good agreement with the measurement. The deviations are lower than two and one percent for PrecisePLAN and BEAMnrc, respectively, for the investigated field sizes. Also most of the profiles and pdds fulfill the criteria of acceptability given above, but for the large field sizes some of the profiles and pdds fall outside the threshold values. The overall agreement between measurements and calculations, especially for the clinically relevant situations in modern conformal/IMRT techniques, is clinically acceptable.
Sci‐Fri PM: Planning‐10: The replacement correction factors for cylindrical chambers in megavoltage beams
Authors: Wang L , Rogers DWO
Published: July 2008

The replacement correction factor (Prepl) in ion chamber dosimetry accounts for the effects of the medium being replaced by the air cavity of the chamber. In TG‐21, Prepl was conceptually separated into two components: fluence correction, Pfl, and gradient correction, Pgr. In TG‐51, for electron beams, the calibration is at dref where Pgr is required for cylindrical chambers and Pfl is unknown and assumed to be the same as that for a beam having the same mean electron energy at dmax. For cylindrical chambers in high‐energy photon beams, Prepl also represents a major uncertainty in current dosimetry protocols. In this study, Prepl is calculated with high precision (<0.1%) by the Monte Carlo method as the ratio of the dose in a phantom to the dose scored in water‐walled cylindrical cavities of various radii (with the center of the cavity being the point of measurement) in both high energy photon and electron beams. It is found that, for electron beams, the mean electron energy at depth is a good beam quality specifier for Pfl; and TG‐51's adoption of Pfl at dmax with the same mean electron energy for use at dref is proven to be accurate. For Farmer chambers in photon beams, there is essentially no beam quality dependence for Prepl values. In a Co photon beam, the calculated Prepl is about 0.4–0.6% higher than the TG‐21 value, indicating TG‐21 (and TG‐51) used incorrect values of Prepl for cylindrical chambers.
Sci‐Fri PM: Planning‐12: Class II division interpretation of the amended Class II regulations
Authors: Plante J
Published: July 2008

The proposed amendments to the Class II regulations are expected to come into effect in May 2008. This presentation will provide highlights of the change to Class II regulations and how those changes will be interpreted by the CNSC during licence assessments and inspections. The changes to the regulations are designed to correct a number of regulatory deficiencies that have come to light since the regulations came into force.
Sci‐Sat AM(1): Imaging‐02: Comparison between experimental measurements and Monte Carlo simulations for the off‐focal radiation in diagnostic x‐ray systems
Authors: Ali ESM , Rogers DWO
Published: July 2008

In a typical x‐ray tube, off‐focal radiation is mainly generated by the backscattered electrons that re‐enter the anode outside the focal spot. In an earlier study, the EGSnrc/BEAMnrc system was modified to be able to properly transport the anode backscattered electrons, and to tally their subsequent generation of off‐focal x‐rays. In the current study, a diagnostic system and a recent digital mammography system are simulated using the modified BEAMnrc code, and the simulation results are compared with experimental measurements from the literature. Simulation results show excellent agreement with experimental measurements for the spectral shape of both the primary and the off‐focal components, and also for the integral off‐focal‐to‐primary ratio. The spectrum of the off‐focal component at the patient plane is softer than the primary, which causes a slight softening in the overall spectrum. For a given configuration, the off‐focal component increases with tube voltage because of the increased probability for off‐focal x‐rays to escape the anode self‐filtration and the total filtration. This study validates our earlier implementation of off‐focal radiation in EGSnrc/BEAMnrc, and provides a well‐benchmarked tool that simulates x‐ray tubes more realistically. The macro to add this feature to BEAMnrc is available from the authors.
Sci‐Sat AM(1): Imaging‐04: Respiratory errors in cardiac PET/CT with manual alignment of the CT image
Authors: Wells RG
Published: July 2008

