bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐DD‐A2‐06: Improved Phantom and Method for Measuring the Low Contrast Detectability Performance of Fluoroscopic and Radiographic Systems
Authors: Ranallo F
Published: June 2005

Purpose: To develop an easy and reliable method of determining the low contrast detectability (LCD) performance of fluoroscopic and radiographic imaging systems Method and Materials: A phantom has been developed containing objects made of water equivalent material of varying contrast and diameters. Randomization of the positions of these objects is easily accomplished via the design of the phantom. To measure the LCD one would first decide what objects are visible in the fluoroscopic image. The phantom is then designed to allow one to easily see the actual positions of the objects in the phantom, once this visual judgment is made. Only correctly identified objects are scored. This method greatly reduces the subjectivity of present methods of performing this test, including the eventual memorization of a fixed “random” phantoms. The use of tissue equivalent materials for this test also gives a more true result of LCD for clinical studies and is much less biased by changes in kV and grid use. The use of this phantom can also be extended into evaluation of radiographic and digital imaging systems. Results: The use of this phantom provides accurate, reproducible measurements of LCD for fluoroscopic imaging as long as certain viewing precautions are observed for the fluoroscopic image. Conclusion: Current methods of evaluating fluoroscopic and radiographic image quality by means of LCD performance are relatively unreliable and quite variable between different observers. This new method allow for more accurate, reproducible LCD measurement.
SU‐DD‐A3‐01: Novel Geometric and Dosimetric On‐Line Correction Strategies: Can Chance Work in Your Favor?
Authors: Keller H , Couillard M , Davison M , Moseley D , Jaffray D
Published: June 2005

Purpose: Investigate the efficacy of three novel geometric and dosimetric on‐line strategies for adaptive radiotherapy in terms of workload and compliance with original treatment plan intent. Method and Materials: The three proposed on‐line strategies are: Selective setup corrections (S1), Combined dose‐per‐fraction adaptation and setup corrections (S2) and Optimal dose‐per‐fraction adaptation (S3). In S1, setup corrections will only be performed if the displacement is “unfavorable” in terms of a radiobiological score based on equivalent uniform dose. The score function encodes a clinical preference for maintaining dose to the target, the critical organs or an arbitrary combination. S2 combines the selective setup corrections of S1 with a change in daily dose‐per‐fraction. In S3, only dose‐per‐fraction is a variable and is determined using a rigorous constraint stochastic optimization procedure. In a retrospective study the efficacy of these strategies was investigated. They were applied to a displacement dataset of 5 prostate patients. Results: For S1, maintaining the planned dose to the prostate is costly and requires many setup corrections. In contrast, a rectum‐weighted score requires far less interventions and decreases the dose to the rectum on the order of 1.5 Gy, while approximately maintaining the dose to the prostate. Strategy S2 allows a considerable boost to the prostate dose for a preference to maintain the dose to the rectum. However, in this case, the bladder may exceed the dose limits. An equal‐weighted preference is able to moderately boost the prostate dose while decreasing rectal dose and only moderately increasing bladder dose. S3 showed the biggest potential, however, it is computationally more involved. Conclusion: Flexible correction strategies can be designed using information about treatment anatomy and planned dose distribution. Such radiobiologically motivated strategies can be made highly compliant with initial treatment plan intent while often significantly reducing the number of interventions.
SU‐DD‐A3‐03: Evaluation of An Infrared Camera and X‐Ray System for Gated Radiation Therapy
Authors: Willoughby T , Wagner T , Langen K , Forbes A , Buchholz D , Kupelian P , Meeks S
Published: June 2005

Purpose: To determine the clinical feasibility of a gated treatment delivery system from BrainLab™. Method and Materials: The Exactrac from BrainLab™ is a localization system that uses both infrared cameras and x‐rays. In gated mode, target location is determined by implanted fiducials. Breathing patterns are determined by infrared reflectors attached to the patient's surface. The User selects an x‐ray trigger point and radiotherapy beam‐on window relative to the breathing cycle. Multiple trigger levels may be selected to simulate a fluoroscopic mode to measure organ motion. Prior to clinical use feasibility tests including localization accuracy, gating window accuracy, and beam‐on accuracy were performed. Patients with small lung lesions were selected for treatment and implanted with a 20 by 0.7 mm gold fiducial. Treatment planning CT scans were taken at expiration breath hold with internal and external fiducials present. Results:_Localization accuracy was within 3mm when using 20% of the breathing cycle for beam on. To date, five patients with lung lesions were treated. Treatment times were approximately twenty minutes (standard dose fractionations). Implanted fiducials were well localizable in all patients. Target motion was on the order of 5mm average. Repeat CT scans showed implants did not migrate. The primary limitations with the system were related to breathing signal due to placement of external fiducials. Conclusion: Gating treatment technique from Exactrac™ has been used to treat lung lesions. This initial evaluation of the system verified the accuracy of the localization system under Gated mode. Implanted fiducials are localizable in patients, and gating is possible. The benefit of this system is the potential to decrease treatment margins and improve targeting. Continued evaluation of this system would help to define patient specific dose margins and beam‐on windows for treatment.
SU‐DD‐A3‐05: Real Time DMLC IMRT Delivery for Mobile and Deforming Target
Authors: Papiez L , Rangaraj D
Published: June 2005

