bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐29: Working Memory Deficits of Facial Images in Patients with Schizophrenia Using FMRI
Authors: Juh R , Suh T , Choe B
Published: June 2005

Objectives: Impaired processing of facial information is one of the broad ranges of cognitive deficits seen in patients with schizophrenia. We aimed to elucidate the differences in brain activities involved in the process of facial working memory between schizophrenic patients and healthy comparison subjects. Method and Materials: Twelve patients with schizophrenia were recruited along with twelve demographically matched healthy volunteers as a comparison group. Functional magnetic resonance imaging (fMRI) was used to assess cortical activities during the performance of a 1‐back working memory paradigm using images of neutral faces as mnemonic content. Results: The patient group performed the tasks with reduced accuracy. Group analysis revealed that left fusiform gyrus, right superior frontal gyrus, bilateral middle frontal gyri/insula, left middle temporal gyrus, precuneus, quadrangular lobules and vermis of cerebellum and showed decreased cortical activities in the patient group. On the other hand, an increased level of activation in lateral prefrontal cortex and parietal lobule was observed from the patient group, all in the right hemisphere. Conclusion: A decreased level of activity in the left fusiform gyrus among the patient group implicates inefficient processing of facial information. An increased level of activation in prefrontal and parietal neural networks from the patient group confirms earlier findings on the impaired working memory of patients with schizophrenia.
SU‐FF‐I‐32: Detectability of Vasodilatation During Breath Holding by Dynamic CBV‐Based MRI: Comparison with BOLD‐Based MRI
Authors: Liu H , Hsu Y , Huang J , Kwan W , Wu C , Mahankali S
Published: June 2005

Purpose: To investigate the sensitivity of a CBV‐based MR technique, vascular space occupancy (VASO) imaging, in the detection of vasodilatation during different durations of breath holding (BH) and its clinical feasibility as compared with BOLD MRI. Method and Materials: Experiments were performed on a 1.5T Siemens MRI scanner. For VASO, a non‐slice‐selective IR‐GE‐EPI was used with TR/TE/TI = 2000/9.3/665 ms, SW = 6 mm and in‐plane resolution = 3 mm. For BOLD, a GE‐EPI was used with TR/TE = 2000/ 60 ms. Two normal volunteers each performed 4 experimental runs, including two‐cycle 30‐s and 15‐s BH each for BOLD and VASO. CNRs of were determined from ROIs drawn within the thalamus. A similar protocol was also carried out in a patient with right frontal anaplastic astrocytoma to review clinical feasibility. Results: Positive BOLD signal changes were noted during 30‐s and 15‐s BH (4.9 and 2.2 %), and the CNRs were 4.0 and 2.5. VASO method was able to detect CBV related negative signal changes (−3.1 and −1.8%, for 30‐s and 15‐s BH), and the CNRs were 2.3 and 1.8. Initial analysis of the patient data set revealed negative intra‐tumoral BOLD signal changes. While the global pattern of the VASO map agreed well with BOLD, the extent of intra‐tumoral changes was smaller. The BOLD map was then re‐thresholded to a lower p‐value which demonstrated intra‐tumoral changes similar to those with VASO. Conclusion: CNRs of VASO were lower than those from BOLD. However, they were closer to BOLD (58 and 72% for 30‐s and 15‐s BH) than previously published results from visual stimulation (∼ 30%). Discrepancies between two techniques in the clinical case were likely resulted from the differences in sensitivity. However, given that CBV‐based signal change is more directly related with the vasomotor response, it could potentially be more clinically relevant.
SU‐FF‐I‐33: T2‐Weighted Prostate Imaging Using Echo‐Planar Imaging at 3T
Authors: Ragan D , Ma J
Published: June 2005

Purpose: T2‐weighting in fast spin echo (FSE) images is unavoidably affected by T1‐mixing due to stimulated echoes. The purpose of this research is to evaluate the feasibility of using a multishot echo‐planar (EPI) technique to image the prostate at 3 Tesla without an endorectal coil and to compare T2 quantification using EPI with that based off of FSE images. Method and Materials: All experiments were performed on a GE Signa 3 Tesla whole body scanner with an 8‐channel torso phased‐array coil. T2‐weighted images were acquired of a healthy volunteer at echo times (TEs) of 40, 80 and 110 ms with a multishot spin‐echo EPI. Other imaging parameters were: 32cm FOV, 16 shots, TR = 2000ms, acquisition matrix = 256×512, receiver bandwidth = ±250 kHz. FSE images were obtained of the same volunteer with TEs of 60, 120, and 180ms and these acquisition parameters: 16cm FOV, TR = 3900ms, acquisition matrix = 256×256, ETL = 16, bandwidth = ±32kHz. A total of eleven slices covering the entire prostate were collected using both techniques. Results: The EPI images showed few artifacts and were noted to provide better T2‐contrast than the FSE images. For a region‐of‐interest in the peripheral zone of the prostate, T2 values derived from FSE images (134±15 ms) are substantially larger than those based on EPI images (76±1 ms). This observation is consistent with the apparent lengthening of T2 due to T1 mixing in FSE images. Conclusion: Using EPI with high receiver bandwidth, our results indicate that high quality T2‐weighted images of the prostate can be obtained at 3T without an endorectal coil. T2‐weighted images by EPI provide pure T2‐contrast and possibly more accurate T2‐determination than conventional FSE images.
SU‐FF‐I‐34: PSF and S/P in Mammography: A Validation of Simulations Using the GEANT4 Code
Authors: Grabski V , Brandan M‐E , Ruiz‐Trejo C. , Villaseñor Y.
Published: June 2005

