bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐EE‐A1‐02: Common Dosimetry Errors in Cervix Patients Treated with Brachytherapy On Clinical Trials
Authors: Lowenstein J , Roll J , Ibbott G
Published: June 2005

Purpose: The mission of the Radiological Physics Center (RPC) is to assure NCI and the Cooperative Groups that institutions participating in clinical trials deliver radiation doses that are clinically comparable and consistent. Records of patients treated with brachytherapy on a cervix trial were reviewed for completeness, consistency with the protocol, and dosimetric accuracy. Independent dose calculations were performed at points A, B, vaginal surface, bladder and rectum. Method & Materials: The RPC reviewed 271 HDR and LDR implants. Doses were calculated to points A, B, bladder, rectum and the vaginal surface as defined by the protocol in accordance with ICRU‐38. The vaginal surface was defined as a point lateral to the center of the source(s) at the surface of the ovoid. RPC doses were compared to the institution's reported doses. Results: Dosimetry dose reporting errors were discovered in 78% of the implants. Most errors resulted from incorrectly defining calculation points. For example, point B frequently was measured from the tandem rather than midline of the patient. Other errors were caused by planning only the first implant and not subsequent implants. Conclusion: Points A, B, bladder, rectum and vaginal surface have been defined in publications, but a significant percentage of the community incorrectly calculates doses at these points. These reporting errors lead to inconsistencies in reported doses for the trial. This work was supported by PHS grant CA 10953 awarded by NCI, DHHS.
TU‐EE‐A1‐05: External Beam Radiotherapy Boosts to Reduce the Impacts Caused by Edema in Prostate Permanent Seed Implants
Authors: Yue N , Mori J , Heron D , Huq M
Published: June 2005

Purpose: In prostate permanent seed implants, it has been shown that edema caused by the surgical procedure decreases dose coverage and hence may reduce treatment efficacy. External beam boosts can be utilized to neutralize the negative impact of edema so that originally desired treatment efficacy can be achieved. This study is to investigate the number of fractions needed in these external beam boosts. Method and Materials: The reduction in treatment efficacy can be characterized with an increase in tumor cell survivals and biomathematical models have been developed to calculate the tumor cell survival increases in seed implanted prostates of different edema sizes and durations. A linear quadratic radiobiological model was used to derive the number of fractions needed in the external beam boosts with which the tumor cell survival fractions will be reduced to the desired levels. Prostate edema of different durations and sizes was taken into consideration in tumor cell survival fraction calculations. Results: As edema duration and size increased, the fraction number needed in the external beam boosts increased for both and seed implants. For edema of same duration and size, the needed number of fractions was higher in implants than in implants. External beam boost is needed for all the edemas investigated in implants while in implants the boost can be avoided for edemas of relatively short duration (3 days) and sizes (less than 20%). Conclusion: In conclusion, fractionation sizes have been determined for the external beam boosts that are needed to neutralize the negative impacts caused by edema in both and prostate seed implants. The number of fractions needed is larger in implants than in implants. The fractionation sizes are also influenced by various radiobiological parameters, and these influences increase as edema size increases.
TU‐EE‐A1‐06: Transrectal Fiducial Carrier for Radiographic Image Registration in Prostate Brachytherapy
Authors: Kemper J , Burkholder A , Jain A , Mustufa T , Wyrobek K , Burdette C , Song D , Okamura A , Fichtinger G
Published: June 2005

Motivation: Intraoperative dosimetric optimization of TRUS‐guided prostate brachytherapy implants requires localization of seeds relative to prostate[1], for which radiographic fiducial‐based registration of fluoroscopy and TRUS seems appropriate[2,3]. It is critical to mount the fiducials rigidly and stabilize the prostate, because TRUS and fluoroscopy are sequential and the moving TRUS probe may dislocate the prostate. Transrectal approach provides the shortest distance to the implanted seeds and prostate, thereby maximizing registration accuracy. Method and Materials: A precision‐machined transrectal sheath containing fiducials is mounted rigidly on the stepper and wraps around the TRUS probe. It mechanically decouples the prostate from the TRUS probe and thus stabilizes the prostate. Acoustic impedance, wall thickness, and diameter were optimized. Acoustic coupling is maintained by circulating liquid gel. The system is depressurized during probe motion. Two embodiments accommodate various types of radiographic fiducial markers. A closed 360‐degree sheath of 30mm diameter was developed for conics that are extremely robust to segmentation and image distortion, being mathematically invariant to projective transformation. A partial 180‐degree sheath was developed for straight lines and point fiducials that are computationally simpler to localize but inherently less accurate. The sheath connects to a commercially available TRUS stepper. Results: Phantom and in‐vivo canine tests were performed. Prostate motion and sheath stability were quantitatively analyzed with volume CT by tracking both structures and implanted markers while the TRUS probe was retracted by 5mm increments. With the sheath in place, prostate and sheath both were stationary in CT imaging and the fiducials did not interfere with the TRUS image. Excellent acoustic coupling was achieved during probe motion with acceptable degradation of ultrasound image quality. Funding: NIH‐1R41CA106152‐01A, NIH‐1R43CA099374‐01, NSF‐9731478.
TU‐EE‐A2‐04: Helical Tomotherapy Leakage Radiation Half and Tenth Value Layers in Concrete and Lead
Authors: Mirzasadeghi M , Wu H , Akpati H , Rosen L , Katz S , Kandler E , Massey J
Published: June 2005