Purpose: Assume image system in the treatment room provides the information about target motion/deformation during therapy in real time. The ultimate utilization of this information calls for applying it to the intensity modulated therapy so that intensity maps dynamically shift and deform in conjunction with the target motion. This presentation describes algorithms for the control of MLC leaves that deliver real time image guided therapy described above. Method and Materials: Target motions and deformations are modeled from data registered in real time. Real time IMRT aims for (1) delivery of predetermined intensity to target and surrounding tissue, (2) minimized time of delivery and (3) limitation of maximum speed of leaf motions to below the speed of maximum velocity admissible for MLC. As goals (1) and (3) constitute indispensable conditions of IMRT delivery the minimization of the time of delivery (2) has to bee sacrificed. Thus the original set of equations relating leaf positions and velocities to deliver the predetermined intensity is set as the problem with over‐restrictive conditions on leaf speeds. Random perturbations are then imposed over target motions and relationships between leaf velocities are appropriately modified to respond to perturbations. This assures that the slope of local intensity is properly shaped at each point of moving target with unpredictable real time registered motions of the target. Results: A sequence of representative examples delivering real time IMRT to moving/deforming targets is presented. Examples considered are characterized by varied intensities and different pattern of target motions/deformations. Deliveries of planned intensities, with and without corrections for changes in target motions/deformations, are calculated and inter‐compared. Conclusion: MLC leaf motions can be controlled in real time so that image guided DMLC IMRT delivery is feasible provided image system in the treatment room communicates to MLC controller target motion/deformation data during therapy in real time.
SU‐DD‐A3‐06: Model‐Based Probabilistic Prediction of Tumor Respiratory Motion
Authors: Wu H , Sharp G , Salzberg B , Kaeli D , Shirato H , Jiang S
Published: June 2005

Purpose: The effectiveness of radiation therapy is degraded by respiratory motion, especially in the thoracic and abdominal regions of the body. Precise tumor localization, motion characteristics, and motion prediction are essential for accurate radiation dose delivery in real‐time image‐guided radiation treatment. To address this problem, we propose a model‐based probabilistic solution for prediction of tumor respiratory motion. Method and Materials: By analyzing the historical motion data based on a finite state model, two probability distributions are proposed for knowledge discovery of tumor moving status. These probabilities can be used to determine the current motion state and capture transitions from one state to another. They are dynamically built and used in real‐time motion prediction. Two prediction problems are studied for beam tracking and respiratory gating. The first requires continuous prediction of the exact tumor position, while the second requires predicting when the tumor will be IN or OUT of the gating window during radiation treatment. Results: Three metrics are used to evaluate the accuracy of the prediction Results: 1) the root mean square (RMS) error, 2) the gating duty cycle, and 3) the gating failure rate. Experiments on real patient data have been performed. Our model‐based probabilistic prediction approach results in smaller RMS error, higher gating duty cycle, and lower gating failure rate than linear prediction. The same pattern has been observed for different patients, and with different latency. Conclusion: A probabilistic model‐based approach can be used to characterize and predict tumor motion, and offer better prediction accuracy than linear prediction.
SU‐DD‐A4‐01: Multi‐Day Multi‐Modality Image Co‐Registration
Authors: Smith E , Barbee D , Pyzalski R , Jeraj R
Published: June 2005

Purpose: To develop a methodology for multi‐day co‐registration of multi‐modality images taken throughout the course of radiotherapy, for the assessment of tumor response to treatment. Method and Materials: CT and PET image data sets of canines with various tumors were taken on a PET/CT scanner and were automatically co‐registered to each other by the scanner software. Using a commercial software package, ROI segmentation was performed on the CT data to define the tumor boundaries. Each PET data set was then masked by the ROI of its aligned CT image and then rigidly co‐registered with the masked PET data from other days. To align more specific uptake regions within the tumor, image warping was performed via landmarks placed on the co‐registered multi‐day PET data. Results: We found that ROIs can be roughly aligned by rigid registration of the outer tumor region as defined by the segmentation of CT data. Histogram correlation plots, aided by visual assessment, illustrated that normalized mutual information and Euclidean distance were the best‐suited criteria for rigid registration, and that increased accuracy in co‐registration was gained from image warping via landmarks placed on specific structures within the day‐to‐day rigidly co‐registered PET data. A review of warping techniques on the co‐registered PET data and generated data phantoms demonstrated that thin‐plate spline warping provided the most complete warping of landmarked structures, while flow warping was not as aggressive with non‐landmarked structures. Conclusion: Using this methodology of rigid registration of tumor boundaries defined from CT data, followed by inner feature warping of PET data proves to be an accurate and usable way to perform multi‐day multi‐modality image co‐registration. Further investigations include additional contouring of segmented regions, adding scaling parameters to the initial registrations, and refining landmark placement and warping techniques.
SU‐DD‐A4‐02: Fast Multimodal Image Registration Using Mutual Information and Variable Step‐Size Grid Search Algorithm
Authors: Wu J , Samant S
Published: June 2005