Purpose: To study GEANT4 predictions for low‐energy (10–40 keV) photon transmission and scattering through tissue‐like thick matter, specifically to compare the predicted scatter to primary ratio (S/P) and line and point spread functions (LSF and PSF) against published and new measurements. Method and Materials: Using the GEANT4 code we have performed Monte Carlo simulations of the 1978 Barnes and Brezovich beam stop measurements of S/P, and the 2000 Cooper et al. edge detection experiments to evaluate S/P and LSF. Also, we have measured the PSF with a tungsten 1 mm diameter collimator on 3 – 6 cm thick lucite phantoms, using a Senographe 2000D unit operated at 26–28 kVp. In the simulations we have reproduced the exact experimental geometrical conditions, as well as the rest of parameters, according to the information contained in the original reports. Results: The S/P simulation and data agree within 3–10% accuracy, depending on the data set. The largest difference is with respect to Cooper et al., probably partially related to an inaccurate simulation of the original experimental conditions. For the LSF, the agreement between simulation and data is better than 15%, and for our PSF, better than 12 % at distances smaller than 5 mm. This last value should be taken as an upper limit, because of the lack of complete information on the features of the clinical unit. Conclusion: The analysis of these comparisons confirms that the GEANT4 predictions for low energy photon scattering are described with an accuracy better than 12%, at least up to 8 cm tissue thickness.
SU‐FF‐I‐35: Scatter Correction For Digital Tomosynthesis
Authors: Sechopoulos I , Suryanarayanan S , Vedantham S , Karellas A
Published: June 2005

Purpose: To investigate post acquisition scatter correction for digital tomosynthesis breast imaging. Method and Materials: Images of a composite phantom that was fabricated for evaluating digital breast tomosynthesis and used in a previous contrast‐detail (CD) study [Suryanarayanan et al., Acad Radiol 7: 1085–1097, 2000] were used to test the scatter correction method. These images were acquired using a prototype full‐field digital mammography (FFDM) system (GE Medical Systems, Milwaukee, WI) without an anti‐scatter grid. The phantom comprised of a centrally placed CD insert (MedOptics, Tucson, AZ), blocks of cluttered paraffin and polymethyl methacrylate (PMMA), and beeswax surrounding it to provide a total phantom thickness of 54 mm. A set of 7 projection images of the phantom were acquired over an angular range of ± 18° at 60 intervals at 26 kVp, MoMo, and 32 mAs/view. The projection data sets were corrected for scatter using the scatter correction technique described by Trotter et al. [Proc. SPIE, vol. 4682: 469–478, 2002] and processed with an adaptive noise filter. The projection images were then reconstructed using back‐projection and iterative restoration methods using Tuned Aperture Computed Tomography (TACT) [Webber et al., J. Digit. Imaging, 13: 90–97, 2000] software (developed by R.L. Webber, Wake Forest University, NC). The contrast‐to‐noise (CNR) ratio, signal‐to‐noise ratio (SNR), and % contrast were computed for one of the targets (2.32 mm diameter and 0.24 mm depth). Results: The uncorrected projection data set reconstructed with back‐projection resulted in CNR = 3.0, SNR = 30.4, and % contrast = 11.1, while the scatter corrected and processed projection images yielded CNR = 10.2, SNR =60.7, and %contrast = 20.2. Conclusion: The results of this study indicate improved SNR, CNR, and % contrast after scatter correction in tomosynthesis. We are currently implementing and evaluating other scatter correction and reconstruction methods for digital tomosynthesis.
SU‐FF‐I‐36: Average Glandular Dose with Sectra MDM in Routine Mammography Screening
Authors: Hemdal B , Herrnsdorf L , Martin M , Andersson I , Bengtsson G , Heddson B , Olsson M
Published: June 2005

Purpose: The aim of this work was to implement different International protocols to estimate average glandular dose levels for the first Sectra MicroDose Mammography (MDM) unit used in routine mammography screening (Helsingborg, Sweden). Method and Materials: The Sectra MDM is a scanning multislit digital mammography system which uses a direct photon counting technique with a solid‐state detector, Si(B). A substantial dose reduction can be expected due to high photon absorption in the detector (90%) and scatter rejection (97%) as well as improved energy weighting compared to other mammography systems on the market. The multislit pre‐collimator scans with a distance of only 115 mm above the breast support making it impossible to follow the usual procedure for half value layer (HVL) measurement. Instead, a sensitive and well‐collimated solid state detector with simultaneous correction for the energy dependence (Barracuda X‐ray multimeter, RTI Electronics AB, Sweden) is used for non‐invasive measurements of the HVL. Results: The average glandular dose was found to be e.g. 0.28 mGy for a 50 mm standard breast with 50 % glandularity simulated with 45 mm PMMA according to the so‐called European protocol from 1996. Conclusion: Methods of how to perform absorbed dose measurements according to European and American protocols on the Sectra MDM have been developed. The average glandular dose is much lower than for any other mammography unit on the market today. However, for increased accuracy, the dose protocols should be revised to account for the anode/filter combination used with the Sectra unit (W/Al), the scattered radiation from the multislit pre‐collimator device and the occurrence of a dose profile in the scanning direction.
SU‐FF‐I‐37: Heel‐Effect in Screen‐Film Mammography Artifact Analysis
Authors: Pizzutiello R , Sandrik J , Gray J
Published: June 2005