Respiratory motion can produce misregistration errors between CT and PET images in cardiac PET/CT imaging. The objective of this study was to determine if manual registration of a single‐phase end‐expiration CT scan to the PET image would eliminate respiratory‐induced artifacts. Listmode data from 71 cardiac PET patient scans were rebinned into a 8‐frame respiratory‐gated image series based on a respiratory trigger signal obtained with an optical tracking system. CT‐based attenuation correction (AC) was performed after registering the CT image with the mean position of the PET images. The 8 phases of the gated PET study were coregistered and the breathing motion was measured. Images from end‐inspiration and end‐expiration were compared to assess the effect of motion. Studies in which the motion was >8mm were reconstructed again, with the CT scan aligned to end‐expiration or end‐inspiration, to determine if phase‐specific registration could reduce the residual errors. The motion was found to be greatest in the axial direction (mean 4.1mm +\− 1.8mm) and 4 Rb stress studies (17%) had motion >8mm. The maximum displacement during breathing was greater for Rb‐stress imaging (<15mm) than for resting (<7.5mm) or NH3‐stress (<5.4mm) imaging. No significant differences were noted between the respiratory phases of the rest studies. Errors in myocardial radiotracer uptake of up to 35% were noted between end‐inspiration and end‐expiration for studies with >8mm of motion. Phase‐specific registration of the CT reduced the extent of the errors but did not fully resolve them, suggesting that more sophisticated AC is required.
Sci‐Sat AM(2): Brachy‐02: Image guided brachytherapy (IGBT) for HDR prostate treatment : Pre‐treatment verification using cone beam imaging to determine catheter displacement
Authors: Holly R , Sankreacha R , Morton G
Published: July 2008

Purpose: Prostate HDR brachytherapy utilizes flexible catheters for treatment delivery. Catheters are inserted under US guidance and planning performed on CT images. This study investigates the efficacy of performing kV cone beam imaging prior to treatment to quantify catheter displacement and dose delivered. Materials and Methods: Twenty consecutive patients undergoing HDR prostate brachytherapy were planned using CT images. Under US guidance, catheters and four fiducial markers were placed into the prostate. Before treatment, visual check confirmed no movement of the template sutured to the perineum and no movement relative to the template. Cone beam imaging was performed using an isocentric mobile c‐arm. Catheters were re‐adjusted if required by the Radiation Oncologist. The cone beam images prior to adjustment were later fused with the planning CT. Results and Discussion: In 17 of the 20 patients, catheter displacements exceeding 0.5cm were observed. Compared to the CT based plan, an average catheter displacement of 1.0cm results in a decrease in the V100 of the prostate by approximately 27%, urethra V120 increased by about 7%, and urethra D10 increased by about 4%. Approximately 65% of patients had average catheter displacements of 1.0cm and larger. Three patients had catheter shifts larger than 2cm. Conclusions: Catheter movement within the patient can be significant and cone beam imaging prior to treatment delivery provides precise imaging to determine catheter displacement. Cone beam imaging time using an isocentric C‐arm is sufficiently short enough (∼ 2 minutes) so as to make this a viable quality assurance tool in the OR.
Sci‐Sat AM(2): Brachy‐07: Tomosynthesis‐based seed reconstruction in LDR prostate brachytherapy: A clinical study
Authors: Brunet‐Benkhoucha M , Verhaegen F , Lassalle S , Béliveau‐Nadeau D , Reniers B , Donath D , Taussky D , Carrier J‐F
Published: July 2008

To develop a tomosynthesis‐based dose assessment procedure that can be performed after an I‐125 prostate seed implantation, while the patient is still under anaesthesia on the treatment table. Our seed detection procedure involves the reconstruction of a volume of interest based on the backprojection of 7 seed‐only binary images acquired over an angle of 60° with an isocentric imaging system. A binary seed‐only volume is generated by a simple thresholding of the volume of interest. Seeds positions are extracted from this volume with a 3D connected component analysis and a statistical classifier that determines the number of seeds in each cluster of connected voxels. A graphical user interface (GUI) allows to visualize the result and to introduce corrections, if needed. A phantom and a clinical study (24 patients) were carried out to validate the technique. A phantom study demonstrated a very good localization accuracy of (0.4+/−0.4) mm when compared to CT‐based reconstruction. This leads to dosimetric error on D90 and V100 of respectively 0.5% and 0.1%. In a patient study with an average of 56 seeds per implant, the automatic tomosynthesis‐based reconstruction yields a detection rate of 96% of the seeds and less than 1.5% of false‐positives. With the help of the GUI, the user can achieve a 100% detection rate in an average of 3 minutes. This technique would allow to identify possible underdosage and to correct it by potentially reimplanting additional seeds. A more uniform dose coverage could then be achieved in LDR prostate brachytherapy.
Sci‐Sat AM(2): Brachy‐08: Monte Carlo calculations of high dose rate brachytherapy treatment plans using CT and cone beam CT images
Authors: Poon E , Verhaegen F
Published: July 2008

