bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐330A‐09: Performance Evaluation of Different Fanbeam Algorithms in the Presence of Noise
Authors: Tolakanahalli R , Leng S , Chen GH
Published: July 2006

Purpose: Different fanbeam reconstruction algorithms are being evaluated and the noise performances of these algorithms are compared at equivalent MTF. Method and Materials: The fanbeam reconstruction algorithms under comparison are FBP with Parkers smooth weighting (PFBP), LCFBP, DFBP, reconstruction algorithm by Noo et.al and exact reconstruction algorithm by Kudo et.al . The MTF from the five different algorithms were plotted and compared. In order to establish the basis for an unbiased comparison of the noise variance between different algorithms, we established the condition of equivalent spatial resolution. To achieve this, a window function was applied to the ramp filtering kernel before back‐projection for PFBP, LCFBP and Kudo's algorithm. A homogenous phantom was numerically simulated and Poisson noise with N0= 2e5 was added to the projection data. The images were reconstructed from projection data with and without the Poisson noise added. These images were then subtracted from each other to result in a subtracted or pure noise image. The variance in these noise images over five different ROIs was subsequently compared. FBP with Parkers smooth weighting was chosen as the gold‐standard and percentage decrease in variance in the images reconstructed using other four algorithms with respect to that of PFBP was tabulated. Results: The results showed that the new reconstruction algorithms had better noise performance than state‐of‐the‐art reconstruction algorithm (PFBP) after establishing the condition of equivalent spatial resolution. DFBP and exact reconstruction algorithm by Noo performed much better than the other three algorithms. Equal weighting scheme utilized definitely improved the noise performance over smooth weighting. DFBP showed a decrease of variance by about 23 % compared to PFBP. Conclusion: The reduction in noise variance theoretically leads to a radiation dose reduction by about 23 %. This will be of significant importance especially in pediatric imaging.
MO‐D‐ValB‐01: Characterization of Cardiac Motion in the Lung Using a Novel Electromagnetic System in An Animal Model
Authors: Lechleiter K , Parikh P , Chaudhari A , Malinowski K , Hubenschmidt J , Dimmer S , Bradley J , Mayse M , Low D
Published: July 2006

Purpose: Previous studies have examined the accuracy of the use of three internal AC electromagnetic transponders and wireless tracking system (Calypso® Medical) for tumor localization in prostate cancer. This study focuses on the use of the system to investigate and characterize cardiac induced lung tissue motion to better predict three‐dimensional lung tumor position in real‐time. Method and Materials: Under an institutional approved animal study, three 1.8 mm AC electromagnetic transponders are bronchoscopically implanted in the periphery of the lungs of five hounds. The transponders are positioned in a triangle, each spaced 1–3 cm apart. The transponder positions are sequentially measured every 50 ms at five time points. During each measurement, the subject is stressed with several respiratory patterns. Signal processing of the data involves the design and application of a Butterworth highpass filter to obtain the component of transponder movement due to cardiac motion. Results: The data for the 1st three time points of the first animal are presented. FFT spectrum analysis indicated signal frequency components of 13.05 and 123.8 cycles/minute, due to respiration and cardiac motion respectively. Cardiac‐induced lung tissue motion was detected in vivo, ranging from 0.0007cm – 0.3592cm, by applying the highpass filter to the data. The motion was smaller on the implant day compared with the other two time points. Moreover, transponder position and distance from the heart had an effect on calculated motion. Finally, breathing patterns also affected the observed motion at a statistically significant 0.1% level. Conclusion: Cardiac contractions cause quantifiable motion in surrounding lung tissues that cannot be measured with existing onboard imaging capabilities. The motion varies depending on transponder position, distance from the heart, breathing pattern, and day of measurement. Though the motion maximum was 3.6mm, this motion could cause imaging artifacts when using respiratory correlates.

Research sponsored by Calypso® Medical Technologies.
MO‐D‐ValB‐04: Internal‐External Correlation Investigations of Respiratory Induced Motion of Lung Tumors
Authors: Ionascu D , Jiang S B , Nishioka S , Lonberg F , Shirato H , Berbeco R I
Published: July 2006