Purpose: According to NCRP Report 51, if the leakage TVL is not measured, the primary radiation TVL should be used for the shielding design. Varian measured its own 90° leakage TVL in 1995. To determine which TVL value is most suitable for Hi‐Art II Tomotherapy, its leakage radiation half and tenth value layer in concrete and lead are measured. Methods & Materials: Film dosimetry is used to identify the high leakage region on the Hi‐Art II Tomotherapy machine. The entire surface area of the machine was covered with Kodak XV2 films. After identifying the high leakage region, an ion chamber was used to measure the leakage. The ion chamber (Exardin A12) was placed near the high leakage region, and located 1.13m above floor level and 2m away from the radiation isocenter. To allow for enough build up for high energy photons a 1cm bolus was added to the existing buildup cap. The leakage radiation was measured by adding blocks of concrete and lead in front of the ion chamber. The exposure data was recorded using a PTW Unidose electrometer. The half and tenth value layers of concrete and lead were calculated. All measurements were obtained under normal treatment conditions (800 MU/min, 360° rotation) for a period of 7 minutes. Results: The measured leakage radiation HVL and TVL values of the Hi‐Art II helical Tomotherapy machine are 0.011m (0.44″) and 0.044m (1.74″) in lead, and 0.066m (2.61″) and 0.282m (11.11″) in concrete, respectively. Conclusion: The leakage radiation TVL in concrete and lead obtained for Hi‐Art II helical Tomotherapy machine are close to published data for 90 degree leakage radiation of Varian (1995), but significantly lower than the NCRP (1997) data for primary radiation.
TU‐EE‐A2‐05: Measurements of Dose Averaged LET Distributions in Lateral Direction in Water Using CR‐39 for Collimated Carbon Ion Beam
Authors: Kohno R , Yasuda N , Himukai T , Kase Y
Published: June 2005

Purpose: In order to develop more precise dose averaged LET calculation algorithm on the basis of the pencil beam algorithm (PBA) for carbon ion radiotherapy, we have to calculate depth and lateral dose averaged LET distribution for the pencil beam. Particularly, since the lateral dose averaged LET distribution is formed by scattered particles and fragment particles, we expected the distribution is somewhat complex. In this study, we focused on the lateral dose averaged LET distribution. Lateral dose averaged LET distributions were measured using CR‐39 LET detector and analyzed. Method and Materials: Carbon ion irradiation was carried out using the horizontal beam line at Heavy Ion Medical Accelerator in Chiba. A therapeutic carbon beam with energies of 290 MeV per nucleon (MeV/n) was used. Using a CR‐39 solid state track detector, lateral dose averaged LET distributions in water were measured at various depths for collimated mono‐energetic beam. Results: We analyzed etch pits on the CR‐39, and lateral dose averaged LET distributions in the region of penumbra were obtained. As a result, their LETs in even penumbra region were about constant at each depth. Conclusion: Lateral dose averaged LET distributions in water were measured at various depths for collimated mono‐energetic beam using a CR‐39 solid state track detector. It was obvious that their LETs in even penumbra region about constant at each depth. We found that lateral dose averaged LET can be calculated roughly using depth dose averaged LET for broad beam.
TU‐FF‐A3‐03: Automatic Method of Bone and Static Tissue Removal in Neuro CT Angiography
Authors: Parrish T , Sen A , Walker M
Published: June 2005

Purpose: The purpose of this study was to optimize a post‐processing algorithm to eliminate density from bone or other tissues that remain constant during a contrast enhanced CT angiography procedure without compromising the detection of small lesions. Method and Materials: Five patients were scanned using a standard brain CTA protocol: kv=120, mA=300, thickness=2.5 mm, interval=1.25 mm, contrast volume=75 cc's, delay=12s). An identical acquisition was obtained prior to contrast injection. To eliminate movement related errors, the data sets were aligned using a standard motion correction algorithm within SPM2. The pre‐contrast data were used to form a mask based upon intensity thresholds that would capture bone (>200 HU). Additional image processing was used including smoothing and morphologic operations to improve the removal of the bone signal while minimizing the effects to vessel signal. The optimization process involved successive erosion and dilation operations on the mask. A filter was used on the mask to zero pixels between the skull and the external boundaries of the mask. Subtracting the pre‐contrast data from the post‐contrast data was performed to remove static signal. The bone mask was then applied to the difference data to create the final image. The post‐processed CTA data were transferred to a 3D workstation for viewing and qualitative assessment which included the source images and maximum intensity projections. Results: Bone subtraction was successful in all patients without qualitatively significant degradation in contrast‐to noise. The clinical data shows it is possible to remove non‐vascular signal without compromising the visualization of small aneurysms. Conclusion: An automatic method to remove bone density from brain CTA data sets was developed. The method requires a pre‐ and post‐contrast CTA acquisition and thus increases the patients overall radiation exposure though not to significant levels. The automated method will reduce workload and provide non‐biased angiographic data for clinical review.
TU‐FF‐A4‐01: Respiratory‐Gated Dual Fluoroscopic Imaging for Positioning and Verification
Authors: Sharp G , Jeung A , Ren Y , Povzner S , Berbeco R , Mostafavi H , Chen G , Jiang S
Published: June 2005