The feasibility of using cone beam computed tomography (CBCT) images for Monte Carlo (MC) brachytherapy dose calculations has been investigated. To evaluate the effects of tissue heterogeneities and finite patient dimensions for high dose rate treatment, CT‐based MC calculations for breast and head and neck cases were first performed using the PTRAN_CT photon transport code. PTRAN_CT is an accelerated MC code specifically designed for patient‐specific dose calculations. Muscles and adipose tissues, which are nearly indistinguishable in CBCT images, are found to cause minimal dose perturbations at energies compared to water. The proximity of the tumor to the skin, however, will have an observable impact on the dose up to a few percent. Therefore, for CBCT calculations, a reasonable assignment of material and density values to the patient voxel geometry, with a good delineation of the skin and bony structures, will suffice for MC dose calculations. A CBCT‐based calculation for an actual treatment plan with the tumor close to the cheek was performed. The results were compared to TG43 calculations to quantify the dose differences in the target and critical structures. Since the dose delivered to the tumor is mostly primary dose, deviations are found mostly in the organs at risk where scatter contribution becomes more significant. This study shows that for HDR brachytherapy applications, CBCT‐based MC calculations is a feasible option despite inferior image quality and larger uncertainties in the Hounsfield Units compared to CT images. Research supported by Nucletron BV.
Should carotid stenting replace carotid endarterectomy in routine clinical practice?
Authors: Brown Martin M
Published: July 2008

Carotid stenting has the advantage over endarterectomy of avoiding the complications of neck incision, and often of general anaesthesia too, but it has not yet been shown convincingly to be either as safe or as effective. Only randomised controlled trials allow proper comparison of these aspects of stenting and endarterectomy, but the results to date have been contradictory. Some trials have shown similar 30-day risks of stroke or death, while others have been stopped early because of significantly worse outcome in the stenting group. Inclusion of investigators with limited experience of carotid stenting devices may have contributed to poor results in some trials. The published trials are rather heterogeneous, none is large enough to provide convincing data, and there is very limited long-term follow-up information. We therefore need more data from the ongoing randomised trials before recommending that stenting should in general replace endarterectomy for either symptomatic or asymptomatic carotid stenosis.
Leber’s hereditary optic neuropathy associated with multiple sclerosis: Harding’s syndrome
Authors: Parry-Jones A R , Mitchell J D , Gunarwardena W J , Shaunak S
Published: July 2008

We describe a 32-year-old woman with sequential, severe, painless visual loss in one eye and then the other, and three temporally distinct episodes of neurological disturbance suggestive of demyelination in the spinal cord. She was positive for the T14484C mutation in the mitochondrial genome, one of three common mutations causing Leber’s hereditary optic neuropathy. In addition, MRI identified areas of demyelination within the periventricular white matter of the brain and within the spinal cord. The coexistence of multiple sclerosis and Leber’s hereditary optic neuropathy (Harding’s syndrome) is known to occur more often than would be expected by chance; therefore, screening for the Leber’s mutations in multiple sclerosis patients with severe visual loss should be considered because this has important prognostic and genetic implications.
Leukoaraiosis
Authors: O’Sullivan Mike
Published: July 2008

Leukoaraiosis describes diffuse white matter abnormalities on CT or MR brain scans, often seen in the normal elderly and in association with vascular risk factors such as hypertension, or in the context of cognitive impairment. The term was introduced to avoid confusing an imaging appearance with a specific pathology. Neurologists often come across this appearance, but its significance is sometimes uncertain. The effects on cognitive function and gait are insidious and can be difficult to detect at the bedside, but are nevertheless important. However, gradually it is becoming clearer how leukoaraiosis relates to cerebrovascular disease, Alzheimer’s and other diseases, and how this appearance should influence treatment decisions.
Foot drop: where, why and what to do?
Authors: Stewart John D
Published: July 2008

