bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐D‐342‐01: Advances in Breast Imaging
Authors: Whitman G
Published: July 2008

Over the last decade, there have been tremendous advances in breast imaging. As many facilities make the transition from film screen to digital mammography, it is appropriate to examine the accomplishments of the past and to acknowledge current technological limitations. In addition, we should carefully study evolving technologies in breast imaging with the goal of developing highly sensitive and highly specific techniques. This presentation will examine recent progress in digital mammography, including contrast‐enhanced imaging, tomosynthesis, and breast CT, from a breast imager's perspective.

Randomized clinical trials and meta‐analyses have shown that screening mammography results in a decrease in breast cancer mortality. Although mammography is efficacious in most women, we know that mammography is not a perfect test, epecially in women with radiographically dense breasts. Furthermore, false positive and false negative mammograms are difficult to eliminate. As digital mammography replaces film screen mammography in many practice settings, cancer detection rates may rise slightly and call back rates may decrease slightly.

Overlapping densities and areas of dense tissue often make interpretation of film screen mammograms difficult. Overlapping parenchyma and dense tissue hinder digital mammography less than film screen mammography, but these overlying structures are not eliminated with digital mammography. Major efforts have been made in digital tomosynthesis and breast CT in order to advance beyond projection imaging. Tomosynthesis involves the acquisition of tomographic images in the digital mammography unit, while breast CT is based on a volumetric acquisition with the patient positioned prone in a machine that is similar to a unit used for stereotactic biopsies.

Conventional digital mammography, digital tomosynthesis, and breast CT may be combined with the injection of iodinated contrast material in order to visualize tumor vascularity and increase the conspicuity of breast tumors. These techniques may also be used to monitor response to neoadjuvant chemotherapy.

Over the next decade, tomosynthesis and breast CT will transition from research applications to clinical realities. Further studies are needed in order to determine how to use these emerging tools in an effective, efficacious manner.

Educational Objectives:

1. To review advances in breast imaging over the last decade.

2. To understand the strengths and weaknesses of film screen and digital mammography.

3. To appreciate the potential roles of digital tomosynthesis and breast CT.

4. To understand the application of iodinated contrast material in digital mammography, tomosynthesis, and breast CT.
TU‐D‐342‐03: Contrast‐Enhanced Breast Imaging
Authors: Maidment A
Published: July 2008

For almost 70 years mammography has given insight into breast morphology, allowing cancer detection based on the gross impact of the disease upon body. The advent of tomographic techniques has allowed visualization of morphologic perturbations at a much smaller scale using various techniques including digital breast tomosynthesis (DBT), computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI).

An alternative strategy to improve early detection is to search for functional changes. In 2007, the American Cancer Society revised their breast cancer screening recommendations. Annual screening by mammography is still recommended for women at low‐to‐medium risk for breast cancer; however, women at high risk for breast cancer are now recommended to have annual mammography and MRI. This recommendation is supported by studies which show that MRI is capable of demonstrating mammographically‐occult breast cancer both in both screening and diagnostic populations.

Contrast‐enhanced (CE) radiographic methods, including CE‐mammography, CE‐DBT and CE‐CT, have the potential to rival breast MRI as a sensitive method for diagnosis and screening of breast cancer. In a pilot study of CE‐DBT conducted at the University of Pennsylvania, suspicious enhancing lesions were demonstrated in 14 of 15 cases of breast cancer. The pre‐contrast tomosynthesis images demonstrated lesion morphology and border characteristics in greater detail than digital mammography, while the subtracted contrast‐enhanced tomosynthesis images demonstrated the vascular characteristics of the breast lesions in a manner consistent with breast MRI.

Further advances in CE imaging will be predicated upon shifting our attention from imaging perfusion to imaging specific molecular/cellular events. Research is ongoing in the discovery of specific biological prognostic factors, the development of appropriate imaging technologies and imaging agents, and the adaptation of these technologies to image‐guidance and monitoring of therapeutic interventions.

Educational Objectives:

1. Review the development of contrast‐enhanced breast imaging.

2. Evaluate the results of the existing contrast‐enhanced clinical trials.

3. Examine the clinical roles for contrast‐enhanced imaging.
TU‐EE‐A1‐05: Exploring the Spatial Trade‐Off in Treatment Planning
Authors: Schlaefer A , Blanck O
Published: July 2008