Purpose: To improve the setup and verification of respiratory‐gated treatments that use an external surrogate to track tumor motion. Method and Material: A system was designed to perform respiratory‐gated dual fluoroscopic imaging either before or during treatment. The Varian RPM system is used to track the breathing signal, which is used to turn on and off two x‐ray generators and acquire simultaneous fluoro from two directions. The operator can select between three operation modes: ungated fluoro controlled by the foot pedal, gated fluoro controlled by the foot pedal, and continuous acquisition of gated fluoro. Results: We have built a working prototype of this system, and have conducted early tests on phantoms. We have found that a gated fluoro system should include radiographic or fluoro capture capabilities, automatic and manual control of imaging, and on‐line monitoring tools. Dual imaging allows 3D verification of gated treatment when implanted fiducial markers are used. Conclusion: Respiratory‐gated radiation treatment has a great potential to increase the dose conformality for patients with large intrafractional tumor motion. When using an external surrogate to track the motion, the position of the internal anatomy relative to the surrogate can be verified using respiratory‐gated fluoroscopy. For many applications, gated fluoro is superior to ungated fluoro because the imaging dose is reduced, data storage requirements are reduced, and on‐line analysis is simplified. Conflict of Interest: This research was supported by Varian Medical Systems.
TU‐FF‐A4‐02: Active Tool/Fiducial Segmentation and Tracking in Multiple Modalities
Authors: Siddique MAS , Jepson AD , Moseley DJ , Hatzinakos D , Jaffray DA
Published: June 2005

Purpose: To build a tracking framework that, given a description of a tool/fiducial, the geometry of the imaging system and a sequence of images, outputs estimates of selected kinematics of the tool/fiducial along with a measure of the uncertainty in these estimates. The output of the system may be used as feedback to actively modify the imaging system parameters in order to achieve the desired precision with which the object is tracked while minimizing other parameters (eg. dose delivered to the patient). Method and Materials: A two stage approach is employed where (i) the object is segmented using its invariant features, its model, and other prior information that may be available and (ii) a particle filter is applied to the results of the segmentation for robustly tracking the object. A particle filter is chosen because of its simplicity, its robustness to noise and occlusion, its ability to represent multimodal beliefs, and also because its performance approaches that of the optimal Kalman filter given enough samples. Results: This approach has been applied to a (physically) simulated brachytherapy procedure to track the position of a needle loaded with seeds in an X‐ray fluoroscopic sequence. The system outputs the 3D position and orientation of the needle along with a confidence measure along each dimension. This output is robust to noise and partial occlusion. Conclusion: This work provides a generic framework for segmentation and tracking across multiple modalities that also reports a confidence measure for each estimated parameter. Such a system has many online applications such as radiation therapy guidance, intra‐operative image‐guided laparoscopic surgery, brachytherapy and various biopsy procedures.
TU‐FF‐A4‐05: Feasibility of Tracking Wireless AC Electromagnetic Transponders in Head and Neck Cancer Environment
Authors: Mate T , Zeller T , Douglas R , Harrison L , Shih J , Eidens R , Vertatschitsch E
Published: June 2005

Purpose: Precision setup is essential for head and neck IMRT due to the steep dose gradients used. A new device called the Calypso® 4D Localization System (Seattle, WA) has been developed which is capable of performing objective, real‐time target tracking during radiation. This system is based on non‐ionizing AC electromagnetics that utilizes small wireless Beacon® transponders, and could potentially be used to localize transponders embedded in a mouthpiece as a method to track skull movement during head and neck irradiation. Because AC electromagnetics can be influenced by nearby conductive metals, the effect of dental restorations, such as amalgam, on transponder localization accuracy was studied. Method and Materials: A dental prosthesis was casted from a volunteer. 16 of 28 prosthetic teeth were filled with standard dental amalgam. Three transponders set in a fixture were placed under the detection array and baseline measurements of each transponder's x, y and z coordinates away from the array were obtained. Next the prosthesis was placed immediately posterior to the transponders, simulating a worst‐case scenario of nearby amalgam. Each transponder's coordinates from the array were re‐measured. The transponders coordinates in the presence of the prosthesis were compared to the baseline measurement without the prosthesis. The experiment was repeated with transponders up to 20 cm away from the detection array. Results: Results showed that the presence of amalgams had no measurable effect on the system's capability to localize multiple transponders at distances up to 20 cm from the array. Conclusion: This investigation demonstrates the potential of wireless AC electromagnetic technology embedded in a mouthpiece to enable accurate and continuous tracking of the skull during head and neck IMRT. Conflict of Interest: Work supported by Calypso Medical Technologies; Authors Mate, Zeller, Eidens and Vertatschitsch have a financial interest in Calypso Medical.
TU‐FF‐A1‐01: An Investigation On the Impact of Incident Fluence Prediction On the Computed Doses
Authors: Mihaylov I , Lerma F , Siebers J
Published: June 2005