Purpose: A robust optimization algorithm, referred to as variable step‐size grid search (VSGS), is presented for 2D/2D multimodal image registration, and evaluated using phantom and clinical imaging. Method and Materials: The VSGS optimization algorithm is based on recursive iterations of a geometrically scaled step‐size, and is more likely to converge to the global optimum and be less insensitive to the local optima compared to traditional gradient techniques (i.e. Powell, quasi‐Newton). As an optimization technique, it can be used with any objective function. Here mutual information was used as the similarity measure, and a multiresolution strategy was adopted to accelerate computation without adversely affecting robustness. VSGS was applied to the problem of automatic patient positioning in radiotherapy. The multimodal imaging consists of digitally reconstructed radiographs (DRRs), portal images acquired with electronic portal imaging devices (EPID), and the Varian linac‐based on‐board kilovoltage imager. EPID images were collected using the Siemens BEAMVIEW video EPID and the Varian AS500 flat‐panel imager. Results: Validation was carried out using phantom and clinical imaging data. Measurements indicated that VSGS has an accuracy of 0.5 mm (or 1 pixel) and <0.5°, and required about 8 seconds per registration on a 2 GHz PC. VSGS has an accuracy equivalent to or better than the traditional optimization techniques depending on histogram or Parzen‐windowing based mutual information calculations, but is more robust and faster computationally. This allows VSGS to be used for online real‐time image guided patient positioning without requiring frequent user intervention to recognize shifts associated with registrations trapped in local extrema. Conclusion: VSGS can be used for online real‐time image guided patient positioning to achieve more accurate patient positioning than using visual verification, and is sufficiently robust compared to traditional optimization techniques to make algorithm‐based registrations sufficiently robust for routine clinical use.
SU‐DD‐A4‐03: Spatial and Volumetric Comparison of Liver Tumors On CT and MR Using Finite Element Based Deformable Image Registration
Authors: Dawson L , Voroney J , Eccles C , Haider M , Brock K
Published: June 2005

Purpose: To compare the spatial and volumetric differences in liver tumor definition based on triphasic IV contrast CT and Gadolinium contrast MR. Method and Materials: Changes in patient and liver position and differences in CT and MR imaging make an accurate comparison of tumor representation challenging, as deformation of the liver occurs. A deformable registration method has been developed to generate geometrically resolved views of the different image sets using finite element modeling to take advantage of the biomechanical relationship between the anatomical representations on each modality. The liver and liver tumors are contoured on the CT and MR, using a treatment planning system. A guided surface projection method is used to identify and account for the geometric discrepancies of the liver, allowing a direct comparison of the MR and CT tumors. Results: Triphasic CT and Gadolinium MR images were obtained at end exhale. Differences in tumor volume and center of mass and in the surface area differing by greater than 3 mm in spatial position (PSA3) were measured for patients with liver metastases, cholangiocarcinoma and hepatoma. The tumor comparisons were done following registration of the liver to resolve geometric discrepancies. The average tumor volume change was 52% (19–121%). The average center of mass change was 0.4 cm (0.1–0.6 cm). The average PSA3 was 49% (28–60%). Initial results show that MR GTV was larger then CT GTV in patients with hepatoma, smaller in cholangiocarcinoma and variable in metastases. Conclusion: Deformable image registration improves the spatial correlation of the MR and CT defined liver GTVs compared to rigid body registration alone. This deformable image registration method preserves the spatial integrity of the tumor, while resolving the geometric differences between the MR and CT liver. Conflict of Interest: Research supported in part by Varian Medical Systems. LD is an ASCO career development award recipient.
SU‐DD‐A4‐05: Investigation of a 3D Gradient Based Method for Volume Segmentation in Positron Emission Tomography for Radiation Treatment Planning
Authors: Aristophanous M , Martel M , Pelizzari C , O'Brien‐Penney B
Published: June 2005

Purpose: Over the past few years Positron Emission Tomography (PET) is being used to supplement radiation treatment planning by assisting physicians in the determination of gross tumor volume. A number of studies have also been investigating the new possibilities that PET offers, such as guiding the delivery of a non‐uniform dose in the tumor volume. Defining the surface of the tumor is an essential step in these applications; hence we investigated the use of a 3D gradient based technique for tumor volume segmentation. Method and Materials: We applied the gradient based technique to FDG‐PET images obtained with a PET/CT scan of NEMA 2001 body phantom, with three spheres of different diameters whose FDG concentration was varied against an essentially constant surrounding activity. We measured the volume of the spheres gravimetrically, calculated them from the CT scan and we also estimated them from the PET images using three segmentation methods: 1) simple intensity thresholding on the raw PET data, 2) intensity thresholding on the background subtracted PET data and 3) a previously described 3D gradient based method. The obtained volumes were compared with the CT volumes. Results: The percentage error on volume estimation from the gradient based method varied from 15–38%. It had precision and accuracy similar to the background subtracted thresholding over the whole range of volumes and backgrounds, while it was less accurate than simple thresholding for low background activities, but worked better in regions of high background activity where the simple thresholding fails. Conclusion: We have successfully applied a gradient based volume segmentation technique to a set of phantom images. This method does not require any a priori information, only involves minimal user interaction and most importantly does not depend directly on image intensities. The results are promising, but further work is needed to validate its clinical use.
SU‐DD‐A4‐06: Registration of Volumetric KV Or MV Cone Beam CT with Fan Beam CT
Authors: Schreibmann E , Yang Y , Boyer A , Li T , Xing L
Published: June 2005