Purpose: To include spatial information during multi‐criteria treatment planning. Particularly, to study whether constrained optimization on the voxel level allows to deliberately trade‐off the dose delivered to one region of a volume of interest (VOI) with respect to other clinical goals. Method and Materials: We extended a stepwise optimization method for robotic radiosurgery to interactively modify dose constraints on a voxel level. The optimization problem is solved using linear programming, and every term in the objective function is matched by a corresponding constraint. Clinical goals are addressed separately and maintained using the constraints. A trade‐off among the clinical goals is then explored by a series of optimization steps. For visualization, VOIs are represented by a 3D grid of spheres, where each sphere represents a voxel and can be selected in a 3D scene. Constraints on the dose in the selected voxels can be considered independently for subsequent optimization steps. The method was applied to a prostate case, where we studied trade‐offs with respect to the maximum dose in the rectum. Results: Relaxing the upper dose bound on a set of voxels in the prostate lobes by 150 cGy allowed to reduce the maximum rectum dose by 100 cGy. Likewise, a relaxation of the lower dose bound on a few voxels on the prostate surface by 100 cGy allowed to further reduce the maximum dose in th rectum by 157 cGy. Conclusion: Spatial information is not available from cumulative statistics typically used as criteria for treatment planning. Our results indicate that it is possible to include spatial information in interactive multi‐criteria optimization. The proposed method can be used when clinical goals can be expressed with respect to a subregion of a VOI. Conflict of Interest: Research partially sponsored by Accuray Inc.
TU‐EE‐A2‐04: Increasing the Efficiency and Radiobiological Relevance of IMRT Treatment Planning: Replacing Dose‐Volume Thresholds with Generalized Equivalent Uniform Dose Or Mean‐Tail‐Dose Metrics
Authors: Clark V , Chen Y , Fergus S , Deasy J
Published: July 2008

Purpose: Our goal is to validate treatment planning metrics that are computationally efficient yet have inherent radiobiological meaning, either directly or by correlating highly with more explicitly biological metrics. We show how mean‐tail‐dose and the generalized equivalent uniform dose (gEUD) metrics could be used to replace dose‐volume metrics in IMRT treatment planning. Method and Materials: gEUD and MOH/MOCx (mean of the hottest/coldest x% of a structure) are candidates for dose‐volume metric replacements due both to their averaging‐nature (closer to the expected radiobiology), as well as their convexity (and the linearity of MOH/MOCx), which allows for optimal solutions and faster optimization. We used datasets from both 3DCRT planning (219 lung/pneumonitis; 263 lung/esophagitis; 491 prostate) and IMRT (40 prostate; 398 head and neck). We calculated the Spearman's rank‐correlation coefficient between typical clinical dose‐volume metrics and these quasi‐radiobiological metrics with a range of values for the variable parameter (a for gEUD; x for MOH/MOCx). We also calculated the sensitivity and specificity values resulting from using the quasi‐radiobiological metrics to ‘predict’ violation of a clinical dose‐volume threshold. Results: We found high correlations between the proposed quasi‐radiobiological metrics and clinical dose‐volume metrics. Twenty‐seven out of thirty correlations tested had a Spearman correlation coefficient above 0.90 with highly significant p‐values. We also found, for many of the dose‐volume metrics, the associated quasi‐radiobiological metric was an excellent classifier. Conclusion: There is evidence from large datasets including both 3DCRT and IMRT patients that the biological metrics of gEUD and MOH/MOCx are highly correlated to traditional dose‐volume metrics and are fairly accurate for classifying acceptable from non‐acceptable plans. Many of the gEUD or MOH/MOCx metrics could be substituted for traditional dose‐volume constraints with a sensitivity and specificity well above 0.80. Conflict of Interest: Partially supported by a grant from Tomotherapy, Inc., as well as NIH R01 grant CA85181.
TU‐EE‐A3‐01: Breathing‐Motion Induced Tomotherapy Dose Delivery Errors in the Presence of Beam Modulation
Authors: Chaudhari S , Low D , Rangaraj D , Kintzel E , Goddu S
Published: July 2008

Purpose: To determine breathing‐motion induced Tomotherapy dose delivery errors in the presence of beam modulation. Method and Materials: Previous studies have shown that dose delivery errors are possible due to breathing motion. While these studies have systematically investigated the roles of field size, couch velocity, and breathing motion magnitude on the dose errors, they have neglected the role of intensity modulation. This study used measured breathing patterns and clinically realistic delivery parameters to simulate the breathing‐motion induced errors. Modulation was included by varying the simulated delivered dose on two timescales; the short timescale simulating the 51 angular subsets that subdivide the delivered fluence patterns. A step function was used that varied the leaves open and close time every 0.4 seconds, or every 7.0°, simulating a modulation factor of 2.0. Modulation was also conducted on a longer timescale corresponding to four beam intensity directions (two of high dose and two of low dose). The earlier studies using 52 patients' breathing patterns were repeated with the addition of fluence modulation. Results: The impact of breathing motion on Tomotherapy delivery results in delivery errors of greater than 10%, even for relatively small breathing motions. This is due to the subtle variation in the breathing patterns, including changes in breathing waveform and drifting. The addition of fluence modulation varied the delivered dose patterns slightly, but the magnitude of dose delivery errors was unchanged. Conclusion: These results indicate that previous simulations indicating the challenges of using Tomotherapy dose delivery due to breathing motion are valid in the presence of beam modulation. Treatment planners should take care when planning treatments for mobile tumors.