Purpose: In respiratory‐gated treatments, the successful delivery of the planned dose distribution and sparing of the health tissue is highly dependent upon the assumption of a strong correlation between the external motion and the internal tumor motion. We will present a new internal/external correlation study based on a unique data set. Method and Materials: Radiopaque fiducial markers inside or near the target were implanted and visualized in real time by means of stereoscopic diagnostic x‐ray fluoroscopy. The fluoroscopic images were recorded continuously in synchronization with an external respiratory motion monitoring system. A data analysis methodology was developed in order to assess the correlation of the external breathing motion with the internal 3D position of the implanted fiducials. The methodology is based on a dynamic correlation technique and used to extract global correlation parameters as well as to reveal their instantaneous behavior. Results: We have found that in some cases, the poor internal/external correlation is caused by a time mismatch between the motion of the internal fiducial markers and the external breathing motion. For some cases, there is a sizeable time delay between the internal tumor motion and the external motion of up to 0.8 seconds, revealing that internal‐external motion coupling is dependent on the tumor position. We have also found that the time delay itself is time‐dependent. Conclusion: The proposed technique reveals one of the causes for poor internal‐external correlation and it could be used to improve the current gated treatment methodology by combining the amplitude gating technique with the measured time‐delay. In the course of these investigations, we also found that our technique can reveal difficulties in extracting the underlying time delay (due to its own time dependence) and that one has to be careful of how the time delay is implemented for gating.
MO‐D‐ValB‐05: Commissioning An AC Electromagnetic Localization System for Radiation Therapy
Authors: Willoughby T , Meeks S , Vertatschitsch E , Dimmer S , Riley J , Flynn J , Solberg T , Liu N , Djemil T , Jani S
Published: July 2006

Purpose/Objective: To establish a commissioning and acceptance test protocol for an AC electromagnetic tracking system for use in target localization and tracking during radiation therapy. (Calypso® 4D Localization System, Calypso Medical, Seattle, WA). Materials/Methods: Following installation of infrared cameras and electromagnetic system, compatibility tests were made to ensure the system did not interfere with radiation output, MLCs or IMRT field fluence. The collision space between the linac and the Calypso System was evaluated. System verification included calibration using software and calibration tools, one of which has embedded RF transponders and optical reflectors. End‐to‐end testing to assess localization accuracy included CT scan of a radiographic phantom with RF transponders, creation of four Calypso Plans, data entry to the Calypso System and execution of treatment sessions. Tracking accuracy was measured using a precision translation table for orthogonal motions ± 5 mm. Results: Calypso System did not affect normal clinical operations of radiation output, MLC, or IMRT field segmentation. Overall accuracy on ten systems at five institutions and 40 treatment plans was 0.068 ± 0.027 cm, incorporating contributing errors from the CT scans, identification of transponders in the phantom, and effects of radiation dose delivery. With stable environment, no systematic drift was noticed over 30 minute. Translations of precise increments from −0.50 cm to +0.05cm were accurately tracked with error of 0.00cm, −0.02cm and 0.01cm (lat, long, vert). The system maintained accuracy with monthly optical calibrations. Changes in system readout of ±0.05 cm (readout quantization) were noticed at certain gantry angles. Conclusion: Evaluations demonstrate the AC electromagnetic system with wireless transponders can be integrated into the radiotherapy environment with existing instrumentation and operates within the designed accuracy specification. Conflict of Interest: Work supported by Calypso Medical Technologies.
TU‐B‐224A‐01: Shielding II:Linac Radiation Monitoring and Surveys: Instruments and Methods
Authors: Ipe N E
Published: July 2006

Regulatory agencies typically require shielding integrity radiation surveys during commissioning of radiation therapy linear accelerators (linacs). While concrete barriers that provide adequate shielding for photons also provide adequate shielding for neutrons, facilities operating at energies above 10 MV shall be checked for neutrons at the door, maze entrance, and any other openings through the shielding. Laminated barriers shall be monitored for neutrons beyond the shielding.

For the primary barrier measurements, the maximum field size is utilized without a phantom in the beam. Gantry angles of 0, 90, 180, 270 degrees as well oblique angles depending upon the shielding configuration are commonly used. Secondary barriers are surveyed with the maximum field size and a phantom in place.

Photon surveys outside the barriers are performed typically with a calibrated ionization chamber which has both rate and integrate modes, at 30 cm from the barrier. Head leakage in the linac room can be established with the use of film wrapped around the linac head and integrating dosimeters.

In this lecture neutron monitoring will be emphasized. Neutron measurements inside the treatment room are fraught with difficulties because of photon interference from the primary and leakage photon beam and the fact that neutron detection is spread over many decades of energy. Thus no single neutron detector can accurately measure neutron fluence or dose equivalent over the entire energy ranges. Additionally neutron detectors can have photon‐induced reactions when used in the primary photon beam. Further because therapy linacs are operated in a pulsed mode, the intense photon pulse overwhelms any active detector that detects particles electronically. Thus active detectors such as such as neutron rem‐meters, fluence meters and spectrometers neutron cannot be used inside the treatment rooms except at or near the maze entrance. They can be used outside the shielded treatment room.

Passive monitors with high neutron sensitivity such as moderated activation foils (gold and indium) and threshold activation detectors (phosphorous) can be typically used inside the treatment room and inside the primary beam. Moderated activation foils can also be used inside the treatment room and outside the primary beam. Solid state neutron detectors (SSNTDs) such as CR‐39 ® and bubble detectors can be used inside the treatment room, but outside the primary beam. Bubble detectors can also be used for radiation surveys outside the shielded treatment room.