Purpose: To quantify the effect of mammographic x‐ray field inhomogeneity due to the “heel effect,” which is routinely observed during the medical physicist's artifact analysis of screen‐film mammography (SFM) systems, and to assist the medical physicist when evaluating artifact analysis test films. Method and Materials: Artifact tests were performed on a variety of common SFM systems using typical screen‐film combinations following the method of the 1999 ACR Mammography QC manual, which is consistent with MQSA requirements for medical physics surveys and equipment evaluations. Measurements of the optical density of 24 × 30 cm test films provided a measure of the density profile along a line parallel to the anode‐cathode axis. To measure the x‐ray field intensity profile independent of screen‐film characteristics, a narrow strip of optically stimulated luminescence (OSL) material was placed on top of the uniform acrylic slabs. Results: Test films demonstrated reduction of optical density with distance from the chest wall for all x‐ray machines tested and all screen‐film combinations tested. Variation in the degree of density reduction was observed among individual x‐ray machine models and for different screen‐film combinations. The OSL data correlated the trends in x‐ray exposure with those in optical density observed on test films. Conclusion: The “heel‐effect” is a well‐known source of field inhomogeneity which can be amplified by the contrast of the screen‐film combination. This industry‐wide sampling illustrates the range of variation to be expected both in terms of x‐ray exposure and film optical density and provides a guide to the medical physicist who must evaluate whether or not an individual artifact analysis test result is “Acceptable”. Conflict of Interest: J.S. is employed by a manufacturer of mammographic x‐ray systems. J.G. is employed by a manufacturer of OSL media.
SU‐FF‐I‐41: Phased Attenuation Correction in Respiration Correlated PET/CT
Authors: Nagel C , Dekker A , Bosmans G , Öllers M , Minken A , Lambin P , Schäfers K , Lang N
Published: June 2005

Purpose: Evaluate the potential of phased attenuation correction in respiration correlated PET/CT. Method and Materials: Respiration correlated scans were made on a Siemens Biograph PET/CT scanner which was modified to make an extremely low pitch CT scan and list mode PET scan possible. After collection of the raw CT, list mode PET data, and the respiration signal via a pressure load cell, PET/CT images were binned into ten phases of the respiration with help of in‐house built software. Attenuation correction was next performed for each phase. Experiments were performed with a lollypop phantom. The sphere at the end of the rod was filled with approximately 20MBq FDG. For the first experiment a sphere with a diameter of 3.3cm was used. The second experiment was performed with a large sphere with a diameter of 3.7cm in which a second smaller sphere of 2.2cm was situated. The inner sphere was filled with water or air in order to simulate a tumor with a necrotic core. The sphere movement had an amplitude of 5.0cm, and a frequency of 0.3Hz. Results: Both CT and PET images of the ten phases in the first experiment show well‐defined spheres in all orthogonal directions. In phased PET images corrected with the phased CT data, the sphere has a clearer outline as compared to images that were corrected with uncorrelated CT data. The images of the second experiment indicate that phased attenuation correction also results in a better detection of inhomogeneous structures. Conclusion: In this phantom study we have shown that phased attenuation correction after respiration correlation of CT and PET is feasible. Application of phased attenuation correction reduces motion artifacts and improves image quality. In future research the feasibility of phased attenuation correction in PET/CT for lung cancer patients will be examined.
SU‐FF‐I‐44: Air Bubble‐Free Motorized PET‐CT QA Phantom with Shielding Well
Authors: Huh S , Cho W , Park Y , Jeong H , Lim C
Published: June 2005

Purpose: Performance phantom for PET‐CT scanner (Philips Gemini scanner, UK) with special features such as air bubble‐free, motorized shaking mechanism, and >95% shielding well is designed to evaluate imaging performance of the scanner. Method and Materials: The phantom consists of three parts: (1) a phantom, (2) a motor, (3) a carrier device with 4cm thick Lipowitz shielding well. The phantom is implemented in a 16cm‐diameter * 25cm‐length water phantom with acrylic housing. Various internal structures include (a) many discs for linearity, resolution, (b) cones for axial coordinates, and (c) a long disc holder for fixing each disc and for shaking. Each disk has two small wings in the disc edges, thus effectively perturbing water while it is rotating. Proper discs can be chosen and inserted in the disc holder. The holder is inserted onto the housing and extended out of the phantom, and connected to a motor via a plastic belt, thus making possible rotating the internal structures. Also, the phantom has a conical top in the internal cylinder housing, so air bubbles produced during rotation are pushed toward an air pocket and trapped there. The radioactive material is injected through the air pocket, and plugged. The phantom is placed in the radiation shielding well while it is prepared. Results: The shaking mechanism of the PET‐CT scanner is evaluated with different shaking speeds and different amounts of radioisotopes (0.1 to 10mCi 18FDG). The air bubbles are eliminated 100% during shaking mechanism, and does not introduce any artifacts in even CT images. Total preparation time with this phantom is about 10 minute. The shielding well attenuates radiation exposure by 95%. Detailed measured data will be presented. Conclusion: The phantom was very handy and effective to measure simple imaging QA in 10 minute preparation time with minimum radiation exposure.
SU‐FF‐I‐45: Effects of Patient Positions On PET Tumor Volume Assessment in Lung Cancer
Authors: Jang S , Tran H , Alavi A
Published: June 2005