This work supported in part by Tomotherapy.
TU‐EE‐A3‐05: Simultaneous Tracking and Four‐Dimensional Radiotherapy Delivery: Accounting for Spatial and Morphological Tumor Changes
Authors: Keall P , Cho B , Poulsen P , Sawant A , Suh Y , Venkat R
Published: July 2008

Purpose: The aim of this work was to develop the formalism for, and experimentally verify, radiotherapy delivery to tumors undergoing spatial and morphological changes induced by respiration. Method and Materials: To determine the leaf sequence to be delivered at a given time based on a 4D plan, LPlan(M,θ), in which the leaf sequence varies not only with monitor units, M, but also respiratory phase θ can be summarized by
urn:x-wiley:00942405:media:mp2621:mp2621-math-0001 where T is the 3D target position and L are leaf positions. A 4D treatment plan of a translating, rotating, deforming tumor exhibiting hysteresis with values well above those typically observed clinically was created. The theory derived was coded into a prototype 4D MLC controller. The treatment plan was loaded onto the controller, and delivered on a linear accelerator. The motion was detected by the monitoring of the marker block by the RPM system. The RPM signal was output in real time to the MLC controller that reshaped the beam according to the position and phase of the incoming signal. An EPID, operating in cine mode was used as the detector. Results: The treatment plan from phase T0–T9 matched the real‐time EPID images. The EPID images demonstrate the ability of the MLC leaves, driven based on the theory derived above, to conform to spatial and morphological changes. Conclusion: A theory has been developed to deliver 4D plans in which the leaf sequences can vary as a function of phase to account for the spatial and morphological tumor and normal tissue changes with respiration. This theory has been integrated into a MLC controller. A 4D radiotherapy treatment plan that includes translation, rotation, hysteresis and deformation was delivered. The method allows for variable respiratory patterns during treatment delivery. Conflict of Interest: Research supported by Varian Medical Systems.
TU‐EE‐A4‐06: Fast DRR and CBCT Reconstruction On GPU
Authors: Després P , Lacroix F , Carrier J
Published: July 2008

Purpose: To accelerate the synthesis of digitally reconstructed radiographs (DRRs) and the reconstruction of cone‐beam CT (CBCT) data with the help of commodity graphics processing units (GPUs). The massively parallel architecture of GPUs allows significant improvements in execution speed for algorithms that present various levels of symmetry. Method and Materials: We have implemented DRR synthesis and CBCT reconstruction algorithms on GPUs and have compared their execution speed and accuracy with those of traditional CPU implementations. DRRs were obtained with an incremental version of Siddon's algorithm, an exact raytracing routine, while CBCT reconstructions were based on the FDK algorithm. The benchmarking was conducted with a nVidia GeForce 8800 GTX graphics board hosted in a 2.4 GHz Intel Quad Core PC. The Cg shading language was used for GPU programming, and all calculations were performed in single precision. Results: We have achieved execution speed improvement factors of 47x for DDR synthesis and of 100x for CBCT reconstruction with the GPU implementation. These figures, obtained with relatively large, clinically relevant datasets (512 Mb), could further be improved by using smaller datasets that fit entirely in the video memory. The DRRs obtained with the GPU implementation were identical to their CPU versions while the CBCT images presented slight differences (2% standard deviation), most likely due to discrepancies in the CPU‐GPU floating‐point rounding conventions. Conclusion: We have implemented on a streaming architecture two algorithms relevant to many branches of medical physics. We have achieved significant speed increase factors while preserving the accuracy of the results. The rapid development of GPU products sporting more memory, supporting double‐precision and running at higher clock speeds lets envision even faster execution and more accurate results, thereby opening the way to new, innovative applications in medical physics.
TU‐E‐350‐04: The Practice of Clinical Therapy Medical Physics
Authors: Hevezi J
Published: July 2008

Clinical Therapy Physics is the real “practice” of Medical Physics. Therapy Medical Physics is reimbursed explicitly and implicitly as having direct contribution to specific patient care — the only Medical Physics sub‐field with this advantage. Whether it is in establishing External Beam, IMRT, SRS or SBRT programs with IGRT or providing Brachytherapy (HDR & LDR) programs for cancer therapy, the Clinical Therapy Medical Physicist works in partnership with the Radiation Oncologist to provide quality services in cancer care. Supervision of dosimetrists and therapists, the other members of the radiation oncology team is an important part played by us.

Dr. Hevezi was Director of Medical Physics at the Cancer Therapy & Research Center for 15 years and built an important clinical therapy physics program there. A broad range of clinical services there included not only the above mentioned procedures, but procedures like Total Body Photon Therapy, COMS Eye Plaque therapy, and others. He currently serves as Lead CyberKnife Physicist with the South Texas RadioSurgery Associantion in San Antonio and directs Medical Physics graduate students in the University of Texas Health Science Center at San Antonio. Dr. Hevezi has been recently elected to the Board of Chancellors of the American College of Radiology where he serves as Chair of the Medical Physics Commission. He is current Chair of AAPM's Professional Economics Committee and most recent clinical interest is in developing the CyberKnife SBRT treatment modality for cancer therapy.
TU‐E‐352‐01: Medical Physics Education of Diagnostic Radiology Residents
Authors: Rzeszotarski M , Heintz P , Sprawls P
Published: July 2008

This session provides a forum for discussion of the progress made in improving diagnostic radiology resident education and some of the opportunities in education becoming available due to new technologies available to the teacher and student.