Educational Objectives:

1. Understand how to perform shielding integrity radiation surveys.

2. Understand the various neutron monitoring methods and instruments.

3. Understand under which conditions these monitors can be used.
TU‐C‐330A‐04: Preliminary Study of Glu and Gln Metabolites in Brain Tumors at a 4T System
Authors: Feng W , Amans M , Xuan Y , Sehgal V , Hu J
Published: July 2006

Purpose: in vitro 1H MRS studies have suggested that Gln/Glu ratio is useful in detecting an early stage of malignant transformation. Due in part to the technical difficulty, in vivo detection of well‐separated Gln and Glu of human tumors has not been reported. A recent study proposed that a standard STEAM sequence with optimized TE/TM (80/50 ms) can be used to simultaneously detect Gln and Glu peaks around 2.4 ppm with virtually no spectral overlap at 4T. In this study, we report preliminary results of the application of this technique for brain tumors. Method and Materials: 1H MRS of eight patients with brain tumors were acquired with a quadrature head coil in a 4T system. Four patients had biopsies within two weeks of their respective MRS study, and the remainder had biopsies prior to their scans. A standard STEAM sequence was used with TE=80ms, TM=50 ms, TR = 2–3 seconds, spatial resolution = 4–12 cm3, and acquisition time = 15–30 minutes. All data sets were processed using LCModel. Results: In addition to providing “typical” characteristics of NAA, Cho, and Cr for brain tumors, one of the striking observations is consistent and remarkable increase in Gln concentration (water as reference) and Gln/Cr ratio for all cases studied; while decrease in Glu concentration (water as reference) but wide variability in Glu/Cr ratio (0–3 times of corresponding contralateral control). The results also demonstrate occurrences of opposite changes between Gln and Glu content for brain tumors, illustrating the importance of simultaneously detecting Gln and Glu for the study of tumor metabolism. The consistent and remarkable increases in Gln content suggest direct Gln involvement in tumor metabolism, in agreement with previous biochemical analysis. Conclusion: In vivo Glu, Gln can provide useful information to help diagnosis of brain tumors.
TU‐C‐330A‐05: Optimization of Outer Volume Suppression for Improved Prostate MR Spectroscopic Imaging
Authors: Venugopal Niranjan , McCurdy Boyd , Ryner Lawrence
Published: July 2006

Purpose: To adapt a new MR Spectroscopy (MRS) technique employing non‐cuboidal voxels, called conformal voxel MRS (CV‐MRS), for use in prostate spectroscopic imaging in order to reduce contamination of spectra by lipid signal surrounding the prostate.

Method and Materials: CV‐MRS uses twenty or more spatial saturation (SS) pulses, placed around the prostate, to reduce the lipid signal affecting the spectra within the prostate. A water/oil phantom was designed to simulate the prostate and surrounding lipid signal. Use of the new CV‐MRS technique reduced the lipid signal contamination by 84% as compared to standard cuboidal voxel MRS. To further reduce the lipid contamination, the routinely used 90 degree flip angle used for each SS pulse was modified to take into account the regrowth of lipid signal with its short T1 relaxation time. Results: Contrary to our expectations, resulting spectra from the optimized approach actually showed an increase in lipid contamination by 10%. We tracked the problem down to overlapping SS pulses. Using a simulated 3D model, we found that 68% of the volume we were trying to saturate experienced multiple overlapping SS pulses, with some regions being saturated 7 or more times. Regions of the volume experiencing an even number of SS pulses were found to increase the lipid contamination signal by 88% to 200%. Conversely, regions experiencing an odd number of SS pulses had a reduction in lipid contamination of 55%. Conclusion: Changing the ordering of the SS pulses, such that the overlapping pulses occur later in the train of 20 SS pulses reduced the problem of lipid signal from those overlapping volumes. In summary, we have developed an improved outer volume saturation technique which reduces lipid contamination problems in prostate MR spectroscopic imaging.
TU‐C‐ValA‐04: Deformable Registration Using Regularization That Accommodates Local Tissue Rigidity
Authors: Ruan D , Fessler J , Roberson M , Balter J , Kessler M
Published: July 2006

Purpose: Existing methods for deformable image registration typically use homogeneous regularization to encourage global smoothness. Less work has been done to incorporate voxel‐level tissue‐specific elasticity information. Ignoring differences in elasticity can, however, result in non‐physiological registrations, such as bone warping. We propose an approach to incorporate tissue rigidity information using a spatial variant regularization. Method and Materials: Regularized image registration algorithms estimate the deformation by minimizing a cost function, consisting of a dis‐similarity metric and regularization. To account for tissue‐type‐dependent rigidity information, we incorporate into the cost function a non‐rigidity penalty: an integral of stiffness index for local deformation weighted by spatial variant regularization factor depending on tissue type. For CT data, a simple monotonic increasing function of the CT number is used as a rigidity index for local tissue type. A necessary and sufficient condition for stiff local deformation is derived, and the local non‐stiffness is measured by the deviation of local Jacobian from orthnormality using the Frobenius norm. Tensor B‐Splines are used to parameterize the deformation field. A multi‐resolution scheme and gradient‐based approach are applied for optimization. Performance was accessed by registering 3D thorax CT‐images obtained from different breathing phases. Results: Experiments with clinical data demonstrate higher accuracy for inhale‐exhale thorax CT registration with the proposed approach. We observe comparable intensity match as the unregularized approaches, but more physiologically reasonable results with respect to different tissue types; in particular bone warping phenomena is eliminated in general. Conclusion: This work provides a way to incorporate tissue‐type‐dependent information into deformable registration framework with regularization design. Inference from image intensity avoids explicit segmentation, and is robust to partial volume effect. Our formulation based on local Jacobian and Frobenius norm provides analytical expression for the regularization and its derivative. More physiological results are achieved with minor computation expense.

