bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐B‐330A‐01: Shielding Design Workshop: PET/CT
Authors: Martin M , Frey G
Published: July 2006

The application of the structural shielding design techniques and goals as outlined in AAPM Task Group Report 108: PET and PET/CT Shielding Requirements Medical Physics (Vol. 33., Issue 1 (2006)) will be the basis for this practical course. As the use of PET and PET/CT units expands rapidly in the medical arena, the requirements for providing adequate radiation protection for both occupational personnel in these facilities and the public in uncontrolled areas around them necessitate the involvement of a qualified medical physicist. The many areas involved in implementing a PET/CT program including the Hot Lab, Patient Uptake Rooms, Patient Restrooms, Scan Rooms, and Disposal areas will be used as practical examples of typical structural shielding designs and evaluation methods. The testing of PET shielding insures that the shielding is properly installed and that individuals do not exceed the radiation exposure levels required by applicable regulations and ALARA policies. Testing of PET and PET/CT shielding is a complex multidimensional problem since there are multiple sources and the radiation is emitted isotropically from the patients. Thus efficient testing can both save time and reduce radiation exposure to the physicists doing the testing. This course will discuss efficient methods for shielding testing. It will also review the instrumentation available to physicists for making the measurements. Practical methods of testing of a PET/CT facility will be presented.

Educational Objectives:

1. Understand the exposure factors to be used for currently used PET isotopes to determine required structural shielding to meet exposure limits for occupational personnel and the public.

2. Understand the effectiveness of existing and additional structural shielding materials that provide radiation protection and methods to calculate the required amounts of these materials.

3. Understand the methods to be used to evaluate the adequacy of PET and PET/CT installations to insure adequate shielding has been provided to meet applicable state and ALARA requirements.
WE‐B‐ValA‐01: Interventional Fluoroscopy Imaging Equipment — What to Know Before You Buy
Authors: Cusma J
Published: July 2006

The number of fluoroscopy‐guided interventional procedures performed continues to grow, accompanied by an increasing complexity in these clinical procedures. Technical improvement in the x‐ray imaging equipment utilized for these procedures continues at a fast pace as well, driven in part by the clinical requirements but also by the overall advance of computational technology. It remains a challenge for an interventional laboratory to ensure that its imaging equipment provides state‐of‐the‐art capabilities in a manner consistent with internal workflow and economic factors. The situation is further complicated by the fact that the replacement cycle for this equipment can be on the order of a decade ‐ an extraordinarily long time in the arena of technological advances. These factors place a high premium on careful analysis of the requirements and technical capabilities of the fluoroscopic and angiographic equipment being considered by a laboratory for purchase.

The primary factors to be addressed in the purchase of modern interventional x‐ray imaging equipment remain the same as with any imaging equipment: the type of clinical procedures for which the equipment will be utilized. Since traditional clinical boundaries continue to evolve, equipment must be flexible to perform a range of procedures throughout a patient's anatomy. The specific concerns are the combination of cardiac, peripheral vascular, and neurovascular procedures to be performed. The answer to that question will have significant implications for the size of detector, image acquisition parameters, image processing options, and the display and storage requirements. As noted, the replacement cycle is long and these systems are not easily upgraded after purchase so identification of the procedure mix is important at the outset.

Once the procedure requirement is determined, equipment can be evaluated with regard to how well it meets those requirements. Among the options related to the type of procedure are type of detector, field‐of‐view, x‐ray tube capacity, and image processing options. Functionality relevant for all types of procedures include: (i) patient exposure monitoring and exposure reduction methods; (ii) image analysis and quantification; (iii) storage capacity; (iv) options for archive and display. In addition, local factors such as service and maintenance must also be considered.

Educational Objectives:

1. Understand the relationship between clinical procedure requirements and the corresponding capabilities of interventional fluoroscopy equipment.

2. Understand the range of options available in fluoroscopy and angiography x‐ray systems.

3. Be able to assess and compare different imaging systems and prioritize local factors important for purchase decisions.
WE‐B‐ValB‐01: Physics Procedures for ACR MRI Accreditation
Authors: Keener C
Published: July 2006

In recent years, the American College of Radiology (ACR) Magnetic Resonance Accreditation Program (MRAP) has been adopted by over 3000 sites, nearly half of the estimated MRI facilities in the United States. Those sites agree to follow a weekly QC program set up and monitored by a qualified medical physicist or MR scientist. They also agree to undergo initial and annual equipment performance evaluations by a qualified medical physicist/MR scientist. There are several published documents, including the ACR Phantom Testing Guidance and the 2004 ACR MRI QC Manual, which describe the tests and the performance criteria. These documents are helpful in providing guidance on submitting phantom images for accreditation. However, they allow considerable discretion to physicists doing these tests, and the scanners change more frequently than the published guidance.

A consulting medical physicist may see a variety of scanners, each for a short period of time, and needs to provide the sites with useful recommendations beyond the pass/fail status of the phantom tests. The physicist must gather this information from existing data and tests performed with the ACR and other available phantoms. This lecture will describe information which can be derived from those data and how it may be used for improving MR image quality.