The first speaker will discuss the status of the curriculum for medical physics education of residents. At RSNA in November 2007, the AAPM medical physics resident curriculum committee met to review the first draft of new learning objectives which are being written for each section of the curriculum. The learning objectives are defined in three areas: 1) Fundamental Knowledge; 2) Clinical Application; and 3) Clinical Problem Solving. Radiologists and physicists are working together to develop these with a strong emphasis on clinical relevance.

The second speaker will describe the efforts of a task force formed under the leadership of William Hendee, Ph.D. (AAPM) and George Bissett, M.D. (RSNA) to develop free web‐based educational modules for radiologic science (medical physics) education of residents. Two modules have been developed: one on CT dose and a second on interventional radiology dose and safety. RSNA has agreed to host these modules on their web site and will make them available free of charge to any AAPM (physicists) or RSNA members (radiologists and residents). Most important, both AAPM and RSNA have contributed substantial funds to encourage the development of these education modules. Authors will receive $3,000–$4,000 for the development of each module. Approximately 50 modules are planned. A Request for Proposals has been distributed requesting authors to contribute modules. Each physics module must be authored by a physicist and a radiologist and must follow specific guidelines regarding content, objectives, required post test and the use of clinical materials in the educational process. These modules will be useful for both residents in training and radiologists in clinical practice through their maintenance of certification process.

The third speaker will provide a keynote lecture on “Evolving Models of Medical Image Physics and Technology Education.” See his abstract description for further details.
TU‐FF‐A1‐06: The Impact of Dose Rate Variations On Helical Tomotherapy Delivery
Authors: Harris C , Usynin A , Ramsey C
Published: July 2008

Purpose: Intensity modulated radiation therapy treatments using helical tomotherapy involve detector arrays which collect data and stores it in the form of sinograms. This detector data can be used to verify that treatments are being correctly delivered to the patient. The purpose of this work was to examine the dosimetric effect due to dose rate variations. Method and Materials: During a helical tomotherapy treatment, the intensity of a rotating fan beam is modulated using a 64 leaf binary multi‐leaf collimator (MLC). The beam passes through the patient and is incident on the detector array, where detector counts are stored as sinogram data. For this study, a total of 53 fractions were evaluated for two different patients (1 Prostate and 1 Head & Neck). MLC controller files, which run the delivery sequence for each fraction, were extracted from the data archive system, along with the treatment delivery sinograms from all fractions. Because machine output has a cyclical pattern, errors were first simulated as sine curves with magnitudes varying from 2 to 10%. Then machine output sequences were extracted from the treatment fractions and modified by using the actual variation. Results: After visual inspection, it was observed that machine output can vary anywhere from 0−3%. When error simulations were inserted, dose differences ranged from 0.6−3%. The results from inserting actual treatment error back into the delivery sequence show that, with even a 1% variation in output, the dose difference is almost 0.5%. Conclusion: The results show that dose differences for actual error insertions, while not very large, could still cause a discrepancy when routine QA is performed. Changes in machine output vary from patient to patient as well as from day to day, which can cause a difference in the planned and delivered dose.
TU‐FF‐A2‐06: The Verification of Respiratory‐Gated Radiation Treatments Using 3D Dosimetry Techniques
Authors: Brady S , Sakhalkar H , Maurer J , Yoo S , Adamovics J , Gluckman G , Oldham M
Published: July 2008

Purpose: This work investigates the feasibility of verifying respiratory gated treatments using a new 3D dosimetry system consisting of a radiochromic plastic (PRESAGE™) with optical‐CT readout. Method and Materials: Three identical PRESAGE™ dosimeters (5cm radius × 5cm length) were manufactured for insertion into a CIRS' Dynamic Thorax Phantom. CT scans of the phantom were acquired corresponding to 3 motion scenarios; (1) static CT (no motion), (2) moving non‐gated CT (free‐breathing), and (3) moving gated CT. In the moving scans, the PRESAGE™ insert sinusoidally oscillated in the sup‐inf direction with a 3cm amplitude and 4.5sec period. A simple plan with AP/PA parallel opposed beams was created in the Eclipse planning system to treat a simulated small lung nodule (1.5cm), central to the insert, for all 3 scenarios. The simple plan enabled accurate independent measurement using EBT films. Each plan was then delivered to the phantom twice, first containing the PRESAGE™ insert and second the EBT insert. The gated treatments were delivered using the Varian RPM gating system. The dose recorded in the PRESAGE™ dosimeters was determined by optical‐CT using a novel, fast, in‐house CCD based scanner, which acquired all data in ∼10min. The doses among PRESAGE™, EBT, and Eclipse were compared. Results: In the cases of static and moving gated treatments, excellent agreement (<1mm distance‐to‐agreement) was observed between the PRESAGE™ and EBT measurements. For the moving non‐gated treatment, good agreement was again observed between PRESAGE™ and EBT. Significant differences are seen between the PRESAGE™/EBT films and the Eclipse distribution due to the modeling effects of penumbral broadening at small fields. Conclusion: The combination of small field sizes and sophisticated gating techniques represents a challenging scenario for dosimetry verification. The PRESAGE™ /optical‐CT 3D dosimetry system is demonstrated to achieve high quality, fast, relative dosimetry verification of gating treatments.
TU‐FF‐A3‐06: Improving Tracking of Implanted Radio‐Opaque Markers On MV and KV Imaging with Techniques From Computer Vision and Machine Learning
Authors: Riaz N , Mao W , Wiersma R , Xing L
Published: July 2008