Supported by NIH P01‐CA59827.
TU‐C‐ValB‐05: The Effects of Radiation Treatment On Respiration‐Induced Lung Tumor Motion
Authors: Britton K , Starkschall G , Nelson C , Komaki R , Mohan R
Published: July 2006

Purpose: The purpose of the present work is to assess the changes in size and respiration‐induced motion of lung tumors resulting from radiation treatment. Methods and Materials: Six to ten four‐dimensional computed tomography (4‐DCT) image datasets were acquired for each of 5 stage‐III non‐small‐cell lung cancer patients who received chemoradiotherapy treatment over six weeks. Serial 4‐D datasets were obtained each week. Gross tumor volumes (GTV) were outlined on each data set. Software tools in the radiation treatment planning system were used to calculate the volumes and centroids of the GTVs on the 0% (end‐inspiration) and 50% (end‐expiration) phase for each dataset. Interfractional changes in GTV location was assessed by registering corresponding phases of the datasets based on vertebral body landmarks and determining variations in the position of the GTV centroids relative to the landmarks. Forty‐six scans including six primary tumors (involved nodal stations were not included) were analyzed. Results: The initial mean tumor volume was 53 cm3 (range: 1 to 137cm3). The interfractional changes in GTV position were predominantly in the superior‐inferior direction with a mean magnitude of 3.4mm (range: 0.1 to 9.3mm). Overall tumor regression ranged from 20–71% (0% phase) and 15–70% (50% phase). As tumors shrunk, the magnitude of intrafractional GTV motion increased in the anterior‐posterior and superior‐inferior directions while remaining constant in the right‐left direction. Reproducibility of the GTV‐centroid position at the 50% phase, based on same‐day repeat CT scans, was within 2 mm in each direction. Conclusions: Because of changes in tumor size and intrafractional tumor motion, care must be taken when reducing treatment portals based on explicit determination of the internal target volume (ITV). Repeat 4‐DCT scans might be warranted during treatment.
TU‐C‐230A‐02: Error Analysis/reduction Philosophy/theory
Authors: Pawlicki T
Published: July 2006

The purpose of this presentation is to discuss the philosophy and theory of error analysis and reduction. This talk will be equal parts conveyance of technical information and provocation to action on the important issue of medical errors. Although a somewhat obvious connection, we begin by providing a sound framework that relates errors and quality assurance. The scope of technical information within this presentation will be an attempt to wade through the myriad of theories and philosophy related to errors and quality, much of which is new to our field. For example, the JCAHO Lexicon describes quality as, “Designing a product or service as well as controlling its production so well that quality is inevitable.” What does it actually mean to control a product or service? This will be described. The leadership of the AAPM has taken the ambitious step to change the emphasis of quality assurance from simply checking specifications to investigating processes via the new quality assurance task group (TG100). This is a significant and necessary paradigm shift in our approach to medical errors and quality that deserves a detailed discussion. An understanding of how to reduce errors and improve quality begins with an appreciation of two realities: 1) everything we do involves a process, and 2) every process has unavoidable variation. If one controls variation in a process, then one will reduce errors and improve quality. The implementation of process identification and control to clinical practice will be discussed in detail and by example where appropriate. Furthermore, there is a significant history of error reduction and quality research and this context will be maintained throughout the presentation. In addition to specific techniques of error analysis and reduction such as failure modes and effects analysis (FMEA), root cause analysis (RCA), pareto charts, fishbone diagrams and statistical process control (SPC) we will discuss the philosophies of define, measure, analyze, improve, control (DMAIC) and total quality management by the six‐sigma approach.

