bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐D‐BRB‐08: Validation of the Commissioning of an Optically Stimulated Luminescence (OSL) System for Remote Dosimetry Audits
Authors: Aguirre J , Alvarez P , Amador C , Tailor A , Followill D , Ibbott G
Published: August 2010

Purpose: Validate an Optically Stimulated Luminescence (OSL) dosimetry system based on the microStar® reader and a batch of nanoDot dosimeters from Landauer for use by the Radiological Physics Center (RPC). Materials and Methods: The factors involved in the calculation of dose from OSL, the calculation algorithm and the results of the commissioning were previously presented (AAPM 2009). The steps for determining dose from OSL were designed to resemble those used by the RPC for the TLD remote dosimetry audit program. As with TLD, the OSL dosimeters are irradiated in acrylic miniphantoms under standardized geometric conditions. The steps for a reading session, criteria for the number of dosimeters, readings per dosimeter, interspersing of “standard” and “control” dosimeters, and quality control steps have been determined. A method was developed and tested for the determination of the individual OSL correction factors used for the large number of OSL dosimeters (4,000) employed by the RPC. Validation of the process and assessment of the accuracy of the OSL system were performed through comparisons against TLD results. TLD and OSL were irradiated sequentially multiple times with photon and electron beams of varying energies at MD Anderson and at several other institutions and the results were compared. Results: Under reference conditions (60Co beam), the ratio of the OSL dose, read as described above, to ion chamber dose had a mean value of 0.997 ± 0.5% (1 SD). TLD versus OSL comparison based on irradiations at MD Anderson were within ±2%. The results from eleven institution agreed to within 1.1% for photon energies (60‐23MV) and electrons (5–23MeV). Conclusion: The OSL system has been commissioned and validated as an RPC remote audit tool for verification of beam output of photons and electron beams and electron energy. Work supported by PHS CA010953 (NCI, DHHS)
WE‐D‐204B‐03: Evaluating Intra‐Fractional Prostate Motions by Post‐Treatment PET/CT Imaging in In‐Vivo Verification
Authors: Hsi W , Indelicato D , Vargas C , Duvvuri S , Li Z , Palta J
Published: August 2010

Purpose: To evaluate intra‐fractional prostate motion by post‐treatment PET/CT imaging in in‐vivo verification. Methods: A total of 50 PET/CT imaging studies were performed immediately after daily proton therapy treatment through a single lateral portal. The PET/CT and planning CT were registered by matching the pelvic bones, and the beam path of delivered protons was defined in‐vivo by the positron emission distribution seen only within the pelvic bones. At each fraction treatment, a beam path defined by the fiducial markers seen in the post‐treatment CT is used as a surrogate for the intended beam; it can be different from its planned location at initial treatment planning due to a translational shift during the patient positioning. The discordance between the PET‐defined path and the intended path were derived. The PET‐defined path was compared to the positron‐emission distribution in lipomatous tissues around prostate to determine whether the prostate motion occurred before or after beam delivery. Results: For 30 of the 50 studies with small discordance between the intended and PET‐defined paths, average displacements are 0.6 mm and 1.3 mm along anterior‐posterior (DAP) and superior‐inferior (DSI) directions, respectively. For the remaining 20 studies demonstrating a large discordance, 13 studies also show large misalignment while 7 studies show no mismatch between the field edge and the positron emission distribution in lipomatous tissues around the prostate. The standard deviations for DAP and DSI are 5.0 mm and 3.0 mm are for these 13 studies, and 4.6 mm and 3.6 mm for last 7 studies. Conclusion: Systematic analyses of proton‐activated positron emission distributions provide patient‐specific information on prostate motion and patient position variability during daily proton beam delivery. Small fraction of PET/CT studies (approximately 14%) with ∼4‐mm displacement variations may require different margins. Such data are useful in establishing patient‐specific planning target volume (PTV) margins
WE‐D‐204B‐06: Does the Shape and Size of Clinical Target Volume Affect the Planning Target Volume Margin?
Authors: Zheng B , Liang J
Published: August 2010

Purpose: Recipes for margin design generally depend on clinical target geometric variation/motion characterization (the mean and the Standard Deviation). Tumor specific geometry was not considered. This study is to investigate the influence of the shape and size of a CTV on the design of non‐uniform margin. Method and Materials: Criterion of the target margin design is to ensure that at lest 95% probability of CTV occupancy is inside the PTV. The random error and the systematic error were considered separately in our margin calculation. Target margins are represented by kr−95σr and ks−95σs for compensation of the random error and the systematic error respectively, where kr−95 and ks−95 are coefficients, σr and σs are the SDs of the random error and the systematic error. We evaluated the value of kr−95 and kks−95 for CTVs with different shape and size. The shapes of CTV were chosen as point, sphere, cylinder and concave shapes. Results: For the random error, kr−95 is 2.79 for the point CTV. For the sphere CTVs, kr−95 is in the range of (1.65, 2.79). The upper and lower bounds correspond to the sphere size with zero and infinite large radius. The kr−95 for the cylinder CTV is in the range of (1.65, 2.45), the actual value for any surface point depends on its position and cylinder size. For points at the concave region, kr−95 depends on the local shape, and it could be less than 1.65. For systematic error, no matter what the shape and size the CTV is, the ks−95 is always 2.79. Conclusion: In addition to the random error of target position variation, the target margin also depends on a CTV's shape and size. However, for the systematic error of target motion, the shape and size of a CTV have no effect on the target margin design.
WE‐D‐204B‐07: The Effect of Uterine Motion and Margins on Doses in Intensity Modulated Radiation Therapy of Cervical Cancer
Authors: Gordon J , Weiss E , Abayomi O , Dogan N
Published: August 2010

