bluuebunny/crossref_metadata_2025_split huggingface dataset:
TU‐C‐330A‐01: The History (and Future) of MRI Physics
Authors: Roberts T 
Published: July 2006

The history of MRI is now a little over 30 years old. It's impact on the scientific, and in particular medical, community has been immense, and shows no sign of slowing. From the first demonstration in 1973 of the spatial encoding of proton density information in the nuclear magnetic resonance signal, via the application of pulsed magnetic field gradients, a succession of technological developments now makes MRI the modality of choice for a wide range of cross sectional biomedical imaging applications. This talk will offer some insights into the origins of MRI, the rapid development of spin echo and gradient recalled echo, 2D and 3D, imaging and the birth of faster and faster imaging involving multiple echoes (RARE and echo planar imaging). Additionally, interpretation of MRI‐accessible contrasts emerged, offering specific insights into physiology via NMR relaxation time constants and such MRI “flavors” as diffusion weighted imaging. In parallel, MRI‐specific contrast media (“magnetic dyes”) were introduced in the 1980's offering both “enhancement” of MRI signal as well as the opportunity to study dynamic processes (such as bolus tracer passage, with concomitant estimation of perfusion and, later, microvascular permeability). The 1990's saw the continued clinical adoption of MRI as well as the commitment to physiologically‐specific imaging and the introduction of blood oxygenation level dependent (BOLD) contrast and the birth of “functional magnetic resonance imaging, fMRI”, for the spatial mapping of brain functional organization. More recently yet further acceleration in image acquisition speed has been offered by the introduction of multiple (parallel) receiver coil elements and the adoption of the principles of sensitivity encoding. Presently, acceleration factors of ×2 are routine, ×4 are commonplace and ×9 or more are in development. The future offers the possibility of massively parallel acquisitions with effectively single‐shot temporal resolution of the order of milliseconds. While the contrast resolution of MRI is transitioning from anatomy through physiology towards biochemical processes, the speed of MRI is accelerating from static to real‐time, hurdling successive physical and physiological boundaries (such, as involuntary motion, breath‐hold, cardiac cycle and ultimately towards the speed of neuronal processes). The overall vision of this talk is to convey the ongoing development of MRI towards both increasing spatial and temporal resolution as well as towards increasingly specific biological interpretation.Educational Objectives:1. To understand the origins and background of today's MRI.2. To understand the rapid development of MRI acquisition speed.3. To understand the use of tailored MRI to derive physiologically specific image contrast.4. To anticipate the continued acceleration of both imaging speed and biological application of MRI.
TU‐C‐330D‐02: Digital Breast Tomosynthesis
Authors: Maidment A 
Published: July 2006

Both film‐screen and digital mammography are subject to a number of fundamental limitations related to the projection process, whereby 2D images are produced of the 3D breast anatomy. Mammography can produce artifactual densities from the superposition of normal tissues that are separated in space; although only visible in a single view, these often appear sufficiently suspicious to necessitate a biopsy, leading to a loss in specificity. Furthermore, true lesions in mammograms can be masked by superimposed normal tissue and thereby rendered undetectable; this reduces the sensitivity of mammography.Numerous tomographic methods have been proposed to overcome these limitations, including digital breast tomosynthesis (DBT). DBT is a tomographic imaging technique in which a set of tomographic images can be reconstructed from a limited number of x‐ray projection images. DBT has the potential to mitigate against both the superposition of non‐adjacent tissue (false positive densities) and the masking of real lesions (false negatives) observed in projection mammography, while also providing a simple means of localizing lesions in 3D. A preliminary retrospective study of breast tomosynthesis by Rafferty et al. has demonstrated a 16% increase in sensitivity and 85% decrease in false positives as compared to digital mammography. Our own experience at the University of Pennsylvania with 51 patients has provided supported anecdotal evidence.DBT also offers the potential for functional imaging. Breast tumor growth and metastasis are accompanied by the development of new blood vessels. We have used a modified GE 2000D under IRB approval, to gain initial experience in contrast‐enhanced DBT (CE‐DBT). To date we have acquired 13 CE‐DBT clinical cases. Suspicious enhancing lesions were demonstrated with CE‐DBT in 10 of 11 cases of pathology‐proven breast cancer. The cases illustrated that CE‐DBT could provide information in concordance with multimodality imaging evaluation. The pre‐contrast tomosynthesis images demonstrated lesion morphology and border characteristics in greater detail than the digital mammography images, and the CE‐DBT data sets demonstrated vascular characteristics of the breast lesions of interest that were consistent with the vascular information provided by MR. In addition, quantitative evaluation of contrast uptake is anticipated to be more easily standardized with CE‐DBT due to the linear relationship between attenuation and contrast concentration compared to MRI.In this presentation, the following education objectives will be addressed:1. Review the development and design of digital breast tomosynthesis systems.2. Evaluate the results of the existing DBT clinical trials.3. Examine advanced applications of DBT including contrast‐enhanced DBT and CAD.4. Compare DBT to other x‐ray tomographic imaging modalities.
TU‐C‐330D‐03: Computed Tomography of the Breast: Design, Fabrication, Characterization, and Initial Clinical Testing
Authors: Boone J , Nelson T , Kwan A , Yang K 
Published: July 2006