Error analysis and reduction (and quality assurance in general) are built on a mature body of research from other fields. There is much work to do toward implementing these techniques in radiotherapy practices to minimize errors and optimize quality. There are no turn‐key solutions to quality. As will be described, the business world has become fanatical about quality to stay competitive. Why should the medical world be any different with our patients' well‐being at stake? Medical physicists, above anyone else in the typical department, have the analytical ability to understand and implement these techniques. We must accept the challenge and as a first step, future AAPM meetings should have a research session specific for quality, error analysis/reduction and cost analysis/reduction.
TU‐C‐224C‐04: Computed Radiography for Helical Tomotherapy Quality Assurance
Authors: Ramsey C , Harris C
Published: July 2006

Purpose: To determine if a CR system that had been used for radiation therapy digital imaging since 2001 could also be used for IMRT quality assurance, and if the system could be used in helical tomotherapy quality assurance. Methods and Materials: The CR system used consisted of a desktop CR reader that utilizes storage phosphor plates, a 650 nm laser diode scanning beam source, and a high luminance light box for plate erasure. The CR plates are made of phosphor, coated with a photostimulable storage phosphor (BaFBR:Eu2+). Three types of dose‐to‐response calibrations were performed 1.) Static square fields; 2.) An IMRT step‐wedge; and 3.) A rotational helical tomotherapy delivery with concentric rings of known dose. All readings were taken with 6 MV beams. Like TLDs, some of the trapped charge carriers in the storage phosphor gradually decay with time. Because of the decay effect, it was important to determine the best time to wait between exposure and scanning. Five helical tomotherapy patients were selected as test cases for the CR dosimetry. Measurements were made in a cylindrical phantom with the CR plate and again with radiographic film. Calibration techniques #1, #2, and #3 were applied to the CR images to determine which was the most appropriate. Dose differences and gamma comparisons were made between the calculated and measured doses. Results: A time and field size dependence was observed. After comparing readings from different time intervals, ranging from one to twenty minutes, it was decided that four minutes was an optimal time to wait between exposure and scanning. Also, gamma for the CR images was significantly worse than the film images taken for the same patient. Conclusions: The field‐size dependences, inconsistencies between calibration techniques, and plate decay make the CR system used in this study non‐usable for IMRT dosimetry.
TU‐C‐224C‐10: Transfer‐Function Characterization of Heat Conduction in Water Calorimetry
Authors: Tosh R , Chen‐Mayer H
Published: July 2006

Purpose: To elaborate a transfer‐function approach to characterizing the response of water calorimeters to abbreviated exposures in radiation beams. Method and Materials: Typical water calorimeters in use today derive from the original design of Domen, inferring absorbed dose from temperature measurements at a single point in a partially irradiated, extended volume. The success of the approach in deducing locally absorbed dose depends on heat transfer being “sufficiently” slow temporally and broad spatially compared to time‐ and space‐scales of the measurement. In order to address these issues of “sufficiency” more quantitatively, we have undertaken an approach to the problem that assesses the impulse‐response of the calorimeter to spatially and temporally localized radiation. The approach involves simple analytical models of heat conduction and finite‐element methods that yield predictions of single‐point temperature waveforms obtained from thermistors in a calorimeter. Output from the models is compared with experiment over wide variations in shutter period (30s–10,800s) and duty cycle (5%–50%). Results: Our findings show that heat conduction due to typical dose inhomogeneities within water calorimeters induces systematic variations in estimated dose that traditional data‐analysis techniques ignore. Moreover, these variations do not diminish at smaller duty cycle, suggesting that they are intrinsic to the exposure time of the experiment, and not to the use of periodic exposure techniques. Essential features of the measurements are reproduced by both finite‐element simulations and a simple analytical model. An RC‐circuit analogue derived from the latter suggests that conduction phenomena with a spatially masked beam proceed by a multiplicity of times scales, ranging from seconds to hours, which contribute significantly to systematic variations in estimated dose. Conclusions: The variations of estimated absorbed dose described here suggest that a small systematic error (<1%) may affect existing standards measurements based on water calorimetry.
WE‐C‐330A‐06: FEA and Phantom Tests of Ultrasound Temperature Maps During Thermal Therapy
Authors: Daniels M , Jiang J , Madsen E , Zagzebski J , Varghese T
Published: July 2006

Purpose: The ability to noninvasively monitor heating patterns during radiofrequency ablation therapy would provide invaluable guidance to clinicians during these procedures. We are investigating ultrasonically recorded and scaled “apparent tissue displacements”, caused by sound speed changes and tissue expansion, for generating temperature maps during ablation. This paper reports FEA simulations and experiments in novel phantoms to determine whether ultrasound can successfully record temperatures. Method and Materials: FEA models were applied to determine the temperature distribution from a radiofrequency ablation electrode in liver. FEA analysis enabled creation of both temperature and tissue expansion maps during simulated procedures. The expansion maps in turn were combined with sound speed changes and used to model ultrasound echo data at intervals during the ablation. In addition, experimental data were acquired using a reusable slurry phantom with embedded sensors surrounding an ablation electrode. Frames of echo data were acquired using a linear array transducer during a 15‐minute heating sequence. For both simulated and real data, two‐dimensional cross‐correlation of echo signals from successive frames yielded accumulated tissue displacements. Scaled gradients of these displacements estimate local temperatures. Results: Temperature maps generated from simulated echo signals correspond well to the underlying temperature maps created with FEA. The zone of elevated temperatures can be easily visualized on these maps. Isothermal curves on the temperature maps may be useful in determining areas that may have incurred cell death or tissue necrosis. Preliminary results indicate good correlation between fiber optic temperature sensor measurements and ultrasound temperature measurements over 1cm2 ROI's surrounding the probe. Conclusion: Temperature maps estimated using ultrasound signals correspond well to the FEA generated temperature maps. Temperature mapping can therefore be used to visualize the zone of heating during a radiofrequency ablation procedure. This result is confirmed by temperature measurements done in an ultrasound phantom.
WE‐C‐330A‐07: Radiofrequency Ablation Electrode Displacement Elastography
Authors: Bharat S , Zagzebski J , Madsen E , Varghese T
Published: July 2006