Purpose: In cervical cancer, uterine motion can be large relative to cervix motion. Target vs normal tissue (NT) dose tradeoffs are quantified using published motion estimates and margins derived from standard formulas. Methods: 10 anonymized cervical cancer patients had prescription dose of 48.75Gy over 25 fractions. Plans were created with a uniform 1cm margin (PTVA), and a margin tapering from 2.4cm at the uterine fundus to 1cm at the cervix (PTVB). These were combined with motion model 1 (MM1) in which all structures moved normally with 3mm standard deviation (SD), and motion model 2 (MM2) in which the motion SD increased from 3mm at the cervix to 7.5mm at the fundus. 3mm SDs (1cm margins) are consistent with measured cervix motion, usually extrapolated to the entire PTV (upper vagina+cervix+uterus). 7.5mm SDs (2.4cm margins) are consistent with more recent uterine motion estimates. Plan evaluation utilized dose volume histograms (DVHs). Results: For MM2, PTVA gives inadequate dose to the fundus and CTV. The 95th percentile of fundus D98 dose, denoted D98,95, drops from 49.8Gy in MM1 to 44.5Gy in MM2. Target dose is restored by using PTVB. However, NT volumes receiving doses of 30–50Gy increase by up to 11%. Half the increase can be attributed to the normal tissues' own motion moving them into the radiation field, the other half to the expanded margin in PTVB. Conclusions: For a uniform 1cm margin, larger uterine motion reduces fundus dose by about 5Gy and increases NT volumes receiving 30–50Gy by ∼5%, relative to plans where the uterus has cervix‐like motion. Use of a tapered margin (PTVB) can restore fundus and CTV dose, but will increase NT volumes receiving 30–50Gy by a further ∼5%. Use of percentile doses and DVHs is a useful method of evaluating the dosimetric effect of different motion scenarios.
WE‐D‐204B‐09: Interfraction Variability of Tumor Motion Trajectory from Serial 4D Cone‐Beam CT Imaging during Audio‐Visual Biofeedback
Authors: Vile D , Hugo G , Weiss E , Lu J , Roman N , Williamson J
Published: August 2010

Purpose: To quantify interfraction variations in position, volume, and intrafraction breathing motion trajectory of lung tumors and critical structures with 4DCT and 4D cone beam CT (4D CBCT) images, for patients undergoing audiovisual biofeedback. Method and Materials: A pretreatment 4D fan beam CT (4DCT) and 35–40 daily 4D CBCTs were acquired daily throughout the treatment for 7 non‐small cell lung cancer patients. The tumor, esophagus, and trachea were contoured for all 10 phases of each CT. Each phase‐specific image was registered manually on bony anatomy to the end‐inhalation phase image from the 4DCT. The centroid and volume of each structure were calculated for each phase, and used to quantify the variability of the tumor and critical structure locations during each fraction. The tumor volume, relative to its end‐inhalation volume on 4DCT, was calculated for end‐inhalation and end‐exhalation phases for each fraction. The mean position of each organ, relative to the 4DCT, was calculated for each 4D CBCT scan. Results: Analysis has been completed for one patient to date consisting of 27 fractions, consisting of 7 4D CBCTs. Over the course of treatment, the tumor volume at end‐inhalation decreased by 31%. The systematic (random) error in mean tumor position was found to be 0.12cm (0.14 cm), 0.29cm (0.12 cm), and 0.31cm (0.62 cm) in the mediolateral, anterior‐posterior, and superior inferior directions respectively. These were large in comparison to the average range of tumor motion, which was 0.09cm, 0.21cm, 0.25cm in the corresponding axes. The corresponding ranges of motion over the treatment course, were 0.06–0.13cm, 0.14–0.26cm, and 0.12–0.42cm. Conclusion: For this patient, the interfractional variation in mean tumor position was the dominant variation with fraction‐to‐fraction changes as large as 2 cm. Audiovisual biofeedback did not adequately control these baseline variations. Supported by Grant P01 CA 116602
WE‐D‐201C‐01: Advanced Ultrasound Imaging in Interventional Medicine
Authors: Boctor E
Published: August 2010

Minimally invasive ultrasound‐guided ablative procedures are a promising therapeutic option in many patients with primary liver cancer or isolated hepatic metastases. However, the effectiveness of thermal ablation is currently limited by the lack of precision in the ablation probe placement at the tumor site, and the inability to monitor the progress and document success of the thermal lesion. In this presentation, we will introduce an integrated platform that can utilize 3D ultrasound imaging for both guidance and monitoring of ablative therapies. We will present a rapid US‐based approach to monitor ablative therapy based on elasticity imaging. Also, we will highlight new applications for elasticity imaging in guiding interventions, including multi‐modality registration, and visualization.