Purpose: The purpose of this study is to investigate the effects of different patient positions on the PET and CT image registration, and to delineate more accurate PET metabolic tumor volumes (MTVs) using a deformable image registration in lung cancer. When PET and CT systems are used as stand alone modalities, the patient arm positions are usually different. We used a deformable image registration method to fuse PET and CT images with different patient positions. Method and Materials: PET and CT images were acquired for 10 lung cancer patients. Both arms were placed at sides for PET imaging, but arms were up for CT imaging. The images were registered using an iterative non‐rigid algorithm (REVEAL‐MVS) based on voxel intensities. The displacements after the image registration were measured in the lung boundaries with axial and coronal images. The MTV and its mean standardized uptake value (SUV) in the PET images were measured before and after the non‐rigid image registration. Results: The displacements in the lung boundaries and diaphragm ranged from 1.85 to 3.89 cm for coronal images and from 1.57 to 2.42 cm for axial images. In 5 out of 10 cases the PET‐MTV became greater and the mean SUV became smaller after the non‐rigid image registration. The PET MTVs before and after the deformable image registration resulted in the volume differences of −1.8 cm3 to +29.3 cm3 and in the percent difference of −25% to ±41%. Conclusion: The different patient positions (arms‐down for PET; arms‐up for CT) in stand alone PET and CT systems yielded different PET tumor volume, extent and location. The non‐rigid image registration should be used to obtain more accurate PET MTV and its location. The PET MTV using a deformable registration method may be utilized for CT‐based radiation treatment planning in lung cancer.
SU‐FF‐I‐46: Performance Evaluation and Comparison of Two Cadmium Zinc Telluride Gamma Cameras
Authors: Kelly L , Matthews K
Published: June 2005

Purpose: We evaluate and compare the imaging performance of two prototype Cadmium Zinc Telluride (CZT) gamma cameras. The long‐term use of these systems is gamma‐ray imaging of small animals and laboratory research. Method and Materials: The two systems, made by Mosaic Imaging Technology, Inc., using CZT modules and components from IMARAD, Ltd., consist of a 25‐module carrier board, power supplies, and pulse processing and data acquisition boards. In testing we used 2 modules in the original prototype and 3 modules in the newer system. Each CZT module is a 38×38×5 mm monolithic crystal divided into 16×16 pixels, with two logic/pulse‐shaping ASICs. The original prototype uses older ASIC designs. We developed detector initialization and control software in LabVIEW 7.0. In operation, the detector processes each gamma ray interaction to produce energy and pixel information, which the LabVIEW program converts into energy spectra and images. The imaging performance of the two systems is evaluated using the NEMA NU 1 (2001) guidelines. Performance tests include energy resolution, spatial resolution, flood field uniformity, linearity and count rate performance. Results: In operation, the original prototype's modules generally show better performance than the newer modules, which require more tuning to achieve satisfactory imaging performance. Intrinsic spatial resolution is limited by the 2.4‐mm pixel pitch of the CZT modules. The original prototype's overall energy resolution is 7.2% FWHM for Tc‐99m and somewhat worse for the new system. Energy resolution for individual pixels is even better, but photopeak locations vary. Linearity, uniformity and count‐rate performance are comparable for the two systems, but the new modules generally have more dead pixels than the older modules. Conclusion: Individual CZT pixels have superior energy resolution compared to NaI(Tl), but intrinsic spatial resolution is slightly worse. The large pixel size impacts the utility of CZT gamma cameras for high‐resolution applications.
SU‐FF‐I‐47: Air Bubble‐Free Motorized Flood Phantom
Authors: Cho W , Huh S , Park Y , Jeong H , Lee H
Published: June 2005

Purpose: An air bubble‐free flood phantom with grid patterns is fabricated to measure extrinsic resolution and linearity of PET scanner. It is designed to implement a 99m‐Tc flood phantom with motorized water pump to reduce the shaking procedure as well as reduce radiation exposure to workers. Method and Materials: The flood phantom is fabricated with circular (50cm diameter) and rectangular shapes (60cm*40cm) to measure the extrinsic resolution of conventional gamma camera. It has a handle in which an air pocket and water pump are placed. The air pocket is made of two chambers with conical valve between them. During the shaking procedure, the air bubbles are sucked into to the air pocket due to gravity effect and water perturbation. Once the air bubbles are trapped in the air pocket. They could not escape from it. After the radioisotopes are injected through a pin hole in the air pocket, water pump is turned on. The shaking procedure starts. In order to estimate the effectiveness of the shaking mechanism, the survey meter with well‐guided collimator is manually rotated on the flood phantom until uniformity of 3% is reached. It take approximately 5 minutes to mix the water with radioisotopes thoroughly. Results: The phantom is used to evaluate the extrinsic resolution and to estimate the uniformity/linearity of gamma camera or SPECT camera. The images are analyzed to quantitatively measure the integral and differential uniformity and the non‐linearity of the imaging system. The detailed data will be presented in the meeting. Conclusion: The phantom was very handy and effective to minimize radiation exposure to an operator. The multi‐channel ionization chamber will be replaced manual rotation procedure to design fully automatic monitoring system.
SU‐FF‐I‐48: A Comparative PET Study of Regional Cerebral Metabolism with Multiple System Atrophy
Authors: Juh R , Suh T , Choe B , Lee C
Published: June 2005