Purpose: Elastography can be used to image the position and location of thermal lesions created using radiofrequency (RF) ablation. A challenge, however, when applying this technique to guide treatment of liver tumors is that of producing a controlled compression of the tissue. We are testing a new method, ‘electrode displacement elastography’, for producing elasticity images of ablation therapy treatments. This paper presents results of tests in a custom elastography phantom. Method and Materials: An elastography phantom containing a stiff inclusion (50 kPa) embedded in a soft (11kPa) background was used. A discarded RF electrode was mounted firmly into the inclusion with the handle extending outside the phantom container. A stepper motor applied small (0.1mm) displacements while the phantom was imaged using an ultrasound machine equipped with a research interface, acquiring raw echo data before and after small perturbations of the electrode. One‐dimensional cross correlation was used to estimate displacements. Finite element analyses were also performed to characterize the contrast‐transfer efficiency (CTE) of the conversion from the underlying modulus domain to the observed strain domain. Results: On elastograms the inclusion has a characteristic halo appearance, similar to that observed in in‐vivo tests of this technique. Strain contrast is consistently higher than the underlying modulus contrast, confirmed by a study of the CTE. On simulated strain images, stiffer inclusions in softer backgrounds have CTE values in excess of 0 dB. Conclusions: Feasibility of electrode displacement elastography is shown. The strain contrast observed exceeds the underlying modulus contrast, for stiffer inclusions. This characteristic of the method may provide RF ablation practitioners with added lesion contrast in situations where the actual stiffness ratio between the lesion and surrounding normal tissue is not significantly greater than 1:1.

This work is supported by Whitaker Foundation grant RG‐02‐0457.
WE‐C‐330A‐09: Dynamic, MultiModality Imaging: Temporal Precision and US Artifact Reduction
Authors: Oldham S , Molloy J
Published: July 2006

Purpose: Herein we describe the development of a dynamic fusion technology for ultrasound (US) and other static 3D data sets. We tested whether the high US frame rate is sufficient to accurately track objects subject to respiratory motion. In addition, we used the spatial registration functions of the system to test whether aggressive compounding of US images would be efficacious in terms of artifact reduction and boundary detection. Materials/Methods: The system's dynamic spatial accuracy was tested using a phantom translated at a velocity of either 4 or 16 mm/s. To test inaccuracies due to video processing we offset the arm and video frame data in single frame increments. Static 3D US data sets were acquired incorporating an acoustic obstruction. Data sets were reconstructed using images from multiple angles of interrogation. Similar experiments were performed to assess the system's ability to reduce reverberation artifacts and tested on a human subject. Results: By correcting for video processing latency, the system was able to track object motion to 0.2 and 0.5 mm for speeds of 4 and 16 mm/s, respectively. Aggressive image compounding was able to reveal objects that were otherwise obstructed from a single view. Reverberation artifacts were reduced, in addition to enhancing certain object boundaries . These results were present although less obvious in early human testing. Conclusions: Our imaging system is spatially accurate over a range that permits interrogation of an adult abdomen from a wide range of angles. The system's ability to track respiratory motion has been demonstrated. Aggressive compounding demonstrated that obstructed test objects could be visualized by non‐intelligently summing images from varying angles. Soft tissue boundaries and other US artifacts may also benefit from application of the technology.

Supported by NIH R01EB002899.
WE‐C‐330D‐01: The Future of Image Science
Authors: Cunningham I
Published: July 2006

The characterization and classification of image quality in radiographic imaging is a complex and illusive goal. It involves understanding the physics of x‐ray interactions and how these influence statistical properties of image signals and noise. It requires an understanding of how observers can extract non‐random structures from random (and sometimes not random) image details. Finally, it requires an understanding of how observers are able to extract clinically meaningful information from the complicated clutter of background structural information. As processes responsible for producing image signals are often non‐linear, non‐stationary, multi‐dimensional and task dependent, simpler metrics of image quality and detector performance are at best idealized approximations.

Scientists have attacked this multi‐faceted problem from a number of directions. As a result, a wide spectrum of terminology and concepts have become commonplace. This talk will address some aspects of how far “image science” has come and where it may be going. It will highlight accomplishments that have become established in both academic and commercial fields, and problems that have not been solved. Hopefully, improved understanding of these issues will enable the development of better detectors and systems and improved patient outcomes.