Foot drop is a common and distressing problem that can lead to falls and injury. Although the most frequent cause is a (common) peroneal neuropathy at the neck of the fibula, other causes include anterior horn cell disease, lumbar plexopathies, L5 radiculopathy and partial sciatic neuropathy. And even when the nerve lesion is clearly at the fibular neck there are a variety of causes that may not be immediately obvious; habitual leg crossing may well be the most frequent cause and most patients improve when they stop this habit. A meticulous neurological evaluation goes a long way to ascertain the site of the lesion. Nerve conduction and electromyographic studies are useful adjuncts in localising the site of injury, establishing the degree of damage and predicting the degree of recovery. Imaging is important in establishing the cause of foot drop be it at the level of the spine, along the course of the sciatic nerve or in the popliteal fossa; ultrasonography, CT and MR imaging are all useful. For patients with a severe foot drop of any cause, an ankle foot orthosis is a helpful device that enables them to walk better and more safely.
When a Parkinson’s disease patient starts to hallucinate
Authors: Poewe W
Published: July 2008

Visual hallucinations are a typical feature of Lewy body parkinsonism and occur in some 40% of patients with Parkinson’s disease. Age and cognitive decline are the most important intrinsic risk factors, but hallucinosis is often triggered by comorbid conditions such as infection and dehydration. The single most important trigger, however, is exposure to CNS drugs, in particular antiparkinsonian agents. While hallucinosis and psychosis can be triggered by amantadine and anticholinergics, they are more commonly experienced after changes in dopaminergic medication. Dopamine agonists have greater potential to induce hallucinosis compared with L-dopa. Attempting to reduce antiparkinsonian drugs is an important part in the management of these patients, but atypical neuroleptics like clozapine or quetiapine are frequently necessary. Visual hallucinations in Parkinson’s disease patients with dementia can also be improved by treatment with the cholinesterase inhibitor rivastigmine.
Lacunar infarcts: no black holes in the brain are benign
Authors: Norrving B
Published: July 2008

Lacunar infarcts—small subcortical infarcts that result from occlusion of a single penetrating artery—account for about one quarter of all ischaemic strokes. However, there are many diagnostic pitfalls, and causes other than penetrating small vessel disease in up to one third of cases. Recent studies have shown that the prognosis after lacunar infarcts is not benign; the risk of recurrent stroke is no lower than for other ischaemic stroke subtypes, and there is an increased risk for cognitive decline, dementia and death in the long term. Furthermore, silent small vessel disease in the brain at the time of an index stroke has significant prognostic implications. In the acute phase, response to intravenous thrombolysis appears to be similar to other subtypes of ischaemic strokes. Antiplatelet drugs, careful blood pressure control, statins and modification of lifestyle risk factors are key elements in secondary prevention after lacunar infarcts.
Ecological uses for genetic algorithms: predicting fish distributions in complex physical habitats
Authors: D'Angelo Donna J. , Meyer Judy L. , Howard Leslie M. , Gregory Stanley V. , Ashkenas Linda R.
Published: July 2008

Genetic algorithms (GA) are artificial intelligence techniques based on the theory of evolution that through the process of natural selection evolve formulae to solve problems or develop control strategies. We designed a GA to examine relationships between stream physical characteristics and trout distribution data for 3rd-, 5th-, and 7th-order stream sites in the Cascade Mountains, Oregon. Although traditional multivariate statistical techniques can perform this particular task, GAs are not constrained by assumptions of independence and linearity and therefore provide a useful alternative. To help gauge the effectiveness of the GA, we compared GA results with results from proportional trout distributions and multiple linear regression equations. The GA was a more effective predictor of trout distributions (paired t test, P < 0.05) than other methods and also provided new insights into relationships between stream geomorphology and trout distributions. Most importantly, GA equations emphasized the nonindependence of stream channel units by revealing that (i) the factors that influence trout distributions change along a downstream continuum, and (ii) channel unit sequence can be critical. Superior performance of the GA, along with the new information it provided, indicates that genetic algorithms may provide a useful alternative or supportive method to statistical techniques.
The migratory behaviour of wild Atlantic salmon (Salmo salar) smolts in the estuary of the River Conwy, North Wales
Authors: Moore A. , Potter E. C. E. , Milner N. J. , Bamber S.
Published: July 2008