Purpose: The 18F‐FDG PET images of the Multiple System Atrophy (MSA) and Idiopathic Parkinsonian Disease (IPD) patients were assessed by statistical parametric mapping (SPM) and image registration in order to determine the useful metabolic patterns between the two groups. A differential diagnosis of IPD and MSA is difficult due to the common of signs and symptoms. The aim of this study was to compare the regional cerebral glucose metabolism of MSA from IPD. Method and Materials: Eight clinically probable, IPD patients (3/5:M/F; age, 67.9 ± 10.7 y) and 11 probable MSA patients (4/7:M/F; age, 58.5 ± 8.4 y) were included in the study. Twenty‐two ages matched healthy controls (9/13:M/F, age, 67.8 ± 14.4 y) were examined and were used as the controls for the comparison between the patients with Parkinsonism. All subjects underwent 18F‐FDG PET. Results: The IPD patients was found to have significantly low hypometabolism in comparison with the healthy controls on the prefrontal and lateral frontal cortex, the parietotemporal cortex, and the cingulated and caudate (p≤0.01, 100 voxel‐level). As to patients with MSA, hypometabolism was observed in the putamen, pons and cerebellum in comparison with the healthy controls and IPD patients. Voxel‐based analysis of 18F‐FDG PET showed detailed differences between IPD and MSA, which may be useful for differentiating both disease entities, evidenced by the correlation of glucose metabolism with the disease severity and the dopamine agonist medication. Conclusion: Voxel‐based analysis of 18F‐FDG PET showed detailed differences between IPD and MSA, which may be useful for differentiating both disease entities, evidenced by the correlation of glucose metabolism with the disease severity and the dopamine agonist medication. The 18 F‐FDG PET images using mapping analysis might be a useful adjunctive tool for a clinical examination when making a differential diagnosis of Parkinsonism.
SU‐FF‐I‐51: Interoperability Validation of DICOM Portable Data for Imaging in Nuclear Medicine
Authors: Jung H , Kang W , Kim J , Yang K , Han D , Kim H
Published: June 2005

Purpose: In PACS (Picture Archiving and Communications System) environment, the export of DICOM portable data for imaging (PDI) has been increased in accordance with the demands of patents referring to other hospitals. The DICOM PDI currently stored in a CD (Compact Disk) causes the problems of retrieve and archive occasionally in PACS environment of destination hospital although it was created under obeying DICOM standards. Method and Materials: DICOM validation toolkit was developed for verifying the DICOM data sets complying with the DICOM standard PS 3.3 to improve compatibility between the DICOM PDI and multi‐vendor PACSs. The interoperability of problematic PDI in nuclear medicine imported to Yonsei University Medical Center in Seoul, Korea was evaluated through validation of DICOM CD data using the DICOM data validation toolkit. The evaluated PDIs were 5 NM (Nuclear Medicine) series and 10 PT (Positron Emission Tomography) series. Results: The main factors of the problematic NM PDI are that series number, content data, and content time presented null value and detector vector had no tag. As for the problematic PT PDI, series number presented null value, pixel aspect ratio had no tag, and both of image orientation and image position had no any values for VM=3 and VM=6 defined by DICOM standards. Conclusion: The DICOM data validation toolkit is expected to play an important role in validation of problematic PDI for patients and hospitals. Evaluation of problematic PDI will enable to bring the feedback of incompatibility to PACS vendors and PACS operating team in hospitals to improve interoperability of PDI.
SU‐FF‐J‐46: A Probabilistic Method for Online Treatment Plan Modification
Authors: Flynn R , Jeraj R , Mackie T
Published: June 2005

Purpose: To develop an IMRT treatment planning method that accounts for increased knowledge of tumor and normal tissue location gained from inter‐ or intra‐fractional imaging. Method and Materials: Knowledge of tumor location in each fraction or sub‐fraction is represented by a probability density function (pdf), p(n,n′,t), that describes the probability that a voxel at index n in the planning image will be located at voxel n′ at a later time t. The pdf is changing as the new information becomes available. A set of beam profiles for each fraction or sub‐fraction is then obtained by minimizing the quadratic objective function by accounting for probabilistic nature of the beamlet dose distribution: in each fraction. This optimization problem is set with the intention that the beamlets that have the highest risk of missing the tumor will not be delivered until adequate knowledge of tumor location becomes available. We apply this method to a case of a disk‐shaped tumor inside a disk‐shaped phantom with a tomotherapy beam geometry. Results: The method proved to deliver more conservative dose distributions at the beginning of treatment than at the end for both inter‐ and intra‐fractional cases. For early fractions and sub‐fractions, low‐risk doses were delivered to regions where the probability was high that the tumor would be present during the treatment. As knowledge of tumor location improved, the remaining dose at the periphery of the tumor was filled‐in. Conclusion: We showed that incorporating increased knowledge about tumor and normal tissue location, obtained by repeatitive on‐line imaging leads to superior treatment plans.
SU‐FF‐J‐47: A Proposal of Respiratory Phantom Driven by Double‐Motor
Authors: Liu Q , Guan H
Published: June 2005