Learning Objectives:

1. Understand the limitations of current ablative monitoring methods.

2. Review solutions based on ultrasound technology.

3. Understand the potential advantages/disadvantages and future applications of elasticity imaging in monitoring and guiding ablative therapies.
WE‐D‐201C‐03: Ultrasound Modulation of the Blood‐Brain‐Barrier for Targeted Drug Delivery
Authors: McDannold N
Published: August 2010

The blood‐brain barrier is a primary limitation to the use of many drugs in the central nervous system. This barrier, which normally serves to protect the brain, with few exceptions limits the delivery of only small molecules from the circulation. We have found that when relatively low‐intensity ultrasound bursts are combined with circulating microbubbles (commercially‐available ultrasound contrast agents) that the blood‐brain barrier is temporarily disrupted for a few hours with little or no other effects in the brain. The ultrasound beam can be applied transcranially, resulting in a potential noninvasive means to target drugs to the brain. To date we have demonstrated this technique in small animal models. If this technology can be translated to humans, it could provide new opportunities for the development and use of drugs in the brain.

Learning Objectives:

1. Learn how ultrasound and microbubbles are applied for blood‐brain barrier disruption

2. Identify histological effects of the ultrasound exposures that have been observed in animal studies

3. Learn about potential mechanisms that might be involved with the disruption

4. Learn how ultrasound can be focused into the brain transcranially and potential methods to guide the procedure.
WE‐D‐201B‐02: Cardiovascular MR Imaging: Recent Improvements in Speed, Resolution, and Contrast
Authors: Riederer S
Published: August 2010

Within the last decade a number of “parallel acquisition” methods have been developed which allow reduction of acquisition time in MRI. With these, the MRI signal is simultaneously measured by multiple receiver coils, and the redundancy of information allows reduction in the number of necessary measurements. Such methods are particularly well suited to cardiovascular imaging, for which 3D images are generally desired. The practical limit of acceleration is primarily limited by the geometry of the RF receiver coils. MRI systems having coil arrays consisting of several dozen or more elements are becoming commonplace. Of these elements, eight or more might be activated for any one scan. When used in conjunction with other techniques, accelerations of ten‐fold or more can be routinely obtained.

Even with acceleration methods, the generation of a high spatial resolution 3D MRI data set still requires scan times on the order of ten seconds or more. However, the unique aspect of MRI compared to other modalities that the data are acquired in Fourier space allows the reconstructed image to appear as if it were acquired in a much smaller time. This is allowed by preferential sampling of the low order spatial frequencies of Fourier space. These advances in parallel acquisition and in effective ordering of Fourier sampling now permit contrast‐enhanced MR angiograms which are markedly superior in spatial and temporal resolution to what they were a decade ago. This thus addresses what is perhaps the principal disadvantage of MRI vs. other modalities for cardiovascular imaging, namely relatively long scan time. The intrinsic advantages of MRI thus can become a greater determinant of its ultimate utilization. These include the 3D nature of the data, the lack of ionizing radiation, the relatively small contrast dose, and the high vascular signal.

This presentation will briefly review the physics of the acceleration techniques, discuss the unique synergistic benefits of implementation in cardiovascular imaging, and illustrate the various points with results from multiple in vivo imaging studies.

Learning Objectives:

1. Understand recently developed physics techniques which have allowed a 10x improvement in the speed of data acquisition for MR cardiovascular imaging

2. Understand the impact of improved speed on improvements in image quality.

3. Understand some of the relative advantages of MRI vs. other modalities in imaging the cardiovascular system.
WE‐D‐201B‐04: Advances in Instrumentation and Techniques for Quantitative Myocardial Perfusion SPECT
Authors: Tsui B
Published: August 2010

Myocardial perfusion (MP) SPECT (single‐photon emission computed tomography) is a leading diagnostic tool for cardiovascular disease. Its continued importance and popularity have been fueled by new advances in instrumentation and image reconstruction and processing methods. Quantitative three‐dimensional (3D) image reconstruction methods that model the counting statistics in the acquired data and the physics of the imaging process have been widely adopted in clinical practice. They provide improved reconstructed image noise and accurate compensation of image degrading factors including collimator‐detector blur, and photon attenuation and scatter in the patient resulting in significant improvement in both the quality and quantitative accuracy of MP SPECT images. Extension of the quantitative 3D image reconstruction method to four‐dimensional (4D) has been shown to benefit 4D gated MP SPECT. Special collimators designed to provide both improved spatial resolution and increased detection efficiency have been developed and implemented on conventional SPECT systems for application to MP SPECT. The need to provide accurate attenuation compensation and anatomical correlation with MP information for individual patient has resulted in the development of multimodality SPECT/CT systems which have become standard system configuration. More recently, dedicated cardiac SPECT and SPECT/CT systems have emerged in the market place that hold great promise to advance MP SPECT a big step forward. The presentation will describe the basic principles of quantitative 3D and 4D image reconstruction methods. Advances in special collimation and SPECT/CT system designs for MP SPECT will be presented. The improvement in image quality and quantitative accuracy will be demonstrated by simulated, experimental phantom and clinical images.