Purpose: Although there is overwhelming evidence that mammographic screening has led to a reduction in breast cancer mortality, most breast imaging experts agree that screening technology could be improved. We have developed a dedicated breast CT scanner which may be appropriate for breast cancer screening in some groups of women. Methods and Materials: A breast CT scanner was designed and fabricated in our laboratory using off‐the‐shelf components (an x‐ray system, flat panel detector, and motor) and custom‐manufactured parts. Image quality was assessed subjectively in terms of artifacts, and by conventional metrics (MTF for spatial resolution, RMS noise, etc.). Radiation dose levels were adjusted to be comparable to two‐view mammography, using a series of physical measurements and Monte Carlo computations. Evaluation in patients has begun with both Phase I and Phase II clinical trials. Results: The spatial resolution of the bCT system exceeds that of commercial scanners, with a 10 percent MTF corresponding to XX inverse mm (center of field, 80 kVp, 500 views). Noise metrics demonstrates that the scanner performs in a quantum limited manner. Ten healthy volunteers have been scanned, and as of this writing 35 women with BIRADS 4 or 5 diagnoses have been scanned. Subjective evaluation of image quality clearly indicates detail not seen mammographically. The volume dataset (300 512 × 512 pixel images) can be displayed in coronal, axial, saggital or any arbitrary view angle. Conclusions: The clinical evaluation of the bCT system is underway, and early subjective results have generated interesting images with excellent anatomical depiction. The use of contrast agents has added a functional component to breast CT imaging. Further patient accrual with subsequent quantitative (ROC) analysis is needed.Learning Objectives:1. Status of breast CT implementation at UC Davis.
TU‐C‐ValA‐02: A Simple Iterative Method to Invert a Deformation Field
Authors: Chen M , Lu W , Ruchala K , Chen Q , Pan Y , Olivera G 
Published: July 2006

Purpose: Inversion of a deformation field is applied frequently to map dose and regions of interest to a reference frame. A prevailing naïve approach that takes the opposite displacement of the forward deformation as the displacement of the inverse is mathematically wrong and can cause large errors for large or accumulative deformation. Inversion by “scattered data interpolation” has O(N2) complexity and is difficult to implement. We propose a simple iterative approach with O(N) complexity. Method: Instead of calculating the inverse, we calculate the displacement of the inverse. The displacement of the inverse is iteratively refined through the displacement of the forward map. We prove that such iterative scheme converges exponentially to the true solution when the deformation field is subject to a condition of the Lipschitz type. The Lipschitz type condition essentially states that the difference of the deformation of two points can not be too far. This is a mild restriction on the deformation field and is usually a valid assumption for any deformable registration method with regularization.Results: We tested the proposed method on both simulated 2D data and real 4D CT data of lung patient. The simulations showed that the proposed method has exponential convergences to the true inverse. For real 4D CT data, the forward deformation field constructed by deformable registration mapped the test phase to the reference phase and the inverse of that deformation field accurately map the reference phase to the test phase. Conclusions: A simple, accurate and fast method for inverting a deformation field is presented. Both the mathematical proof and the simulations showed its exponential convergence. Simulations and real data tests demonstrated its efficacy in medical image analysis and radiotherapy applications. Typically less than 10 iterations are needed to get an inverse deformation field with clinically relavent accuracy.
TU‐C‐ValA‐05: Assessment of a Model‐Based Deformable Image Registration Approach for Radiotherapy Planning
Authors: Kaus M , Brock K , Pekar V , Bzdusek K , Dawson L , Nichol A , Jaffray D 
Published: July 2006