Purpose: For IMRT, most dose calculation algorithms modify the incident energy fluence by a scalar transmission matrix which represents the radiation transmitted through the moving multi‐leaf collimator (MLC). These matrices inherently exclude the effects of beam hardening by the MLC and only approximate the radiation scattered from the MLC. The purpose of this study is to determine how such approximations effects patient doses distributions in the limit of a realistic transmission matrix (TM). Method and Materials: Monte Carlo (MC) dose calculations were utilized in this study. The reference calculation utilized full MC transport through the moving MLC during the dose computation. The test calculation employed a realistic TM, determined by scoring the ratio of the incident and transmitted energy fluence through the MLC from the reference MC simulation, during the patient dose calculation to include the effects of the MLC on the patient treatment. Ten head‐and‐neck dynamic IMRT patient treatment plans were computed with each method and dose indices were compared. Dose indices used in the evaluation included the GTV D98, CTV D95, Brainstem D02, Cord D02, and Parotids D50. Results: For each target index studied, the maximum deviation observed was ⩽−1.5% of the treatment dose. The TM dose calculation systematically underestimated the full MC target dose by ∼1%. The local differences between the dose indices for the cord and the brainstem were within ±2.4%. Local dose differences of up to 2.9% were observed for the parotid D50. Conclusion: When a realistic transmission matrix is used, patient local dose results in the targets differ by ⩽1.5% of the treatment dose computed with full MC dose simulations, justifying the use of such matrices for both MC and other dose calculation algorithms for the cases studied. This work is supported by NIH‐1R01CA98524.
TU‐FF‐A1‐04: Determining Parameters for a Multiple‐Source Model of a Linear Accelerator Using Optimization Techniques
Authors: Siljamäki S , Tillikainen L , Helminen H , Pyyry J
Published: June 2005

Purpose: To determine the parameters of a multiple‐source model for an arbitrary linear accelerator using optimization methods. Method and Materials: A multiple‐source model describing the energy fluence output of a linear accelerator was developed in this study. A point source modeled radiation from the target, a finite‐size source all extra‐focal radiation, and an electron source contaminant particles. The parameters determined were the mean energy curve (for off‐axis softening), intensity profile curve (for non‐uniform photon energy fluence), electron source values, extra‐focal source size, energy, and intensity. The parameters were optimized by minimizing the gamma error between the dose calculation results and the beam data measurements by applying a non‐linear optimization technique not requiring gradient information. The dose was calculated by an algorithm based on superposition/convolution of Monte Carlo determined scatter kernels. The beam data measurements required were depth dose curves, lateral profiles, and diagonal profiles for multiple field sizes. The model requires minimal data about the internal dimensions and construction of the accelerator head. Results: The method was applied to 231 realistic data sets of varying quality and consistency for Elekta, Siemens and Varian accelerators. The gamma error (1%, 3 mm) for an average optimized model was lower than 1.0 for 98% of the measurement points. Typical duration of the optimization to derive the model parameters was 5–15 minutes. In cases where the measurements contained inconsistencies, the resulting gamma errors were significant, which indicates that the method could be useful in quality assurance of measurement data. Conclusion: This study demonstrated that the parameters for a multiple‐source model can be determined in an efficient and stable manner using optimization methods. The model is applicable to an arbitrary accelerator and has clinically acceptable accuracy and execution time. Conflict of Interest: This work was supported by Varian Medical Systems.
TU‐FF‐A2‐04: Geometric Parameter Analysis to Predetermine Optimal Radiosurgery Technique for the Treatment of Arteriovenous Malformation
Authors: Mestrovic A , Clark B
Published: June 2005

Purpose: To develop a method of predicting the values of dose distribution parameters of different radiosurgery techniques for treatment of arteriovenous malformations (AVM) based on internal geometric parameters. Method and Materials: For each of eighteen previously treated AVM patients, four treatment plans were created: circular collimator arcs, dynamic conformal arcs, fixed conformal fields and intensity modulated radiosurgery (IMRS). An algorithm was developed to characterize the target and critical structure shape complexity and the position of the critical structures with respect to the target. Multiple regression was employed to establish the correlation between the internal geometric parameters and the dose distributions for different treatment techniques. The results were used develop a statistical model which predicts the values of dose distribution parameters based on internal geometric parameters. The model was applied to predict the dosimetric outcomes of different radiosurgery techniques and select the optimal radiosurgery technique for a random AVM patient. Results: Several internal geometric parameters showing statistically significant correlation (p < 0.05) with the treatment planning results for each technique were identified. The target volume and the average minimum distance between the target and the critical structures were the most effective predictors for normal tissue dose distribution. The structure overlap volume with the target and the mean distance between the target and the critical structure were the most effective predictors for critical structure dose distribution. When the model was applied to a random patient, the predicted treatment results were in close agreement with the original data. Conclusion: A statistical model has been described which successfully predicts the values of dose distribution parameters of different radiosurgery techniques and may be used to determine the optimal technique on patient‐to‐patient basis.
WE‐B‐I‐609‐01: The Ultrasound Research Interface: A New Tool for Biomedical Investigations
Authors: Zagzebski J , Brunke S , Pelissier L , Hall T , Wilson T
Published: June 2005