Educational Objectives:

1. Understand issues that influence image quality and observer performance for simple tasks.

2. Understand limitations of simple metrics.

3. Understand some directions being followed to better understand what determines image quality for the development of better detectors and systems.
WE‐C‐ValA‐04: Derivation of the Tumor Position From External Respiratory Surrogates with Periodical Updating of External/internal Correlation
Authors: Kanoulas E , Aslam J , Sharp G , Berbeco R , Nishioka S , Shirato H , Jiang S
Published: July 2006

Purpose: To develop techniques that can derive the tumor position from external respiratory surrogates through periodically updated internal/external correlation. Method and Materials: A simple linear function is used to express the correlation between tumor and surrogate motion. The function parameters are established during patient setup session with both tumor and surrogate positions measured at 30Hz rate. During treatment, the surrogate position, constantly acquired at 30Hz, is used to derive the tumor position. Occasionally, a tumor image is acquired to enable the updating of the correlation function. Four update methods are investigated. (a) Line shift. (b) Fit model — through point. (c) Fit model — extra weight. (d) Function difference — fit point. Results: Tumor and external surrogate motion demonstrates a high degree of correlation however it dynamically changes over time. Occasionally updating the correlation function leads to more accurate predictions than using external surrogates alone. At the lowest tumor imaging rate tested in this work (0.1Hz) an accuracy improvement of 10% over the prediction by the mere use of external surrogate was observed for the best update method. Update methods (a) and (b) derive the tumor position with larger accuracy than (c) and (d) in case of high imaging rates. The opposite is observed in case of low imaging rates. Conclusion: Occasional calibration of the tumor/external surrogate correlation during treatment substantially increases the accuracy of the tumor localization compared to tumor position derivation by using the external surrogate alone.

This work is partially supported by CenSSIS.
WE‐C‐ValA‐07: Statistical Analysis of Respiratory Motion and Knowledge Discovery
Authors: Wu H , Sharp G , Shmukler E , Shirato H , Jiang S
Published: July 2006

Purpose: Quantified characterization and better understanding of tumor respiratory motion is valuable for understanding of respiration, motion‐included treatment planning, online prediction, and real‐time control algorithm for dose delivery in image guided radiotherapy. There are two goals of this work: (1) to discover the correlation among various motion variables so that we can understand patient respiratory better and (2) to build an analytical system for online motion modeling and prediction during real‐time treatment delivery. Method and Materials: Statistical analysis of tumor respiratory motion has been performed over 48 real patient data. Quantified information of different motion characteristics, including amplitude, frequency, velocity and the mean positions are computed over different granularities. Sample granularities include a breathing state, a breathing cycle, a treatment session, a patient and the whole patient population. Association rules among different motion characteristics are mined and formulated. Results: We have implemented the software packages for statistical analysis and correlation presentation. Quantified motion information have been computed and displayed. The spatio‐temporal changes of these properties are studied. Knowledge of respiratory motion and the underlying physiological explanation have been exploited. The probability distribution functions of various correlations among different properties have been calculated and visualized. Conclusion: Different statistical analyses over a set of tumor motion characteristics have shown that there are some general rules regarding tumor motion. The analytical results help us to obtain new knowledge and to understand the physiological actions of tumor motion and to treatment moving tumor more efficiently. Conflict of Interest:
WE‐C‐224C‐01: Buried Emanation: The Dawn of Prostate Brachytherapy
Authors: Aronowitz JN
Published: July 2006

Although radical prostatectomy was introduced in 1905, few cases of prostate cancer were diagnosed at a stage amenable to curative resection. Megavoltage equipment that could safely deliver a curative dose of radiation to the prostate did not become widely available until the 1960's. To fill this therapeutic void, leading urologists often turned to brachytherapy. This presentation follows the development of intracavitary and interstitial techniques during the second and third decades of the 20th century.
WE‐C‐224C‐03: Analysis of Technical Failures in 1000 Clinical Applications of Pulsed Dose Rate Brachytherapy
Authors: Koedooder C , van Herten Y , van der Grient H , van Wieringen N , van de Kamer J
Published: July 2006

Purpose: Investigation of safety and reliability of Pulsed Dose Rate brachytherapy within and outside office hours.

Method and Materials: More than 1000 patients were treated with two first generation (1996–2004) and three second generation (starting 2004) PDR afterloaders (Nucletron, The Netherlands). The most frequently treated tumorsites were breast, esophagus, gynecology, prostate and bladder. The number of pulses and the overall treatment time ranged from 4 pulses in 30 minutes for esophagus to 62 pulses in 135 hours for anal carcinoma. Apart from treatment‐related parameters the type and frequency of technical failures, e.g. source obstruction, were registered for each treatment. From these data the fractions of disturbed pulses and treatments were determined for all tumor sites. Also the behavior of these fractions over time was studied. Results: Error frequency depended strongly on treated tumor site. For breast 149 out of 5936 pulses were disturbed (2.5%). For prostate the error fraction decreased from 16% in 11 patients to 11.7% after 49 patients. Gynecology scored well with only 28 disturbed pulses out of 2002 pulses given (1.4%).