Educational Objectives:

1. Learn the current status of the ACR MRAP program and the role of the medical physicist in that program.

2. Understand how to perform required phantom and annual tests on various scanners and the performance criteria for those tests.

3. Understand how the results of those tests can be combined and analyzed to troubleshoot problems.

4. Understand how QC test and phantom availability and results may vary depending on scanner manufacturer.
WE‐C‐330A‐04: Effect of Projection Angles Used in Multi‐View Reconstruction (MVR) Using Images From a Microangiographic (MA) Detector and An Image‐Intensifier (II) System
Authors: Patel V , Kuhls A , Noël P , Walczak A , Ionita C , Chityala R , Tranquebar R , Rangwala H , Kasodekar S , Yadava G , Hoffmann K , Bednarek D , Rudin S
Published: July 2006

Purpose: The sensitivity of a new 3D Multi‐View Reconstruction (MVR) angiography technique to the projection angles used is evaluated by comparing 3D centerlines calculated from combinations of three projections acquired from two imaging systems with that from micro‐Cone Beam CT (μCBCT), which is taken as truth. Method and Materials: A 3D centerline of a contrast‐filled carotid vessel phantom was reconstructed from image data acquired using a custom‐made μCBCT system with a microangiographic (MA) detector (45 μm pixels, 4.5 cm field‐of‐view (FOV)). Projection images of the same phantom were also acquired using the MA and an image intensifier (II) detector system (120 μm pixels, 4.5 in FOV) on a C‐arm x‐ray unit. The MVR technique was used to compute 3D centerlines for 12 combinations of projection angles. Each 3D MVR centerline was aligned with the μCBCT “true” 3D centerline using a Procrustes technique, and a root‐mean‐square (RMS) deviation was calculated. Results: The average RMS deviation for the MA‐MVR centerlines is 25 μm with a standard deviation of 3 μm over the 12 different projection‐angle combinations, whereas the average RMS deviation for the II‐MVR centerlines is 41 μm with a standard deviation of 4 μm over these same combinations. The RMS deviation as a percent of the internal vessel diameter, 0.75 mm, is 3.3% for the MA and 5.5% for the II and appears to be independent of view selection. Conclusion: For the MVR technique, the improved resolution of the MA resulted in improved centerline determination compared to the II system. For both detectors, the selection of a particular projection set had little effect on the RMS centerline deviation. The low RMS deviations for both detectors indicate that the MVR technique can provide accurate 3D centerlines.

(Partial support from NIH Grants R01‐NS43924, R01‐EB02873, R01‐HL52567, R01‐EB02916, and Toshiba Medical Systems Corporation).
WE‐C‐330D‐03: Bioinformatics, the Multiple‐Biomarker Classifier Problem, Complexity, and Uncertainty
Authors: Wagner R F
Published: July 2006

The most celebrated landmark of modern bioinformatics has been the sequencing of the human genome. Early in the project it was commonly believed that humans have about 100,000 genes and as the project neared completion the estimates came down into the neighborhood of 25,000–30,000. Hidden Markov Models (HMM) are used to carry out statistical parsing of the “linguistics” of such bioinformation. Such massively complex analysis has been facilitated by modern developments in massively complex hardware and software—but such analysis is naturally accompanied by great uncertainties. At a lower level of complexity are the algorithms used for computer‐aided diagnosis in medical imaging, and at an intermediate level are the tools under current development for fusing multiple biomarkers—for example, from a large number of spectral lines in mass spectroscopy of protein fragments in blood samples and other mutliplex data from protein and gene microarrays. This talk will review the uncertainties in measured performance of such diagnostic tests as a function of the sample sizes available for training and testing as well as the dependence on the number of fused biomarkers and the complexity of the associated statistical learning algorithm. A strategy for designing large trials based on pilot studies will be outlined.

Educational Objectives:

1. Understand the multiple‐biomarker classifier problem.

2. Understand the uncertainties in its performance assessment due to finite training and testing.

3. Understand the dependence on number of biomarkers and complexity of statistical learning algorithm.
WE‐C‐ValA‐01: Evaluation of Image Quality in 4DCT and Improving Temporal Accuracy
Authors: Mutaf Y D , Antolak J A , Brinkmann D H
Published: July 2006