Purpose: To assess the accuracy of a surface‐based deformable image registration strategy as a function of the elasticity model for the integration of multi‐modality imaging, image‐guided radiation therapy, and quantification of geometrical change during and following therapy.Method and Materials: A surface‐model based deformable image registration system has been developed that enables quantitative description of geometrical change in multi‐modal images. Based on the deformation of organ surfaces represented by triangular surface meshes, a volumetric deformation field is derived using different volumetric elasticity models (Thin‐Plate Splines, Wendland functions, Elastic Body Splines) as alternatives to finite‐element modeling. Results: The system was demonstrated on five liver cancer patients, ten prostate cancer patients, thorax in five healthy volunteers, and abdomen in five healthy volunteers. The accuracy of the system was assessed by tracking visible fiducials (bronchial bifurcations in the lung, vessel bifurcations in the liver, implanted gold markers in the prostate). The maximum displacements for lung, liver and prostate were 5.3 cm, 3.2 cm, and 1.8 cm respectively. The largest registration error (direction, mean ± standard deviation) for lung, liver and prostate were (inferior‐superior, −0.21 ± 0.38 cm), (anterior‐posterior, −0.09 ± 0.34 cm), and (left‐right, 0.04 ± 0.38 cm) respectively, which was within the image resolution regardless of the deformation model. The computation time (2.7 GHz Intel Xeon) was on the order of seconds (e.g. 10 seconds for two prostate data sets), and image deformation results could be viewed at interactive speed (less than 1 second for 512×512 voxels). Conclusion: Surface‐based deformable image registration enables the quantification of geometrical change in normal tissue and tumor with acceptable accuracy and speed.
TU‐C‐ValB‐01: Evaluation of Clinical Margins Via Simulation of Patient Setup Errors in 27 Prostate IMRT Plans
Authors: Gordon J , Crimaldi A , Siebers J 
Published: July 2006

Purpose: To evaluate: (i) the size of random and systematic setup errors that can be absorbed by 5mm CTV‐to‐PTV margins in prostate IMRT treatment plans; (ii) whether findings are consistent with published margin recipes; (iii) if shifting contours with respect to a static dose distribution accurately predicts dose coverage due to setup errors.Method and Materials: 27 IMRT treatment plans with 5mm CTV‐to‐PTV margins were utilized. Random setup errors with standard deviations (SDs) of 1.5, 3 and 5mm were simulated by fluence convolution. Systematic errors with the same SDs were simulated using two methods: (a) shifting the isocenter and recomputing dose (isocenter shift), and (b) shifting patient contours with respect to the static dose distribution (contour shift). Maximum tolerated errors were evaluated such that 90% of plans had target coverage greater than a specified minimum. Results: For coverage criteria consistent with margin formulas, plans generated with a 5mm margin were able to absorb SDs >3mm. Most structures, including the prostate CTV, showed close agreement between isocenter and contour shift methods. Exceptions were the nodal CTV and small bowel. For 3mm SDs, contour vs isocenter shift estimates for the percent of plans with acceptable dose differed by >2% for the nodal CTV, and >7% for the small bowel. Contour shift small bowel D30 values differed from isocenter shift values by >120% for some simulated shifts. Conclusion: Published recipes require margins of 8–10mm for 3mm SDs. For the IMRT cases presented here, a 5mm margin would suffice. Approximating structure doses by shifting contours with respect to a static dose distribution was acceptable for most structures, but resulted in significant errors for the nodal CTV and small bowel doses for some shifts due to proximity to high dose gradients. (Work supported by NIH R01CA98524).
TU‐C‐ValB‐08: Modeling Dose Delivery Accuracy of IMRT Head‐And‐Neck Cancer Treatment
Authors: O'Daniel J , Garden A , Wang H , Asper J , Ang K , Ahamad A , Schwartz D , Rosenthal D , Morisson W , Zhang L , Tung S , Mohan R , Dong L 
Published: July 2006