Learning Objectives:

1. Describe the basic principles of quantitative 3D and 4D image reconstruction methods that have led to significant improved quality and quantitative accuracy of 3D and 4D gated myocardial perfusion and SPECT images.

2. Describe the recent advances in instrumentation for improve myocardial perfusion SPECT.

3. Demonstrate the advances using simulated, experimental phantom and clinical MP SPECT images.
WE‐E‐203‐02: Collaborative Teaching; a Model for Enriching the Medical Physics Learning Environment
Authors: Sprawls P
Published: August 2010

The classroom remains a valuable element in medical physics education because it brings the learners (students, residents, etc.) into direct contact with knowledgeable and experienced medical physicists who can motivate and guide the learning process. A longstanding limitation of the traditional classroom is its separation and isolation from the actual physical realities (medical imaging procedures, radiation therapy applications, etc.) that are being studied.

Most learning facilitators (medical physics teachers) recognize the effectiveness and value of high‐quality visuals for the classroom as a “window” to the world of physical reality. It is generally not practical or efficient for each teacher to produce all of the visuals needed for his or her classroom activities. This is a limitation because of time, resources, and probably the experience and skills to produce effective visuals.

The objective of the Collaborative Teaching Model and Project reported here is to enrich medical physics classrooms and collaborative learning discussions by providing high‐quality and effective visuals as an open and free resource that eliminates the limitation of efficiency for individual on‐site teachers and institutions. The collaborative model is composed of the synergistic combination of many on‐site class/conference room teacher/facilitators and a centralized supporting facilitator. Each makes specific and unique contributions to the learning environment.

The on‐site classroom teacher/facilitators contribute to the learning environment and process in many ways. They provide knowledge and experience that is specific to the local applied physics and clinical environment, have an interactive relationship with the learners, motivate and guide the learning process, and play a major role in helping the learners understand and apply the science and technology to clinical procedures.

The centralized supporting facilitator translates extensive career experience into high‐quality visuals and related materials that are available online as an open resource (http://www.sprawls.org/resources) to all learning facilitators and learners around the world.
WE‐E‐203‐03: Encyclopaedia of Medical Physics EMITEL
Authors: Tabakov S , Sprawls P
Published: August 2010

The Encyclopaedia of Medical Physics EMITEL was developed under the EU pilot project European Medical Imaging Technology e‐Encyclopaedia for Lifelong Learning. This reference material includes 3400 encylopaedic entries (approximately 2100 pages), supported by thousands of illustrations. All materials are available free at the web site www.emite12.eu.

The work on the project was initiated in 2001 and its main development was from 2006 to 2009. The core project Consortium includes specialists from King's College London (Contractor) and Ring's College Hospital, University of Lund and Lund University Hospital, University of Florence, AM Studio Plovdiv and the International Organization for Medical Physics (IOMP). Later the contributors grew to more than hundred (listed at the web above).

The articles (entries) in the Encyclopaedia are grouped in 7 categories ‐ Physics of: X‐ray Diagnostic Radiology, Nuclear Medicine; Radiotherapy; Magnetic Resonance Imaging; Ultrasound Imaging; Radiation Protection and General terms. Each entry is refereed.

EMITEL used as background a specially developed database of specific terms covering the main areas of Medical Physics (listed above). These terms (article titles) were translated into 25 languages by specially formed Working groups. Thus the Dictionary associated with the Encyclopaedia includes: English, Swedish, Italian, French, German, Portuguese, Spanish, Bulgarian, Czech, Estonian, Greek, Hungarian, Latvian, Lithuanian, Polish, Romanian, Russian, Slovenian, Bengal, Chinese, Iranian, Arabic, Malaysian, Thai, Turkish.

The web site is build with two Search Engines ‐ one searching into the Lists of terms (in all languages) and another one searching inside the text of the articles. The latest allowed significant increase of the potential of the e‐Encyclopaedia, including search for related terms, acronyms and synonyms. To use this facility the user has to select Search in Full Text and specify the category/area of the search (as described above).

EMITEL includes also a Content Management System, allowing future editing and update.
WE‐E‐203‐05: Medical Physics Teaching Opportunites in an ITunes World
Authors: Watchman C , Jang S , Hamilton R
Published: August 2010