Purpose: To assess the effect of incorrect assignment of respiration phases and irregular breathing on 4DCT image quality. Artifacts are manifested as deformations in the reconstructed images and quantitative effects are measured along with qualitative evaluations. Modifications to the current 4DCT implementation are recommended. Methods and Materials: For the evaluation of image artifacts, we used a motion simulation platform and simulated the respiration patterns of real patients. Artifacts due to inaccurate phase sorting are quantitatively evaluated by comparing differences in the volumes of spherical phantoms with and without the presence of phase assignment problems. Artifacts due to irregular breathing are demonstrated using 4DCT and recommendations are made for modifying the standard acquisition mode to enable gating for motion reproducibility. The advantage of this modified acquisition is proved using an electronic portal imager. Results: Review of clinical 4D scans performed in our clinic showed discrepancies in the phase assignments for about 45% of the cases when compared to our independent check. Significant image artifacts are also observed and measured as a function of the respiration motion amplitude and target size. Volumetric inaccuracies of up to 43% are measured. For the evaluation of irregular breathing, our proposed technique of gated imaging for the reproducibility of the respiration proved to yield superior image integrity when compared to standard acquisition mode. Conclusions: We identified two sources of quality degradation factors associated with 4DCT images and performed quantitative evaluations of associated artifacts. We conclude that for improved image reconstruction, an independent check of the sorting procedure should be performed for each clinical case; also we recommend a modification to the 4DCT acquisition technique to include gating of the x‐rays for the reproducibility of the respiration pattern. Conflict of Interest: Research supported by GE Medical Systems.
WE‐C‐ValA‐02: The Impact of 4D Breathing Motion Effects Versus Tissue Heterogeneity in Lung Cancer Treatment Planning
Authors: Rosu M , Chetty I , Tatro D , Ten Haken R
Published: July 2006

Purpose: To investigate the relative magnitudes and clinical importances of the dosimetric effects related to 4D breathing motion and tissue heterogeneity for thoracic tumors treatment planning. Methods: Scans were acquired at normal exhale/inhale breathing phases. The target was the union of the exhale and inhale GTVs, uniformly expanded by 5mm(ITV). Patients were planned with both AP/PA and 3‐D conformal plans using the exhale (“static”) dataset, assuming unit density, for 100±5% ITV dose coverage. Each of these plans was further used to calculate: (a) heterogeneous “static” dose; (b) homogeneous cumulative dose; (c) heterogeneous cumulative dose. The same number of MU were used for each of the calculations and was based on the homogeneous “static” plan. Cumulative dose distributions consisted of a time‐weighted sum of exhale and inhale doses. Doses were calculated using the DPM_MC code which includes secondary electron transport for the heterogeneous computations. Results: Relative to unit‐density plans, tumor EUD, and lung NTCP increased in the heterogeneity corrected plans; primarily due to the reduced beam attenuation through lungs and the larger than coin‐size tumors investigated. In comparing 4D cumulative dose plans with static plans, clinical EUD and NTCP estimates were relatively unchanged. The insignificant tumor EUD change was a consequence of good target design, while the small lung NTCP change was due to its large volume effect. Accounting for tissue heterogeneity resulted in average changes of 10% in MLD. Accounting for 4D breathing motion effects resulted in <1% changes in MLD from the static value. The magnitude of these effects was not correlated with the dose distribution conformality. Conclusions: In this study we found that tissue heterogeneity effects are likely to have a larger clinical significance on tumor (if ITV is properly designed) and normal lung clinical treatment evaluation metrics than occurs with 4‐D respiratory‐induced changes.

Supported by P01‐CA59827, R01‐CA106770.
WE‐C‐ValA‐08: Development of a Patient Specific Respiratory Motion Model for Predicting Dose to Moving Organs During Radiotherapy
Authors: Zhang Q , Mageras G
Published: July 2006

Purpose: Respiratory motion is an important limitation to accurate calculation of dose to organs in the thorax and abdomen during treatment. We describe a model to estimate 3‐dimensional motion in patient CT images. This model can be parameterized by navigators such as a signal from a respiratory monitor, or diaphragm position measured in fluoroscopy. We evaluate the accuracy of the model in predicting anatomic changes in respiration‐correlated CT (RCCT) images of lung cancer patients. Method and Experiment: Our method makes use of deformable image registration, thereby automating the model calibration and providing a complete determination of 3D trajectories for all tissue voxels of the moving organs. Calibration of the model uses a series of RCCT images. Each 3D image in the series is tagged by two navigators: current diaphragm position and precursor position which distinguishes between the inspiration and expiration portion of the respiratory cycle. Nonrigid registration is used to calculate the deformation field that maps each 3D image to a reference 3D image at end expiration. We perform a principle component analysis (PCA) to determine the 3D deformation parameterized by navigators. We evaluate the model by comparing the predicted 3D images with actual 3D images at different phases in the breathing cycle. Results: For RCCT images, predicted images calculated from the first two principal components at different respiration phases are found to accurately reproduce anatomic motion observed in the actual images, indicating the model's ability to predict the voxel trajectory anywhere in the cycle. Furthermore, the model can predict motion induced changes that were not in the original image set, such as deeper and shallower breathing. Conclusion: Preliminary experimental results indicate that the proposed method is a potentially useful tool for treatment planning and evaluation of dose to moving organs when patient breathing is monitored.
WE‐C‐ValA‐09: A Biological Lung Phantom for IGRT Studies
Authors: Folkert M , Dedual N , Chen G
Published: July 2006