Purpose: Kilovoltage (kV) cone beam CT (CBCT) provides the patient's volumetric information and is valuable for patient positioning verification. An important step in this application is the registration of CBCT acquired at simulation or before treatment with the planning CT (PCT). The purpose of this work is to investigate several specific issues involved in CBCT‐TPCT registration and develop an effective algorithm to effectively utilize the volumetric imaging system for IGRT. Method and Materials: The PCT data were acquired using Picker PQ5000 scanner, and the CBCT images were obtained using Varian Trilogy OBI system. The image quality of CBCT is generally poor as compared with conventional CT: Low soft tissue contrast, artifacts/distortions, and limited width/length present practical problems for its clinical application. A BSpline based non‐rigid image fusion software was implemented to provide voxel‐to‐voxel matching between PCT and CBCT. Results: For the phantom study, the quality of CBCT has little effect on the registration and the CBCT‐PCT mapping was relatively straightforward because of the absence of motion artifacts. Examination of “bony” landmarks indicated that an accuracy less than 2mm was achievable. The patient registrations were complicated by artifacts and, in the cervix case, the limited field size of CBCT. While the bony landmarks can be registered to within 2mm, the motion artifacts complicated registration and caused a large uncertainty in the PCT‐CBCT mapping. Conclusion: Low soft tissue contrast and artifacts of CBCT posed a challenge for CBCT‐PCT registration. While continuous effect is needed to improve the CBCT, a robust registration tool that can cope with specific issues of CBCT is highly desirable to fully exploit the volumetric CBCT technology.
SU‐DD‐A1‐01: A Dosimetric Comparison Between Laser‐Proton Therapy and Photon IMRT
Authors: Luo W , Fourkal E , Li J , Fan J , Yang J , Ma C
Published: June 2005

Purpose: Advanced treatment modalities are being developed for radiation oncology to improve local control and normal tissue sparing. The goal of this study was to perform patient dose calculations for laser‐accelerated proton beams and to compare treatment advantages using laser‐proton therapy with conventional photon IMRT. Method and Materials: Laser‐accelerated proton beams have broad energy and angular distributions. Small proton beams (beamlets) with limited energy spread were selected by a magnet system, and superimposed to generate spread out Bragg peaks (SOBPs) for proton therapy. The weights of the beamlets for the superposition were derived based on the Boltzmann transport equation and parameterization together with a gradient‐search algorithm for plan optimization through intensity modulation. Monte Carlo simulations were performed for laser‐proton treatment planning that used the same dose prescription and beam arrangement as those used in IMRT planning. Results: Twenty prostate patients previously treated with IMRT have been included in this study. The comparison is made between IMRT planned on Corvus and laser‐proton therapy on a home‐grown Monte Carlo based inverse planning system. Our results show that better target coverage is achieved by proton therapy. Compared with IMRT, the target dose inhomogeneity ((D5% – D95%)/D95%) can be reduced by 20–30%. The bladder dose can be reduced by up to 55% with proton therapy. Up to 40% of the rectum dose can be reduced using intensity modulated proton therapy. Conclusion: Significant improvement in target dose uniformity and normal tissue sparing can be achieved using laser‐accelerated proton beams. Intensity modulation can further improve the dose distributions for proton therapy of prostate cancer.
SU‐DD‐A1‐02: Commissioning and Clinical Implementation of Elekta MLC IMRT with Corvus Inverse Treatment Planning
Authors: Wallace S , Bobba V , Koll W , Zhang Y , Holt R
Published: June 2005

Purpose: This presentation details commissioning and clinical implementation of IMRT with the Elekta MLC and Corvus inverse treatment planning system. Particular attention is paid to features unique to this hardware and software that are not addressed in general IMRT guidance literature. Method and Materials: An Elekta Precise accelerator, equipped with 6 and 15MV photon beams and 80 leaf MLC, was commissioned for clinical usage IMRT with Corvus version 5.0. Data required by the planning system was collected using equipment and techniques consistent with current recommendations. A series of user defined intensity shapes, were used for initial testing of both energies by comparing calculated and film measured dose distributions. Five multifield clinical plans for each energy were compared to film in axial, coronal and sagittal planes, with an additional ionization chamber measurement at the intersection point of the three film planes. Results: When a dual off axis segment is defined by Corvus, a common occurrence in IMRT plans, the segment boundaries may be delineated by up to five different penumbra forming hardware combinations, 1) curved end MLC alone, 2) curved end MLC with backup jaw, 3) backup jaw alone, 4) divergent MLC side face alone and 5) divergent main jaw alone. This implies that both sets of jaws, in addition to the MLCs, must be calibrated to a relative accuracy of 0.2mm. When penumbra 1 and 5 were used in the Corvus pencil beam model, optimum agreement was found between plan and measurements. Conclusion: The physicist must be aware of leaf and jaw motion constraints that are unique to the Elekta Accelerator and how they are used in IMRT segment delineation by Corvus. When these factors are considered in hardware calibration and beam modeling, dose accuracy of 3% or 2mm is achievable over a range of stringent tests and clinical plans.
SU‐DD‐A1‐03: Dosimetric Properties of Photon Beams From a Flattening Filter Free Clinical Accelerator
Authors: Vassiliev O , Titt U , Kry S , Poenisch F , Gillin M , Mohan R
Published: June 2005