Introduction: Today's students have come up in a world where online audio and video content is widely available. Through the use of television production and iTunes, increased opportunities for out of the classroom learning are available. Method and Materials: During the last three years at the University of Arizona, we have used the medical TV resources in our institution to record our medical physics courses. The class studio is equipped with computers, pad camera and video players. An integrated teaching environment is achieved where one may transfer from traditional “chalk board” (pad camera) methods to advanced computational and video presentations. In class lectures proceed as normal with the inclusion of microphones for recording. Lectures are then placed on University iTunes with in a few days of class. Recordings of past years lectures are made available to the students in addition to the current instructor's lectures. Video podcasts of advanced topics not covered in lectures can also be made available which may allow for instructors to maintain course schedules. Other laboratory podcasts may also be developed for QA, machine engineering and machine operation. These will allow for students to participate in labs independently outside of normal clinic hours. Results: Students have multiple opportunities to review the lecture and other material regardless of class time. Content that may have been missed due to illness or other absence may still be covered. Additionally, competing course schedules may now be accommodated without rescheduling class times. Use of the TV/iTunes system has allowed for students in any semester to view the same topic from multiple instructors. This has given a diversity of presentation which may allow for students to better understand topics. Conclusion: Use of video lectures and podcasts in an integrated iTunes environment allows for increased opportunities for learning for medical physics students.
WE‐E‐203‐06: Pilot Study of Interactive Physics Course for Radiation Oncology Residents
Authors: Becker S
Published: August 2010

Purpose: Pilot a new approach to teaching physics to Radiation Oncology residents that seeks to maximize the learning experience under the constraint of limited class time provided for teaching. The pilot is limited to a few lectures during the year. Method and Materials: Class time is devoted to the interactive learning of the key concepts instead of reciting the text book by rote to the students by means of prepared in‐class lectures. Two types of classes are given. The first class is spent asking the residents prepared questions on the key concepts of the subject material. These questions involve no calculations and are multiple‐choice. The second class consists of reviewing problem set questions that were distributed beforehand. The residents are encouraged to teach each other to help the class understand the concepts and problem solving methods with the instructor acting as the guide in the process. In order to be prepared for class, the residents are required to review the material beforehand. To facilitate this, audio/visual (A/V) lectures are created in Adobe Captive for them to view. These lectures are kept short (∼20 min) and are focused on the key concepts instead of the details. Results: The residents viewed the A/V lectures and came to class prepared for discussion. The in‐class question sessions on concepts supported by a group learning approach enabled the residents to teach their peers and focus on the essential material. The problem sessions allowed them to apply their knowledge of the concepts to learn the details and calculation process. Conclusions: This pilot study has been successful as evidenced by the residents' increased exam scores and attendance to class. This program will be expanded to cover more lectures. In addition, the material (lectures, questions, problem sets and detailed answers) will be made available via the department website.
WE‐E‐204B‐01: Development of an X‐Ray/Optical Luminescence Imager for Improved X‐Ray Contrast Sensitivity
Authors: Carpenter CM , Pratx G , Sun C , Xing L , Ravilisetty P
Published: August 2010

Purpose: A dual‐modality X‐ray/optical imaging system is being developed to enable the imaging of ultra‐low concentrations of contrast agents under X‐ray excitation. This imaging system uses nano‐sized inorganic phosphors to convert X‐ray photons into optical photons, which are then imaged with an optical camera. This work presents initial data on the performance capabilities of this system, and demonstrates a significant improvement in contrast agent sensitivity over X‐ray fluoroscopy. Method and Materials: Nano‐sized phosphors were fabricated from Gadolinium Oxysulfide and doped with Terbium (a green‐emitting dopant) or Europium, (a red emitting dopant). A 2.5×4cm cylindrical optical/X‐ray phantom was constructed from l%Agar:99%Distilled water, india ink (for optical absorption), and titanium oxide (for optical scatter) to match biological tissue optical properties. Phosphors were homogeneously mixed at a concentration of 10mg/ml, and poured into a 1cm plug‐shaped inclusion in the phantom. An X‐ray fluoroscopy scanner was positioned vertically above the setup, with the tube voltage/current at 100keV/10mA. Light output was imaged on a lead‐shielded CCD camera, placed 15cm from the phantom, during sample irradiation. An X‐ray fluoroscopy image was collected for comparison. Images acquired via the optical camera and the X‐ray fluoroscopy system were compared to measure the Weber contrast between the phosphor‐filled inclusion and the background. Results: Analysis performed on the X‐ray fluoroscopy image showed a 0.6% contrast between the inclusion and the background. This slight contrast difference is due to the fact that Gadolinium has relatively high X‐ray stopping power compared to water. In contrast, the X‐ray/optical luminescence image showed a 260% difference. Conclusion: The potential of a hybrid X‐ray/optical imaging system was shown in a tissue‐simulating phantom. This technique showed improved contrast to background; this contrast is expected to increase with the addition of Diffuse Optical Tomographic methods, which take into account photon scatter into the background.
WE‐E‐204B‐02: Release Kinetics of Radio‐Sensitizers from Nanoporous Coatings on Gold Fiducials: Biological In‐Situ Dose‐Painting for IGRT
Authors: Stambaugh C , Tada D , Nagesha D , Jost E , Levy C , Cormack RA , Makrigiorgos M , Sridhar S
Published: August 2010