Purpose: We are evaluating the feasibility of a dynamic biological lung phantom for IGRT studies, with the initial goal of developing a reliable phantom suitable for use in validation of deformable registration and volume rendering studies of the lung. The properties of an ideal lung phantom would include complex geometry, anisotropic inflation, and composition, lobar structure and internal airway architecture similar to that of human lung. Method and Materials: Preserved swine lung was obtained and compared to human lung. The prepared lung was statically inflated to different volumes using a regulated nitrogen supply, and can also be dynamically inflated using a medical ventilator. The inflated phantom was imaged on a GE Lightspeed CT scanner. Volume rendering of the CT image data was performed to visualize and determine coordinates of airway bifurcations. Results: Preserved swine lung was determined to be comparable to human lung in terms of tissue radiological and physical properties, lobar structure, airway architecture, volume and mass. Rendered airway vs. physiologic airway dimensions are undergoing verification by dissection. Analysis of CT images and volume rendering data demonstrates that the airway architecture may be followed to at least the 5th airway bifurcation, yielding a conservative minimum of 31 reproducible anatomic landmarks evenly distributed throughout the lung. By visual inspection, it is possible to follow the displacement vector of these landmarks in sequential images. Conclusion: Initial analysis shows that a swine lung phantom meets a number of the requirements of a reliable and functional phantom for validation of deformable registration and volume rendering methods. Reference points generated using the CT/volume rendering technique may be useful as a validation tool for both feature‐ and intensity‐based deformable registration techniques. Ongoing study will evaluate the potential of the lung phantom for use in planning, delivering, and validating 4D IGRT.
WE‐C‐ValA‐10: 4D Cone‐Beam CT (CBCT) Using An On‐Board Imager
Authors: Li T , Xing L , Munro P , Yang Y , Loo B , Koong A
Published: July 2006

Purpose: To develop an artifact‐free four‐dimensional (4D) cone‐beam CT (CBCT) imaging technique for image‐guided radiotherapy, and to optimize the image quality, scanning time, and patient radiation dose with respect to acquisition parameters such as the number of gantry rotations, gantry‐rotation speed, and x‐ray tube current. Method and Materials: A Varian Trilogy™ system was employed for this study. To sort CBCT projections in terms of patient breathing phase, a CT‐opaque fiducial was adhered to the patient skin and tracked automatically in the projection space, and the phases of the fiducial trajectory were used to tag the projections. Projections after phase‐binning were subsequently reconstructed to yield 4D‐CBCT images. To reduce/eliminate view‐aliasing artifacts due to limited number of projections in each phase, both “multiple‐rotation” and “slow‐gantry‐rotation” strategies were investigated. Quantitative evaluation and comparison were performed with a motion phantom for the following acquisition settings: (i)varying number of gantry rotations (1∼8) with all other scanning parameters kept the same; (ii)varying x‐ray tube current together with the number of rotations while keeping the radiation dose constant, namely, 1‐rotation‐80mA, 2‐rotation‐40mA, 4‐rotation‐20mA, and 8‐rotation‐10mA; (iii)varying gantry‐rotation speed (1deg/sec∼8deg/sec). Three patient cases were used in the study. Results: The image quality, represented by relative error (RE), varied nonlinearly with the number of rotations: RE reduction became less pronounced as the number of rotations increased. After 3∼5 rotations, the benefit resulting from more rotations started saturating. When the dose level was kept the same, the images of 1‐rotation‐80mA and 8‐rotation‐10mA acquisitions had the largest and smallest REs, respectively. Similar RE reduction behaviors were found when slowing down the gantry‐rotation speed. For the patient cases, 4D images were obtained with negligible motion or view‐aliasing artifacts. Conclusion: We have successfully demonstrated that the commercially available OBI system can be utilized to acquire artifacts‐free 4D‐CBCT images without increasing the patient radiation dose.
WE‐C‐ValB‐01: Introduction
Authors: Siemann D
Published: July 2006

The reasons for the failures of conventional anticancer therapies are varied and multiple. It is however, becoming increasingly clear that physiological conditions in tumors, arising primarily from inadequate and non‐uniform vascular networks, can play significant roles in the lack of therapeutic responsiveness of neoplasms. However, the impact of the tumor microenvironment far exceeds its direct effects on therapeutic treatment modalities. For example, tumor hypoxia can contribute to processes that directly favor malignant progression and increased metastasis. New treatment strategies aimed at improving tumor response through targeting cells existing in these microenvironments or the aberrant tumor vasculature itself, therefore are of high interest. Non‐invasive imaging strategies may aid not only in identifying tumors that would be effectively treated with such strategies but also in providing effective means of monitoring treatment effectiveness and therapeutic outcomes.
WE‐C‐ValB‐03: Functional Analysis of Tumor Vasculature Post Antiangiogenic Intervention with Argeted Anti‐VEGFR2 Therapy
Authors: Brown AS
Published: July 2006

High frequency ultrasound biomicroscopy (UBM) permits in vivo assessment of anatomical and physiological parameters at high resolution. The ability to image the mouse noninvasively facilitates longitudinal studies with repeated measurements in the same animal over time, to follow normal development or disease processes as well as response to therapeutic intervention. Anatomical images are obtained using B mode, giving a cross‐section of the structure of interest. Anatomical changes can now be quantitated using 3D volumetric B mode imaging, and rendered to give an accurate contour of the structure of interest. 3D UBM may be used to measure organ growth through normal development, or to compare treated versus untreated populations in mouse models of human disease. High frequency ultrasound Doppler permits measurement of blood flow velocity in selected vessels of interest. Recent advances in blood flow analysis, including speckle variance analysis, permit investigation of blood flow velocity of flow velocities down to 100 microns per second, as well as perfusion alterations.