Purpose: To evaluate the impact of internal organ variations on IMRT treatments of head‐and‐neck cancers using different daily alignment techniques. Method and Materials: Eleven head‐and‐neck cancer patients were imaged twice weekly during their course of treatment (141 CT scans total) using an integrated CT‐linear accelerator (EXaCT, Varian Oncology Systems). The clinical IMRT plans were copied onto the daily CT images. The plans were aligned with (1) the daily marked isocenter using three radio‐opaque markers (BBs) and (2) bone alignment, using in‐house software to align the cervical vertebrae. Daily dose distributions were mapped from the daily CT images onto the planning CT image with an in‐house deformable image registration algorithm. Cumulative dose‐volume histograms from the planning CT image were analyzed. Results: The differences in the clinical target volumes (CTV) gEUD between the planned and delivered doses (with BB or bone alignment) were typically ⩽1Gy; therefore the differences in target coverage were most likely clinically insignificant. However, the alignment method did have a statistically significant impact on the percentage‐volume of the CTV at the prescription dose. Neither BB alignment nor bone alignment maintained the planned coverage (average=98.2%), which was reduced to 95.6% with bone alignment (p=0.000) and 94.3% with BB alignment (p=0.000).BB alignment significantly increased the average percentage‐volume receiving ⩾25Gy above the original plan for the ipsilateral (59.6% vs. 51.4%, p=0.003) and contralateral (42.0% vs. 36.4%, p=0.016) parotid glands. The parotid gland gEUD increased by more than 5Gy in 35% of BB alignments and 15% of bone alignments. However, there was no statistically significant difference between BB and bone alignments in parotid dose received. Conclusions: The differences in CTV coverage between bone and BB alignment were statistically significant but small. Bone alignment more closely reproduced the planned parotid dose than BB alignment, although both gave higher dose than the original plan.
TU‐C‐224A‐03: 4D‐Image‐Guided Treatment Planning Optimization for Management of Organ Motion in Radiotherapy Planning
Authors: Lee E , Cha K , Bortfeld T , Deasy J 
Published: July 2006

The management of breathing‐registered IMRT treatment planning is explored by direct incorporation of 4D images within the planning process. The movement of the voxels from one CT timeframe to another is “tracked” and modeled. A timestamp for each voxel is used to specify its position throughout the breathing cycle. A single treatment model incorporates planning constraints throughout multiple time periods. Robustness of the algorithm, plan quality, and potential clinical significance are evaluated.4D‐CT scans of lung/liver cancer patients were acquired with different breathing phases(phases 0–9, 0:full‐inhale, 5:full‐exhale), Three treatment planning strategies are performed and compared. 1)Standard planning with a static PTV based on a single selected phase (control). 2)The Internal Target Volume (ITV) approach, where ITV is defined as the union of CTVs in all breathing phases. 3)Single‐stage‐4D‐image‐guided planning, where within a single treatment optimization model, planning constraints are incorporated on each voxel for each phase throughout the multiple‐phase period. Sophisticated computational optimization techniques are used to solve these models.For both lung/liver cases, the static‐PTV‐plan results in unacceptable PTV‐underdose. Compared to ITV‐pamns, 4D‐image‐guided‐plans offer good coverage and comparable min‐PTV‐dose; while in lung, it reduces normal‐lung‐mean‐dose by 20%, heart‐mean‐dose by 20%, and esophagus‐max‐dose by 15%; and in liver, it reduces normal‐liver mean‐dose by 15% and other normal‐tissue mean‐dose by 20%, with improved PTV‐conformity of 10%.4D‐Image‐Guided treatment planning optimization can provide good PTV‐coverage plans, improve PTV‐underdose, and significantly reduce dose to organs‐at‐risk, especially those organs in the proximity of the tumor. Evidence of morbidity reduction to organs‐at‐risk is observed. The challenge involves the ability to solve a large‐scale treatment planning problem. With sophisticated mathematical optimization modeling and computational strategies, such planning is possible and can be made available for clinical use. Clinical studies are needed to validate the importance of our approach to treatment outcome.
TU‐C‐224A‐04: Simplifying Parameter Adjustment for Prostate IMRT Planning Using Sensitivity Analysis
Authors: Lu R , Radke R , Happersett L , Chui C , Yorke E , Jackson A 
Published: July 2006