Purpose: Image‐guided radiation treatments routinely utilize radio‐opaque implantable devices, such as fiducials or brachytherapy spacers, for improved spatial accuracy. We study the hypothesis that the therapeutic efficiency of IGRT can be enhanced through simultaneous in‐situ delivery of radiosensitizers, contained within nanoparticles and nanoporous polymer matrices coating gold fiducial markers or spacers implanted in the tumor (BIS‐IGRT, Biological In‐Situ Image‐Guided Radiation Therapy). Methods and Materials: Biocompatible polymers loaded with model molecules were coated as a thin film on gold fiducials. The nanoporous morphology of the polymer coatings allowed controlled release of molecules and nanoparticles. Two experimental approaches were studied: (i) a free drug release system, (Doxorubicin, a hydrophilic drug in Poly(methyl methacrylate (PMMA) coating) and (ii) Poly(D,L‐lactic‐co‐glycolic acid) (PLGA) nanoparticles loaded with Coumarin‐6, a fluorescent model for a hydrophobic drug, in a chitosan matrix applied as gold fiducial coating. Measurements of temporal release kinetics in buffer and spatial release profiles in agarose were carried out using fluorescence spectroscopy. Results: For gold fiducials coated with Doxorubicin in PMMA matrix an initial release of Dox within the first few hours was followed by a sustained release over the course of next 3 months. Release of Dox from within PMMA matrix is dependent on the concentration of Dox, ratio of PMMA/Dox, thickness of PMMA/Dox coating on gold surface. The release profile of coumarin‐6 loaded nanoparticles from chitosan film on gold fiducials showed that (63±10)% of NPs were released in twenty days, and after that, the release became slower and additional 37% of release was observed after additional twenty‐days. Spatial release profiles in an agarose phantom were also measured and compared with release kinetics models. Conclusions: The results show that dosage and rate of release of these radiosenstizers can be precisely tailored to achieve the desired release profile for BIS‐IGRT.
TH‐A‐201C‐01: Quantitative Molecular Imaging Using PET/CT to Assess Response to Therapy
Authors: Kinahan P
Published: August 2010

Recent publications have established quantitative measures of tracer uptake used in positron emission tomography (PET) imaging as a predictor of patient outcome including pathologic response disease‐free survival and overall survival in single institution imaging and therapy trials. There is increasing interest in using PET as a biomarker to evaluate response to therapy and possibly as an endpoint for cancer therapeutic response in multi‐center trials. However several sources of variance and inherent in quantifying PET tracer uptake should understood and determined in order to ascertain the significance of differences in serial measurements and aid estimation of expected variances during clinical trial design.

In this presentation we will review the major sources of bias and variability from the patient imaging protocol data processing and image analysis. We will also briefly discuss artifacts from PET and PET/CT imaging.

The presentation will conclude with a review of efforts to address complexities that arise from combining quantitative PET/CT data from multiple patients at multiple sites. Research partially supported by NIH grant U01‐CA148131 and NCI Contract 24XS036‐004 (RIDER).
TH‐B‐204C‐01: Parallel Imaging: Technology Clinical Applications and Image Quality Issues
Authors: Yanasak N
Published: August 2010

Parallel imaging in magnetic resonance imaging (or “pMRI”) is a family of techniques that uses the position of multiple RF coil elements to assist in spatial localization of signal as opposed to phase‐encoding techniques. This approach provides a wealth of new imaging options and advantages to the MR user. Basically the reduction in the number of required phase encodings to produce an image can be used to acquire image data within a shorter window of time. This characteristic can be used in a variety of ways to reduce image acquisition time; to increase image matrices for a given acquisition time; to mitigate geometric distortion; or to reduce SAR over the duration of a scan. Finally pMRI can be implemented in virtually all existing sequences. The current use of pMRI is widespread as a result of these advantages with a tendency toward increased utilization as the technology matures.

The advantages that pMRI provides are not without cost. pMRI is implemented in multiple “flavors” all of which require some degree of mathematical prowess to understand fully. Although pMRI is frequently useful it can cause problems within some imaging contexts (e.g. low SNR imaging patients prone to movement). Artifacts associated with pMRI are odd and varied in appearance. Finally an MR system that passes quality assurance tests for non parallel imaging on a given day may not have the necessary performance for pMRI. In 2005 the AAPM MRI subcommittee created Task Group #118 in order to provide guidelines to the Medical Physics community that address these concerns.

This presentation will provide an overview of pMRI from concept to application. Conclusions and recommendations determined within Task Group #118 will also be summarized.

Learning Objectives:

1. To understand the basis of the pMRI technique including required hardware and reconstruction methods.

2. To conceptualize what components of a quality assurance program may be important for MR systems using pMRI.

3. To gain insight into the suggested (and inappropriate) uses of the technique for clinical benefit.

4. To observe new directions of pMRI development and how this may change clinical practice in the next few years.
TH‐C‐BRA‐01: An introduction to GPU Computing
Authors: Sharp G
Published: August 2010

The graphical processing unit (GPU) is a special‐purpose co‐processor used to perform fast calculation of 2D and 3D graphics commands for computer displays. Recently GPUs have begun to be used as general‐purpose vector processors for a wide range of scientific programs. GPU programming is used in domains such as medical imaging financial analysis and oil exploration.

This talk will introduce the history and capabilities of modern GPU‐based computing systems. I will describe the hardware organization of GPUs and describe how multithreaded GPU programs map onto the hardware. Next I will introduce the CUDA language and software tools used to create GPU‐accelerated programs. Finally I will present an overview of existing libraries and applications.