High frequency ultrasound imaging modes, imaging strategies, and post‐processing methods used to generate anatomical and physiological data will be discussed.

Educational Objectives:

1. Understand the concepts behind high frequency ultrasound imaging modes.

2. Understand the application of high frequency ultrasound to image development and disease processes in the mouse, including experimental design, data acquisition and data processing.

3. Understand therapeutic study design, data acquisition and analysis using UBM.
WE‐C‐230A‐01: The Application of Error Reduction QA Philosophy in HDR Brachytherapy
Authors: Thomadsen B
Published: July 2006

Routine quality assurance (QA) in brachytherapy developed quickly through the 1990s, and fairly standard practices became common. The reports of Task Groups 40, 56 and 59 established formalized, accepted standards for QA in brachytherapy, and textbooks covered QA procedures in detail (1). Why, with a solid understanding of QA procedures, were there still many reported brachytherapy medical events, and likely many more unreported or unrecognized? A review of such events (2) notes that for many cases, the facility had QA procedures in place, but they were ineffectual because they either did not cover the situations that evolved or, often, simply were not performed, frequently because of time constraints. Current high dose‐rate (HDR) brachytherapy QA focuses heavily on equipment and instrumentation. Very few events resulted from errors in the equipment (although, equipment failures often set the stage), due in part to the extremely high reliability built into the devices and, possibly in part, because of the attention paid to equipment QA by the medical physicists. A soon to be released report from the International Atomic Energy Agency will note that the greatest danger in radiotherapy is not equipment malfunctions but the human activities related to the procedures. (3) Much of the current QA for HDR brachytherapy stems from regulations of the Nuclear Regulatory Commission. Some of the regulations expend effort with little expected return. For example, daily QA requires a check of the door interlock at the room entrance. For many facilities, the operator has the door in clear view during treatments; the probability of a person trying to enter the room during a treatment with a failure of the interlock becomes vanishingly small. With each new source, the length and function of transfer tubes and applicators must be checked. Most of these instruments cannot change their length, and the functioning would be (and should be) determined at each use. Measuring exposure readings outside the HDR room with each source change wastes time. Such requirements divert resources from useful activities. The new paradigm for QA first assesses all the possible ways things can go wrong (and the list is a long one), rating the likelihood of occurrence, and severity of the result if it does happen, and the probability of detecting the failure before it propagates into the event. These ranking provide the priorities for allocating resources for activities to prevent failures This process will naturally place a greater emphasis on the human role in the procedures.

Learning Objectives: To understand

1. The problem with the current QA paradigm, and

2. The advantage of the new paradigm
WE‐C‐230A‐02: The Application of Error Reduction QA Philosophy in IMRT
Authors: Palta J , Huq M
Published: July 2006

The increasing complexity, functionality, and site‐to‐site variability of modern radiation therapy planning and delivery techniques challenge the traditional prescriptive quality control/quality assurance (QC/QA) programs that ensure safety and reliability of treatment planning and delivery systems under all clinical scenarios. The manufacturing industry has historically relied on extensive testing and use of techniques such as probabilistic reliability modeling for developing and maintaining new products. Among the most widely used method of risk analyses are Failure Modes and Effects Analysis (FMEA). This is a methodology for analyzing potential reliability problems early in the development cycle where it is easier to take actions to overcome these issues, thereby enhancing reliability through design. FMEA is used to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures. From a manufacturer's perspective, FMEA is a valuable method to systematically evaluate a device design's potential for inducing user errors. User errors are defined as a pattern of predictable human errors that can be attributable to inadequate or improper design. When these risk analyses are done early in the development cycle, potential faults and their resulting hazards are identifiable and much easier to mitigate with error‐reducing designs. These risk management methods are excellent complements to other important user‐centered design best practices. Risk analysis, or hazard analysis, is a structured tool for the evaluation of potential problems which could be encountered in connection with the use of a device. The early and consistent use of FMEAs in the design process allows the engineers to design out failures and produce reliable and safe products. FMEAs also capture historical information for use in future product improvement.

We will first review current paradigms of QC/QA issues in IMRT with a goal to define the problems and challenges associated with the implementation of traditional methods of quality assurance. This will be followed by a second presentation, which will describe a step‐by‐step implementation of the aforementioned hazard analyses and error mitigation methodologies of industrial engineering in addressing QA/QC and safety issues in IMRT. Such an approach should result in a QA/QC program for IMRT that has a good scientific rationale and justification.
WE‐C‐224C‐04: Correlated Sampling for Accelerating CT‐Based Monte Carlo Dose Calculations for Brachytherapy Treatment Planning
Authors: Le Y , Todor D , Williamson J
Published: July 2006

Purpose: To investigate the potential of correlated sampling variance reduction technique for accelerating CT‐based Monte Carlo (MC) simulations for calculating 3D brachytherapy dose distributions.