Purpose: Investigation of the basic dosimetric properties of 6‐MV and 18‐MV photon beams, generated by a clinical accelerator, without the flattening filter. Comparison with flattened beams. Exploration of potential benefits of using nonflattened beams in radiation therapy. Application of a flattening filter free accelerator in intensity modulated radiation treatments. Method and Materials: In a Varian Clinac 2100 accelerator the flatting filter was removed from the beamline. Dosimetric properties of 6‐MV and 18‐MV photon beams were measured using ionization chambers and radiographic films. Results: As a result of removing the flattening filter: (1) the dose rate on the central axis increases by factors of 2.3 (6‐MV) and 5.5 (18‐MV), in 10×10 cm2 fields at the depth of 10 cm; (2) the penumbra width decreases by 4–5% (6‐MV) and 8–20% (18‐MV) at small depths; (3) out of field dose close to the treatment field edge decreases by 15% (6‐MV), 30–40% (18‐MV) and tends to decrease more, farther away from the field; (4) the total scatter factor varies less with the field size; (5) multileaf collimator transmission decreases by 20% (6‐MV) and 10% (18‐MV); (6) dose per monitor unit increases to 2.15 cGy (6‐MV) and 3.81 cGy (18‐MV), according to the TG51 protocol; (7) the energy spectra of the nonflattened beams become softer, especially on the central axis; (8) dose close to the surface increases; (9) the ratio of dose on the central axis to that at 80% of field width (for 4×4 to 40×40 fields) increases to 1.1–1.7 (6‐MV) and 1.2–3.2 (18‐MV); (10) shapes of 6‐MV lateral profiles change less with depth. Conclusion: With the flattening filter free accelerator potentially better treatments can be developed, characterized by substantially shorter delivery times, sharper penumbras, and reduced out of field doses. Conflict of Interest: Research is supported by Varian Medical Systems.
SU‐DD‐A1‐05: Real‐Time Isodose Sculpting, CDVH Manipulation, and Delivery Efficiency Control in IMRT
Authors: Romesberg M , Riker R , Hill R , Denisi J , Spellman D
Published: June 2005

Purpose: We investigate the computational feasibility of tools enabling real‐time adjustment of isodose contours, CDVHs, min/max statistics, and delivery efficiency in IMRT treatment plans. We are motivated to provide direct customization of the attributes used for clinical IMRT evaluation departing from the less direct, traditional prescription process. Method and Materials: We design an objective function to enable real‐time adjustment of arbitrary dose distributions. We start from CORVUS inverse plans. To achieve each adjustment, we modify the objective function and apply gradient‐based optimization within a discrete search space. Dose planes, CDVHs, and statistics are recalculated and displayed following optimization. CDVHs and statistics are computed using stochastic estimation. Dose planes are computed on demand for three orthogonal views using multi‐resolution grids. We compare dose distributions before and after adjustment and record computation time. We use a prostate case, C‐shaped thoracic case, and radio‐surgical case treated with a Varian MLC, MIMiC, and BEAK respectively. We also evaluate dose accuracy by comparing the novel system's dose calculation with full CORVUS calculation. Results: We judged each tool to be effective in achieving its primary goal in all three cases. We note that local adjustments did induce some non‐local changes. Isodose contouring, CDVH dragging, min/max adjustment, and delivery efficiency adjustment had average computing times of 6s, 14s, 30s, and 6s respectively running on a dual‐processor, 2GHz PowerPC G5. Dose slices agreed so that 98% of pixels agreed within 5%, 5mm, while min/max statistics agreed to 0.65% RMS compared with CORVUS full calculation. Conclusion: Real‐time manipulation of isodose contours, CDVHs, min/max statistics, and delivery efficiency in IMRT is feasible. Local manipulation has some long‐range effects because of coupling. Conflict of Interest: The authors are employed at North American Scientific, NOMOS Radiation Oncology Division. The system studied here has become Active Rx in CORVUS 6.0.
SU‐EE‐A2‐01: Evaluation Based On Breast Tomosynthesis of Amorphous Selenium Full Field Digital Mammography System
Authors: Varjonen M , Strommer P
Published: June 2005

Purpose: Our goal is to develop and evaluate breast tomosynthesis of amorphous selenium (a‐Se) based full field digital mammography (FFDM) system. The clinical value of tomosynthesis will be to provide additional clinical information in order to improve decision making accuracy to either confirm or exclude a suspected abnormality, verify correct target for biopsies and analyze tumor margin better to get knowledge of the possible extent breast cancer. Method and Materials: The prototype of tomosynthesis full field digital mammography system which is used in evaluation is based on amorphous selenium flat‐panel detector technology. The overall thickness of the selenium structure is 200μm, and the pixel size on this detector is 85μm. The total arc of the breast tomosynthesis system is 60° (−30° to +30°) and tomosynthesis sequence is performed at approximately 1–1.5 times the radiation dose of a conventional mammogram including 15 low‐dose exposures. Reconstruction methods will be also discussed. Results: Based on the experimental results of this study, we believe that FFDM tomosynthesis can be used to determine whether a mammography finding is caused by a real abnormal lesion or by superimposition of normal parenchymal structures to be able to diagnose and analyze the findings properly. Conclusion: We need to be able to find screening and diagnostic method, which has high sensitivity as well high specificity to avoid unnecessary surgical interventions and to be able to detect breast cancer in its early stage. The technology has already proved its benefits in detecting early breast cancers and the capability of diagnosing breast cancers. Although FFDM tomosynthesis evaluation needs to concentrate on proving that it is clinically successful in the sense of increased sensitivity and specificity, with lower cost of workflow and reduced risk. Conflict of Interest: Mari Varjonen and Pekka Strommer are employees of Planmed Oy.
SU‐EE‐A2‐02: Efficient Automatic Pre‐Selection of Mass Lesion Candidates in DBT Breast Volumes
Authors: Reiser I , Nishikawa R , Giger M , Rafferty E , Moore R , Kopans D , Wu T
Published: June 2005