Respiratory motion phantom has been widely used in the current study of gated radiotherapy. Most of the phantoms are driven by a single motor, which can only simulate one‐dimensional sinusoidal motion. However, many studies had shown the normal breathing pattern is asymmetric between the inhale phase and the exhale phase. Fourier transform analysis shows that a double harmonic model, including the first and second harmonics, could give a good reproduction of the normal breath pattern. Based on this fact, we propose the design of a double‐motor driven phantom, which can produce a periodic motion with asymmetric pattern. In this design, the phantom is driven by the first motor. This motor is fixed on a sliding platform, which is further driven by a secondary motor. The frequency for each motor can be adjusted with the input voltage, and should be set exactly according to the first and second harmonics, respectively. Amplitude of each sinusoidal component can be adjusted by changing the location of the arm on the wheel. Based on the Fourier analysis of real volunteer's data, the ratio of their amplitudes should be around 3:1 to 5:1, but could also patient adapted. This design can be valuable in phantom studies where a symmetric sinusoidal motion is not sufficient. Although a programmable phantom shows promising of an ideal solution, this design is easier to be implemented and also cost effective.
SU‐FF‐J‐48: A Slice‐By‐Slice CT‐Guided Adaptive Radiation Therapy Technique for Twisting Targets
Authors: Court L , Cormack R , Petit J , Tishler R , Xiang H , Chin L
Published: June 2005

Purpose: To investigate a CT‐guided adaptive radiation therapy technique capable of correcting for complex shape changes, including twisting around the longitudinal axis, such as found when treating head and neck patients with a head rotation. Method and Materials: For co‐planar beams, the dose in an axial plane is primarily associated with the positions of a single MLC pair. We start with a primary plan, and automatically generate several secondary plans with gantry angles offset by regular increments. MLC sequences for each plan are calculated keeping MUs and number of segments constant for a given beam (fluences are different). Bulk registration (3D) of planning and daily CT images gives global shifts. Slice‐by‐slice (2D) registration gives local shifts and rotations about the longitudinal axis for each axial slice. The daily MLC sequence is then created for each axial slice/MLC leaf pair combination, by taking the MLC positions from the pre‐calculated plan with the nearest rotation, and shifting using a beams‐eye‐view calculation to account for local linear shifts. A planning study was carried out using two MR images of a healthy volunteer, contoured to simulate a base‐of‐tongue treatment: One with the head straight (used to simulate the plan image) and one with the head tilted to the left (the daily image). Results: On a slice‐by‐slice basis, local rotations in the daily image varied from 2 – 31degrees. Local shifts ranged from −0.2 – 0.5cm and −0.4 – 0.0cm in right‐left and posterior‐anterior directions, respectively. The adapted treatment gave good target coverage, and kept the daily cord dose below the limit used in the original plan (65%, equivalent to 46Gy over 35 fractions). Conclusion: This technique may be useful for adaptive radiation therapy of targets where twisting around the longitudinal axis is significant. These results also demonstrate the feasibility of combining MLC sequences from different pre‐approved treatment plans.
SU‐FF‐J‐49: A Technique for Dose Reconstruction in Image‐Guided Radiation Therapy
Authors: Mahan S , Ramsey C
Published: June 2005

Purpose: Images from volumetric CT‐based image‐guided radiation therapy (IGRT) can be used to reconstruct the doses delivered to the patient. The goal of this work was to develop a technique for data preparation and dose reconstructions for Megavoltage CT (MVCT) images acquired on a helical tomotherapy system. Method and Materials: MVCT images must be processed prior to dose reconstruction. The first step is for the MVCT images to be re‐sampled to the dimensions of the kVCT images. The second step was to map the CT numbers (i.e. electron density) for the voxels within the MVCT data sets to match the kVCT CT numbers. Next, any missing data in the MVCT images (due to field‐of‐view limitations) must be padded with the data from the kVCT image set. The composite image set was then gaussian filtered. Finally, the treatment‐planning cluster was used to re‐compute doses based on the MVCT anatomy imaged during a particular fraction. Results: The goal of this work was to develop a system to perform dose reconstruction on MVCT images. A process was developed to match image dimensions, boundaries, resolutions and final completion of limited field of view. A custom program was then written that creates an input deck with the appropriate machine parameters, data files and treatment delivery sinogram for dose reconstruction. Dose reconstruction has been performed for prostate, head & neck, and lung cases. Conclusion: A technique has been developed to pre‐process MVCT data and to perform dose reconstruction. Conflict of Interest: Research supported by TomoTherapy, Inc.
SU‐FF‐J‐50: Assessment of Intrafraction Motion and Rotation During Head and Neck Treatments Based on 6D Analysis of Daily Stereoscopic Xray Imaging
Authors: Linthout N , Verellen D , Tournel K , Wauters T
Published: June 2005