Purpose: Several groups have investigated implanting gold markers into tumors and tracking these markers with kV imaging during a radiotherapy treatment session. Our group has recently published an algorithm robust enough to detect moving markers in implanted tumors on kV and MV images. Our prior work is limited to tumors moving slower than 1.6 cm/s. Here, we expand on our prior work and the work by other groups by using techniques from computer vision and machine learning to improve the performance of the tracking algorithm and remove the need for any data‐set/patient specific parameters or breathing wave form data. Method and Materials: We replace the classification function in our prior algorithm with a support vector machine (SVM) classifier. To drop the need for data‐set specific thresholds, we use techniques from computer vision to examine additional features of the fiducial. Once a location is selected as a possible marker by template matching (correlation) we run a Sobel edge detector to trace the outline of the potential marker. With this outline, we can compute a series of morphological parameters, including the area, major and minor axis, and statistical moments. These additional features provide the SVM classifier with enough information to distinguish true and false markers without the need for data‐set specific thresholds or weights. To test our new algorithm, we image a moving MV phantom with two implanted markers, moving at various speeds. Results: We can now track markers on MV images moving at speeds between 1.6 cm/s to 3.14 cm/s with 95% efficiency. Conclusion: Compared to our prior approach and the approach of other groups, we can now track faster moving fiducials and do not require manual adjustment of threshold parameters.
TU‐FF‐A4‐03: Improving the Accuracy of Optical‐Emission‐CT Imaging Through Application of a Non‐Uniform Attenuation Correction
Authors: Kim E , Bowsher J , Sakhalkar H , Dewhirst M , Oldham M
Published: July 2008

Purpose: Optical computed tomography (optical‐CT) and emission tomography (optical‐ECT) are new techniques with demonstrated potential for imaging structure and function (including gene expression) in unsectioned tissue samples. This work presents the first attempts to improve the accuracy of optical‐ECT by incorporating an attenuation correction analogous to that applied in SPECT. Method and Materials: Optical‐ECT can be described as a linear system Ax=b, where x is the fluorescing distribution, b is the expected value of measured projections, and A describes the mapping from x to b. An in‐house code (Spect‐Map) originally developed for SPECT reconstruction was adapted for application to optical‐ECT. Verification of the method was performed by imaging a phantom containing a known distribution of fluorescing wires. Optical‐CT/ECT projections were taken consecutively to ensure accurate co‐registration. Attenuation‐uncorrected and ‐corrected optical‐ECT images were reconstructed by calculating A assuming zero attenuation and the optical‐CT‐measured non‐uniform attenuation, respectively. Successful preliminary verification led to the application of attenuation correction to optical‐ECT images of unsectioned human breast xenograft tumors which had transcribed fluorescing proteins labeling viable tumor burden (RFP) and HIF1 distribution (GFP). Results: Significant attenuation artifacts were observed in the uncorrected optical‐ECT image of the phantom. The middle wire appeared artificially less intense due to greater attenuation from the surrounding ink‐doped gel. This artifact was successfully removed in the attenuation‐corrected image, demonstrating basic performance of the method. Fluorescence intensities of the wires varied by as much as 29% in the uncorrected image versus 3% in the corrected image. Application of the attenuation correction to xenograft tumor images shows significant changes in apparent expression of fluorescing proteins. Interpretation and results will be presented. Conclusion: These results suggest that Spect‐Map has been successfully adapted to perform attenuation correction for optical‐ECT imaging. Preliminary xenograft tumor reconstructions indicate that attenuation correction is vital for accurate optical‐ECT imaging.
TU‐FF‐A4‐04: Comparison of Optical Diffusion Approximation and Delta P1 Approximation Models for Laser Fluence in Cancer Treatment
Authors: Elliott A , Scwartz J , Wang J , Shetty A , O'Neal D , Bourgoyne C , Hazle J , Stafford R
Published: July 2008