Method and Materials: Correlated MC (CMC) simulations generate photon histories in the homogeneous geometry. By recomputing particle weights to account for non‐water composition of the CT voxels and applicator and seed components, a second highly correlated set of histories is constructed, resulting in a lower variance estimate of the dose difference, ΔD=Dhet‐Dhom To evaluate the accuracy and efficiency of CMC, a clinical permanent prostate implant with 78 I‐125 seeds was simulated using both CMC and UMC versions of our accelerated CT‐based MC dose‐computation code, PTRAN_CT for voxel sizes ranging from 1×1×1mm3 to 2×2×2mm3. Mean efficiency gains were estimated for regions with minimum doses greater than 20%, 50% and 90% of D90, as well as different anatomical regions.

Results: Systematic differences between UMC and CMC PTRAN_CT were less than 0.4%. Efficiency gains ranged from 4.68 to 15.76 depending on the voxel size and region. CMC can achieve a 2% average precision with 2 mm cubic voxels in 23 seconds on a single P4 processor for voxels with doses > 50%D90. Voxels with very low doses and/or large dose perturbations can experience efficiency losses. Because ΔD is a relatively smoothly varying quantity compared to Dhet, CMC efficiency maybe enhanced using coarser voxel sizes than UMC for the same level of volume‐averaging artifact. Conclusion: Correlated sampling MC can reduce CPU times by an additional 4–15 fold compared to accelerated uncorrelated MC. In practice, larger efficiency enhancements can be achieved because correlated sampling volume‐averaging errors are smaller. MC‐based brachytherapy treatment planning, requiring only a few seconds of CPU time, is achievable. (Supported by NIH‐R01CA46640).
WE‐C‐224C‐05: Tumor Brachytherapy Using Intratumoral Injection of Beta‐Emitting Therapeutic Radionuclides Carried Within Nanoparticles
Authors: Bao A , Phillips W , Goins B , Otto R
Published: July 2006

The use of beta‐emitting therapeutic radionuclides carried within nanoparticles for brachytherapy potentially offers significantl advantages over sealed sources. By using an active trapping technique, both therapeutic radionuclides, 186Re and 188Re, and diagnostic radionuclides, 99mTc, can be encapsulated in liposomes with high efficiency and high specific activity. 186Re and 188Re are beta emitters with appropriate ratio and energies of gamma emission which enable the imaging of in vivo distribution with a clinical gamma camera. The 90% absorbed dose deposit distances in soft tissue of beta ray from 186Re and 188Re are 1.8 mm and 4.2 mm respectively. To study the potential of using therapeutic radionuclides carried within liposomes for tumor brachytherapy, the intratumoral distribution and retention of 99mTc‐liposomes in head and neck squamous cell carcinoma xenografts in nude rats were determined using imaging with a dedicated dual modality animal micro‐SPECT / CT scanner. Using an intratumoral administration technique developed in our lab, the volume of administered radioactivity up to over 40 % of tumor volume can be delivered to tumor with a high local retention. The 99mTc‐liposome studies show that about 40 % of injected activity remained in tumor with a very slow clearance. The cleared activity was not retained in the nearby critical organ. Using pin‐hole collimators with a spatial resolution of 1 mm, the 99mTc‐activity had a broad diffusion throughout the tumor even though the injection was at one point within the tumor. This study has shown the potential of using beta‐emitting therapeutic radionuclides carried within nanoparticles for tumor brachytherapy. The high intratumoral retention enables a high intratumoral radiation absorbed dose, while the penetration of beta‐particles within only a few mm decreases the toxicity to nearby critical organs, and the intratumoral diffusion makes the intratumoral administration simpler and provides for a better intratumoral absorbed dose homogeneity.
WE‐C‐224C‐07: Cervical Cancer Treatment: 3D Dose Determination Based On Low Energy and High Energy CT Image
Authors: Hui S , Gerbi B , Meigooni A , Higgins P , Watanabe Y , Ozer M , Awan S , Weaver R , Tomblyn M , Dusenbery K
Published: July 2006