Purpose: To determine intrafraction motion and rotation of patients immobilized with a 5‐point thermoplastic mask for head and neck treatments. Method and Materials: 13 patients were consecutively assigned to use a 5‐point thermoplastic mask. Patients were positioned by tracking of infrared markers (IR) fixed to the immobilization device and stereoscopic Xray images were used for setup verification. Repositioning was carried out as needed, rotations were not corrected. Movements during treatment were monitored by real‐time IR‐tracking. Intrafraction motion and rotation was assessed by a 6‐degree‐of‐freedom (6D) fusion of Xray images taken before and after all 385 treatments with DRR images generated from the planning CT data. The latter evaluates the patient's movement within the thermoplastic mask, where IR‐tracking only evaluates the mask's movement. Results: The maximum intrafraction movement detected by IR‐tracking showed a shift (mean (SD; range)) of 0.5(0.5; 3.8), 0.5(0.3; 1.9), 0.6(0.4; 3.3) mm in the vertical, longitudinal and lateral direction respectively and rotations of 0.2(0.1; 0.7), 0.2(0.1; 0.7) and 0.3(0.2; 1.0) degree about the vertical, longitudinal and lateral axis respectively. The 6D fusions demonstrate intrafraction patient displacements of −0.5(1.2; 7.4), 0.3(0.7; 5.3), 0.0(0.7; 5.7) mm in the vertical, longitudinal and lateral direction respectively and rotations of −0.1(0.6; 4.1), 0.1(0.7; 8.3) and −0.2(0.8; 8.2) degree about the vertical, longitudinal and lateral axis respectively. The standard deviations and ranges found with 6D fusion are significantly larger than detected by IR‐tracking. This indicates the latter underestimates the magnitude of the actual patient's intrafraction motion and rotation. Conclusion: The 6D image fusion is a useful tool to evaluate the actual patient's intrafraction motion and rotation and shows the latter is not negligible. Thus, immobilization alone is not sufficient to allow narrow treatment margins. Conflict of Interest: This work was supported by BrainLAB AG Germany and Orfit Industries Belgium.
SU‐FF‐J‐52: Breathing Adapted Radiotherapy (BART) Using Modern Gating Technologies
Authors: Cossmann PH , von Briel C
Published: June 2005

Purpose: The aim of this study was to evaluate the impact of the Varian RPM‐gating™ System for gated treatment of breast cancer/thoracic wall cancer as well as Varian On‐Board Imager™ (OBI) Fluoroscopic Pretreatment Setup Verification for gated treatment of lung cancers/upper intestinal tract cancers. Method and Materials: A passive, infrared light reflecting marker is placed on the patient's chest wall over the xiphoid process. The vertical motion of the marker, i.e. the breathing excursion, is tracked by an infrared sensitive video‐camera‐based hardware. The system is used for acquisition of the CT‐Scan (4D‐CT) as well as the treatments; for the latter it manages the controlled switching of the radiation beam during a pre‐selected specific phase of the respiratory cycle. The additional Fluoroscopic Setup Verification allows a fluoroscopy analysis of inner target movement with regard to a chosen therapeutic window of the RPM Gating system just prior to treatment. Results: Varian RPM‐gating technology optimizes the dose delivery to regions with respiration‐induced movements of the target. Safety margins and thereby irradiated critical volumes can be significantly reduced for breast cancer with RPM‐gating as well as lung cancer with the OBI Fluoroscopic Pretreatment Setup Verification. Conclusion: Gating offers the possibility to apply doses with higher accuracy. As typical duty cycles are around 50% ore even 10%, the overall beam‐on time is prolonged by a factor of up to 4. In order to compensate for this effect, a dose rate change from 300 to 600 MU/min when using enhanced dynamic wedges was chosen; in case of electronic compensation a dose rate change is not needed. The additional fluoroscopy mode offers for the very first time the possibility to verify patient positioning with regard to the moving target, which ‐ for most cases — shows a phase shift relative to the RPM marker box movement.
SU‐FF‐J‐53: Breathing Synchronized Irradiation Using Stereoscopic KV‐Imaging to Limit Influence of Interplay Between Leaf Motion and Organ Motion in DMLC IMRT: Dosimetric Verification
Authors: Verellen D , Tournel K , Linthout N , Wauters T , Storme G
Published: June 2005

Purpose: Feasibility study of a prototype developed for breathing synchronized irradiation. Method and Materials: Adaptations to a commercially available image‐guidance technique (NovalisBody/ExacTrac4.0, BrainLAB) have been implemented allowing gating. A simple phantom simulating a breathing pattern of 16 cycles/min and covering 4 cm has been introduced to assess the system's performance to: (a) Trigger the linac at the right moment (using a 3mm metal hidden target (HTT) mounted to the phantom). (b) Assess the delivered dose in non‐gated and gated mode (using an ionization chamber (IC) mounted to the phantom). (c) Evaluate the interplay between organ and leaf motion in IMRT (using radiographic film mounted to the phantom). The effect of interplay has been evaluated by importing measured fluence maps, generated by the linac in non‐gated and gated mode, into the treatment planning system (TPS) and re‐calculate the resulting dose distribution. Results: No measurable delay in the triggering of the linac has been observed with the HTT. The IC measurements showed an improvement in dose absorption from 44% (non‐gated) to 98% (gated) for small field irradiation (3×3 cm2) of a moving target. Importing measured fluence maps actually delivered by the linac into the TPS yielded highly disturbed dose distributions with the non‐gated delivery, whereas the gated delivery showed good agreement with the original theoretical dose distribution. These findings have been confirmed by the dose‐volume histograms. Conclusion: First tests with the prototype for breathing synchronized irradiation showed promising results. The use of measured fluence fields, delivered by the linac in non‐gated and gated mode, as imported fluence maps for the TPS revealed the impact of interplay between leaf and organ motion and the possibility of gating to resolve this issue. The latter should be outweighed against increased treatment time. Conflict of Interest: Part of this work has been supported by BrainLAB AG.
SU‐FF‐J‐55: Cumulative Dose Calculation Using Deformable Image Registration
Authors: Wang H , O'Daniel J , Ahamad A , Garden A , Mohan R , Dong L
Published: June 2005