For breast the first error most often occurred in the first pulse. For prostate and bladder the first error occurred in a further stadium of treatment. By applying dummy checkwire runs, errors with the active source occurred only rarely. Our experience is that 98% of the patients received the intended dose correctly. Only in 2% of the treatments an adjustment of implant geometry or planned dose or a cancellation of part of the treatment was necessary. Of these 2% however, about half was caused by medical rather than technical reasons. No significant difference was seen between the first and second generation afterloader type. Conclusion: Errors do occur and are tumor site dependent. Our experience however shows that PDR can be safely applied, also outside office hours.
WE‐C‐224C‐09: Calculation of the Dose Distribution Around a High Dose‐Rate 192Ir Brachytherapy Source Via a Multi‐Group Discrete Ordinates Method
Authors: Gifford K , Price M , Failla G , Wareing T , Horton J , Mourtada F
Published: July 2006

Purpose: To calculate the dose distribution around a high dose‐rate (HDR) 192Ir brachytherapy source in water by a multi‐group discrete ordinates code and compare with a benchmarked Monte Carlo calculated dose distribution. Methods and Materials: The multi‐group discrete ordinates code, Attila™ version 5.0.2 (Transpire Inc., Gig Harbor, WA) was used to calculate the dose distribution around the Nucletron microSelectron HDR source (Nucletron B.V., Veenendaal, The Netherlands). MCNPX 2.4.k was used to benchmark the deterministic calculations. The source was constructed with Solidworks (Solidworks Corp., Concord, MA), a mechanical design software. The constructed geometry of the source, dose scoring plane and sphere were exported in Parasolid® file format so that it could be imported into Attila.

MCNPX 2.4.k was used to compute the Monte Carlo dose distribution. 50 million histories were simulated resulting in standard errors of the mean of less than 5% at a point 7 cm from the center of the source. The source geometry was identical to that of the Attila run except for minor differences in modeling the source due to limitations of the MCNPX code.

Dose rate matrices were exported from both codes and imported into an in‐house data analysis software. This software overlaid the matrices and quantified the percent dose difference and distance‐to‐agreement for all points in the matrices. The number of points passing a 2%/2mm criterion were reported. Results: Attila calculated dose to within ±2% or 2mm for 99% of the points. The Attila calculations required approximately 38 minutes of CPU versus 568 minutes for MCNPX on the same CPU. Conclusions: The Attila multi‐group discrete ordinates code accurately calculated the anisotropy from the microselectron HDR source. Attila accurately calculated dose in an efficient manner.
WE‐D‐330A‐01: 3D Optical Imaging of Tumor Microvasculature and Viable Cell Distribution
Authors: Sakhalkar H , Wang Y , Oliver T , Dewhirst M , Oldham M
Published: July 2006

Purpose: The ability to image 3D global structure (e.g. microvasculature) and function (e.g. gene expression) in whole unsectioned tumors, in high‐resolution and with high‐contrast, is of significant present interest in cancer research. We have developed novel optical imaging techniques capable of reconstructing the 3D distribution of absorbance or fluorescence‐emitting sources in tumor tissue. Primary advantages include high spatial resolution and contrast, and ability to image a wide range of molecular probes.

Method and Materials: Constitutive RFP expressing HCT116 (human colon carcinoma) xenograft tumors were implanted in hind legs of nude BALBC mice. The tumor microvasculature was dual‐stained by in vivo tail vein injections of light attenuating isotonic ink and FITC lectin. The tumor was excised post‐staining and subjected to a fluorescence‐friendly clearing procedure to render it amenable for optical imaging. Quantitative images of microvascular density and viable‐cell distribution were reconstructed using tomographic algorithms from a set of transmission and fluorescent projection images acquired at multiple angles using appropriate filters, focusing optics and a CCD camera.

Results: Co‐registered, multimodal, high‐resolution and high‐contrast 3D reconstructions were achieved through large, (∼1cm) whole mount, murine tumor samples. Quality assurance tests indicated encouraging accuracy of reconstructed attenuation coefficients and geometry. The 3D reconstructed slices were juxtaposed with histological slices of the same tumor to reveal striking correlation between viable‐cell distribution and well‐perfused regions. A fluorescence friendly clearing procedure was identified.

Conclusion: We present a novel technique for multi‐modality optical imaging of 3D microvasculature and/or viable cell distribution in tumor tissue with unprecedented image resolution and contrast. The technique has potential to image a wide variety of tumor and normal tissue structure and function. Of particular interest is the potential to analyze the effect of anti‐angiogenic agents and radiation therapy on the response of the entire 3D tumor microvasculature network.