Digitally controlled ultrasound scanners offer extensive levels of programmability, which enable manufacturers to explore and to readily incorporate alternative beam formation, signal and image processing, networking, and interfacing capabilities. Recent efforts have led manufacturers to share these tools for innovation with academic and clinical researchers. This discussion will present capabilities of two such machines and present examples of research uses. The Axius Direct Ultrasound Research Interface (URI) available on the Siemens SONOLINE Antares ™ scanner enables users to acquire raw radio frequency data from regions of interest throughout the image plane. Echo data are available in B‐mode, M‐mode, pulse Doppler and color flow imaging modes. Data can be acquired to a file with a simple button press. Also, user defined scripts can be used to record and reproduce RF acquisitions for combinations of front panel control settings such as transmit level, center frequency, beam angle, and focal depth. The NIH supported development of the interface is complemented by a set of Matlab tools developed at the University of California at Davis, which read echo and image data and perform image processing operations. The Sonix RP research system from Ultrasonix is based on an open PC platform, in which the conventional exam software can run either as a single application or as one of separate windows on the display. The PC also runs connectivity, interface and control software in parallel. The computer can control imaging parameters and apply various post‐processing and display methods in real‐time on RF, I/Q and envelope data to output and store the ultrasound information. When in research mode, users can build, develop, and run client software applications in the Microsoft Visual Studio environment to do customized signal processing, carry out special echo acquisition sequences, and synchronize with external devices, such as stepper motors. These tasks can be accomplished either locally or over a network. Examples of the use of these systems that will be outlined include parametric ultrasound imaging, elasticity imaging, and measuring the speed of sound in pulse‐echo mode.
WE‐B‐I‐611‐01: Evaluation and Consulting On Patient Dose In Diagnostic Imaging
Authors: Gray J , Kofler J
Published: June 2005

One of the responsibilities of a clinical medical physicist in diagnostic imaging is to provide both dose and risk information about x‐ray examinations. This is required for several reasons including advising medical staff of the doses and risks associated with specific examinations, consulting with institutional review boards (IRBs) relative to research uses of radiation, and determining specific organ doses such as uterine or fetal doses to assist in medical decision making. In order to provide dose and risk estimates four types of information are necessary including: 1) patient entrance skin exposures; 2) specific organ doses based on these exposures; 3) effective dose which is calculated based upon specific organ doses; and 4) estimation of risk based upon the effective dose. Unfortunately, there is no concise source of the information regarding doses and risk so it is necessary to have access to and knowledge of the sources that are available. This refresher course will provide an overview of resources and methods for determining patient risk from ionizing radiation in medical imaging. Several examples will be provided showing how doses and risks can be reduced easily and inexpensively for both clinical and research applications.
WE‐B‐T‐6C‐01: Positron Emission Tomography for Oncologic Imaging and Treatment
Authors: Bourland JD
Published: June 2005

Purpose: Positron Emission Tomography (PET) provides images that show physiological and biological information through the distribution of a radioactive tracer material. Imaging of oncology patients using PET can demonstrate focal and distributed regions of cancer and its metastases. Uses of PET imaging include cancer diagnosis and especially cancer staging, such that prognosis and appropriate treatment can be rendered. Method and Materials: Fluorine‐18‐labled Fluoro‐deoxyglucose (F‐18 FDG) is the most commonly used radiolabeled agent for PET imaging. Though non‐specific in its deposition, FDG labels those regions with active glucose metabolism, such as for local cancer, metastasis, and for non‐cancer processes such as glucose use by the brain. Non‐FDG positron‐emitting agents that are highly specific in their tissue targeting can also be used, such as Fluorine‐18 Misonidazole (F‐MISO) and Carbon‐11 Methionine, to image biological processes that are important indicators of tumor biology, for instance, hypoxia (F‐MISO) and cell proliferation (Methionine). Results: PET images have relatively coarse spatial resolution compared to computed tomography and magnetic resonance images. Voxel intensity (signal strength) depends on patient and imaging study parameters — quantitative use is possible with limitations. Conclusion: This course reviews the basic physics of PET, the uses of FDG and non‐FDG PET for oncology patient imaging, and logistical and quantitative aspects for uses of PET images in the radiation treatment process. Work by others and the author demonstrates the potential contributions of FDG and non‐FDG PET imaging in the radiation oncology environment. This review course is intended for both imaging and radiation oncology physicists. Conflict of Interest: The author has research grants with Varian Medical Systems and General Electric Healthcare.
WE‐C‐I‐609‐01: Computer‐Aided Diagnosis: Computerized Classification of Malignant and Benign Microcalcifications On Full Field Digital Mammograms
Authors: Chan H‐P , Hadjiiski L , Ge J , Sahiner B , Helvie M
Published: June 2005