Purpose: To employ megavoltage CT (MVCT) to (a) generate an artifact‐free image and compared with the kilovoltage CT (kVCT) image set in presence of Fletcher‐Suit applicators, and (b) calculate precise three‐dimensional anatomical dose distribution for low dose rate (LDR) treatment which can be combined with external treatment (based on kVCT) planning. Method and Materials: Consented patients undergoing radiotherapy treatment for cervical cancer were simulated using orthogonal films and kVCT for external treatment planning and low dose rate brachytherapy. Fletcher‐Suit applicators with shielding were used for pretreatment image scans. Additionally, MVCT images were acquired using the Tomotherapy machine. These image sets (kVCT and MVCT) were fused in a Brachyvision planning system using a pixel registration method. MVCT images were then used for volumetric dose calculations using TG43 model. The MVCT image set and orthogonal film were then used to explore Monte Carlo‐based 3D dose calculations. Results: Artifact‐free images were obtained from MVCT scans using the Fletcher‐Suit applicators. kVCT images were not useful for LDR treatment planning due to the presence of substantial artifacts. The MVCT image set was used in delineating the rectal and bladder tissue margins. However, soft tissue visualization was sub‐optimal for clinical purposes. The MVCT image‐based dose calculation generated three‐dimensional dose distribution for rectum (max. dose of 56 cGy) and bladder (max. dose of 25 cGy) for single fraction prescribed dose of 600 cGy. Maximum rectum and bladder dose calculated using the MVCT image and orthogonal film based plan were very similar. Conclusions: We have showed that the artifact‐free MVCT image offers accurate three‐dimensional LDR treatment planning. In addition, the impact of dose heterogeneity will be calculated using image based Monte Carlo simulation technique. Ideally, truly individualized external beam and intracavitary radiotherapy may lead to higher cure rates and lower complication probabilities.
WE‐C‐224A‐02: Radiation Induced Cancers in Treated Patients
Authors: Suit H
Published: July 2006

The increasing numbers of radiation treated patient surviving for long periods forces an assessment of their risk of radiation associated cancer. Dose response relationships for cancer induction in the laboratory mice varies with strain, gender, tissue/organ of concern, observation period, dose fractionation and LET. For most experiments, risk increased with dose in an orderly manner. However, in some large experiments on mice and one on Macaca mullata, there was no evident increase risk of cancer at 1–2.Gy single dose WBI. These studies were life span and autopsy examinations.

Risk of death due radiation induced solid cancer among 86,611 survivors of the atom bomb explosions in 1945 [entered the study in 1950] increased throughout the observation period of 52 years. There have been 10,127 deaths due to solid cancer and of these, 479 [4.7%] have been attributed to the radiation exposure. The time distribution of these cancer deaths have been: 18%, 19.1%, 27.1% and 35.4 % for the periods 1950–67, 1968–77, 1978–87 and 1988–97. Namely, 35% of these radiation cancer deaths occurred at 42–52 years post irradiation.

Data from 14 large and long follow‐up series of irradiated human patients demonstrate increased risk with dose for cancers of the stomach and pancreas; over the dose range 1–45 Gy. In contrast there was no evident increased risk of bladder or rectal cancer after doses of 1–60 Gy. For the studies on murine, canine, sub‐human and human subjects there is not a constant relative risk for the different organs, viz probability of a radiation cancer for a specified dose varies with the organ.

Consideration will be given to the differential risk between photon [conformal and IMXT], proton [broad beam energy modulated and pencil beam scattered] and 12C ion beams.
WE‐C‐224A‐03: NCI Perspective On Clinical Trials for Emerging RT
Authors: Deye J
Published: July 2006

The National Cancer Institute funds numerous clinical trials that employ radiation therapy either as the primary question in the trial or as standard of care adjuvant therapy that is only secondary to the primary agent. In any case it has been shown that the validity of the trial is strongly dependant upon the quality and reproducibility of the radiation administered. In all cases it is of paramount concern that the risks of the treatments be as quantified as possible so that the study design is valid and there can be a true informed consent. Toward those ends the NCI also funds efforts to ensure the correctness of the physical dosimetry (ie. Radiological Physics Center) and the comparability of advanced technical methods (ie. The Advanced Technology Consortium). This presentation will explain these cooperative agreements and highlight some of their accomplishments that impact upon the risks of using advanced radiotherapy methods in clinical trials.
WE‐C‐224A‐05: Patient Modeling and Organ Dose Calculations Using Monte Carlo Methods
Authors: Xu X G , Paganetti H
Published: July 2006

The risk for a patient to develop secondary cancers from non‐target exposures can be assessed from the equivalent doses to various radiosensitive organs. To determine organ doses, a computational model or physical phantom that represents the whole patient anatomy must be used. Physical phantoms (such as the RANDO and ATOM phantoms) have tiny cavities on each of the tissue‐equivalent slices for inserting TL and MOSFET dosimeters. When beam is delivered according to a patient's treatment plan, the dosimeters are processed to provide organ dose information. The experimental procedures can be time‐consuming and expensive, especially when various patients and treatment plans are studies. Virtual patient models, on the other hand, can be combined with a Monte Carlo code to simulate the transport of radiation in the body. These models cover the entire body and typically contain a large number of defined organs. Coupled with a model of the accelerator, one can calculate detailed information about secondary dose distributions in the patient body. Whole‐body models are classified into three types: 1) Stylized models that are based on surface equations, 2) Tomographic models that are derived from medical images, and 3) Hybrid equation‐voxel models that describe organ boundaries using advanced primitives such as the NURBS for realtime deformation (4D simulations). To date, more than 20 tomographic models have been developed for radiation protection and nuclear medicine applications. An international consortium on computational human models (www.virtualphantoms.org) has been recently formed to promote research in this area. A team of researchers from Rensselaer, Vanderbilt, University of Florida, Massachusetts General Hospital and Johns Hopkins University is working on a project to standardize a library of age‐ and gender‐specific models.