Thirty-two wild Atlantic salmon (Salmo salar) smolts, tagged with miniature acoustic transmitters, were tracked in the River Conwy, North Wales, to describe the freshwater and estuarine patterns of migration. Migration in fresh water was predominantly nocturnal, although there was a seasonal change in this pattern with later run fish moving during both the day and night. Smolts tagged earlier in the study spent significantly longer in the river (mean 456 ± 43 h) before migrating into coastal waters than fish tagged later in the study (mean 201 ± 30 h). The movement of smolts through the estuary was indicative of a nocturnal selective ebb tide transport pattern of migration. All of the smolts migrated seawards on an ebb tide close to the surface and within the fastest moving section of the water column. The nocturnal pattern of migration would appear to be the result of an endogenous rhythm of swimming activity that results in the smolts moving up into the water column after dusk and migrating seawards. Smolt migration in the lower portion of the estuary was indicative of active directed swimming and there was no apparent period of acclimation required when moving from fresh to salt water.
Brown trout avoidance of metals in water characteristic of the Clark Fork River, Montana
Authors: Woodward Daniel F. , Hansen James A. , Bergman Harold L. , DeLonay Aaron J. , Little Edward E.
Published: July 2008

The avoidance response of brown trout (Salmo trutta) to mixtures of cadmium, copper, lead, and zinc was determined in water simulating the Clark Fork River, Montana. Effects of acidification on the avoidance response were also evaluated. Tests were conducted in a cylindrical chamber that received reference water at one end and metal-contaminated water at the other; a distinct boundary formed at the center where the chamber drained. A 1 × mixture of the four metals (Cd, 1.1 μg/L; Cu, 12 μg/L; Pb, 3.2 μg/L; and Zn, 55 μg/L) that was representative of the ambient metals concentrations of the Clark Fork River resulted in avoidance by brown trout. Brown trout also avoided 0.5×, 2×, 4×, and 10× mixtures but not a 0.1 × mixture. A reduction in pH from 8.0 to either 7.0, 6.0, or 5.0 resulted in significant avoidance. Avoidance reactions to metals, similar to those observed in our laboratory experiments, may contribute to the depression of brown trout populations in the Clark Fork River.
The physiological impairment of free-ranging brown trout exposed to metals in the Clark Fork River, Montana
Authors: Farag Aïda M. , Stansbury Mark A. , Bergman Harold L. , Hogstrand Christer , MacConnell Elizabeth
Published: July 2008

Tissue metal accumulation and physiological responses were measured in brown trout (Salmo trutta) collected from two sites on the Clark Fork River, Montana, and two reference sites to determine the health status of the resident fish population. Concentrations of metals in tissues, products of lipid peroxidation, and microscopic Cu inclusions were significantly higher in fish collected from the upper Clark Fork River site than in fish from reference sites. Metallothionein concentrations were higher in the livers of fish from the upper Clark Fork River than in those of fish from reference sites. The health of the fish population in the upper Clark Fork River is probably impaired because of previously reported elevated concentrations of metals including As, Cd, Cu, Pb, and Zn in the surface water and aquatic invertebrates in the upper Clark Fork River. The high concentrations of metals in the surface waters and sediments of the Clark Fork River are typical of rivers in the intermountain western United States where discharges from mining activities have occurred since the late 1800s. Thus, our findings can be used as a guide for researchers throughout the intermountain western United States who may investigate similar field conditions.
Genetic variation and population structure in Fraser fir (Abies fraseri): a microsatellite assessment of young trees
Authors: Potter Kevin M. , Frampton John , Josserand Sedley A. , Nelson C. Dana
Published: July 2008