Learning Objectives:

1. Learn the history and capabilities of GPU‐based computing systems

2. Learn the hardware organization of GPUs

3. Learn tools and procedures for programming GPUs
TH‐C‐BRA‐03: GPU‐Based Cone Beam CT Reconstruction
Authors: Jia X , Lou Y , Li R , Lewis J , Gu X , Men C , Song W , Jiang S
Published: August 2010

Cone‐beam CT (CBCT) has been widely used in image guided radiation therapy (IGRT) to acquire updated volumetric anatomical information before treatment fractions for accurate patient alignment purpose. However the excessive x‐ray imaging doses (a few cGy per scan) delivered to patients from serial CBCT scans raise a clinical concern in most IGRT procedures. This fact has greatly limited exploitation of IGRT's maximal potential. The imaging dose can be effectively reduced by reducing the number of x‐ray projections and/or lowering mAs levels in a CBCT scan. The image quality reconstructed from conventional FDK‐type algorithms however will be highly degraded. Recently total variation (TV) method has demonstrated its ability to reconstruct CBCT images from a few number of noisy x‐ray projections. Nonetheless such a method can hardly be applied in real clinical environments due to its long computational time (a few hours). It is highly desirable to develop a fast reconstruction scheme to obtain high quality CBCT images from undersampled and noisy projection data so as to lower the imaging dose.

Utilizing GPU to speed up the computationally intensive tasks in CBCT reconstruction problems has drawn a lot of attention recently. In this talk GPU‐based CBCT reconstruction algorithms will be reviewed with an emphasis on an iterative CBCT reconstruction algorithm via TV regularization. We have recently developed a GPU‐friendly version of the forward‐backward splitting algorithm to solve the TV‐based reconstruction problem. Multi‐grid technique is also employed. It is found that 40 x‐ray projections are sufficient to reconstruct CBCT images with satisfactory quality for IGRT patient alignment purpose. Phantom studies indicate that CBCT images can be successfully reconstructed with our algorithm under as low as 0.1 mAs/projection level. Comparing with currently widely used full‐fan head‐and‐neck scanning protocol of about 360 projections with 0.4 mAs/projection it is estimated that an overall 36 times dose reduction has been achieved. Moreover the reconstruction time is about 130 sec on an NVIDIA Tesla C1060 GPU card which is estimated ∼100 times faster than similar iterative reconstruction approaches. The high computational efficiency and satisfactory image quality make the iterative low dose CBCT reconstruction approach feasible in real clinical environments.

Learning Objectives:

1. Understand basic concepts of GPU‐based CBCT reconstruction.

2. Understand main challenges in GPU‐based iterative CBCT reconstruction approach and how an iterative CBCT reconstruction problem is solved on GPU.

Conflict of Interest: The research presented here is partially supported by NVIDIA.
TH‐C‐BRA‐04: Radiation Therapy Dose Calculation Using Graphics Processing Units
Authors: McNutt T , Jacques R
Published: August 2010

Dose computation methods in radiotherapy have traditionally been developed for central processing units (CPUs). Methods used in radiation therapy treatment planning must balance clinical accuracy requirements with practical planning time limits. The first commercial 3D treatment planning systems in the early 1990s took between 5–30 minutes to compute a beam depending on the dose grid size and computation method. In the years that followed CPU performance increased with Moore's law and more reasonable dose computation speeds of several seconds to minutes were achieved. However in recent years CPUs have increased computing power with additional cores not clock speed. At the same time graphic processing units (GPUs) have evolved from fixed function devices into flexible general purpose hardware. Today general purpose GPU computing (GPGPU) has turned desktops into supercomputers and languages such as OpenCL CUDA (Compute Unified Device Architecture) Fortran CUDA C and DirectCompute have allowed for fast GPU program development.

Currently convolution/superposition algorithms are the primary computation methods used in treatment planning systems due to their combination of reasonable performance and accuracy. Monte Carlo methods are becoming more prevalent but they still have performance problems. Porting these algorithms to the GPU promises to provide a several orders of magnitude performance increase; resulting in near real‐time convolution/superposition dose computation.

The implementation of these algorithms on the many‐core architecture of the GPU poses several challenges and opportunities. The first concern is dividing the algorithm up into many separate parallel processes that can be run independently of one another. The second concern is memory access patterns; for example the manually caching via shared memory the avoidance of write on write conflicts and the maximization of memory bandwidth efficiency. The third concern is how to best leverage the specific processing capabilities of the GPU such as hardware exponentials.

Several approaches to implementing dose computation algorithms on the GPU will be discussed. The performance increase in these newer algorithms provides new opportunities in the way we approach treatment planning — whether it be real time treatment planning or enabling dosimetric guidance to treatment delivery.