Purpose: Evaluation of competing optical models, the optical diffusion approximation (ODA) and delta P1 approximation for use in ablative laser cancer treatment of nanoparticles impregnated tumors. Method and Materials: Gold‐coated, silica‐core nanoshells, core diameter 180nm were placed in 1.5 wt% agar gel phantoms with nanoshell concentrations of 1.19×109 nanoshells/mL and 2.53×109 nanoshells/mL. Phantoms were cylindrical, 23 mm wide by 69 mm high and heated using laser powers of 0.64, 0.8 and 1.2Watts with 0.5cm spot size. Thermal images of heating were obtained using MRTI on a clinical 1.5 T MRI (Excite, HD, GE Healthcare Technologies, Waukesha, WI). MRTI uses a 2D fast, spoiled, gradient‐echo sequence, with field of view = 12 cm, slice thickness = 3 mm, , TR/TE = 74.5 ms/15 ms, FA = 30°. MRTI utilized the complex phase difference method to calculate temperature images, one image every 5 seconds for 300 seconds. Modeling the thermal response was performed with a finite element solution of the nonhomogenous heat equation using commercial software (Comsol Multiphysics®, Comsol Inc., Burlington, MA, U.S.). Results: For the 1.19×109 nanoshells/mL phantom both ODA and delta P1 give similar results with delta P1 being better overall, root mean square (RMS) difference between experiment and the model was 3 times greater for ODA than delta P1. For the higher concentration gel (2.53×109 nanoshells/mL) the RMS difference between experiment and the model was 4 times greater in the case of ODA compared to delta P1 with ODA failing to describe the experimental data in any adequate way. The greater accuracy of the delta P1 is attributed to its treatment of scattered and unscattered components of the light as separate entities. Conclusion: ODA works for lower nanoshell concentrations, but breaks down at higher concentrations. Delta P1 works well for all concentrations tested.
WE‐E‐AUD B‐04: Commissioning and Validation of the BrainLab Monte Carlo Dose Calculation Algorithm
Authors: Wu T , Labby Z , Al‐Hallaq H , Yenice K
Published: July 2008

Purpose: To validate the accuracy of photon beam modeling for a new commercially available Monte Carlo tool and to assess its performance in clinical settings. Method and Materials: The XVMC photon dose calculation algorithm has been commissioned for 6 MV and 15 MV Varian Trilogy beams with BrainLAB M3 and Varian Millennium MLC devices. Depth doses, profiles, and beam output factors were measured in water with photon diode and results were compared with those calculated by XVMC algorithm in the same geometry. The MLC characterization of beam models were tested in homogeneous phantoms for various combinations of MLC patterns using film and ion chamber measurements. The effects of leaf thickness, intra/inter‐leaf transmission, rounded leaf transmission have been investigated using film and ion‐chamber dosimetry. The accuracy of XVMC dose predictions in tissue inhomogeneities and near interfaces have been investigated with TLD, ion‐chamber, and film measurements in various inhomogeneous phantoms after measurements were corrected for dose in‐medium. Results: XVMC dose calculations in homogeneous phantom predicted the depth doses and profiles within 1%, indicating accurate modeling of beam energy spectra and penumbra, for both 6MV and 15 MV photon beam models using either collimating systems. The rounded leaf end and intra‐leaf transmission were modeled accurately within 2% as determined with film measurements. XVMC dose calculations in tissue inhomogeneities and near interfaces have been verified within 2–3% with TLD and ion chamber measurements, after the measurements were corrected for dose in medium. Conclusion: XVMC algorithm commissioned for 6 and 15 MV photon beams was shown to accurately predict dose buildup/down effects in tissue interfaces in clinically relevant situations increasing the ability to accurately calculate patient dose. Conflict of Interest: XVMC/iPlanDose4.0beta was provided under a clinical cooperation agreement with BrainLAB.
WE‐E‐AUD B‐05: Monte Carlo Dose Verification and Quality Assurance for Multi‐Target SRT
Authors: Lin T , Wang L , Fan J , Li J , Ma C
Published: July 2008

Purpose: To provide accurate, thorough and fast dose verification for hypo‐fractionated stereotactic radiotherapy (SRT) of small and multi targets planned with a Varian Eclipse treatment planning system delivered on a Varian Trilogy accelerator. Method and Materials: Seven brain and lung hypo‐fractionated SRT plans were generated by the Eclipse system for delivery on the Trilogy accelerator with the Millenium‐120 leaf multileaf collimator (MLC). These clinical SRT plans required thorough quality assurance measurements to obtain absolute point dose and 2‐D dose distributions due to the low number of fractions and high fraction dose. For small‐field and multi‐target plans, the EGS4/MCSIM code was used to calculate the dose distribution. A 0.125 cc ion chamber, a 0.016 cc pin‐point chamber and Kodak EDR2 film were used for the measurements and the results were compared with Monte Carlo calculations. Results: The dosimetry for small‐field and multi‐target treatment plans is challenging due to the comparable ranges of secondary electron and the field sizes defined by SRT MLC segments. Our Monte Carlo simulations can accurately reproduce the Trilogy dose distributions (within 1%/1mm). For the clinical SRT plans investigated in this work, the Monte Carlo doses agreed within 3% with ion chamber measurements and within 2%/2mm with film measurements. The doses calculated by the Eclipse AAA algorithm differed by no more than 5% from Monte Carlo calculations for small (4–40 cc) PTVs. Conclusion: Monte Carlo dose calculation provides accurate, thorough and fast dose verification for hypo‐fractionated SRT for small and multi‐target treatment plans generated by a Varian Eclipse treatment planning system on a Varian Trilogy accelerator.
WE‐E‐AUD C‐01: Prediction of Weight Loss, Tumor Response, and Set‐Up Errors For Head and Neck Patients
Authors: Seibert R , Ramsey C , Harris C , Usynin A , Robison B , Neeley M
Published: July 2008