Purpose: To develop a computer‐aided diagnosis (CAD) system for characterization of malignant and benign microcalcifications on mammograms acquired with a full field digital mammography (FFDM) system. Method and Materials: Our computerized classification system uses raw digital mammograms as input. The individual microcalcifications are first segmented by the system from the mammographic breast tissue background. Five morphological features describing the size, the density, and the shape of the individual microcalcifications are extracted. The mean and the variation of each of these features for the individual microcalcifications within a cluster are calculated. These cluster features in combination with the number of microcalcifications in a cluster form the morphological feature space. For texture feature extraction, a region of interest (ROI) containing the cluster of microcalcifications is identified on the mammogram. Background correction is applied to the ROI to reduce the intensity variation in the breast tissue areas. Texture features including the mean, entropy, contrast, and angular second moment are extracted from the gray level dependence difference statistics of the background‐corrected ROIs in four directions. A leave‐one‐case‐out resampling scheme is used to train and test the linear discriminant classifier. The most effective features from the combined morphological and texture feature space are identified using stepwise feature selection with simplex optimization in each training cycle. The performance of the classifier is evaluated by receiver operating characteristic (ROC) analysis. Results: In a preliminary study using digitized mammograms, the computer classifier obtained an area under the ROC curve, Az, of 0.82±0.03 for testing. The performance of the CAD system using a data set of 100 cases of biopsy‐proven microcalcifications on FFDMs will be presented. Conclusion: A trained CAD system can provide an estimate of the likelihood of malignancy of microcalcification on mammograms and thus may be used as a second opinion by radiologists for mammographic interpretation.
WE‐C‐I‐609‐06: Computerized Texture Analysis of Abnormal Areae Gastricae On Double‐Contrast Barium Examinations
Authors: Tomek R , Giger M , Gasparitis A
Published: June 2005

Purpose: Abnormal areae gastricae occur in the body due to gastritis. Very frequently, gastritis is caused by the Heliobactor Pylori bacteria, in which case it can be treated with antibiotics. The purpose of this study is to assess the ability of computerized radiographic texture analysis to recognize the presence of abnormal areae gastricae. Potentially, this could aid radiologists in classifying radiographic features of the areae gastricae in pathologic states. Method and Materials: Digitized double‐contrast radiographs for 23 cases were obtained. Each case was classified as normal or abnormal based on clinical symptoms and the results of endoscopic examination, H Pylori testing, and/or barium examination. Similar locations of the gastric area were selected on each image from the lower region of the stomach. These regions were then divided into 64 × 64 and 128 × 128 regions of interest (ROI) for texture analysis. Standard deviation, and Fourier and Fractal based features were calculated for all ROIs. ROC analysis was performed on the results to test the ability to distinguish between normal and gastritic cases, using round‐robin analysis. Results: The texture analysis showed that there is a separation between the normal and abnormal cases. For 64 × 64 ROIs, ROC analysis yielded Az values in a range of 0.54 to 0.80 for single features and a range of 0.70 to 0.806 for multiple features. For 128 × 128 ROIs, single feature ROC analysis yielded Az values in a range of 0.55 to 0.85 for single features and a range of 0.77 to 0.8694 for multiple features. Conclusion: The results indicate that radiographic texture analysis of digitized double‐contrast radiographs have the potential to distinguish between normal and abnormal cases of areae gastricae. Conflict of Interest: ML Giger is a shareholder in R2 Technology, Inc., Sunnyvale, CA.
WE‐C‐I‐609‐08: Information Theoretic Contours for Radiotherapy Planning
Authors: Hibbard L
Published: June 2005

Purpose: To develop contouring tools that aid in the work of anatomy delineation in CT imagery. Our strategy is to estimate the organ boundary on a CT image using that image's properties and the shape and pixel textures associated with the contour already computed on an adjacent section. Method and Materials: CT image regions can be effectively segmented using information divergences, which expand or shrink a boundary to maximize the differences between the pixel‐sets inside and outside the boundary. Divergences produce non‐parametric, statistical inferences generating minimum average error contours, given the data. We constructed an objective function using divergence functions that 1) maximize the match of regions and edges in multiple images, and 2) constrain the flexible contour to minimize differences between the current image and the prior image's region pixel textures and contour shapes. The resulting contour is the result of literally all the information in both the current and prior images. The novel features of this project are the pixel texture constraint using minimum divergences, an objective function whose term weights may be varied to optimally contour regions in various anatomies in CT, including envelopes of organs that are unresolvable because of patient motion. Results: The information divergence objective function computes series of contours without user input, beginning from an initial section. The contours can describe discrete natomic organs, or regions containing the envelope of an organ in which some of the anatomy is distorted or obscured by patient motion. The computed contours adapt well to changes in size and shape. Conclusion: Nonparametric information theoretic divergences don't require a model (e.g., Gaussian) to make effective estimates of anatomic boundaries in CT images. Their application to RT planning could greatly increase the efficiency of plan preparation.
WE‐C‐I‐609‐09: Autostereoscopic Display of the 3D Dose Distribution to Assess Beam Placement for Robotic Radiosurgery
Authors: Schlaefer A , Blanck O , Schweikard A
Published: June 2005