Purpose: To simplify the trial‐and‐error process of adjusting objective function parameters (e.g. weights, dose limits) in prostate IMRT planning, we present a feasibility study showing that an outer loop optimization over 6 automatically‐identified sensitive parameters can quickly and automatically determine parameters that lead to a plan meeting the clinical requirements. Method and Materials: We apply statistical sensitivity analysis to quantify the effect of each hand‐tunable parameter of the IMRT cost function on each clinical objective, automatically identifying those parameters with the strongest impact. Second, we globally optimize a plan quality score over the six most sensitive parameters in an outer loop to determine acceptable parameters, using a search algorithm based on multiscale random sampling. Results: Experiments on a 36‐patient dataset showed that a clinically acceptable five‐field 8640cGy prostate IMRT plan could be automatically determined in 35 minutes on the average in 87% of the cases. Compared to the plans from the planner's protocol default settings, the mean value of the minimum dose in PTV increased from 67.5% to 79.7%, and the mean value of PTV V95 coverage increased from 82.2% to 94.1%. The mean values of rectal wall V54%, rectal wall V87% and bladder wall V54% are 50.4%, 12.6% and 36.1%, respectively. The outer‐loop‐optimized plans met DVH constraints defining clinical acceptability and were comparable to manually‐determined plans. Confining the parameter search to the sensitive parameter set greatly improves the quality and speed of the outer‐loop optimization. Conclusion: The reduced‐order outer‐loop optimization can facilitate parameter selection for dose‐volume‐based IMRT objectives. It may also be applicable to other types of objective functions, and has the potential to ease the manual burden of IMRT planning in more complex sites (e.g. head and neck).Supported by National Cancer Institute grant 5P01CA59017‐13 and the NSF Center for Subsurface Sensing and Imaging Systems, grant EEC‐9986821.
TU‐C‐224A‐06: Exploiting the Full Potential of MLC Based Aperture Optimization Through Collimator Rotation
Authors: Milette M , Rolles M , Otto K 
Published: July 2006

Purpose: To investigate the benefits of MLC rotation in Direct Aperture Optimization (DAO) inverse treatment planning. Method and Materials: An alternative to fluence based inverse planning is to optimize directly the leaf positions and field weights of MLC apertures. Here we introduce a new technique called Rotating Aperture Optimization (RAO) which is based on an extension of DAO. Our technique differs from existing aperture based IMRT techniques in that the MLC is rotated in between each aperture. Treatment plans are generated for 10 nasopharynx recurrence patients with and without MLC rotation for 5 mm and 1cm leaf width MLCs. A comparison study is performed between RAO and DAO in order to assess the benefits of RAO over and above those available with fixed collimator angle DAO. Film verification is also performed to evaluate the accuracy of fixed and rotated collimator aperture delivery. Results: An analysis of the final cost values and DVHs indicate that plans generated with RAO are as good as or better than DAO while maintaining a smaller number of apertures and MU than conventional IMRT. In particular, RAO with the 1cm leaf width MLC is able to produce better plans than DAO with the 1 cm leaf width MLC and plans that are equivalent to DAO with the higher resolution 5mm leaf width MLC. Film verification results show that RAO is less sensitive to tongue and groove effects than DAO. Although delivery time is increased due to the collimator rotation speed this is a mechanical limit that could be easily overcome. Conclusion: Our results indicate that RAO is able to provide superior dose distributions, particularly with larger (1 cm) leaf width MLCs, while maintaining the lower MU and number of apertures afforded by the direct aperture approach.Conflict of Interest: Supported in part by Varian Medical Systems.