This lecture presents the current status of patient modeling and the application of various tools to study secondary doses from radiation treatment involving both photons and protons. Detailed information on the VIP‐Man model developed from the Visible Human Project is presented. Segmentation of more than 80 organs, including the red bone marrow, and the implementation of the VIP‐Man model into EGS, MCNP/X and GEANT4 are discussed. Finally, organ doses and effective doses for proton treatment plans using various adult and pediatric patient models are presented.

Educational Objectives of this symposium are:

1. Understanding new tools of Monte Carlo‐based patient and accelerator modeling for secondary dose studies.

2. Understanding the effective dose data for various modalities.
WE‐C‐230C‐01: Ultrasound QC Workshop
Authors: Pfeiffer D , Lu Z , Miller H , Spaulding R , Moore W
Published: July 2006

Quality control testing of ultrasound scanners is gaining importance as the use of diagnostic ultrasound become more quantitative in nature and the systems and probes more complex in design. As evidenced by the rise in popularity of the American College of Radiology's ultrasound accreditation program, the need for comprehensive quality control programs is clear. This workshop is designed to provide attendees an opportunity to learn the impact of scanners and probes on various aspects of image quality and to refresh their skills in ultrasound QA/QC testing. The essential physics of ultrasound imaging and instrumentation will be reviewed. QA/QC testing procedures required by accreditation programs and advisory organizations will be presented. The impact of scanner and probe deficiencies on both B‐mode and Doppler performance will be demonstrated. Tools for analyzing probes will also be demonstrated.

Finally, a discussion of quality control of prostate brachytherapy ultrasound will be presented. In the second half of the workshop, attendees will be given the opportunity to use the various tools and phantoms in a hands‐on environment. Experienced instructors will be at the ultrasound scanners to guide the exercises.

Two identical sessions will be conducted, one in the morning and the second in the afternoon.

Educational Objectives:

1. To learn the effect of parameter settings and probes on various aspects of ultrasound imaging.

2. To observe the impact of system and probe deficiencies on ultrasound performance and image quality.

3. To become acquainted with various ultrasound QC phantoms and test tools and learn their proper use.
WE‐E‐ValB‐04: Functional and Molecular Imaging for Radiotherapy Guidance
Authors: Xing L
Published: July 2006

Radiation therapy is an image‐guided procedure whose success depends strongly on the image modality used for treatment planning and the level of integration of the available imaging information. Advancement in IMRT has provided an unprecedented means to produce highly conformable dose distribution while sparing sensitive structures, which calls for better imaging tools for tumor target definition and for the management of inter‐ and intra‐fractional organ motion. In this talk we will summarize recent advances in functional and molecular imaging techniques and discuss various issues related to the integration of the newly emerged imaging data into radiation therapy planning. It is anticipated that the new imaging modalities will play an important role in radiation oncology practice and make significant impact in cancer diagnosis, staging, treatment planning, and monitoring of therapeutic response. The potential impact of biologically conformal radiation therapy (BCRT) or biologically guided radiation therapy (BGRT) will be discussed. Finally, issues related to the quality assurance of functional and molecular imaging and BCRT will also be addressed.

Educational Objectives:

1. Introduce the concept of functional and molecular imaging.

2. Illustrate the steps involved in integrating molecular imaging such as PET and MRSI into treatment planning process.

3. Introduce PET/MRI/MRSI and CT image fusion techniques (including deformable image registration).

4. Provide an overview on recent advances in PET/CT and MRSI, and update on the development of new PET tracers and data acquisition techniques.

This work was supported in part by NCI 5R01 CA98523‐01.
WE‐E‐224C‐05: Uncertainty Analysis of Risk of Secondary Fatal Malignancies From Radiotherapy Treatments Including IMRT
Authors: Kry S , Followill D , White R , Salehpour M
Published: July 2006

Purpose: Radiation away from the treatment field may induce secondary cancers in long‐term survivors. Risk estimates have received increased attention with the increase in out‐of‐field dose associated with IMRT. However, uncertainty in these risk estimates were not previously established, which has left unresolved the significance of these risk estimates. This work examines the uncertainty in the absolute risk estimates, as well as uncertainties in the ratio of risks between treatment modalities. Method and Materials: Effective dose equivalents and estimated risks were taken from the literature for several treatment modalities including IMRT at 6, 10, 15, and 18 MV and conventional therapy. The most recent risk estimates (5.75%/Sv) along with uncertainties in this risk estimate and uncertainties in the dose‐response model were considered in generating 90% confidence intervals for the absolute risk estimates and ratio of the risk estimates. Results: The absolute risks of fatal secondary malignancy were associated with very large uncertainties, which precluded distinguishing between the risks for the different treatment modalities considered. However, a much smaller confidence interval existed for the ratio of the risk. Because of the confidence intervals generated, an effective dose equivalent difference of 50% resulted in a statistically different ratio of the risks. Such differences were observed between some of the treatment modalities considered including 6MV as compared to 18MV IMRT. Conclusion: While no statistically significant difference existed in the absolute risk estimates of the treatment options examined in this study, the ratio of the risks was found to yield statistically significant differences between some treatment modalities considered.