Purpose: To study whether a 3D view of the dose distribution and treatment beams on an autostereoscopic display facilitates a ‘smart’ placement of additional beams for robotic radiosurgery. Method and Materials: Treatment plans for robotic radiosurgery with the CyberKnife system (Accuray Inc., Sunnyvale) consist of a large number of non‐isocentrical, cylindrical beams directed towards arbitrary points within the target volume. We implemented a tool to visualize the resulting 3D dose distribution and the beam directions using the visualization toolkit (VTK). A hypsometric color scheme allows to identify cold and hot spots in the target volume, i.e. regions where the dose is close to the lower or upper bound specified for the target. Given this information we manually added a 20 beams to an existing treatment plan with 1200 beams for an intracranial tumor. The beams where placed such that a large number of cold voxels were hit but hot voxels were avoided. To assess the spatial extent of the cold and hot regions and the orientation of the beams an autostereoscopic display (SeeReal Technologies GmbH, Dresden) was used. An inverse planning algorithm similar to the one used by the CyberKnife system was implemented to re‐optimize the plan, the result was compared to the original plan. Results: The original plan consisted of 119 weighted beams with an accumulated weight of 21763.3 MU. Adding 20 beams we obtained a plan with 123 beams with the total weight reduced to 21610.7 MU. All 20 new beams got the maximum weight of 250 MU per beam, i.e. other, less efficient beams were discarded by the optimizer. Conclusion: The visualization tool proved to be useful in the guidance of beam placement. A direction of additional beams towards cold spots in the target volume can improve the plan quality.
WE‐C‐J‐6C‐03: A Novel Respiratory Gating Method Based On Automated Analysis of Ultrasonic Diaphragm Motion
Authors: Xu Q , Hamilton R
Published: June 2005

Purpose: Most of the current respiratory gating systems monitor the abdominal wall movement for lung cancer radiotherapy. These systems make the assumption that this motion and that of the lung tumor are correlated. Diaphragm motion is also correlated with lung tumor motion. Research shows there is a phase shift between the abdominal wall and diaphragm motions. Previous studies used fluoroscopy to evaluate diaphragm motion. We developed a method to extract a respiratory gating signal by automatically analyzing ultrasonic diaphragm video. Method and Materials: Volunteers were examined in a supine position and their right diaphragms were imaged with B‐mode ultrasonography using a standard unit (Siemens Sonaline Prima). The analog video signal was captured with a standard pc video card (RADEON 9600XT, ATI Technologies Inc.) at a rate of 30 frames per second to decompose the video stream into frames. To reduce computation time and complexity, the region encompassing the diaphragm motion was segmented from all frames. The mutual information and correlation coefficient between a selected reference frame and all others were calculated and normalized. Diaphragm motion information was extracted for use as a respiratory gating signal. Results: Plots of either the mutual information or correlation coefficient vs time (frame number) are periodic and match the respiratory cycle. The periodicity is independent of the selected reference frame and the shape shows only minor variations. Thus, this method provides a robust signal of respiratory motion that could be used to trigger the radiation beam. Conclusion: A novel respiratory gating system is proposed for lung cancer therapy based on ultrasound imaging. The method is noninvasive, nonionizing, and specific, thus has the potential to be a useful respiratory gating system.
WE‐C‐J‐6C‐04: Image‐Guided Adaptive Therapy for Lung Cancer
Authors: Ramsey C , Mahan S
Published: June 2005

Purpose: Because the GTV for many lung cancer patients decreased during the course of treatment, the margin effectively gets larger as the tumor reduces in size. This work describes the development and assessment of a technique for image‐guided adaptive radiation therapy for lung cancer. Method and Materials: Megavoltage CT (MVCT) images of the GTV were acquired daily on a helical tomotherapy system. These images were used to position the patient and to measure reduction in GTV volume. A planning study was conducted to determine the amount of lung‐sparing that could have been achieved if adaptive therapy were utilized. Treatment plans were created where the target volumes were reduced following measured tumor reduction. Results: A total of 158 MVCT imaging sessions have been performed on 7 lung patients. The GTV reduced by 60 to 80% during the course of treatment. The tumor reduction in the first 60 days of treatment can be modeled using the 2nd order polynomial R = 0.0002t 2−0.0219 t+1.0, where (R) is the percent reduction in GTV and (t) is the elapsed days. Based on these treatment‐planning studies, the absolute volume of ipsilateral lung receiving 20 Gy can be reduced between 5 and 25 percent (17% mean) by adapting the treatment delivery. The benefits of adaptive are the greatest for tumor volumes ⩾25 cm 3 and are directly dependent on the GTV reduction during treatment. Conclusion: MVCT based image‐guidance can be used to position lung cancer patients daily. This has the potential to decrease margins associated with daily setup error. Furthermore, the adaptive therapy technique described in this work can decrease the volume of healthy lung tissue receiving above 20 Gy. Conflict of Interest: Research supported by TomoTherapy, Inc.
WE‐C‐J‐6C‐05: Image‐Guided Process for 4D Lung Stereotactic Body Radiation Therapy
Authors: Purdie T , Moseley D , Sharpe M , Bissonnette J , Jaffray D
Published: June 2005