Purpose: We are developing a computerized mass detection algorithm for the DBT breast volume. Extending existing concepts from projection mammography to 3D is computationally expensive. We are presenting an efficient algorithm for the pre‐selection of lesion candidates from the DBT volume for further processing. Method and Materials: We applied a 3D radial gradient filter to the DBT breast volume. The convolution integral was limited to a shell. To account for variablity of mass sizes, volumes were filtered with multiple shell sizes. To increase computational efficiency, convolution was done in the Fourier domain. A maximum‐intensity projection of each filtered volume was processed with a 2D tophat filter, using a structuring element of the same scale as the shell. Projections at multiple scales were combined by chosing the largest filter response, of the 3 scales, at a given pixel location. Algorithm performance was evaluated on a database of 21 breast volumes with 13 malignant and 8 benign lesions. Patient images were acquired at Massachusetts General Hospital. Results: The algorithm had a sensitivity of 100% at 22 false positives and 90% at 13 false positives per breast volume. For this pre‐selection stage, the goal is to achieve high sensitivity. The false positive rate can be reduced subsequently through feature analysis. Conclusion: We have developed an efficien pre‐selection stage for a 3D mass detection algorithm. The radial filtering stage uses a 3D filter which is less sensitive to reconstruction artifacts and responds more accurately to 3D spherical structures. Future work will include feature analysis to further reduce false positive detections. Conflict of Interest: RMN and MLG are shareholders in R2 Technology, Inc. (Sunnyvale, CA). DBK is patent holder for the technique of DBT and has received research funding from GE.
SU‐EE‐A2‐04: Tone Mapping Operators for Contrast Enhancement of Mammograms
Authors: Mantri A , Laine A , Jin Y , Suri J
Published: June 2005

Purpose: To investigate the effect of different tone mapping operators in contrast enhancement of mammograms. A concave piecewise linear operator is proposed and is compared to a convex (logarithmic) and linear operator. Method and Materials: Tone mapping is performed prior to contrast enhancement to elevate the lower intensities that mainly correspond to the skin‐line zone. However, this leads to a loss in contrast due to compression of the gray levels. Gaussian band‐pass filtering is then performed to enhance the contrast of the mammogram. Filtering highlights the structure of breast while suppressing noise and the slowly varying high‐density structure. The filtering is done in the frequency domain and the image is mirrored and tiled prior to taking its Fourier transform to minimize edge effects. The tone mapping operators studied are logarithmic, linear and piecewise linear. The logarithmic operator has an adaptive base, the linear operator has constant slope in the intensities corresponding to the skin‐line zone, and the piecewise linear operator has varying slope in those intensities. Results: The enhanced images were viewed on a calibrated Dome C5i display. The logarithmic operator compresses the intensities near the threshold excessively which results in substantial loss of information. The linear and piecewise linear operators do not compress to the same extent. The piecewise linear operator compresses more in the range where there is not much information than in the range where there is more information. Also, tone mapping decreases the magnitude of the intensity step‐change from the breast region to the background. This reduces the ringing artifacts that result from the filtering operation Conclusion: The tone mapping operation improved the visual characteristics of the mammograms. Piecewise linear operator performed the best. The linear operator is comparable to the piecewise linear operator in most cases, though not as consistent. The logarithmic operator fared poorly.
SU‐EE‐A2‐06: Non‐Contact, Non‐Invasive Breast Thermography Has Potential to Evaluate Treatment Response in Breast Cancer Patients
Authors: Craciunescu O , Blackwell K , Wong T , Rosen E , Raidy T , Jones E , Vujaskovic Z , Liotcheva V , Covington W , Arabe O , Samulski T , Dewhirst M
Published: June 2005