Purpose: The objective of this study was to develop a novel tool using Kernel Classification that can be used to automatically identify patients that have, or will have, setup issues requiring intervention such as re‐simulation and/or re‐planning. Method and Materials: Inter‐Fraction motion was retrospectively analyzed for 43 H&N patients that were treated on a helical tomotherapy system. For each patient, CT images were acquired and transferred to the tomotherapy database for treatment planning and image‐guided patient setup. Both custom aquaplastic masks and a positioning mouthpiece were used in 10 of the 43 patients. Results: Fifteen patients had greater than 10% weight loss during the course of treatment. Six patients had a visible reduction in GTV volume. Immobilization effectiveness decreased as the tumors regressed in size and/or the patients lost weight. If the tumor regression was occurred then time could be scheduled to periodically check the mask fit and to make a new mask if needed. The kernel classification technique correctly identified all 43 H&N patients as either having normal or problematic setup using their respective shift data sets. Classifications were made using only the shift values from the first 14 treatments. The predictive performance seriously degraded when data from fewer than 14 treatments were used. However, adding more did little to improve the performance. Conclusion: This study demonstrated that the kernel regression classification method was able to correctly identify the cause behind IGRT positioning problems for H&N patients. The study validated that IGRT positioning problems cause abnormal problem‐specific distributions in the shift data without using statistical distribution tests. Since this technique is fully automated, it could potentially be used during IGRT sessions to help the therapists decipher the factors that hinder patient setup early in a patient's treatment so that the proper precautions can be in place.
WE‐E‐AUD C‐03: Determining An Appropriate Margin Around CTV to Account for Interfraction Motion During IMRT for Cervical Cancer Patients Based On Daily Imaging
Authors: Tyagi N , Lewis J , Vo D , Yashar C , Mell L , Mundt A , Jiang S
Published: July 2008

Purpose: To derive an appropriate CTV‐to‐PTV margin that will ensure delivery of 100% of the prescribed dose to 95% (on average) of daily CTV's during a treatment course. Method and Materials: Daily CBCT images are taken for setup of Stage I–IVa cervical cancer patients at our institution. Daily CTV contours drawn on these images take into account the effect of interfraction motion due to organ motion/deformation and tumor regression. To date, we have acquired CBCT data for 15 patients out of which 5 have been analyzed so far. On each CBCT, expert radiation oncologists manually segment CTV, bladder and rectum of that particular day. The CTV contours from all the CBCT scans of the same patient are superimposed on the planning CT scan after rigidly registering each CBCT scan to the planning CT scan. A uniform margin of 0, 3, 5, 7, 10, or 15 mm etc is added around the planning CTV and the average volume of CTV missed over all fractions is analyzed. The isotropic margin that encompasses 95% of daily CTVs on an average is considered adequate for the patient. Results: Statistical analysis of 5 patient's shows that a 7 mm margin is sufficient to cover on an average 98% (min: 95.2, max: 99.6) of daily CTVs of these 5 patients. However a bigger margin of 15 mm is required to adequately cover the high risk cervix region. The mean of the standard deviations in average volume of CTV covered for these 5 patients at 7 mm margin is 2.4 % indicating large inter‐patient variation. Analysis of more patients is required to reduce variation in average CTV volumes among patients. Conclusion: Clinical implementation of CBCT imaging devices has made possible margin evaluation based on daily images that provides a more accurate means of accounting for interfraction motion.
WE‐E‐351‐02: The Fusion of Molecular Imaging Into Clinical Medicine: A Role for AAPM?
Authors: Fullerton G
Published: July 2008

The accelerating introduction of molecular imaging into medicine holds promise for cures of numerous intractable diseases. In vivo measurements of pathologic details at the molecular level are on the horizon but substantial work on improved precision and accuracy are necessary before methods can be clinically useful. Accurate knowledge of spatial and temporal dimensions of molecular measures is necessary before such measures can be validated as biomarkers of clinically significant endpoints. These are functions that AAPM members have performed over and over again in medicine over the five decade history of the association. The extension into molecular imaging, however, requires even broader participation in multi‐disciplinary teams extending beyond traditional departmental boundaries of radiology and radiation oncology. This presentation reviews developments in molecular imaging and the growing need to fuse molecular events to the spatial framework of well known anatomical imaging methods. The process of translation requires participation in preclinical studies using animal models to validate methods in experimentally controllable environments. The AAPM can play an important role in this process at numerous levels. Members can participate in the design and testing of new instrumentation for both preclinical/animal and human uses. Members can also use well documented society methods for developing nationally acceptable imaging standards and procedures for assuring the quality of data. This is especially important when data is intended for the use of regulatory agencies such as the FDA to prove the safety and efficacy of new methods of medical care.

Educational Objectives:

1. Understanding the meaning of “molecular imaging”

2. Understanding the process for fusing molecular imaging into clinical medicine.

3. Understand the potential role for medical physics in applying molecular imaging.
TH‐SAMS‐AUD B‐02: Image Fusion for Target Definition
Authors: Ulin K
Published: July 2008

Imaging studies acquired at multiple times and using different modalities are important components to many clinical trials. Imaging is used for staging and protocol eligibility, for radiation therapy target definition, for adaptive radiation treatment delivery, for assessing response to therapy, and for outcome analysis. Currently co‐registration of CT, MR and PET scans may be important for any of these purposes; in the future, molecular and biomarker imaging may be incorporated.