The island-like populations of Fraser fir ( Abies fraseri (Pursh) Poir.) have been isolated since the end of the late-Wisconsinian glaciation on the highest peaks of the Southern Appalachian Mountains and therefore offer an opportunity to investigate the genetic dynamics of a long-fragmented forest tree species. An analysis of eight microsatellite markers isolated from Fraser fir found that the species was out of Hardy–Weinberg equilibrium, with a significant deficiency of heterozygosity and a high degree of inbreeding (FIS= 0.223) relative to other conifers, perhaps associated in part with the young life stage of the trees included in the analysis. The analysis detected a significant but small amount of genetic differentiation among Fraser fir populations (FST= 0.004) and revealed that the geographical and latitudinal distances between populations, but not population area, were significantly correlated with their pairwise genetic differences. Both gene flow and postglacial migration history may have influenced the genetic architecture of the species. The results will be useful in the genetic conservation of Fraser fir, a species experiencing severe mortality following infestation by an exotic insect.
Forest disturbance frequency and patch structure from pre-European settlement to present in the Mixed Forest Province of Minnesota, USA
Authors: White M. A. , Host G. E.
Published: July 2008

We used General Land Office survey data (1860–1890) and interpreted aerial photography from the 1930s, 1970s, and 1990s to quantify forest disturbance frequency and spatial patterns for four time periods in the Mixed Forest Province of Minnesota. The study region included eight subsections within the Mixed Forest Province of Minnesota’s Ecological Classification System. Presettlement disturbance and spatial pattern estimates varied across the eight subsections indicating a strong relationship to soil and landform characteristics. Land surveyors primarily recorded higher severity disturbances that resulted in significant tree mortality. The 1900–1940 era was characterized by a short-term increase in fire frequency that was relatively uniform across the study region, in contrast to the variability of the presettlement (1860–1890) landscape. In the postsettlement period (1940–1995), timber harvest replaced fire as the dominant disturbance factor. Similar management practices among subsections created similar harvest rates throughout the study region. These management practices imposed a more homogeneous pattern dominated by small (10–25 ha) patches. Management practices now have a greater influence than natural processes in the generation of landscape pattern in the Mixed Forest Province of Minnesota. Information on presettlement forest conditions and subsequent changes can be used by land managers to restore spatial pattern variability in managed forest landscapes.
Diagnostic tools to evaluate the foliar nutrition and growth of hybrid poplars
Authors: Lteif Arlette , Whalen Joann K. , Bradley Robert L. , Camiré Claude
Published: July 2008

This 2-year study examined the effect of fertilizers on tree growth and foliar nutrition in a Populus trichocarpa Torr. & A. Gray × Populus deltoides Bartr. ex Marsh. plantation located in southwestern Québec. The treatments included a control that did not receive N or P fertilizer, inorganic NP fertilizers, organic fertilizers applied at 65–70 kg N·ha–1, and organic fertilizers applied at 130–140 kg N·ha–1. Fertilized trees were taller and had larger diameters than control trees. Three methods were used to diagnose limiting nutrients and nutrient imbalances, and compare the nutrient supply from different fertilizer sources. The critical value approach and the compositional nutrient diagnosis methods found below-optimum N and P concentrations, sufficient K and Mg concentrations, and an excessive Ca concentration in foliage. Vector analysis compared the N nutrition in foliage from fertilized trees and the control trees. The compositional nutrient diagnosis r2(nutrient imbalance index) was negatively correlated with annual tree growth in height (r = –0.46, P < 0.05) and diameter (r = –0.59, P < 0.05), meaning that trees with a greater nutrient imbalance grew less in height and diameter than trees with balanced foliar nutrition. Of these diagnostic methods, compositional nutrient diagnosis holds promise for identifying nutrient limitations and predicting growth responses to fertilization in hybrid poplar plantations.
Conditionality: Forms, Function, and History
Authors: Babb Sarah L. , Carruthers Bruce G.
Published: July 2008

The International Monetary Fund (IMF) is famous for its practice of conditionality—making the disbursement of resources to national governments contingent on the performance of certain policies. We survey the history of conditionality and show that the IMF is only one of many organizations that have historically engaged in this practice. Conditionality can be imposed by either private lenders (such as banks) or official organizations (such as international financial institutions), through a range of policy instruments, and to serve different kinds of goals. Over the course of the twentieth century, the conditionality of private lenders came to be replaced by official conditionality and was increasingly applied exclusively to the governments of developing countries. Today, conditionality is being used by more official organizations to address a broader range of goals than ever before. At the same time, however, conditionality is beset by critics who argue that it is illegitimate or ineffective. In response to such criticisms, the IMF and other practitioners of conditionality have developed new techniques and have attempted to bolster their legitimacy by making their operations more transparent and by emphasizing recipient-country participation.