Purpose: The purpose of the study is to determine the feasibility of using Breast Thermography (BT) to improve the evaluation of treatment response in breast cancer patients. Method and Materials: A protocol is underway at our institution that enlisted 17/30 breast cancer patients treated for: I) locally advanced breast cancer (LABC) on a phase I/II study of neoadjuvant chemotherapy (ChT) and hyperthermia (HT) (4/17); II) chest wall recurrence treated with radiation (RT) and HT (4/17); III) LABC treated with neoadjuvant ChT (2/17), and IV) chest wall recurrence treated with ChT (7/17). The patients are imaged before and after the completion of the prescribed treatment. Patients from group II were imaged before and at the end of each week of treatment. Six of the seven patients in group IV were either not due for follow up at the time of this report, or haven't reported yet. For the patients in group I, BT was used in conjunction with other imaging and pathologic studies to correlate the skin thermal signature with physiologic (perfusion, oxygenation) and pathologic (size, grade, hormonal receptor status, and lymphovascular invasion) characteristics of intact breast tumors. For patients in the other groups, either established imaging studies (MRI, PET), or clinical inspection was used to correlate and validate the BT data. Results: Preliminary results demonstrate that the BT data correlates well with MR and PET. Thermographic changes in the breast as captured with a high resolution infrared camera correlate with treatment response as demonstrated by clinical exam and pathologic response (in patients where this data was available). Conclusion: Breast Themography contributes additional information regarding treatment response than just visual clinical inspection in patients with chest wall recurrence or inflammatory breast cancer. This non‐invasive, non‐contact, cost‐effective tool has potential for evaluating patients undergoing neoadjuvant therapies for breast cancer.
SU‐EE‐A3‐01: Evaluation of Image‐Guided Radiation Therapy (IGRT) Technology and Their Impact On the Outcome of Hypofractionated Prostate Cancer Treatments: A Radiobiological Analysis
Authors: Song W , Schaly B , Bauman G , Battista J , Van Dyk J
Published: June 2005

Purpose: To evaluate various image‐guidance technologies and their potential impact on the outcome of hypofractionated prostate cancer radiation therapy to mitigate against geometric uncertainties. Method and Materials: Five prostate cancer patients were analyzed. All patients were planned twice with an 18MV six‐field conformal technique with a 10 and 5 mm margin sizes, with various prescription doses (35 to 70 Gy) of equal late complications (assuming normal tissue α/β = 3 Gy). The various target localization techniques simulated were (1) laser alignment to external tattoo marks, (2) alignment to bony landmarks with daily portal images, (3) alignment to the clinical target volume (CTV) with daily CT imaging, and (4) the repeat of technique (3) with daily monitor unit updates to account for patient shape changes. The impact of uncertainty in the assumed α/β value for the prostate was also assessed. Results: For all treatment schedules simulated, technique (4) achieved the ideal condition most closely (i.e., ΔTCP = TCPtechnique − TCPplan ≈ 0 %), then followed by (3), (2) and (1). As the number of fractions decreased (i.e., increasingly hypofractionated), the ΔTCP generally decreased for all techniques. Because the hypofractionated schedules were designed to keep late complications constant, the NTCP values were also relatively constant for all treatment schedules. Generally, the average NTCP values were lower than the plan for all techniques. However, the most effective way to reduce NTCP was to reduce the margin size from 10 to 5 mm. Overall, the uncertainty in α/β values had a far more influence on the outcome of the hypofractionated treatment than would the geometric uncertainties. Conclusion: This study suggests that, although the impact of geometric uncertainties increases as the number of fractions decrease, the reduction in TCP due to the uncertainties does not significantly offset the expected gain in TCP by hypofractionation.
SU‐EE‐A3‐02: Feasibility Study of Dose Compensation in Image‐Guided Radiotherapy (IGRT) of Prostate Cancer
Authors: Wu Q , Liang J , Yan D
Published: June 2005

Purpose: In image‐guided radiotherapy (IGRT), volumetric information of patient anatomy at treatment conditions is made available with in‐room imaging devices such as cone‐beam CT. Planning margin can therefore be reduced significantly through online guidance. However, uncertainties such as organ deformation and intra‐fraction motion cannot be considered this way. The purpose of this study is to investigate the use of offline dose compensation to further reduce the margin safely. Method and Materials: In IGRT, CT scan of patient is performed at each fraction. Setup error and inter‐fraction rigid motion are corrected online through couch translation and collimator rotation. The regions of interest are registered offline between treatment and planning CTs using a finite element method to account for non‐rigid motion. Cumulative dose distribution is calculated and compared with the prescribed one. The discrepancy, if significant, is repaired using dose compensation technique, in which the cumulative dose distribution is incorporated in adaptive planning for future fractions. Both 3DCRT and IMRT can be used for the boost. One patient with one planning CT and 15 treatment CTs was used in this simulation. Four‐field box was used in the plan where CTV was prostate itself. Zero margin from CTV to PTV was chosen to demonstrate the technique. Results: Due to the aggressive margins, severe underdose was observed in anterior portion of CTV. The size and magnitude of underdose was reduced substantially with online guidance but was still significant. Both 3DCRT and IMRT boost were able to compensate the dose deficit without any CTV to PTV margins. Dose compensation using 3DCRT caused hot spots in CTV. Conclusion: We have demonstrated the effectiveness of offline dose compensation technique in IGRT. It complements the online guidance by compensating for other uncertainties that cannot be reduced online. The use of dose compensation allows further margin reduction in IGRT.
SU‐EE‐A3‐05: Robustness of Two 4D Radiotherapy Approaches with Respect to Temporal Irregularity in Organ Motion
Authors: Chang S , Cullip T , Schulman D , Erdi Y , Nehmeh S , Mageras G , Keall P , Joshi S
Published: June 2005