The challenges for the QA centers are to verify that institutions participating in protocols requiring image registration have the tools and expertise to perform the registrations, and to verify the appropriate registration for individual protocol patients. There are many software systems, many with multiple methods, available for image registration.

One method to credential institutions is by benchmarking. QARC's “image fusion” benchmark requires the institution to download a DICOM MR and a DICOM CT scan set. The datasets are to be registered, the small lesion is to be outlined on the MR scan, and the geometrical center of the lesion on the CT scan is to be reported (lesion not visible on CT). Results from more than 50 institutions will be discussed.

An increasing number of protocols require PET imaging. Registration of PET imaging is problematic, except for PET/CT. Since the DICOM standard does not include specifications for SUV calculations, currently only ACRIN, by using the manufacturers' workstations, is able to receive PET images and recalculate SUVs. Ideally these PET images would be registered with the planning CT in radiotherapy protocols.

More and more protocols propose requiring IGRT, particularly for treatments with few fractions. For protocol participation, institutions need to demonstrate the reproducibility and accuracy of the imaging system used to adapt the daily treatment to the daily target position. Extensive questionnaires (QARC) and submission of representative patient data (RTOG) are required by the QA centers. The variety of systems — MV CT, kV CT, Tomotherapy, Cyberknife, ultrasound — provide a challenge for the QA center.

An even greater challenge is how to provide QA for individual patient treatments. If CT/CT or CT/MR registration is used for target delineation, assessment of the registration presents the QA center with several questions. Should the QA center redo the registration? What tools can be developed to register and verify CT/PET registration? For adaptive radiotherapy, what is the benefit of reviewing the daily assessment of required repositioning? Is the benefit worth the cost of such an effort?

Educational Objectives:

1. Understand the issues faced by the QA centers in reviewing image registrations.

2. Understand the difference between credentialing and providing individual patient QA for image registration.

3. Become familiar with the current strategies of QA for image registration by the QA centers.
TH‐SAMS‐332‐02: ACR CT Accreditation Overview
Authors: Hernandez D
Published: July 2008

The American College of Radiology CT accreditation program was launched in 2002. It has approximately 3320 active units and is growing daily.

All sites that apply for CT accreditation receive a testing packet with the necessary paperwork and labels required for their testing material submission. CT accreditation involves the submission of clinical and phantom images. Qualified radiologists and medical physicists review all submissions.

The medical physicist plays a vital role in the achievement of ACR accreditation. A team approach involving the supervising physician, lead technologist and medical physicist is necessary to ensure that all information is accurate and appropriate for ACR accreditation submission.

For sites with filming capability, the phantom testing images are submitted on hard copy film. As more and more sites become film‐less, the need for electronic submission of phantom testing material has increased. Sites that have no filming capability can call the ACR and receive permission and instructions for submitting the CT phantom images electronically. Electronic phantom submission is currently a pilot program as the ACR actively works to define the process.

Educational Objectives:

1. Understand the basic materials and process of ACR CT accreditation.

2. Understand the importance of a “team approach” in achievement of ACR accreditation.

3. Understand the process of electronic submission of the CT phantom images.
TH‐B‐352‐01: Current IHE Topics: Mammography Display and CD Export
Authors: Flynn M , Peck D
Published: July 2008

As a collaboration of professional societies and companies, Integrating the Healthcare Enterprise (IHE, www.ihe.net) seeks to establish methods wherein health computer systems can communicate to achieve specific functional objectives. IHE profiles define the detailed requirements that systems must meet in order to achieve the objective. These requirements often involve DICOM and HL7 standards. Periodic industry test sessions (called Connectathons) are used to demonstrate the conformance of specific products. Health domains include Radiology and Radiation Oncology. AAPM along with RSNA, SNM, and SIIM are member organizations and about 100 companies also participate. We focus this year on two recent IHE efforts which impact diagnostic radiology.

1.)Radiology: Mammography Image (MAMMO) Integration Profile. In the Radiology Technical Framework, the MAMMO profile specifies how DICOM full field mammography images are created, exchanged, and used.

The detailed specifications are supplemented in the IHE Radiology: Mammography User's Handbook. This profile provides important requirements for department implementing a mammography PACS system with workstation interpretation. Of particular importance are display specifications regarding presentation size, CAD overlays, and presentation states.

2.)Radiology: Portable Data for Imaging (PDI) Integration Profile. This profile specifies methods that allow patients and referring physicians to obtain and view diagnostic images and reports. It is not intended to provide archival solutions. Use in operating rooms is specifically delineated. The use of CD media is specified along with both web based viewing support and DICOM standard CD records that can be imported and/or viewed by DICOM devices. The profile has taken on recent importance due to chronic problems in surgical specialties resulting from the prevalent use of proprietary formats on exported CDs. A problem now considered by the AMA to be a patient safety issue.

Educational Objectives:

1. Understand from two examples how the IHE profiles impact diagnostic radiology PACS.

2. Learn how recent mammography profiles can be used when specifying systems for digital mammography reading.

3. Understand how to avoid problems when exchanging image data between institutions.