Purpose: To present the image‐guided process used clinically at Princess Margaret Hospital for stereotactic body radiation therapy (SBRT) of small lung lesions. Respiration correlated cone‐beam computed tomography (CBCT) was also investigated retrospectively to assess inter‐fraction and intra‐fraction target motion on the treatment unit. Method and Materials: Five patients with inoperable early stage non‐small cell lung carcinoma were treated using image‐guided SBRT. For each patient, tumor motion was assessed initially using fluoroscopy on a conventional simulator to determine the requirement for abdominal compression to limit tumor excursion. The planning computed tomography (CT) session involved both helical and four‐dimensional CT (4DCT) with compression applied as indicated by fluoroscopy. For SBRT, image guidance was achieved using a kV x‐ray tube and amorphous silicon flat‐panel detector mounted to the gantry drum of a linear accelerator (Elekta Synergy). Respiration correlated CBCT was also investigated, whereby the kV projections acquired for localization are sorted based on an internal surrogate of the respiration cycle. These sorted projections were reconstructed retrospectively to provide volumetric datasets at different phases in the respiratory cycle. Results: Respiration correlated CBCT image datasets were generated for one patient undergoing SBRT. For each treatment fraction, the lung lesion demonstrated excursions consistent with the excursion measured by 4DCT at the time of planning. The lesion was within the limits of the PTV as determined by 4DCT. Conclusion: We have established an efficient and streamlined image‐guided process that is in clinical use for SBRT of small lung lesions. A framework for on‐line respiration correlated CBCT acquisition on the treatment unit is being investigated to allow target motion to be assessed for each treatment fraction. Conflict of Interest: Princess Margaret Hospital is part of the Elekta Synergy Consortium. The research presented is supported, in part, by Elekta Inc.
WE‐C‐J‐6C‐07: Dose Reconstruction and Adaptive Radiation Therapy in Prostate Cancer
Authors: Byrne T , Ramsey C , Mahan S , Desai D
Published: June 2005

Purpose: The purpose of this work was 1.) Perform dose reconstruction for prostate patients imaged and treated with helical tomotherapy and 2.) Calculate the minimum treatment margins for non‐adaptive treatment delivery. Method and Materials: Megavoltage CT (MVCT) images are acquired prior to each treatment fraction for prostate patients. The daily corrections were recorded for each treatment fraction and used to calculate the random positional setup errors between setup marks on the skin and internal anatomy. Dosimetric error from organ deformation was calculated by contouring the prostate, seminal vesicles, and rectum on each MVCT image. Dose volume histograms were then calculated for each fraction. In addition to the initial margin 10‐mm/5‐mm (5‐mm posterior, and 10‐mm in all other directions) that was used clinically, treatment plans were also created with 8‐mm/4‐mm, 6‐mm/3‐mm, 4‐mm/2‐mm, and 2‐mm/0‐mm. These treatment plans were used to assess the minimum margins that could be used for each fraction. Results: The total shifts from the external laser marks were measured for over 1200 treatment fractions. The standard deviation was ±4.1 mm in the AP direction, ±3.9 mm in the lateral direction, and ±2.9 mm in the SI direction. Without CT‐based IGRT, an addition 6 to 8‐mm of margin would be required to account for random setup variations. Treatment plans with 6‐mm/3‐mm of margin would have covered the prostate and seminal vesicles in 7 out of the 10 patients analyzed. Two patients would have required the 8‐mm/4‐mm margins, and one patient's seminal vesicles would not have been adequately covered with the 10‐mm/5‐mm. Conclusion: A dose reconstruction analysis has been performed for patients treated with CT based IGRT. Treatment margins of 6‐mm/3‐mm would have been acceptable for 70 percent of the analyzed patients. Patients with large fluctuations in bowel gas will require larger planning margins, even with IGRT.
WE‐C‐J‐6C‐08: Target Refixation Through Automatic Mapping Of Real‐Time Surface Images With The Planning‐Used Images
Authors: Li S , Liu D , Yin G , Geng J
Published: June 2005

Purpose: to develop an accurate and precise surface‐guided target refixation through optimally mapping real‐time surface images with planning volume images. Method and Materials: An algorithm of merging the real‐time surface images captured by a video camera and the simulation‐planning volume images obtained through a CT or MR scanner is presented. The first concern is the systematic difference between CT/MRI skin contours and optic surface. The surface image artifacts are removed at the surface reconstruction by setting a limit on jumps at the neighboring facets. The partial‐volume effect and table‐patient movement in CT/MR images are corrected through comparison of the skin contours with an instant surface image without motion and partial‐volume effect. The second concern is that the skin surface is not rigid and it changes with the facial expression such as opening and closing of the mouth. To capture the consistent surface images, we have added a function of continuous monitoring of facial movement. A template‐based image registration and automatic surface alignment using a modified ICP algorithm have characterized the surface shape and landmarks' information and organize them into a reliable representation of the patient head position, which has lead to improve efficiency and robustness in surface‐guided target localization and radiation dose delivery. Results: Accuracy and precision of < 1 mm and efficacy of < 1 minute have been obtained in phantom experiments and on patients in a clinical trial. Conclusion: By using this refixation system, one can directly transform the surface images into the planned treatment position, quickly visualize the anatomical information relative to the treatment machine, and accurately detect the target positioning error in all six degrees of freedom. Conflict of Interest: Authors are either consultant or employees of the camera company.