Purpose: Respiratory motion of cancer patients during radiotherapy often lacks spatial and temporal regularity. Delays between motion monitoring and radiation adjustment in motion tracking treatment can cause large deviations between the delivered and the intended dosimetry. We demonstrate the advantage of a motion‐pattern‐based 4D approach we developed previously with regard to organ motion temporal variation for lung cancer radiotherapy. Method and Materials: A 4D CT image set of a lung cancer patient and a moving phantom were studied using 4D treatment planning in the in‐house TPS PLUNC, with and without the 4D optimization that is based on large‐deformation diffeomorphic registration and index‐dose gradient optimization algorithms. 4D dosimetry refers to the cumulative dose received by anatomical structures in patients with deformable organ motion. The 4D optimization generates static IMRT plans that can be delivered via compensators. The 4D IMRT treatment is compared with non‐IMRT motion tracking treatment, with and without tracking delay, for robustness against temporal motion pattern irregularity. The same beam setup, field margin, and dosimetric goal were used by all the plans in the comparison. Results: The perfect motion tracking technique gave the best CTV 4D DVH. The 4D IMRT performed better than the motion tracking treatment with systematic delays of 0.5 second or larger (motion cycle is 4 seconds). The 4D IMRT yielded better sparing of lung tissue and heart than all the non‐IMRT motion tracking treatments. Results on EUD are also presented. Conclusion: The motion‐pattern‐based 4D IMRT has the advantages of treatment delivery simplicity and robustness with respect to organ motion temporal irregularity. Compared to non‐IMRT motion tracking, it gives better 4D dosimetry for the moving tumor, lung, and heart in treatments of small‐size and large‐motion lung tumors having irregular temporal motion pattern. Conflict of interest: Research is partially supported by Siemens.
SU‐EE‐A4‐02: Quantitative Assessment of Tumor Heterogeneity Using Spatial Statistical Methods
Authors: Barbee D , Smith E , Jeraj R
Published: June 2005

Purpose: To quantitatively define and compare tumor heterogeneity via spatial statistical analyses of PET images for assessment of tumor response to treatment. Method and Materials: Canine tumor images, acquired through 65 minute dynamic 18F‐thymidine PET scans pre and three, six days post treatment, displayed varying heterogeneous uptake and tracer concentration in specific regions. CT/PET scans co‐registered over multiple scan days provided single day slices averaged after uptake (16–65 min) and cropped to the tumor area for each imaging stage. Images were tested for correlation and clustering using global Moran I and local G spatial statistics. Results: For each image, global I(d) statistics gave values greater than 0.5 (indicating positive spatial correlation) within a distance of 10 mm before going to zero (no correlation) at longer distances. The rate at which I(d) went to zero for each image differed. Six days post treatment decreased to zero most rapidly, three days post decreased most slowly, and the pre scan between these two rates. Local G statistics revealed the position and redistribution of high Z(G) value cluster regions in the pre and post six day scans over various distances. The post three day image revealed uniform Z(G) values over the majority of the tumor region. Conclusion: Results showed that global Moran I(d) and local G statistics are useful tools in assessment of tumor heterogeneity. Mean correlation lengths and cluster re‐distribution can be obtained through I and G statistics. Greater I(d) values and a slower I(d) rate to zero for three days post treatment implied that a longer correlation length was present after radiotherapy as FLT uptake and proliferation increased in uniformity. Shorter correlation lengths six days post treatment indicated uptake and proliferation heterogeneities returning larger than prior to treatment. Local G statistics visually displayed how regions of proliferation clusters were re‐distributed throughout treatment.
SU‐EE‐A4‐03: Validation of GATE Monte Carlo Simulations of the Noise Equivalent Count Rate and Image Quailty for the GE Discovery LS PET Scanner
Authors: Schmidtlein CR , Kirov AS , Nehmeh SA , Bidaut LM , Erdi YE , Hamacher KA , Humm JL , Amols HI
Published: June 2005

Purpose: The needs of radiation therapy treatment planning impose higher demands on PET/CT imaging accuracy. The recently developed GATE (Geant4 Application for Tomographic Emission) Monte Carlo package, provides the possibility to model accurately the factors contributing to decreased PET resolution and image degradation. The purpose of this study is to test GATE's ability to predict time curves and image quality (IQ) for the GE Discovery LS/Advance PET scanner. Method and Materials: Our 3D PET simulation model of the GE Discovery LS scanner and phantoms follows both the vendor's and NEMA's specifications and was previously validated for the PET scatter fraction and sensitivity tests. Simulations with this model were performed for the count rate and IQ NEMA‐2001 tests as a function of activity concentration. The Software for Tomographic Image Reconstruction (STIR) package was used to reconstruct the simulated data which was then compared to experiment. Results: Our simulations correctly predict the shape and magnitude of the true, scatter, random, and NEC rates. The simulated peak true and NEC rates are both within 3 kBq/cc of the measured data. Scatter and random rejection in the Monte Carlo data dramatically improved the agreement between measured and simulated contrast ratios. The cold sphere contrast ratio is within 9% of the measured data when the scatter and random coincidences were rejected. Larger discrepancies for the hot sphere contrast are currently observed and investigated. Conclusion: Monte Carlo simulation of PET images and the corresponding NEC rates can aid in improving PET image quality. The ability to model the features of PET scanners accurately makes GATE a potentially useful tool in improving PET's performance, which is necessary for its effective use in radiation treatment planning This work is sponsored by Program Project Grant CA059017‐12 from the National Cancer Institute and by an internal departmental grant.