Learning Objectives;

1. To understand the architecture differences between CPU and GPU

2. To understand approaches complications and advantages to implementing pencil beam convolution/superposition algorithm and Monte Carlo algorithms on the GPU

3. To understand the implications of the performance gain on treatment planning processes
TH‐C‐BRA‐05: Real‐Time Re‐planning for Online Adaptive Radiotherapy
Authors: Jiang S , Gu X , Men C , Jia X , Fluck O , Choi D , Majumdar A
Published: August 2010

By seamlessly integrating treatment simulation and planning into the treatment delivery process online adaptive radiation therapy (ART) allows real‐time treatment adaptations based on the current patient anatomy and therefore holds significant promise in maximally compensating for interfraction anatomical uncertainties. The clinical realization of online ART is extremely challenging mainly due to the inability for real‐time treatment re‐planning. For real‐time treatment re‐planning three key components need to be done in real time: anatomy segmentation dose calculation and treatment plan (re‐)optimization. We have implemented all three components on GPU and gained real‐time efficiency. Our preliminary results on an NVIDIA Tesla C1060 GPU card for various clinical scenarios are very promising. For a typical 9‐field prostate IMRT case the deformable registration can be done in 7 seconds the dose calculation takes less than 2 seconds and the plan re‐optimization takes less than 3 seconds. Therefore a new plan can be developed in about 12 seconds. These results laid a solid foundation for the development of a clinically functioning online ART re‐planning system.

Learning Objectives:

1. Understand the basic concept and main challenge of online ART

2. Gain knowledge in the use of GPU for real‐time re‐planning

Conflict of Interest: The research presented here is partially supported by NVIDIA.
TH‐C‐BRB‐01: Characterization of Optically‐Stimulated Luminescent Detectors (OSLDs) in Photon & Proton Beams
Authors: Kerns J , Ibbott G , Johnson V , Kry S , Sahoo N , Followill D
Published: August 2010

Purpose: To investigate characteristics of optically‐stimulated luminescent detectors (OSLDs) to protons thus allowing comparison to thermoluminescent detectors and implementation into a quality assurance program. Methods & Materials: The OSLDs used were aluminum oxide (Al2O3) nanodots (Landauer Inc. Glenwood IL) measuring 10×10×2 mm3. A 20(L)×20(W)×0.5(H) cm3 volume of solid water was fabricated with pockets to allow OSLDs and TLDs to be irradiated simultaneously and perpendicular to the beam. Irradiations were performed at a 5 cm depth for photons and in the center of a 10 cm SOBP for a 200 MeV proton beam. Additionally the Radiological Physics Center's (RPC) anthropomorphic pelvic phantom was used to test the angular dependence of OSLDs for photons and protons. A cylindrical insert in the phantom allows the dosimeters to be rotated to any angle with a fixed gantry angle. OSLDs were irradiated at 8 angles between 0 and 360 degrees. OSLDs were read out with a Landauer Microstar reader. Results: Dose response measurements indicate for photons that at angles where the dosimeter is near parallel with the radiation beam response is slightly reduced. Results in protons do not seem to show significant angular dependence. OSLDs and TLDs are comparable within 3% for both photons and protons during perpendicular measurements. Conclusion: OSLDs and TLDs are comparable dosimeters in 6 MV photon and 200 MeV protons beams in a perpendicular irradiation. Preliminary results show that OSLDs might have some angular dependence to photons but not protons. With angular dependence characteristics defined OSLDs can be implemented into multiple‐field treatment plans in photons and protons and used in the RPC's quality assurance program.
TH‐C‐BRB‐05: Status of the NIST Primary Standard Water Calorimeter for 60Co Beams
Authors: Chen‐Mayer H , Tosh R
Published: August 2010

Purpose: Validation of a second‐generation primary standard water calorimeter for use in 60Co radiation beams. Method and Materials: Work on a second‐generation water calorimeter at NIST has progressed to a stage in which extensive comparison tests are being conducted with a transfer chamber connecting the historical value determined by Steve Domen. The present water calorimeter based upon Domen's original design consists of a thin‐walled cylindrical glass vessel of ∼2 cm radius and ∼12 cm length with two thermistor probes mounted along the axis. The response of the thermistors which are wired into opposite arms of a Wheatstone bridge is measured with a lock‐in amplifier (LIA). The calorimeter situated at 5 cm depth in a water phantom at various SDD (77.4 cm and 100.0 cm) is subject to periodic 70s radiation exposures from a vertical 60Co radiation beam and its steady‐state response is obtained both by Fourier analysis and midpoint extrapolation of the time waveform obtained from the LIA. A separate vessel of similar but not identical dimensions containing a calibrated Farmer chamber then replaces the thermistor system to obtain a dose rate under identical conditions. Results: Agreement between chamber and calorimeter estimates of dose is within 0.4% for SDD of 77.4 cm and 0.13% at 100 cm. At 77.4 cm dependence on spatial variations due to possible nonuniformities in the beam were faithfully replicated by the thermistor system however the latter estimates of dose rate were lower in all cases. At 100 cm there is no spatial dependence and no evidence of systematic error. Conclusion: The differences between calorimeter and transfer standard were within the 1 sigma statistical uncertainty of+/− 0.13% at 1 m; consistency of the new calorimeter with the historical value is obtained. Reproducibility and possible corrections are needed before the primary standard can be reestablished.