Purpose: To use deformable image registration to calculate cumulative dose distributions received by a radiotherapy patient in order to evaluate the dosimetric impact of anatomical variations during the course of treatment. Method and Materials: An intensity‐based deformable registration algorithm was developed to register the anatomy between the planning CT image and the daily CT images acquired from an in‐room CT‐on‐rails system. After the transformation from daily CT to planning CT was found, daily treatment doses delivered to an organ can be meaningfully accumulated. For one head‐and‐neck patient, the treatment plan was transferred to 15 daily CT scans using bony registration, and the dose distributions were calculated for the daily anatomy without daily setup errors. Using deformable image registration, these daily dose distributions were mapped back to the planning CT image. The cumulative dose was calculated and compared to the original plan using dose‐volume histograms (DVHs). Results: The dose delivered to the patient had minimal changes from the plan. Dose coverage for clinical target volumes at 70Gy, 63Gy, and 56Gy, left and right parotids at 25Gy, and mandible at 70Gy were evaluated. At these dose levels, the DVHs showed less than 1% difference, except for the left parotid, which had a 6% volume difference. The maximum dose in brainstem was 1.4% less than planned, the maximum dose in spinal cord was 2.2% higher than planned. The mean doses in left and right parotid were 4.4% higher and 2.5% lower than planned. Conclusion: In this case, we found little dosimetric differences due to changing anatomy during the course of treatment. Future studies will include daily setup errors. Deformable image registration is proven to be an effective approach for calculating cumulative dose distributions delivered to the patient, which can be used to evaluate the quality of treatment execution.
SU‐FF‐J‐56: Detecting Treatment Setup Errors for Head and Neck IMRT Patients with Multiple CT Scans
Authors: Ezzell L , Xia P
Published: June 2005

Purpose: Conventional methods determine treatment setup errors in patients undergoing intensity‐modulated radiotherapy (IMRT) by using orthogonal portal images that only detect translational errors. This study utilizes image‐guided radiotherapy to develop and test an algorithm for detecting both translational and rotational setup errors in head and neck patients with multiple CT scans. Method and Materials: To confirm the accuracy of the proposed algorithm to detect translational shifts, it was tested using a constructed phantom with four embedded metal marks. Upon verification, ten head and neck patients with two temporally‐independent CT scans were selected. For each patient, the translational and rotational errors were calculated by aligning selected bony landmarks from the two scans using matrix transformation with an incremental guess‐check method. For comparison, the translational errors were also obtained by co‐registering the two scans using the same landmarks with a commercial treatment planning system and comparing the isocenter of the second CT with that of the first CT. The contribution of the rotation to the translational error represents the difference between the translational shifts as computed by the algorithm and the conventional method. Results: The results of this study showed that the average magnitude of the rotational errors about the transverse, anterior‐posterior, and longitudinal axes were 2.3° ± 2.2°, 1.3° ± 0.9°, 2.1° ± 1.6°, respectively. The average contribution of this rotation to the translational error in the left‐right, anterior‐posterior, and longitudinal directions were 3.1 ± 3.2, 2.0 ± 4.4, 4.4 ± 7.3 mm, respectively. In general, the greater the rotational error in the setup, the greater the subsequent translational difference between the methods. Conclusion: This study found that rotational errors do contribute significantly to the treatment setup error for head and neck IMRT patients. The proposed algorithm can detect these rotations and, consequently, more accurately determine the translations setup error.
SU‐FF‐J‐58: DMLC Leaf‐Pair Optimal Control for Mobile, Deforming Target
Authors: Papiez L , Rangaraj D
Published: June 2005

Purpose: Tumors in the lung and abdomen tend to move and deform during the course of respiratory cycle. To deliver the intensity modulated therapy, in which intensity map dynamically shifts and deforms in conjunction with the target motion, algorithms have to be developed that control appropriately leaf progression in DMLC IMRT. Description of such algorithms is the purpose of this presentation. Method and Materials: Target motions and deformations are simulated by analytic, periodic functions dependent on position and time. Derived infinitesimal relationships between leaf velocities at all leaf positions assure delivery of the predetermined intensity map. Derived formulas lead to a system of interdependent ordinary, differential equations. When minimization of time of DMLC IMRT delivery is required equations are uniquely defined by scalar fields that are determined by intensity function, target local velocities and target local parameters of deformation, together with constraints on maximum leaf speeds. Integration of differential equations provides trajectories for MLC leaves and thus determines the algorithm for relevant DMLC motion controls. Results: A representative example of DMLC IMRT delivery to deforming target is presented. The example shows the delivery of analytically defined double parabolic intensity function to target undergoing oscillatory type deformation. Target deformation is assumed to be spatially uniform. Deformation of the target, as well as trajectories of leading and following leaves, are calculated and graphically represented for this example. The snapshots of leaf positions at various stages of intensity delivery are also shown. Conclusion: Algorithms are developed for the control of MLC leaf motions that make possible delivery of DMLC IMRT to targets experiencing deforming motions. These realizations of IMRT therapies to deforming targets prevent any discrepancies, rooted in target's dynamic distortions during treatment, between intended and actual intensities delivered to the target.